Head gasket advice needed
David Montgomery
I wound up helping my dad replace the head gasket on his car when one
of his friends borrowed the car and decided to keep driving it after the
thermostat went out. It should be necessary to have the head machined but if
you want to be sure you can take to a machine shop and they should be able to
tell you if it is flat or not. As far as gaskets go, don't buy anything that
isn't sold by the dealer. We actually had to replace the gasket twice because
the first time we did it, my dad bought a gray market gasket and it didn't
match the head perfectly. Unfortunately we didn't realize this until after we
tried to start the car. It turned over a few times then died. When we opened
it back up, we found water in the fourth cylinder. That kinda pissed us off
and it created a lot more work. Whatever you do, make sure all the holes
match the head EXACTLY before you put it back together. Have fun.
David Montgomery
Sales Technologies
--
David Montgomery gatech!stiatl!david
Sales Technologies, Inc
3399 Peachtree Rd, NE
Atlanta, GA (404) 841-4000
John G. De Armond
>My 84 626 is having head gasket problems AGAIN. I have had the
>car since it was new and the first head gasket was replaced at
>78,000 miles. The car now has 108,000, and is showing the same
>symptoms (unexplained loss of coolant, rough running and steamy
>exhaust when first started). I want to replace the gasket myself.
>Those of you who have done this before may be able to answer my
>questions:
>
>1) Should I have the head surfaced? The mechanic who did the
>first replacement checked the head and said it was fine. The car
>has NEVER overheated, so I can believe that the head isn't warped. He
>showed me the previous gasket and there was a break between the
>cylinder and water jacket (on the gasket). All that was
>needed was to clean the head thouroughly.
That is why you are having to replace the gasket again. You MUST ALWAYS
surface ANY aluminum head when you release tension on the head bolts.
Anyone who says you don't either is reckless or has not rebuilt enough
engines to have it bite him. I have NEVER taken a head off that has not
shown some warping. Even a couple of thousands is enough on many engines
whose mating surface is marginal to start with. Considering that it
only costs a few dollars and a bit of work, it's cheap insurance.
If your car never pings, you can remove a bit of material to slightly
raise compression. If you have pings under acceleration or light
throttle cruising, then tell the shop to only remove enough metal to
get a clean surface.
I have had much better long term results with surfacing done on a mill
as opposed to the abrasive-based resurfacing machines. In any event,
DO NOT allow the shop that does your surfacing polish the face. Surface
roughness is necessary to achieve proper bite on the head gasket.
>2) Can I have the block surfaced? Surfacing the head and
>the block would seem to be the only way to ensure smooth
>surfaces on both sides of the gasket. I don't want to pull
>the engine.
Unless your block is aluminum, you should not have to surface the block.
I've never measured warpage on an iron block that has not been overheated.
If I have a block out for other reasons, I'll have a cleanup cut made in
order to get the necessary surface roughness but there are other ways
to achieve this result.
>
>3) Should I have the valves done at the same time? I know
>108,000 miles is a lot, but the compression seems great (no
>smoke, plenty of power) and it uses maybe half a quart of oil
>every 4000 miles. I change the oil every 3500 miles, so I
>don't need to add oil between changes. I have a feeling that
>the average machine shop valve job is not as good as the
>original.
>
The answer to that will depend on an inspection of the head when you
disassemble it. The critical parameters are the wear on the valve seats
and on the valve guides. Your factory service manual will contain
tolerances and checking procedures. I don't believe in replacing
proven parts that are not worn out. The existing parts have
100,000 miles worth of stress normalization and wearin. Don't throw
them away unless they are out of specification.
You are entirely correct in your suspicion of average valve jobs.
That is one task I reserve for myself. If you have to have it done
outside, your best bet is to find a high performance engine shop
that builds racing engines as a main product. If all else fails,
a shop called Race Engine Design in Chattanooga, TN is one I've used
for years and is proven.
>4) Should I get the gasket set from the Mazda dealer or are
>the ones from the independents just as good. Any particular
>brand recommendations?
YES! Buy the factory part. The tiny bit of extra money is worth the
insurance of knowing you have the factory engineered part. I've had
much less success with aftermarket gaskets in working with Datsuns.
>
>5) Should I replace the timing belt? It was replaced after
>the last headgasket job, 30,000 miles ago.
Yes. Cheap insurance.
>6) What torque wrench should I buy? Are the Kragen $30 dial
>types good enough? If not, which ones are? The cost?
I personally prefer the old-style beam arm and pointer type. I conducted
a study a few years ago for a client regarding the long term reliability
of torque wrenches used in nuclear safety-related systems. We found that
even the high priced one like Snap-On will not hold calibration over the
long term. On the other hand, the simple, inexpensive beam-arm type are
very accurate if used properly and not over-stressed. And they're the
cheapest to boot.
>
>7) Should I use new head bolts? I have heard old ones may
>"stretch".
Probably not. Follow your service manual recommendation if it has any.
If it does not, measure the length of the bolts. If they differ by more
than about 1%, replace them. Otherwise, use them as is.
>8) Should I apply anything special before installing the
>head bolts. I am assuming I just coat the head bolts with
>motor oil to get the correct torque readings.
Follow your service manual's instructions. Since torque is only an indirect
of tension on the bolts, the state of the threads and the contact face has
a heavy influence on required torque to achieve a specified tension. If
the book says do it dry, that means absolutely dry, including the bolt holes.
More likely, it will specify a light coating of oil. Under no conditions,
apply Loctite or other thread sealants.
>Do I need to
>use any sealer on the gasket, or where the bolts go into the
>block?
Not only NO but HELL NO. Do NOTHING to "improve" on what the factory
does to the head gasket. Most are coated with a thermoset coating that
cures when heated and forms a nice bond to the head and block. Any
mechanic's goop will degrade that bond.
>
>9) Should I retorque the head bolts periodically? After the
>first replacement the head was retorqued after 3000 miles, but
>not after that. Would retorquing every 15,000 (when I do the
>valve adjustments) be a good idea?
I generally do it after a thousand miles and again after about 10k.
Never seen anything loosten up after that. You probably won't hurt
anything by doing it more often but you run the risk of breaking
a bolt off when you break it free preparatory to torquing. Then you
get to pull the head off again.
>
>Any other tips on head gasket work would be appreciated. I believe
>a head gasket should last more than 30,000 miles. Maybe the first
>job wasn't done right, or maybe Mazda has a design problem (too
>much expansion/contraction of the cylinder head ?).
One thing I've found to tremendously improve the bonding of the head
and block to the gasket is to rough the surfaces in a controlled manner.
This technique has allowed me to dispense with O-ringing the block on
Datsun turbo motors as long as I keep the boost moderate.
I use a common engraving tool such as you use to etch valuables with
a serial number. What you want to do is use the point of the engraver
to make tiny craters on the surface of the block and head. Turn the
engraver up to maximum stroke. Then hold it very lightly and sweep
it a very delicatly contacting circular motion across the block. I
rotate in ~ 1 inch spirals. You want the tip to hit and bounce, leaving
distinct craters instead of drawing an engraved line. The craters will
have a little puckered, projecting rim and a few thousands depth.
It's hard to describe how dense to make these. I like them to be
fairly dense but sparse enough that you can see smooth surface between
the craters. The surface will have a feel similiar to fine sandpaper
and will pick lint from fine cloth when done correctly.
When you are ready to reassemble the head and block, be sure and thoroughly
degrease the surfaces. Don't use gasoline, as it leaves residue. I use
1,1,1 TCE. Alcohol or acetone works well too. Even though a head is
fairly light, I still use a lift to set the head so as not to bruise the
gasket or damage the surfaces.
Other than that, not much more advice other than to remember that "Clean-
leness is next to Godliness" in dealing with engines.
John
--
John De Armond, WD4OQC | The Fano Factor -
Radiation Systems, Inc. Atlanta, GA | Where Theory meets Reality.
emory!rsiatl!jgd **I am the NRA** |
Sriram Narayan
I have a related question to those who may know. Is is possible
that engine coolant loss is greater in winter than in summer?
I own a 1981 Datsun 510 with 85k miles (not too many posts
about this car here) and had changed the cylinder head 2 years ago.
The previous owner had really abused the car.
I don't have an Owner's manual, but perhaps those who do, can
you tell me what the rated BHP for this car is? The Haynes
manual does not say anything about this. The motor is
a "Z20" if I recall correctly (1.9 L). I get about 25 mpg on
mostly highway driving (wish I had a 5-speed :-)).
It has 8 spark-plugs (2 per cylinder).
If anyone out there has any good/bad experiences about this
car please email. I have had this car for 2.5 years and it has
never broken down on me, although I have had to work on it, as
preventive maintenance goes.
-----------------------------------------------------------------------------
Sriram Narayan 810446 Texas A&M University |
INTERNET: nar...@photon.tamu.edu | Go Alain Prost!
US Mail: X4 Hensel #K, College Station, TX 77840.|
Peter Sheriff
These are my opinions on head gaskets:
1.Check the head for obvious damage and then check for warpage using
a metal straight-edge and feeler guages. A good shop manual should tell
you the maximum size of feeler guage that you use for the check. If the
head passes these tests OK don't bother to have it shaved.
2. Check the block surfaces the same way but these do not usually
warp as much as a cylinder head because of the amount of metal in them.
3. Having the valves done is a matter for you to decide. If they are
OK now you could forget about them for now. Bear in mind though that
there will never be a more convenient time to do them than when you
already have the heads pulled for the gasket change.
4. If you have already had unsatisfactory performance from dealer
supplied gaskets, I would tend to go with aftermarket ones. I have
had good results from Felpro head gaskets.
5. From previous postings on the net 30,000 miles seems to be the
recommended change period for the timing belt so I would change it
at the same time.
6. I have no knowledge of the Kragen torque wrench but an accurate
one is necessary.
7. Head bolts are designed to stretch when torqued properly but do
not usually take on a permanent set unless overtorqued. I would
make sure that they are not corroded or damaged in any way and reuse
them. If you are dubious, replace them. The cost is minimal.
8. I never oil head bolt threads. A cheap set of thread runners will
ensure that the threads on the bolts and in the block are clean and
will help with accurate torquing. One warning here. Check with a shop
manual for any of the bolts that may pass through water passages. These
bolts may require an application of sealer.
9. Head bolts do require retorquing after head removal. Do it about
2000 to 3000 miles. After this you can check the torque periodically
but resist the temptation to crank the bolt down 'just to make sure'.
This can cause the head to twist.
P.S. Don't forget to read the shop manual for tightening sequences.
These are given for a good reason.
Pete
Galen J. Hekhuis
> You MUST ALWAYS
>surface ANY aluminum head when you release tension on the head bolts.
>Anyone who says you don't either is reckless or has not rebuilt enough
>engines to have it bite him.
This just isn't true at all. You do not ALWAYS have to resurface an
aluminum head when you release tension on the head bolts. I don't
know of a manufacturer that states this. It is often a good idea.
BTW, I am not reckless and have rebuilt a few engines, but like Mr.
De Armond says, probably not enough to have "it bite" me. I'll bet
I've rebuilt considerably more than he has though, and his mother too.
Neener, neener.
>>Do I need to
>>use any sealer on the gasket, or where the bolts go into the
>>block?
>
>Not only NO but HELL NO. Do NOTHING to "improve" on what the factory
>does to the head gasket. Most are coated with a thermoset coating that
>cures when heated and forms a nice bond to the head and block. Any
>mechanic's goop will degrade that bond.
Again, while you don't need to use any kind of head gasket sealer assuming
the parts are clean and in good condition, it isn't the end of the world
if you do. I worked in several different shops where the accepted
practice was to spray (I forget the brand) a copper type tacky "sealant"
on the head gasket all the time. I didn't suffer a higher comeback rate
because of it.
>Other than that, not much more advice other than to remember that "Clean-
>leness is next to Godliness" in dealing with engines.
If being "next to Godliness" doesn't appeal to you, "cleanleness" also
is the best insurance against having to take apart your engine again.
There is no substitute for cleaning stuff before assembly, in my
experience. When you think it is clean enough, clean it again, just to
be sure.
hang gliding mailing list: hang-g...@virginia.edu
Galen Hekhuis UVa Health Sci Ctr (804)982-1646 g...@virginia.edu
What goes around, gathers no moss.
Peter Sheriff
>I have had much better long term results with surfacing done on a mill
>as opposed to the abrasive-based resurfacing machines. In any event,
>DO NOT allow the shop that does your surfacing polish the face. Surface
>roughness is necessary to achieve proper bite on the head gasket.
>One thing I've found to tremendously improve the bonding of the head
>and block to the gasket is to rough the surfaces in a controlled manner.
>This technique has allowed me to dispense with O-ringing the block on
>Datsun turbo motors as long as I keep the boost moderate.
>--
>John De Armond, WD4OQC | The Fano Factor -
>Radiation Systems, Inc. Atlanta, GA | Where Theory meets Reality.
>emory!rsiatl!jgd **I am the NRA** |
I have never heard of this being done before. In fact every book I
have read on the subject of gaskets stresses that the surfaces should
be as smooth as possible. Some books even state that when scraping old
gasket material off you should be extremely careful not to mark the
surface. I have replaced gaskets only on smooth, highly polished
surfaces and had no leaks yet.
Also, why should it be necessary to achieve 'bite' on a gasket. It
certainly isn't going to move very far.
Can anyone else give some input here?
Pete
Roger Garnett
>>My 84 626 is having head gasket problems AGAIN.
>You MUST ALWAYS
^^^^^^
>surface ANY aluminum head when you release tension on the head bolts.
Well, not quite. Some engines tend to get taken apart *frequently*, and if
you needed to surface them every time, there wouldn't be much left soon.
But for this situation, the head should probably be surfaced, due to
the effects of corrosion as well as warpage.
>I have had much better long term results with surfacing done on a mill
I've gone as far as using a precision surface grinder. :-) Increments of
.0001 (or less!) insure that things are flat and ground no more than necessary.
>>4) Should I get the gasket set from the Mazda dealer or are
>YES! Buy the factory part. The tiny bit of extra money is worth the
>insurance of knowing you have the factory engineered part. I've had
>much less success with aftermarket gaskets in working with Datsuns.
Some aftermarket gaskets are *better* than the factory, but you need to
make sure of what you are getting. For your Mazda, go dealer.
>>7) Should I use new head bolts? I have heard old ones may
>>"stretch".
There *are* some types of head bolts that are made to be used only once,
they are *designed* to stretch, and should not be reused. Check with the manual
and the dealer.
>>8) Should I apply anything special before installing the
>>head bolts. I am assuming I just coat the head bolts with
>>motor oil to get the correct torque readings.
Anti-seize is often reccommended for head bolts. Makes removal easier the next
time. All bolts should thread in and out easily.
>>Do I need to use any sealer on the gasket, or where the bolts go into the
>>block?
>
>Not only NO but HELL NO. Do NOTHING to "improve" on what the factory
>does to the head gasket.
But note: There are some designs that do require a special sealant on certain
head bolts, when the bolt hole passes through the water jacket. Once again,
read-the-manual!
>One thing I've found to tremendously improve the bonding of the head
>and block to the gasket is to rough the surfaces in a controlled manner.
>
>I use a common engraving tool such as you use to etch valuables with
>a serial number. What you want to do is use the point of the engraver
>to make tiny craters on the surface of the block and head.
>John
Careful here! This could quickly do a number on an aluminum head or block!
And some types of gaskets might have a harder time sealing such a surface.
Sing Along:
--- I want a Dyno, Just like the Dyno, that John is Building Now. ---
So, has anyone built their own magafluxing setup?
___________________________________________________________
Roger Garnett (gar...@tcgould.TN.CORNELL.EDU)
Cornell University Agricultural Economics Ithaca, N.Y.
charles.a.sherwood
> These are my opinions on head gaskets:
> Pete
I seem to remember that every bolt that I have torqued, it was clearly stated
that the threads should be lightly oiled to get an accurate torque reading.
chuck sherwood
att!ihc!cas
William Caloccia
> As far as gaskets go, don't buy anything that
>isn't sold by the dealer. We actually had to replace the gasket twice because
>the first time we did it, my dad bought a gray market gasket and it didn't
>match the head perfectly.
Yes, I, and people I know, have had problems with 'no-name' gaskets,
(the kind we get from our [sometimes] buddy harry, at fly-by-night auto parts).
And I would echo the above advice so as to stay away from them.
However, there are a couple reputable after-market gasket makers,
(Fel-pro, and victor are names that come to mind), who are well known and
are certainly an alternative to buying from a dealer. (I used felpro gaskets
in my engine rebuild last october, now 20,000 miles ago.)
--bill
--
--------
"tcp-ip doesn't care whether it's twisted pair or baling wire. :-) "
-- quote attributed to Kent England, BU
Galen J. Hekhuis
}>In article <9...@rsiatl.UUCP> j...@rsiatl.UUCP (John G. De Armond) writes:
}>
}>> You MUST ALWAYS
}>>surface ANY aluminum head when you release tension on the head bolts.
}>>Anyone who says you don't either is reckless or has not rebuilt enough
}>>engines to have it bite him.
}>
}>This just isn't true at all. You do not ALWAYS have to resurface an
}>aluminum head when you release tension on the head bolts. I don't
}>know of a manufacturer that states this. It is often a good idea.
}>BTW, I am not reckless and have rebuilt a few engines, but like Mr.
}>De Armond says, probably not enough to have "it bite" me.
}
}why someone would debate this point, even in theory. The $50 or so it
}costs is a pittance versus the cost of redoing the job.
}
}>I'll bet
}>I've rebuilt considerably more than he has though, and his mother too.
}>Neener, neener.
}
}National wins in Junior/expert combined and which launched the career of
}Dale Singleton, who won 2 world championships, my karting, and my Datsun
}engine works, I'd guess I have between 3 and 400 engines under my belt -
}and a trophy room to prove it. And probably 3 to 400 hours of dyno time.
}Mom did pitch in and help with the finishing or trial assembly
}operations. Damn good, too.
}
}>
}>>>Do I need to
}>>>use any sealer on the gasket, or where the bolts go into the
}>>>block?
}>>
}>>Not only NO but HELL NO. Do NOTHING to "improve" on what the factory
}>>does to the head gasket. Most are coated with a thermoset coating that
}>>cures when heated and forms a nice bond to the head and block. Any
}>>mechanic's goop will degrade that bond.
}>
}>Again, while you don't need to use any kind of head gasket sealer assuming
}>the parts are clean and in good condition, it isn't the end of the world
}>if you do. I worked in several different shops where the accepted
}>practice was to spray (I forget the brand) a copper type tacky "sealant"
}>on the head gasket all the time. I didn't suffer a higher comeback rate
}>because of it.
}
Every mechanic has a discernable comeback rate, Mr. De Armond.
}Probably better that you're dispensing
}advice here than still working on cars. Any connection?
}
}If you are going to offer advice that runs counter to both the manufacturer
}and a vast amount of experience, perhaps you should back up your
}advice with facts. Consider that not only does Datsun warn you not to
}"improve" on the gasket in the shop manual, they print the warning on
}the plastic wrapping AND insert a flyer inside the wrap. Do you REALLY
}want to advise going against that level of warning? If so, I bet you
}scrape bearings too, just it help 'em bed in a bit.
}
}I've spent many hours in the shop and on the dyno figuring out how to
}keep the head gasket intact on Datsun Z turbo-motors. This work
}covered all manner of goops and salves and magic and even includes machining
}a head gasket on a CNC mill from a piece of copper. I have watched
}a turbo motor under full throttle on the dyno literally extrude a
}factory head gasket coated with goop. This very same type head gasket would
}work reliably under the same conditions if assembled according to specs, ie,
}DRY, and with the metal surface treatment I described in my original
}post.
Oh cheese and rice, Mr. De Armond. I made my living rebuilding engines
for several many years and have been an NIASE certified general mechanic
for over 10 years. I respect your world championships and engine
rebuilding experience, I'm sorry I besmirtched both your mechanical
skills and those of your mother. While I wouldn't want to counter your
absolutely worthwhile advice I just wanted to mention that a couple of
points "t'aint necessairly so."
}I'll repeat my previous advice. Smear a salve or glop on a head gasket
}only at your own risk. Or put it together according to spec and have
}some confidence that the factory engineers had at least a clue as to
}what they were doing.
Oh pooh.
Paul Spencer
>Let's see.. Between my motorcycle racing oprations, which brought several
>National wins in Junior/expert combined and which launched the career of
>Dale Singleton, who won 2 world championships, my karting, and my Datsun
^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^
Sorry to burst your bubble, but..... Dale Singleton (known as 'the pig
farmer', for his other occupation), never won a single world championship.
He never even competed in any world championship events.
He DID win Daytona a few times in the early '80s, and a few other US
national road race events; but that's a far cry from the World FIM
500cc championship. (I don't remember whether he ever won the U.S.
F-1 championship or not).
....paul
(Followups to rec.motorcycles, if you must know more facts!)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
...!uunet!matrox!paul paul spencer
pa...@matrox.COM matrox electronic systems
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
--
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
...!uunet!matrox!paul paul spencer
pa...@matrox.COM matrox electronic systems
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
John G. De Armond
>
>
Me ...
>
>>One thing I've found to tremendously improve the bonding of the head
>>and block to the gasket is to rough the surfaces in a controlled manner.
>>This technique has allowed me to dispense with O-ringing the block on
>>Datsun turbo motors as long as I keep the boost moderate.
>
>
> I have never heard of this being done before. In fact every book I
>have read on the subject of gaskets stresses that the surfaces should
>be as smooth as possible. Some books even state that when scraping old
>gasket material off you should be extremely careful not to mark the
>surface. I have replaced gaskets only on smooth, highly polished
>surfaces and had no leaks yet.
>
Why have you not read about it before? Easy. I developed the procedure
about 15 years ago (1975) in an effort to make highly turbocharged
Datsun Z engines stay together under high boost conditions. In other
words, this is a genuine Trick of the Trade from John's Dopebag :-)
A little background. Most inline engines I've worked on have one or more
areas on the head mating surface where the contact area is marginal.
In the Datsun engine, the area is between the cylinder and water jacket
to the rear of the #6 cylinder. Here the mating surface is less than
a quarter inch wide. Gasket failures were very common in this area,
especially if the owner did not have the head retorqued at the first
service interval as specified by the factory.
A stock engine does pretty well as long as it is not overheated. A
high performance engine, on the other hand and especially a super-
charged one, will run through headgaskets faster than gasoline. On my
first attempt at turbocharging a 240Z, I blew the gasket literally on
the first run around the block. (BTW, when I mention "turbocharging",
I'm refering to true high performance turbocharging involving boost
in the 15 to 30 psi range, not this 5 to 8 psi stuff that many factory
engines now have.)
The conventional treatment in such cases is to O-ring the head, or
more correctly, O-ring the block. This involves cutting a shallow
groove around the circumfrence of each cylinder. The groove is cut
to a depth of approximately 1/2 the diameter of the very hard stainless
steel wire that is inserted to form the O-ring. When the head is
mounted, the O-ring concentrates the stress on the metal sealing ring of
the head gasket, thereby forming an extremely strong seal. Integral
to this solution is to ensure that the headbolts don't stretch under
operating conditions. This WAS a problem in 240 engines, easily solved
with 1/2" grade 8 allen bolts.
While this works, there are tactical problems involved. My experience has
shown me that it is wise to move as many tasks in-house as possible.
Outside shops never work exactly to my schedule. I've gone to more than
one race without a spare engine because the machine shop did not get
around to finishing my work.
The second problem is that O-ringing a block is a very tedious job
that is very prone to errors. Most errors result in a ruined block.
So I looked for alternatives.
One alternative was to make a head gasket by machining it out of a sheet
of soft copper. Worked but VERY expensive and one-use-only. Another
alternative was to sit down with a stock head gasket and carefully remove
the sealing compound from the metal rings in the cylinder openings
and then very carefully superglue a fine, hard stainless steel wire to
each ring. When the head was cinched down, the hard wire embedded itself
a bit in the aluminum head, thereby forming an improvised O-ring.
This technique works but is VERY time consuming and requires the block
and head to be perfectly square and flat and assembly is very tedious.
Another alternative is the cratering process I described before. When
properly done, the craters have a profile approximately like this:
----------/ \ / \---------
\ /
V
This profile allows the gasket to extrude down into the depth of the
crater while the protruding ridges bite into the surface. When prpperly
applied, these craters tremendously increase the bond between the gasket
and the head and block. One un-scientific test to determine if the profile
is correct is to lightly drag a shop rag across the surface. A properly
cratered surface will pick lint from the rag.
It is important to note that this technique is NOT a substitute for O-rings
in a full race or heavily turbocharged engine. Up to about 15 psi of boost
in the absence of detonation is OK. Any higher than that and O-rings are
the order of the day.
"Why do the books recommend smooth surfaces?" you ask. A number of reasons.
First we have to make a distinction between macro finish and micro finish.
Macro finish is what you measure when you put a head on a machinist's
flat and probe with a feeler gage for warpage. The microfinish is
what we associate with the feel of a surface or the "roughness" of the
surface. To define some terms (From the New American Machinist's Handbook):
Roughness - Irregularities spaced less than 1/32" apart.
Waviness - Irregularities spaced more than 1/32" apart.
Waviness is to be minimized while roughness enhances the bite of the
gasket. Remember that the gasket is held in place by an interference
fit on a micro scale between the metal surfaces and the gasket. The
gasket has a gooey feel so that it can flow to fill minor waviness and
bond to the roughness peaks. Clamping pressure alone is ineffective.
To demonstrate this, repeat the old trick of coating the tip of a flat
screwdriver with STP and then try to hold it by pinching the flats.
An ideal gasket mating surface would have irregularities dispersed across
the surface in a gaussian distribution. The cratering technique is a
workable substitute.
A second consideration is to realize the audience self-help books and
hot-rod magazines are intended for. The writers have to assume a
fairly low level of reading skills and education (think about the
greaseballs you typically find hanging out at the parts store.).
If some writer outlined my method in a magazine, some yokel would probably
figure that since he did not have an engraver, he could just use a punch
and ball pein hammer! And then want the magazine to pay for his screwed
up engine. You pretty much get a lowest common denominator in these
rags.
And lastly, consider that a significant portion of the advice in certain
rags is just plain wrong. I'll cite Chiltons as one of the worse.
> Also, why should it be necessary to achieve 'bite' on a gasket. It
>certainly isn't going to move very far.
It becomes apparent when you watch an engine on a dyno extrude a gasket
from between the head and block right before your eyes!
John
John G. De Armond
In article <4...@matrox.com> you write:
>Sorry to burst your bubble, but..... Dale Singleton (known as 'the pig
>farmer', for his other occupation), never won a single world championship.
>He never even competed in any world championship events.
>
>He DID win Daytona a few times in the early '80s, and a few other US
>national road race events; but that's a far cry from the World FIM
>500cc championship. (I don't remember whether he ever won the U.S.
>F-1 championship or not).
Say WHAT? As to the exact details of his championships, I'll be seeing
his brother and hopefully his dad over the christmas break. I'll find
out for sure the details.
As to his nick-name of "Georgia Pig Farmer", where'd you get the idea
that came from his occupation? The nick-name came from his preferance
to wearing overalls in the pits and for his pet minerature pig named
Sam (I think). They lived in a suburb not too far from the Old Cleveland
Highway. His dad sold insurance as I recall.
He got too big for us (B&G Cycles, Cleveland, TN) after ~74, and
picked up a sponsorship from White Construction in Chigaco. Factory
bikes, transporter, the works. I kinda lost track of him on a personal
basis after that, as my new "nukler" job had me traveling a lot.
My last contact was right before he was killed in the airplane crash.