Engine bore measurements
Christopher Tidy
I have a question for the engine guys. I'm working on a JAP Model 5 Type
53 single cylinder petrol engine mounted on a Ransomes "Mastiff"
cylinder mower. The engine dates from 1962. Cubic capacity is 412 cc
with a power output of 4.5 hp at 2,200 rpm. I particularly like this
engine because it's solid yet very precisely built.
I want the engine to be reliable so I can use the mower frequently. When
I first turned the starting handle to test the compression, it seemed
poor. I then removed the cylinder head and found that the piston seemed
loose in the bore. I could see a gap around the piston and thought that
I could even see the top compression ring through the gap (but it was
hard to be sure because of the reflections). With the piston at the top
of the bore I estimated the gap to be 0.025" on the diameter with a
feeler gauge. The piston wobbled in both directions, but slightly more
perpendicular to the crankshaft. The only other engine I've seen with a
piston this wobbly would never run reliably (I just realised that the
unreliable engine used a cast iron piston in an aluminium bore, whereas
this latest engine uses an aluminium piston in a cast iron bore -
perhaps a wobbly piston is a much bigger deal in the first case because
of the differing coefficients of thermal expansion?).
But the bore looked good. I wondered if perhaps the wear was much worse
on the piston than the bore, because the aluminium piston is softer than
the cast iron bore, and obviously the piston is in contact with the
cylinder wall all the time, whereas parts of the wall are only
intermittently in contact with the piston. So I bought a bore gauge to
measure the wear. I now feel a bit dumb, because I later discovered two
other problems that were causing the compression to seem poor: a
slightly loose spark plug and a deliberate blockage in the inlet
manifold left by the previous owner to stop dirt getting inside. I have
now checked the poppet valves too. The seats look good and the valves
are closing properly. The compression is now better, but not as good as
in some other engines I own.
I went ahead and measured the bore. Here are three pictures. The first
shows the bore (that ridge looks far worse in the picture than in
reality; it's actually only visible on one side of the bore, and can
barely be felt). The second shows my Etalon vernier calipers, which I
used to set the zero on the bore gauge. The third shows my Mercer bore
gauge.
http://www.mythic-beasts.com/~cdt22/jap_engine_bore.jpg
http://www.mythic-beasts.com/~cdt22/etalon_vernier_calipers.jpg
http://www.mythic-beasts.com/~cdt22/mercer_bore_gauge.jpg
The bore is nominally 80 mm or 3.150".
I got the following measurements with the bore gauge:
Perpendicular (to crankshaft) Parallel
Top (of bore) +0.0035" +0.0030"
Middle +0.0030" +0.0025"
Bottom -0.0000" -0.0005"
I considered setting the vernier calipers using the top land of the
piston for a relative measurement, instead of using the nominal 80 mm,
but didn't try it because I was interested in the distribution of the
wear. I was careful to avoid ridges and chamfers. I repeated the
measurements, including setting the 80 mm using the vernier calipers
(oddly, I found the vernier scale easier to read with the lines
horizontal - I wonder if it's related to this?
http://en.wikipedia.org/wiki/Vertical%E2%80%93horizontal_illusion), and
reversed the sense of the bore gauge. I got exactly the same results, so
the repeatability is good. The bore gauge is graduated down to 0.0005"
and the vernier calipers to 0.001".
I also measured the piston diameter using the calipers, with the
following results:
Perpendicular (to crankshaft) Parallel
Top land 3.126" 3.131"
Middle (or close) 3.138" 3.135"
Skirt 3.140" 3.136"
That looks like a fairly consistent 0.003" wear on the bore in the area
swept by the rings. I don't have an official diameter for the piston,
but Don Nichols suggested finding the recommended clearance between the
piston and bore. The engine's manual states 'RECOMMENDED CLEARANCES ON
RECONDITIONING Piston - On diameter of piston: 0.009" skirt, 0.018" top
land'. Presumably that means the piston is slightly conical?
The gap around the piston really bugged me at first, but given those
figures, maybe the wear isn't so bad. The clearances sound big, but I
wonder if I'm making the error of expecting an aluminium piston to fit a
cast iron bore as closely as a cast iron piston at room temperature?
Looking at the coefficients of expansion, a temperature rise of a few
hundred centigrade is going to close that gap considerably.
Almost all parts are available for this engine, so I have a lot of
options, ranging from free to expensive. But I want to get this rebuild
right first time.
I could:
- Do nothing.
- Replace the piston rings only.
- Replace the piston with a new standard piston and new rings.
- Get the cylinder bored oversize, fit an oversize piston and rings.
- Fit a brand new cylinder, new piston and rings.
My priorities are (in order):
- To have a reliable engine that starts easily and develops rated power.
- To maximise the life of the engine (i.e., not rebore if unnecessary).
- To save money.
Based on the evidence, my gut reaction is to go for a new set of piston
rings only. But I'm unsure how to inspect rings for wear. Can anyone
advise me here?
Sorry for the length of this message! I'd be very interested to hear
what people think.
Best wishes,
Chris
cl...@snyder.on.ca
I'd likely put it back together and see how it runs with the existing
rings, but better to lightly deglaze the cyl and replace the rings as
well as touching up the valves.
If you are going to do anything else the complete cyl and piston set
would be the best - basically a full rebuild to original.
Also check all the bearings - likely replace the con-rod along with
the piston if you are going that far.
Greg O
"Christopher Tidy" <cdt22...@cantabgold.net> wrote in message
news:4B8B3F87...@cantabgold.net...
> Hi folks,
>
> I have a question for the engine guys. I'm working on a JAP Model 5 Type
> 53 single cylinder petrol engine mounted on a Ransomes "Mastiff" cylinder
> mower. The engine dates from 1962. Cubic capacity is 412 cc with a power
> output of 4.5 hp at 2,200 rpm. I particularly like this engine because
> it's solid yet very precisely built.
Just looking at the picture I would say it is an oil burner. All that black
crud on the top of the block confirms it. Also .003"wear seems a bit
excessive, does the manufacturer give a maximum cylinder wear spec?
All said, it will probably run fine as is, but consume some oil. If money
was no object a total rebuild would be in order if you can still get parts.
Greg O
sta...@prolynx.com
wrote:
>
> The bore is nominally 80 mm or 3.150".
>
> I got the following measurements with the bore gauge:
>
> Perpendicular (to crankshaft) Parallel
> Top (of bore) +0.0035" +0.0030"
> Middle +0.0030" +0.0025"
> Bottom -0.0000" -0.0005"
>
> I considered setting the vernier calipers using the top land of the
> piston for a relative measurement, instead of using the nominal 80 mm,
> but didn't try it because I was interested in the distribution of the
> wear. I was careful to avoid ridges and chamfers. I repeated the
> measurements, including setting the 80 mm using the vernier calipers
> (oddly, I found the vernier scale easier to read with the lines
The rings are really what seals the works, the piston is just the
carrier. You need to check the ring grooves for wear, too. Most any
book on engine rebuilding will have suggested limits which should
applicable for similar sized bores and pistons. I know B&S has limits
on the ring gaps when inserted in the bore. Slop up and down in the
piston ring grooves is checked with feeler gauges. Too much and you'll
need a new piston. Don't forget to check the rod for twist, too.
Crankpin needs to be checked for wear, too. No sense putting a lot of
effort into redoing the cylinder bore if the bearings are shot. Hope
you can get replacement parts.
Stan
RoyJ
To put in top condition would be a full rebuild, you can get by with
just rings.
This engine seems to be very similar in design and construction to the
old Kohler cast iron engines. I have all the shop manuals for these,
they are pretty explicit on tolerances and rebuild procedures.
.003" wear in the ring area is pretty normal, no taper and no egg shape
is a strong plus. .003" over will still work fairly well with new rings
but of course it is not perfect. Standard rings in the bore will give
you around .010" additional end gap. Your picture does not show any
signs of long vertical scratches, so much the better.
An undersized piston is not too much of a worry. It may rattle a bit
when cold but once up to temp it's just not that big a deal A bigger
concern is the quality of the ring groves: if these are buggered, the
rings twist, all is lost, replace the piston.
I'd suggest taking the rings out of the piston, measuring the end gaps
of the rings in the bore at various points. I'll bet that you have .045"
or more on the compression rings, more on the oil rings, and the oil
rings have virtually no spring left in them.
My suggestions for a decent engine at reasonable cost:
Since the bore is not egg shaped or tapered, use a standard 3 stone
spring deglazing in the electric drill, be a bit heavier on the lower
bore. Try for the usual 30 degree diamond pattern on the walls. Use lots
of kerosene, mineral spirits, or similar for wash down to carry away the
grit. If you can get access to the clamp on deglazing tool, it's much
preferred since it can clean up the dimensions if used carefully.
Clean up the piston, clean out the ring groves, install .003" over rings
if you can get them. Use standard rings if you can't get the oversixed
ones.
Check the con rod bearing to crankshaft clearance. Plastigage works
nicely, may or may not be available across the pond. .0025" to .003" is
about the max before you need to deal with regrind on the crank and new
con rod. For reference, I paid US$47 at at top shop for a reground
crankpin on a 12hp Kohler engine last fall. I considered that quite
reasonable.
Valves are likely pretty tired. They need to be pulled out, cleaned up
in the lathe, seats checked, seats ground. Replace valves as needed, pay
close attention to the exhaust valve to make sure it is not warped or
eroded.
Have fun. I sent you a copy of the Kohler specs via e-mail.
Wild_Bill
compression test, but the rings aren't supposed to be dry for the test (long
period of storage or non-use).
The piston and bore are probably fine, as-is. You mentioned that there was
very little ridge at the top of the cylinder. The ridge is an excellent
indicator of wear, generally, if no other problems are present (piston
cracks, scored cylinder, signs of being run with too little oil, etc).
The piston skirt, for the most part, is what guides the piston in the
cylinder. There were high performance modifications done to racing pistons
where several "buttons" of synthetic material were set into counnterbored
holes in the skirts.
The buttons then guided the piston, reducing the area of the skirt contact
with the cylinder to just a couple of square inches, thereby reducing
friction and heat.
At the point where you are now, the valves should be re-done, and the valve
guides checked and/or replaced. Replacement would be best if they're
available.
The length of the valve stems will most likely need to be shortened after
grinding the valve faces and seats. There will be a spec for the gap to the
cam surface wih the valves closed. The gap insures that the valves will
fully seat after the parts have expanded from normal engine heat.
After checking the piston grooves with a new set of rings, if the grooves
are OK, then removing the ridge and honing may be all the cylinder work you
need to do.
Slightly oversize rings, as recommended earlier, would be best, and there is
a spec for the gap at the ends of the rings (while each ring is positioned
squarely in the cylinder (pushed down in the cylinder a certain distance
with the bare piston).
After checking rod bearing and the main bearing surfaces and dimensions, you
should be ready to reassemble the engine.
The ring replacement procedure, for now, will very likely give you years of
reliable performance.
In another 50 years, or for the engine's 100th anniversary, you can go for
the .010" oversize piston and cylinder boring job (better get the parts now,
though).
--
WB
.........
"Christopher Tidy" <cdt22...@cantabgold.net> wrote in message
news:4B8B3F87...@cantabgold.net...
> Hi folks,
>
> I have a question for the engine guys. I'm working on a JAP Model 5 Type
> 53 single cylinder petrol engine mounted on a Ransomes "Mastiff" cylinder
> mower. The engine dates from 1962. Cubic capacity is 412 cc with a power
> output of 4.5 hp at 2,200 rpm. I particularly like this engine because
> it's solid yet very precisely built.
>
>
> Best wishes,
>
> Chris
>
Christopher Tidy
Thanks to everyone for the suggestions!
> Just looking at the picture I would say it is an oil burner. All that
> black crud on the top of the block confirms it. Also .003"wear seems a
> bit excessive, does the manufacturer give a maximum cylinder wear spec?
> All said, it will probably run fine as is, but consume some oil. If
> money was no object a total rebuild would be in order if you can still
> get parts.
The manual suggests decarbonising the engine every 400 hours, so the
build-up of soot may be normal.
Best wishes,
Chris
Christopher Tidy
> Have fun. I sent you a copy of the Kohler specs via e-mail.
Thanks for the advice. I just replied to your Kohler e-mail with some
thoughts.
Best wishes,
Chris
Christopher Tidy
> You didn't mention whether you had run the engine before taking the
> compression test, but the rings aren't supposed to be dry for the test
> (long period of storage or non-use).
I hadn't run the engine first, no. So the bore was likely drier than it
would be in normal use.
> The piston and bore are probably fine, as-is. You mentioned that there
> was very little ridge at the top of the cylinder. The ridge is an
> excellent indicator of wear, generally, if no other problems are present
> (piston cracks, scored cylinder, signs of being run with too little oil,
> etc).
No marks on the bore. It's smooth and shiny. Very few marks on the
piston either. Parallel to the crankshaft, I can still see some
machining marks on the piston.
> The piston skirt, for the most part, is what guides the piston in the
> cylinder. There were high performance modifications done to racing
> pistons where several "buttons" of synthetic material were set into
> counnterbored holes in the skirts.
> The buttons then guided the piston, reducing the area of the skirt
> contact with the cylinder to just a couple of square inches, thereby
> reducing friction and heat.
>
> At the point where you are now, the valves should be re-done, and the
> valve guides checked and/or replaced. Replacement would be best if
> they're available.
> The length of the valve stems will most likely need to be shortened
> after grinding the valve faces and seats. There will be a spec for the
> gap to the cam surface wih the valves closed. The gap insures that the
> valves will fully seat after the parts have expanded from normal engine
> heat.
The valves look good, at least visually. The seats are smooth and
without erosion, and the tappet clearances are close to the specified
values. Adjustment of the clearances is using circular shims, a system I
haven't seen before. I'm somewhat reluctant to grind the valves because
of having to clean up the paste afterwards, but I might be persuaded.
> After checking the piston grooves with a new set of rings, if the
> grooves are OK, then removing the ridge and honing may be all the
> cylinder work you need to do.
> Slightly oversize rings, as recommended earlier, would be best, and
> there is a spec for the gap at the ends of the rings (while each ring is
> positioned squarely in the cylinder (pushed down in the cylinder a
> certain distance with the bare piston).
I'm doubtful I can get slightly oversize rings, but I'll check.
> After checking rod bearing and the main bearing surfaces and dimensions,
> you should be ready to reassemble the engine.
>
> The ring replacement procedure, for now, will very likely give you years
> of reliable performance.
> In another 50 years, or for the engine's 100th anniversary, you can go
> for the .010" oversize piston and cylinder boring job (better get the
> parts now, though).
Now that's a nice thought!
Best wishes,
Chris
Richard W.
Pistons are not round they are tapered in length when new and oval shaped.
Pistons should only be measured on the skirt near the bottom. That will tell
you how bad they are worn. Also Pistons are usually about .025 undersize
where the rings are. So checking with a feeler gauge tells you nothing. On
cars engines it recommended to rebore when the taper in the bore is .005" or
greater. If you use cast iron rings I have seen as much as .012" taper and
not burn oil. Only you may get 60 to 70K miles before it becomes an oil
burner. I have seen this with SBC engines.
The reasons for the undersize around the rings is, 1 the difference in
expansion in this area, 2 the compressed gas/air mixture goes around the
groove to force the rings against the cylinder wall. That is why there is a
45 degree bevel on the bore of the ring on one side. This bevel side is
installed so it's toward the top of the piston. This forces the ring out and
down to form a better ring seal.
From what you are telling us is you could ring the engine and install new
bearings if they are worn out of spec. Most likely on such an old engine the
valve seats are cast iron and worn and or corroded. A valve grind is good
idea. It may be that all you need is a valve grind to bring compression back
up. A lawn mower shop can grind the valves with out tearing the engine down
and install new bronze guides at the same time if necessary. Most likely the
carbon is from worn valve guides.
If this were my engine I would grind the valves and put it back together.
But then it's not mine. Also parts may be hard to find.
Richard W.
Greg O
Carbon is one thing, oily soot is another.
I ran a small engine shop for a few years. I can not tell you how many of
these small engines I have rebuilt over the years!
Do what you want, but with .003" wear in the cylinder even with new piston
rings, it will continue to burn oil!
Someone mentioned Kohler engines, pretty sure maximum wear for a Kohler was
.003", right where you are at. I could run out to the shop and look it up,
but I am too lazy!
If you want a great running engine, it needs a rebuild. It will run good
like it is, but I guaranty it will burn oil!
Greg
cl...@snyder.on.ca
wrote:
And a J.A.P. engine didn't from new??? They ALL burned some. Just
depends on what you consider to be excessive.
Richard W.
<cl...@snyder.on.ca> wrote in message
news:7lrro5t9jgjnqi5hk...@4ax.com...
These small engines don't have valve guide seals, so they all burn some oil.
The more worn the valve guides the more oil is consumed.
Richard W.
Christopher Tidy
> These small engines don't have valve guide seals, so they all burn some oil.
> The more worn the valve guides the more oil is consumed.
The valves, seats and guides all look in good order. I'm sure these
engines burnt a little oil even when new. Surely some oil would sneak
past the rings, even in a new bore? The manual for this engine suggests
adding one tablespoon of engine oil to each gallon of fuel, when
"commercial petrol" is used. Whether this is to lubricate the
carburettor or to make up for burnt engine oil, I don't know. But as
long as I don't have to top up the oil too often, I don't mind.
Hopefully it won't burn enough oil to get from the "High" to "Low" mark
in a season, but I'll still check the level every time I start the engine.
Best wishes,
Chris
Christopher Tidy
> Pistons are not round they are tapered in length when new and oval shaped.
> Pistons should only be measured on the skirt near the bottom. That will tell
> you how bad they are worn. Also Pistons are usually about .025 undersize
> where the rings are. So checking with a feeler gauge tells you nothing. On
> cars engines it recommended to rebore when the taper in the bore is .005" or
> greater. If you use cast iron rings I have seen as much as .012" taper and
> not burn oil. Only you may get 60 to 70K miles before it becomes an oil
> burner. I have seen this with SBC engines.
I think they're cast iron rings in a cast iron bore, with an aluminium
piston.
Chris
Christopher Tidy
> After checking the piston grooves with a new set of rings, if the
> grooves are OK, then removing the ridge and honing may be all the
> cylinder work you need to do.
Is ridge removal essential? How do you remove the ridge without reboring
the cylinder? I remember being told once that if the piston rings hit
the ridge when the engine was run fast, it could damage the rings, but I
don't know if this is true.
Chris
Richard W.
Yes it's true. They use a ridge reamer for this. It's used with a wrench to
spin it.
http://www.amazon.com/Lisle-36500-Cylinder-Ridge-Reamer/dp/B000P0ZK1O
Richard W.
Richard W.
Some are CI rings and others are chrome rings. I don't think I have ever
heard of a chrome-molly option for small engines. Cast Iron rings are fine
unless you have the aluminum cylinder.
Also I forgot to say in the earlier post, pistons are not only oval, but
taper in length. That is why you measure at the bottom of the piston.
From what I see I would put it back together and see how it runs. I have
seen Briggs engines run with as little as 5 pounds of compression.
Richard W.
Gerald Miller
My 24 yr old tech snow blower engine goes down about 1/4 of the range
in a season. I had one B&S 3.5 that would go down 1/2 per season of
grass - maybe 10 hours as opposed to 5 for the snow blower. We're not
talking high time seasons here now that I'm only doing my own property
with no offspring trying to earn comic book money.
Gerry :-)}
London, Canada
Wild_Bill
remove the cylinder ridge with a HSS or possibly carbide cutter that's
rotated with a wrench.
Many RRs have a stop, which will prevent the cutter from cutting oversize.
If the stop isn't adjusted properly, the ridge won't be completely removed,
or the possibility of removing too much cylinder wall exists. The user
should be careful as the RR reaches the size of the cylinder bore.
Not removing the cylinder ridge risks damage to the new top piston ring and
the piston ring land that it sits on, and the second ring.
Small engine repair generally involves having a few specialized tools..
ridge reamer, piston ring compressor, piston ring groove cleaning tool, ring
expander, valve spring compressor and a few others.
http://www.jcwhitney.com/jcwhitney/product/images/large/G_14236G_CL_1.jpg
--
WB
.........
"Christopher Tidy" <cdt22...@cantabgold.net> wrote in message
news:4B90321E...@cantabgold.net...
cl...@snyder.on.ca
It IS true, and there is a little thing called a ridge reamer that
just takes the ridge out. You do this BEFORE removing the piston
unless the piston is removed from below.
Larry Jaques
<cdt22...@cantabgold.net> scrawled the following:
Ridge removal is imperative if you replace pistons, lest you break the
new rings on the slightly lower ridge which was created by the old
rings riding in the worn lands ofthe old pistons. Generally, ridge
removal is required to remove the old pistons, so it's not a problem.
If you can remove the old pistons without removing any small ridge,
there likely isn't a problem, either.
--
An author spends months writing a book, and maybe puts his
heart's blood into it, and then it lies about unread till
the reader has nothing else in the world to do.
-- W. Somerset Maugham, The Razor's Edge, 1943
Larry Jaques
<grmi...@rogers.com> scrawled the following:
Other than annual oil changes (when I remembered) I can remember
buying only a few quarts of oil for my mowers which was used to top
off the crankcase. Most didn't use oil.
Christopher Tidy
> Small engine repair generally involves having a few specialized tools..
> ridge reamer, piston ring compressor, piston ring groove cleaning tool,
> ring expander, valve spring compressor and a few others.
Got a ring compressor, expander, deglazing hone and now a bore gauge. I
don't have a ridge reamer or compression tester yet.
Chris
Christopher Tidy
> It IS true, and there is a little thing called a ridge reamer that
> just takes the ridge out. You do this BEFORE removing the piston
> unless the piston is removed from below.
The piston came out from below, though given the size of the ridge, I
suspect it would have come out the top too.
I just found my lost feeler gauge, so I'm going to check the ring
grooves tomorrow.
Chris
Christopher Tidy
I found my missing feeler gauge, so I've been able to check the
clearances between the piston rings and grooves on my JAP engine.
According to the manual, the clearances should be between 0.0035"
and 0.005" 'on reconditioning'. The measured clearances are:
1st compression ring: 0.008"
2nd compression ring: 0.005"
Oil ring: 0.0025"
The manual doesn't give figures for the ring end gaps. The 1st
compression ring has a gap of about 0.040", and the gaps on the
lower rings are larger, much larger for the oil ring.
My gut reaction is that the figures aren't bad for a worn engine.
I'm inclined to replace the rings only. Does that sound reasonable?
Best wishes,
Chris
Steve R.
Might be OK! You just may have more oil consumption. Are there still parts
available for those old J.A.P. engines? As far as I was aware, their last
product was the Seagull outboard motor. For those who do not know, they were
J.A. Prestwich Industries, in the UK.
Steve R.
John
wrote:
In my younger days, when I thought a motorcycle was the best means of
transportation available, a JAP engine was probably in as a speedway
or grasstrack racer or maybe a Rudge, or some other exotic breed of
motorcycle.... now this guy says he's got one in a LAWNMOWER???? My
goodness, an alcohol fed, 50 HP lawnmower???
I had to google around for a while before I discovered that J.A.P.
made all kinds of engines.
John B.
bw
Ring end gap is not as important as face gap. Your top ring gap is out of
spec, but might work ok in a demo engine. There might be other problems, but
you could try to just break the bore glaze with a light hone. That will
allow the rings to reset with load. Some people might just put in new rings
and hope for the best, but a good engine man with experience should give you
a second opinion. I'd take the engine to a shop and get is properly measured
to see if new rings would seat properly. Then you need to consider an
oversize piston and re-bore
Ed Huntress
"John" <johnbs...@invalid.com> wrote in message
news:be8vp59r050jokcgs...@4ax.com...
I had one of those Seagulls -- a Silver Century. I had no idea they were
made by the same company as J.A.P.
There was a famous dirt track racer here in my township, many decades ago,
who rode a J.A.:P. He was one of my uncle's former students. My uncle was
kind of an engine connoisseur, and thought they were pretty exciting
motorcycles.
I've only seen them in museums.
--
Ed Huntress
David Billington
ago. He had worked for Villiers and he ran it through their
reconditioning program and it had sat in his workshop for 25 years or
more. It came from a small stationary crane IIRC and was governed and
had a huge heavy flywheel. I checked the oil and other bits, turned it
over for awhile to get the oil thrown about, added a spark plug as all
that was fitted was a cork, after cleaning the magneto points it started
on about the second turn of the starting handle. I used to run it about
once a year and the points always needed cleaning with that little use
but it always seemed to start and run well on the second turn of the
starting handle. The stop cock on the petrol tank leaked a bit but a
chap I knew said they always did that. I realised in the end that I
didn't need it and sold it to a chap that was going to use it for a
portable compressor for diving use. He seemed impressed at how well it
started on the 2nd crank, not heard from him since, I don't know if he
still works for the same company a mate does.
My neighbour is more familiar with the higher spec JAP engines as he had
a grand prix Morgan 3 wheeler, amongst other Morgans, with the overhead
valves and that is still in existance. He tells a few tales of the
troublesome acetylene lamps it originally had and fitting a bicycle back
light as the acetylene generator was too feeble to run the front lights
and the rear one at the same time.
Christopher Tidy
> Might be OK! You just may have more oil consumption. Are there still parts
> available for those old J.A.P. engines? As far as I was aware, their last
> product was the Seagull outboard motor. For those who do not know, they were
> J.A. Prestwich Industries, in the UK.
Parts availability is pretty good. You can still get cylinders, pistons,
oversize pistons, rings and most other parts, all new. If you need
suppliers, let me know.
Best wishes,
Chris
Christopher Tidy
> In my younger days, when I thought a motorcycle was the best means of
> transportation available, a JAP engine was probably in as a speedway
> or grasstrack racer or maybe a Rudge, or some other exotic breed of
> motorcycle.... now this guy says he's got one in a LAWNMOWER???? My
> goodness, an alcohol fed, 50 HP lawnmower???
>
> I had to google around for a while before I discovered that J.A.P.
> made all kinds of engines.
The engine is one of these:
http://home-and-garden.webshots.com/photo/2596864820099986903aqPQAa
Chris
Christopher Tidy
They appear to be highly regarded engines. I don't need one in perfect
condition, just a reliable one. I've never seen a JAP 7 hp. What model
was that? Mine is a 4.5 hp Model 5 Type 53. I'm pretty sure the starting
handle is wrong as it wobbles around (it's an S-shaped piece of bent
round bar), whereas in pictures the handle appears to be fabricated from
flat bar. So I'm looking for a handle, if anyone knows of a source.
Best wishes,
Chris
Christopher Tidy
> Ring end gap is not as important as face gap. Your top ring gap is out of
> spec, but might work ok in a demo engine. There might be other problems, but
> you could try to just break the bore glaze with a light hone. That will
> allow the rings to reset with load. Some people might just put in new rings
> and hope for the best, but a good engine man with experience should give you
> a second opinion. I'd take the engine to a shop and get is properly measured
> to see if new rings would seat properly. Then you need to consider an
> oversize piston and re-bore.
Can anyone tell me what a typical end gap for 80 mm piston rings is,
assuming the engine is in top condition?
Chris
Greg O
.014" in your case.
Greg O
>>
> My gut reaction is that the figures aren't bad for a worn engine.
> I'm inclined to replace the rings only. Does that sound reasonable?
>
> Best wishes,
>
> Chris
>
My gut reaction with the .035" cylinder wear you mentioned in your first
post is to bore it over sized. If you don't bore it at least put in new
piston rings.
cl...@snyder.on.ca
Aprox .007 to .010 inches.
cl...@snyder.on.ca
wrote:
I forgot about it being an air cooled engine when I said .007 - .010
inches. .010 to .020 would be more correct - so yes, .014 would be
good.
cl...@snyder.on.ca
But a 356 Porche specs .008 and that is 82.5mm bore - so the rule of
thumb does not ALWAYS hold.
77mm vw says .013.
John
<cdt22...@cantabgold.net> wrote:
I hate to be snippy but Google IS your friend. Try
http://www.aa1car.com/library/ring_end_gap.htm
for a fairly complete discussion of piston rings.
the usual caveat applies: check the manufacturer's recommendations (if
available).
John B.
Garrett Fulton
J.A.P., (James A. Prestwich), made the V-twin engine for the Brough Superior
Motorcycle. That was the one T.S. Lawrence was riding when a crash killed
him. Lawrence of Arabia. Don't know why I remember such useless
information.
Garrett Fulton
Ed Huntress
"Garrett Fulton" <lbfu...@windstream.net> wrote in message
news:7a276$4ba0b2fa$62114e15$24...@ALLTEL.NET...
Because it's the kind of cool factoid that makes life interesting.
--
Ed Huntress
Christopher Tidy
>>Recomended .0045" per inch of bore diameter for an air cooled, or around
>>.014" in your case.
>
> I forgot about it being an air cooled engine when I said .007 - .010
> inches. .010 to .020 would be more correct - so yes, .014 would be
> good.
Thanks for the figures and link, guys. Just what I need. It's strange
that the original manual doesn't give any figures, but neither does it
mention honing when replacing the piston rings.
All the ring gaps are much bigger than those figures. Too big to measure
with a feeler gauge. I would estimate that they're in the 1 to 4 mm
range (perhaps that's a factor in reducing the compression).
There are two compression rings and one scraper ring (all above the
gudgeon pin). Should the end gap be the same for all the rings?
Many thanks,
Chris
Christopher Tidy
> My gut reaction with the .035" cylinder wear you mentioned in your first
> post is to bore it over sized. If you don't bore it at least put in new
> piston rings.
It's actually a tenth of that: 0.0035". Hardly any ridge at the top of
the cylinder. I showed the bore to a friend today, and like me he was
just inclined to replace the rings (he wasn't keen on honing, though).
Chris
Larry Jaques
<cdt22...@cantabgold.net> scrawled the following:
>Greg O wrote:
If you don't hone, how do you expect the rings to seat? Unless the
ridge is non-existent, ream and hone for safety and better life. YOu
don't want to be having to do this over within the year, eh?
--
No matter how cynical you are, it is impossible to keep up.
--Lily Tomlin
cl...@snyder.on.ca
Mabee not HONE (which uses rigid stones) but at least DEGLAZE. The
abrassive "bottle brushes" do a pretty decent job.
Christopher Tidy
> Mabee not HONE (which uses rigid stones) but at least DEGLAZE. The
> abrassive "bottle brushes" do a pretty decent job.
Sorry, that was what I meant. I have the kind of deglazing hone which
has three spring-loaded stones and looks a bit like a camera tripod.
I've never used the "bottle brush" kind.
Chris
Greg O
That was a typo, I ment .0035", right on the edge for a bore job, IMO.
Greg
Larry Jaques
<cdt22...@cantabgold.net> scrawled the following:
>cl...@snyder.on.ca wrote:
The spring loaded monsters work just fine.
--
Adults are obsolete children. --Dr. Seuss (Theodore Geisel, 1904-1991)
--
David Billington
Not sure what model but it looked much like the one in this youtube
video http://www.youtube.com/watch?v=5BvzsuP_8Ww . Big heavy flywheel on
it, may have been due to its use on a stationary crane, the flywheel
probably weighed more than a modern 7hp small engine. IIRC the starting
handle was a S shaped piece of bent bar, not made from flat like the one
in the video.
Christopher Tidy
Chris,
>
> Not sure what model but it looked much like the one in this youtube
> video http://www.youtube.com/watch?v=5BvzsuP_8Ww . Big heavy flywheel on
> it, may have been due to its use on a stationary crane, the flywheel
> probably weighed more than a modern 7hp small engine. IIRC the starting
> handle was a S shaped piece of bent bar, not made from flat like the one
> in the video.
That's a Model 4/3. Smaller and faster running than my Model 5. I had a
look at more pictures of these lawnmowers. I have now come to the
conclusion that my starting handle is probably original, but that it and
the dog in the centre of the flywheel are worn, making the handle a
loose fit. It may also be missing a rotating grip.
Chris
Wild_Bill
or with a new set of rings (I suspect the old used rings).
The top ring groove clearance is fairly bad, but should improve with the new
top ring placed in the groove. If the groove clearance doesn't improve to
almost .005" with a new ring, you should probably replace the piston.
With excessive groove clearance, the ring is probably more likely to break,
resulting in cylinder damage/severe scoring.
The ring end gap will be fairly large when checking with a used ring.
It's a situation where the new replacement part becomes a gage.
I think it's kinda odd that the ring end gap spec isn't included in an
overhaul manual.
It's been a long time since I was familiar with ring specs, but looking up
ring end gap specs for several engines with a similar bore size should give
you a good indication of what size the end gaps should be.
When installing a standard size ring in a slightly worn cylinder, I wouldn't
expect the ring end gaps to be too close (needing filing), but a comparison
to similar engines may provide an appropriate range for the size of the gap.
Previous recommendations from others wrt replacing the valve guides and
possibly new valves would likely be something you'd want to follow up on.
The extreme heat that the exaust valve endures will essentially guarantee
guide wear. For a 50 year old engine, maybe it's likely that the guides have
been replaced before, but they're not expensive to have a new set installed
at a machine shop.
--
WB
.........
"Christopher Tidy" <cdt22...@cantabgold.net> wrote in message
news:4B9EF162...@cantabgold.net...
> Hi folks,
>
> I found my missing feeler gauge, so I've been able to check the clearances
> between the piston rings and grooves on my JAP engine. According to the
> manual, the clearances should be between 0.0035"
> and 0.005" 'on reconditioning'. The measured clearances are:
>
> 1st compression ring: 0.008"
> 2nd compression ring: 0.005"
> Oil ring: 0.0025"
>
> The manual doesn't give figures for the ring end gaps. The 1st compression
> ring has a gap of about 0.040", and the gaps on the
> lower rings are larger, much larger for the oil ring.
>