engine miss- low compression on my 400

SDE

Well-known Member
Initial problem- coolant in oil
drop pan
coolant on the #3 sleeve
remove head and pull piston and sleeve
Sleeve and block look good
Head has crack in the combustion chamber
Tried to weld it myself
assembled the engine and it ran good- twice
still getting coolant in the oil
Warm the engine and add K-Seal to coolant
Next 2 times I run the engine it has a miss on #3
Compression, #3 is 75 lbs. add oil, now get 125.
K-Seal rep says it can not bind movable parts
When I put the sleeve back in, I rotated it a quarter of a turn. I heated the block and cooled the sleeve, but needed to use a block of wood and a hammer to get the sleeve to go in the last two inches. I did not hit it hard to get it in. I did hone it, before putting the piston back in. And it did run good the first two times I ran it. Where or what did I do wrong? I will be tearing it apart soon. If the top ring is broken, is it because there must have an invisible ridge that caused the ring to flex to much?
Thank you
SDE
 
Check that the pushrods are in place and that the valves are correctly set.

Then, do a leakdown test to verify it's leaking past the rings.

If it is, you will simply have to tear into it to see what broke, 'cuz the ones of us out here on the 'net are no better at x-ray vision than you are?

(STILL trying to figure out why you took the piston and sleeve out if it was obvious the head was cracked???)
 
I am also confused why you took the sleeve out. I would think that compression that low would be a valve issue, so good thinking on checking push rods.

What are symptoms now?
 
If you are still getting coolant into the oil, is it getting into the combustion chamber shorting out the sparkplug? You said that you honed the cylinder. What about the piston rings? New or did you reuse?
 
Unless you pressure tested the head after repair its still questionable. If leaking into the combustion chamber it can damage the piston rings or break them on startup if enough fluid gets above the piston. Maybe the first thing to check is after siting overnight, remove spark plugs and see if coolant comes out any of the holes. If not try to move each piston to top and try to see a wet piston top. Depending on pistons that maybe can't be done with the eyeball.
You didn't say if coolant was running down inside of sleeve or outside. If outside you probably missed a crack.
 
When I saw that there was coolant on the bottom of the sleeve, I assumed that it was leaking between the sleeve and the block. So I pulled the sleeve. It was after that I pulled the sleeve, that I saw the crack in the head. Had I seen the crack first, I would not have pulled the sleeve.
Steve
 
I do not think that it is leaking any coolant, any more. I will pull the plugs and check for coolant/wet pistons. It has started easily enough that I did not notice anything that should have broken any rings. If a cylinder had that much coolant in it, wouldn't it blow some of it out the exhaust? I have not noticed anything like that on the ceiling above the exhaust. Thank you
SDE
 
After adding oil to the cylinder, the compression was up to 125. I thought that the increase in the compression indicated that the rings were the problem. Am I wrong on that?
 

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