Blown head gasket?

Geo-TH,In

Well-known Member
I had a service manager at a small engine repair
shop told me I had a blown head gasket on my 20
hp kohler causing the cylinder to run 50 degrees
cooler and richer. How can a blown head gasket
cause a cylinder to run rich. BTW, the exhaust
temps are the same.

I did a compression test and discovered the
cylinder with a so called blown head gasket has
180#. The hotter cylinder, the one that runs
cleaner, has 165#.

Plan to do a leak down test tomorrow.

What are the symptoms of an engine with a blown
head gasket?
 
I have seen a blown gasket cause a lot of blowby on some engines, if it is blown into the rocker arm area.
 
Carbon is a sign of unburnt fuel, my guess is that that cylinder has lost the ability to hold up the compression to spec's, probably the rings are wore. The leak down test should confirm if that is the case.
 
Compression test on rich cylinder 180. lean cylinder 165. Leak down test showed same results on both cylinders, 25%. Valves all good, air was going past rings. No sign of leaking head gasket as service manager told me.

My guess too, unburnt fuel. But how can the same carb make one cylinder richer than the other. Plug was totally black with carbon in 10 minutes.

As a last resort, I instlled a carb off an 18 hp kohler. Seems to work ok. A little on the lean side until it warms up, needs a 1/4 inch of choke or engine stumbles a tick. Good on power under load after it warms up. Running engine around 2500 RPM's. Hope it works better.

Sprayed sea foam in carb, one second at a time to decarbon rich side.

No blow by, no oil consumption. Just one cylinder making carbon. Go figure. Hope what I did works in the long run.
 
" Just one cylinder making carbon. Go figure. Hope what I did works in the long run. " This is how I figure it..
The carb will not make one cylinder richer than the other. There getting the same amount of atomized fuel. The difference is in the compression. One side, the atomized fuel/air ratio makes for a complete fuel burn. The other, the fuel has larger droplets of fuel as a result of less compression. Thus the fuel does not burn completely. The outer covering of the droplet gets burnt and the heat causes the rest to turn to carbon. As this becomes a balancing act to try to get a more complete burn on the lower compression cylinder, their are a couple things you could do. Change the carb setting, you temporarily do this by leaving the choke on until the engine temperature rises. Thus higher cylinder temps help to get a more complete burn. As you noted earlier you can also get a higher temperature in the cylinder by switching to a higher value plug rating. The down side to that is you increase the chances of burning a hole in the piston if push the temps to high. So, the short run, you have tuned the engine to the most reasonable running condition as it exists and may function acceptable for some time. The long run, the engine will deteriorate further over time.
 
One guy said he had seen leaking intake manifold cause the problem. Manifold is plastic too.

I noticed the old carb I removed may have had the float level wrong, too high fuel level.

I also switched to platimun plugs.

Hope it all works out. Know more when it warms up a bit.

THANKS TO ALL.
 

George, sometimes I think people just make wild guesses as to what causes whatever is wrong. In your case, I'd be checking that plastic manifold for leaks on the "cleaner", non-fouling side. If it's leaking you have to run it richer to compensate and that shows on the good side which now becomes the fouler. I don't trust plastic and heat at all.

Just another wild guess! :lol:
 
Bret4207,
Wild guess is all I have to work with. Like
Edison, I try to eliminate things. Learning what
it isn't and then moving on. The manifold is the
next avenue I'll look in to if things don't clear
up.

The kohler is a V-twin. The pistons are set 90
out. Which means the time between intake strokes
are out of sink, which may be causing pulses in
intake manifold vacuum at lower speeds causing a
problem too. Fixed EPA jets may be a part of the
problem if I don't run engine faster.
Wild guesses is all I have to go on at this
point. Test out first before I remove head
gasket, which I'm 99% sure is not my problem.
 

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