hannajc111

I'm having the head reconditioned and valves as well, due to the constant misfire on piston 4. Is there anything I should be aware of or watch out for?


Is there anything specific that would cause the pistons to be so dirty? I bought the car at 87,000 and it has 140,000. Used only premium gas, as well as regular use of Techron.


Thanks.

VVF

The two on the left look pretty normal to me. The two on the right might be because of some valve stem seal oil leak? Or maybe they got soaked during the head removal.

hannajc111

Thanks for your reply. Actually, the far right is piston 4, the one I keep getting misfires on. Nothing got soaked during the head removal. I guess I'll just clean the piston heads and hope for the best after the engine head gets re-done.

hannajc111

That should be far left, not right

VVF

You can also do a leakdown test after the head is on. - Will show you if the rings are worn (since the valves will be new ) But that should not lead to misfires anyway.

Just noticed - is the lower-right valve cracked at the top? two marks at 11 o'clock.

RedGray

Oh, oh, a reply from a newbie - just ignore it.

1) Looks like you had a head gasket problem between #3 and #4. That's oil, coolant, carbon build-up on the pistons.

2) Ask a thousand people and you'll get a thousand different answers. Imho, the Chevy or the Ford crowd have a lot more experience tearing down an engine every race season (/year) or more often. Also, things like heads, cams, pistons, intakes, etc swaps get down a lot more on race cars or the Chevy/Ford sports cars. Part of it comes down to the cost of the parts and the type of part availability. Heck, you can get a rebuilt GM 350 engine for $1,500. That's close to the cost of a rebuilt head for the M111 or M271 MB 4 cylinder engines.

3) I've done 100% complete engine rebuilds many times, and have been working on cars for over 20 years.

4) There is not a 100% correct answer.


5) What *I* have done, and many others, is something similar to the following:
a) You're going to be turning the engine crank. If you're not comfortable with being able to find the correct TDC, then do NOT do the following! On a 4-stroke engine, a piston is at TDC for both the compression and exhaust cycles. When putting on the timing chain back on, the phase needs to be correct.

b) Spray WD 40 on the cylinder walls with the piston all the way down.

c) Rotate the piston all the way up.

d) Mask off (very well) the top holes and the edge of the piston and the cylinder wall.

e) This depends on how good/experienced you are. Gently use a scraper or wire brush to get the carbon/etc off the piston. Be careful to not gouge the piston. If your finger nail doesn't catch in the "gouge/scratch", then it's fine.

f) Use a shop vac while you're scraping!

g) Use Acetone to clean up the piston afterwards.

h) CLEAN the area VERY well.

i) Use the shop vac around the piston to suck up anything.

j) Slowly rotate the piston down. Stop a few times on the way down. Clean the walls, and use the shop vac to clean the piston cylinder walls.

k) After the piston is all the way down, spray the walls with WD40.

l) Rotate the piston up again.

j) Vacuum again.

k) Slowly rotate the piston down, stopping a few times. Clean the walls and vacuum the piston cylinder area.


Doing the above gets most/all of the stuff off the piston. There's very little chance of ring damage.
The above, or similar, gets done hundreds of times each week by people that race their cars.

I've done the above a number of times. I've never had any problems. And, my other car is also my daily summer driver and has plenty of miles on it.

Be wary of people that say "do xyz - my car has been fine for years". You care more about the miles and the type of miles, verses a car that gets driving 150 miles a year and only on a few weekends.

RedGray

Imho, a compression test should be just as good. The problem with a leak-down test is that the valves must be completely shut and tight on the cylinder. That can be a huge hassle, depending on how easy it is to get a ratchet on the harmonic balancer bolt. Also, a compressor with a good enough CFM volume is needed.

I've done plenty of leak-down tests. Imho, I go to a leak-down test if a compression test and a coolant exhaust gas test don't show anything "definitive" - but there is still a problem.

Also, leak-down tests can be affected by whether the engine is cold, warm, or hot. And, doing a leak-down test on a hot engine is often not fun.

Fwiw, from my own personal experience, *I* have seen most of my cold engine leak-down tests to be between worthless to kinda close.


From: https://mechanics.stackexchange.com/...-a-cold-engine
So searching the Internet, I've found some conflicting opinions, with an occasional person saying either that cold leak down tests are completely invalid, or that cold numbers will be two to three times warm numbers.



Fwiw, imho, a compression test (dry and wet) should've been done before the heads were removed. And the results should have been saved/recorded.