Something happened to the engine

[oczuk32]

Tried starting the engine this evening and it sounded like it completely lost compression. Any thoughts?

 

[bushytails]

Are the accessories (alternator, etc) turning?

[oczuk32]

2 hours ago, bushytails said:

Are the accessories (alternator, etc) turning?

Everything is turning over and getting spark. It cranks, but then stalls out. Based on what someone mentioned, the old varnished fuel may have damaged the valve seat seals or piston rings, causing a loss of compression. I drained the old fuel from the tank and blew out the fuel lines with compressed air. Then I added a couple gallons of fresh gas along with a treatment. I suspect the treatment is doing its job by breaking down the varnish in the tank—but that might be sending residue into the engine. I’ll monitor how it performs over the next few days.

[bushytails]

If everything is turning, you probably just washed the cylinder walls, and it'll sound normal again after you fix the fuel problems and get it running for a bit.

[el_freddo]

Worst case scenario your valves are stuck open from some gummy crap. You should be able to pull them closed again with the rocker covers removed. 

If it happens again afterwards, I’d be looking at spraying some sort of solvent or fresh fuel down the intake while cranking to hopefully clean up the gum that’s holding them open. 

Cheers 

Bennie

[bushytails]

I doubt it's anything actually mechanical, just because it's all cylinders at once. 

[el_freddo]

9 hours ago, bushytails said:

I doubt it's anything actually mechanical, just because it's all cylinders at once. 

A complete loss of compression suggests it’s mechanical. It would be odd for all cylinders to lose compression, yes, but stranger things happen though. Someone even suggested that the cylinder walls were washed and will come good. I don’t know what that means exactly though - but it is something mechanical that’s the issue.

I’d be flushing out the old fuel rather than having the engine eat it. I’d put the highest octane fuel you can get and run that for several tanks, then return to your regular fuel octane rating you use. 

Cheers 

[bushytails]

I'm the one who suggested that the cylinders were washed.  lol.

The piston rings seal with a very thin coat of oil on the cylinder wall.  If you ever get fuel without starting, like trying to get a bunch of old gas and a dirty carb to run, the fuel washes this thin oil coat off the cylinder walls, and you lose compression.  Fixing the problem that caused it not to start (i.e. flushing bad fuel, and dismantling and cleaning a gummed up carb), and starting it, will get oil slung back onto the cylinder walls, restoring the ring seal, and restoring compression.

Sticky valves or such aren't going to happen simultaneously to all four cylinders from a running engine...  Mechanical things that could affect all cylinders at once are a broken crank, broken cam (I saw this once! ...  but there was a lot more broken too), broken timing gears, slipping ring gear (so you're not actually cranking the engine), etc...  But if the accessories and dist are turning, those are all going to be fine.  Broken cam or timing gears also cause a distinctly different sound, since some cylinders will be stuck with both valves closed, and compress each revolution - the sound of an EJ ready for a timing belt and half the valves replaced....

Am I positive I'm right?  Of course not.  They could have blown both headgaskets at once, or some other simultaneous multiple failure.  Or the engine is total crap and never actually had any approximation of full compression but was limping along.  But, based on my experience, I think it's the most likely diagnosis, which is why I said "probably".

 

[el_freddo]

Makes sense. Thanks for the explanation of cylinder washing. I wouldn’t think you’d lose that much compression though unless rings are super shot already. But I could be wrong on that too.

I too said it was unlikely all four cylinders would have a stuck valve. This one seems almost the same as removing the spark plugs and cranking. 

Cheers 

Bennie