Generac 10 kVA Generator again.

[WFK]

Calling my fellow shade tree mechanics!
I have a photo and an enlargement of part of it.
(I think the mechanic got me good...)

These are the headbolts of the cylinder in question.
Status was: mechanic ran generator for 3 hours until it stumbled.
He took the head off the questionable cylinder.
He diagnosed bad rings based on the top of cylinder being rather clean at two places of the circumference.
He said he discussed it with B&S.
he ordered a new head gasket, cleaned off the piston top and the mating surfaces and re-assembled the genny.

he did not:
run it again for three hours
did not clean the headbolts.

I then decided to change the rings and disassembly began. :sb:

I noticed that two of the headbolts were heat discolored, but put them aside. (Six were not discolored.)

My thinking began after much doing

There HAD to be a reason for the heat discoloration!
So I looked at the headbolts again tonight and present these photos for your comments. (I already have an opinion, but now I need YOURS!

 

[WFK]

and that is oily carbon muck on the threads:

Got an opinion?

edited: oily carbon (can't wipe it off with a rag)

 

[Green Co.]

WFK...you are so much deeper into this engine than I would ever have contemplated. I'm inquisitive, but most times, lack time/patience.

That being said, if those bolts had come from one of my diesels, it would scare the hell out of me, I would be magna-fluxing the block for cracks.

 

[Satanta]

Thread patterns different?

 

[ittybit]

Looks like the metal has reached tempering temprature, which is too hot for an engine. The oily deposits indicate ... oil leakage.

If these bolts came from the same area/cylinder I'd say that cylinder go real hot at least once.

..

 

[2x2]

LOOKS LIKE THE TWO BOLTS ARE THREAD SHORT....

......Resulting in a "loose" fit of the head,resulting in heat getting to the bolt and sludging up the cylinder. Get the correct head bolts.
Had a similar thing happen to me on a company van.Had a flat tire ,one wheel bolt different size,walked two miles to a Hills store for a "tee wrench".Cussing loudly all the way.

 

[WFK]

Satanta: no...
itybit and 2x2: The bolts are alike in every detail. I am not sure if the dark ones came from the front originally.

"tempering temperature" I agree. And I think they were never torqued to spec. They may no longer have their specified elasticity and will be replaced.

A lot of the engine behavior makes sense when one considers that bolts heated this way also expand. (Increasing misfirings after engine ran for awhile)
I now think that the head gasket was loose enough to have exhaust leaking into bolt holes. But it didn't show up during the compression test (which was done cold...)

The areas (two) observed by the technician as cleaner on the piston circumference are adjacent to the front bolts. I think the crud missing there is on the bolts!

Whether it is carbon or burnt oil I cannot say. But it looks and feels alike in both cyclinders, so I vote for carbon.

The only thing then I don't understand is the mechanism by which a bad seal causes crudding up of the spark plug. Is that to be expected?

If this theory is correct, it would be just ANOTHER item of poor assembly (with really big effects.)

 

[WFK]

Well, it hasn't been reassembled and tested yet. I have re-read the replies to my original thread. So far the first price goes to Rex Jackson for this post:

Try re-torquing the heads. There is a good chance if there was a loose bolt, it could have ruined the gasket as well. Buy a compression tester, see if both cyls are the same.

I may have checked head bolts then on a gasket that was already ruined. Actually, I didn't use a torque wrench then.
The compression tests were misleading for me and the mechanic.
(But the mechanic utimately PULLED the head and the bolts and should have noticed what I saw. He also saw the old gasket but I didn't.)

 

[Jerry]

Have you gotten to rings yet ? My guess is that the oil ring in the offending cylinder is in upside down..... Oil into fuel mix will lower octane rating leading to preignition, leading to burnt head gasket ????? My two cents, J.

 

[WFK]

new rings installed.
Oil ring consist of three parts: upper/spreader/lower.
Can't install the three-part oil ring upside down.
The other two rings had been installed correctly.

Surprises during re-assembly: specified torques seem soo low! Maybe because most is screwed into aluminum.
Newton-meters and inch pounds.
Of course the torque wrench is graduated in foot pounds.

And even WITHIN the engine there is a happy mix of US and metric wrenches required.
Someday we all will love the metric system!

 

[WFK]

I am taking a break!

 

[WFK]

Generator has been running for one hour now. Sounds OK. No load. Output voltage and frequency are OK.
Will have a result in a few hours, one way or the other.
Criterion for successful repair as given to the mechanic is mine as well:
Running for three hours with spark plugs (left/right) looking identical.

 

[WFK]

Would not have been able to re-assemble without digital camera photos printed! One of 25.
At this point the generator is in pieces on the floor and just the engine front end is still in the frame. No other way to get to the pistons and rings:

 

[WFK]

Why is nothing ever definite?

The plugs do NOT look alike...
The plug in the suspect cylinder has now a gray ceramic center while the other one is is not discolored at all. There is no crud on either plug.

4 hours run total, 2 hrs no load but full speed, 2 hrs partial load.
Ran at end of test like at the beginning.

------Had I not looked at the plugs, I would probably have no objection-------

The "suspect" cylinder is far from the original:
It has a NEW (complete) cylinder head
Piston has new rings

Push rods (exhaust -aluminum-) were replaced on both cylinders.

The generator will remain my whole-house emergency generator.
(Short outages are covered by solar/batteries/inverter.)

Changes overall: a gas filter has been added, plugs will be platinum, oil will be synthetic. The oil drain has been upgraded to a DEERE tractor drain which permits connection of a hose.

 

[WFK]

Runs better than before