Generator repair (small 2 stroke)

[Jon Nicholson]

I have a Wolf 800 generator, yesterday I tried to get it started in
ahead of a scheduled power cut tomorrow to no avail.

Cleaned air filter, checked the spark plug and cleaned the float bowl.
The only thing I can see that's obviously wrong is the gasket round the
float bowl has perished.

Does anyone have any suggestions about what might be wrong, or where to
get it repaired (and a new gasket)

Thanks,

Jon

[Jon Green]

I wouldn't worry too much about the float bowl gasket, so long as you're
not leaking fuel. If it is, on the other hand: if it's a rubber-type
gasket, you'll need to get one that's correct for the model; if it's a
thin fibre gasket, you could even make one yourself out of cereal packet
cardboard to the same pattern. I've done that for motorbike carbs, and
never had problems.

Whilst you've the float bowl open, knock out and withdraw the float
pivot pin with a thin drift, making sure to catch the needle valve as
the float drops free. If the needle valve doesn't drop out, you've got
a definite culprit - wiggle it out by hand. Either way, look at both
the needle valve itself its channel and seat in the carb. Use fresh
petrol and a pipe cleaner to dissolve any gluey deposits, making sure
you don't leave any fibres from the pipe cleaner behind to jam the valve
anew. Refit the needle without the float and, holding the carb in its
normal orientation, check that the needle travels cleanly in its channel.

If that doesn't fix it, here's my usual diagnostic sequence for small
engines:

* BATTERY. Check the cells all have the right amount of acid, if its
not a sealed unit. Charge it, then check its output under load. If you
don't have the kit to do that, most garages will happily do a quick test
for a fiver for the tea fund. Bear in mind that for small engines, the
battery is also the voltage regulator, so if one of the cells has gone
wrong, you can get all sorts of problems with over-voltage.

* FUSES. Look for a fuse box or inline fuse, and check.

* DISTRIBUTOR. If the engine uses a distributor instead of an
electronic control unit, check the distributor arm ("brush") and clean
the contact back to bright metal - but without removing any more metal
than you can avoid. Check the distributor cap contact(s), and clean as
before. DO NOT use solvent cleaners, unless you want to put the
distributor cap into orbit!

* POINTS. Remove the distributor arm and you'll see the points. Again,
gently clean both faces of the points - but be VERY careful not to knock
them out of adjustment.

* SPARKS. Remove the spark plug, keeping the plug lead connected.
Switch the fuel isolator cock to "off". Hold the plug body against the
metal body of the engine, and try to start it. (Sometimes this is a
two-person job.) You should see a healthy spark. If you don't, start
tracing the electrical components.

* FUEL. With the plug still out, and disconnected from its lead, switch
the fuel isolator cock back to "on", turn over the engine and have a
good sniff of the cylinder through the plug's hole. You may need to
turn over the engine several times if you've recently reinstalled the
carb. If you don't smell fuel, start diagnosing the fuel system from
tank to carb. If you've an inline fuel filter, remove and clean or
replace it.

* AIR. Reassemble everything, and try to start the motor with the air
filter removed. If it starts, do the same again with the air filter in
place. If it doesn't start any more, either clean the air filter if
it's reusable, or replace it if not.

If the genny hasn't been used for a long time, I'd strongly recommend
purging the fuel system completely (take the purged fuel to a garage for
disposal), and refilling with fresh.

Finally, please don't forget that two-stroke engines need two-stroke oil
added to the fuel, either from a separate tank connected through an oil
pump to the fuel line (post-mix), or mixed by you directly with the fuel
when you refill (pre-mix). If you don't have the correct proportions
added, you'll either seize the engine if there's not enough, or throw
great gouts of smoke if there's too much. I've had a two-stroke
motorbike seize under me at 70mph from oil starvation* - in the depths
of winter. Kinda exciting, that.

Jon
(* It was a post-mix engine. Ironically, I was on my way back from the
British Motorcycle Show at the NEC at the time. I hadn't realised that
it used way more oil per mile at top speed than for pootling around
town, and ran the tank dry. Lesson learnt!)

[Andrew Cleland]

All good stuff. The only thing I'd add is that you can try to give it a
good sniff of Damp Start/EZ Start into the air filter. Less to start the
engine but more to get an idea of whether it's a fuel or ignition
problem - if it still doesn't at least sound like it wants to start it's
an ignition problem; if it does make a few bangs, it's a fuel problem.

FWIW my bet is stale petrol and a gummed-up carb or even a rusty tank
and rust blocking filters/jets - more likely the longer it's been laid-up.

[tony sayer]

>> Finally, please don't forget that two-stroke engines need two-stroke oil
>> added to the fuel, either from a separate tank connected through an oil
>> pump to the fuel line (post-mix), or mixed by you directly with the fuel
>> when you refill (pre-mix). If you don't have the correct proportions
>> added, you'll either seize the engine if there's not enough, or throw
>> great gouts of smoke if there's too much. I've had a two-stroke
>> motorbike seize under me at 70mph from oil starvation* - in the depths
>> of winter. Kinda exciting, that.
>>
>> Jon
>> (* It was a post-mix engine. Ironically, I was on my way back from the
>> British Motorcycle Show at the NEC at the time. I hadn't realised that
>> it used way more oil per mile at top speed than for pootling around
>> town, and ran the tank dry. Lesson learnt!)
>
>All good stuff. The only thing I'd add is that you can try to give it a
>good sniff of Damp Start/EZ Start into the air filter. Less to start the
>engine but more to get an idea of whether it's a fuel or ignition
>problem - if it still doesn't at least sound like it wants to start it's
>an ignition problem; if it does make a few bangs, it's a fuel problem.
>



>FWIW my bet is stale petrol and a gummed-up carb or even a rusty tank
>and rust blocking filters/jets - more likely the longer it's been laid-up.
>

+1 !....
--
Tony Sayer

[Duncan Wood]

Mine just seems to eat fuel pumps :-(

[Jon Nicholson]

Thanks for the suggestions....

Got some more things to try now!

[Jules Richardson]

On Mon, 28 May 2012 14:57:16 +0100, Jon Nicholson wrote:

> I have a Wolf 800 generator, yesterday I tried to get it started in
> ahead of a scheduled power cut tomorrow to no avail.

Does it even try to run?

[Jules Richardson]

On Mon, 28 May 2012 15:47:00 +0100, Jon Green wrote:
> * SPARKS. Remove the spark plug, keeping the plug lead connected.
> Switch the fuel isolator cock to "off". Hold the plug body against the
> metal body of the engine, and try to start it.

I have had the spark track back up the plug body/lead and through my hand
when doing that - wear gloves :-) (or hook a wire up between the plug
body and the engine)

> I've had a two-stroke
> motorbike seize under me at 70mph from oil starvation* - in the depths
> of winter. Kinda exciting, that.

Ahh, engine destruction is fun. This was my (4-stroke) lawn tractor one a
week or so ago: http://www.patooie.com/temp/eng.jpg

cheers

Jules

[Jon Green]

On 29/05/2012 23:04, Jules Richardson wrote:
> On Mon, 28 May 2012 15:47:00 +0100, Jon Green wrote:
>> * SPARKS. Remove the spark plug, keeping the plug lead connected.
>> Switch the fuel isolator cock to "off". Hold the plug body against the
>> metal body of the engine, and try to start it.
>
> I have had the spark track back up the plug body/lead and through my hand
> when doing that - wear gloves :-) (or hook a wire up between the plug
> body and the engine)

That can happen, if the lead's badly worn and the screen has gone, or if
there's a load of dew. Hold it by the plug head only, and it should be
OK if in the dry.

>> I've had a two-stroke
>> motorbike seize under me at 70mph from oil starvation* - in the depths
>> of winter. Kinda exciting, that.
>
> Ahh, engine destruction is fun. This was my (4-stroke) lawn tractor one a
> week or so ago: http://www.patooie.com/temp/eng.jpg

From "Consequences":

Walter: It looks more like an earthquake. Did you notice something ?

Pepperman: Certainly! It's in fifty thousand pieces! Fifty thousand tiny
hand-tooled pieces!

Jon

[Andrew Cleland]

On 29/05/2012 23:04, Jules Richardson wrote:
>

> Ahh, engine destruction is fun. This was my (4-stroke) lawn tractor one a
> week or so ago: http://www.patooie.com/temp/eng.jpg

That looks nasty. I'm trying to work out what happened - looks like a
bit of the main bearing carrier in the debris, but that's an odd thing
to go. I'm guessing the sump was destroyed by a swiftly descending con
rod. Maybe the main bearing cap bolts let go, freeing the con rod which
then went down on the powerstroke. Looks like one main bearing is still
in-place on the crank - is it a twin?

AC.

[Jon Green]

On 30/05/2012 09:05, Andrew Cleland wrote:
> On 29/05/2012 23:04, Jules Richardson wrote:
>>
>> Ahh, engine destruction is fun. This was my (4-stroke) lawn tractor one a
>> week or so ago: http://www.patooie.com/temp/eng.jpg
>
> That looks nasty. I'm trying to work out what happened - looks like a
> bit of the main bearing carrier in the debris, but that's an odd thing
> to go. I'm guessing the sump was destroyed by a swiftly descending con
> rod.

If the sump's air space was topped-up with water (common problem with
lawn mowers, along with water in the cylinders), and/or oil galleries
were blocked, the descending piston would have over-pressured the sump,
causing a casing failure.

Jon

[Jules Richardson]

On Wed, 30 May 2012 09:05:54 +0100, Andrew Cleland wrote:

> On 29/05/2012 23:04, Jules Richardson wrote:
>>
>> Ahh, engine destruction is fun. This was my (4-stroke) lawn tractor one
>> a week or so ago: http://www.patooie.com/temp/eng.jpg
>
> That looks nasty. I'm trying to work out what happened - looks like a
> bit of the main bearing carrier in the debris, but that's an odd thing
> to go. I'm guessing the sump was destroyed by a swiftly descending con
> rod. Maybe the main bearing cap bolts let go, freeing the con rod which
> then went down on the powerstroke.

The root cause was oil starvation; the oil thrower in these engines -
visible as the lump of chewed orange plastic in the photo - is driven by
a gear on the camshaft, and is held in place by a bracket which hooks
over the end of the camshaft. Over time, the mounting hole for the
bracket is prone to wearing oval, resulting in the oil thrower teeth not
meshing properly with the drive gear and eventually stripping out.

Rather than having counterweights built into the crankshaft itself, this
engine variant has pivoting balance weights which are driven back and
forth by cams on the crank (the weights are sitting on the floor at the
bottom of the photo). The shattered remains of the top support/bearing/
cam for the weights show signs of major overheat, so I think this failed
first due to lack of oil. At that point the lower support couldn't handle
the load all by itself, and it gave out too. The descending con rod
collided with the weights, punching them out through the end of the
crankcase.

cheers

Jules

[Andrew Cleland]

Interesting, thanks. Seems like a good case for Keeping It Simple - that
balance weight design seems overly complex for a small lawnmower engine.
On the other hand, once the oil pump's shagged, failure is a given,
normally the mains, pretty sharpish.

AC :)

[Jules Richardson]

On Wed, 30 May 2012 16:09:07 +0100, Andrew Cleland wrote:
> Interesting, thanks. Seems like a good case for Keeping It Simple - that
> balance weight design seems overly complex for a small lawnmower engine.

Well, this engine shares a lot of common parts with the smaller 10HP, but
just has a longer stroke to increase capacity; I wonder if the necessary
counterweights would just have been too large for the crankcase (I'm sure
they'd physically fit, but perhaps would hinder oil dispersal to the
flywheel side of the engine, given that it's all splash-lubricated rather
than pumped via oilways).

> On the other hand, once the oil pump's shagged, failure is a given,
> normally the mains, pretty sharpish.

I'm amazed that damage wasn't more extensive, considering; the bore,
piston, valvegear and crank bearings all survived.

I happened to also have a 10HP (sharing many of the parts, as mentioned
above) with a badly-scored bore, so just for laughs* I stripped and
cleaned the "exploded" 11HP, stitched the crankcase back together, and
put in the conrod, crank, oil thrower and governor arm from the 10HP -
so, it's running again, it's just a 10HP now rather than an 11. That, and
it might shake itself to pieces at any moment ;-)

* I had access to another 11HP with carb issues and a crankcase full of
gunk, so I've fixed that one and stuck it back on the tractor.

cheers

Jules