Very low compression after head gusket replacment

Hey humans:) Been screwing with kz1000 police 1982. Replaced base and head gaskets. Did the job to replace steam seals. Valves were grouted and seals were replaced. It was done not by me so the dude may have confused the shims. Anyway I fired it and it ran like shit backfiring back into the carbs. But all 4 cylinders were working. Next day could not fire it at all. Timing is perfect. Only # 4 cylinder has compression and proper valve clearance 0.05 the rest of cylinders have at least one valve without no valve clearance and very low compression like around 60-70. I wonder how would it ever run with that low compression and what might have happened here. It was running great before I got to it only smoked. Compression was between 150-170 psi on all cylinders.
Any ideas?

Reshim to the correct tolerances.


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Nebr_Rex wrote: Reshim to the correct tolerances.


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Agree. A no brainer.

What was the question again?

Be sure to read the "how to set valve clearances" thread...... all 125 comments first. :lol:

While you have the valve cover check the cam timing. Did he test drive it before he gave it to you. Was he a HD mechanic by any chance?
Steve

Would suspect that supposedly closed valves are for whatever reason failing to seal.

Could be lack of clearance, and/or issue with mating surface between valve and seat (damage to head or seat, or imprecise valve job, or bent valve), and/or weak or broken valve spring, and/or worn guide, and/or other less common issue such as sticking bucket (for whatever reason), etc.

Would perform a leak-down test to identify where the compression is escaping from each combustion chamber.


A leak-down test injects air pressure through the spark plug hole to pressurize the combustion chamber.

Can perform a poor-man's leak-down test by introducing compressed air into a spark plug hole and listening to where it escapes from the combustion clamber. This may be done at TDC or any other cam positions where both valves are fully closed. Top dead center (TDC) is when the piston is at its highest position. An easy way to tell TDC is by alignment of the T mark with the case mark when viewed through the timing window.

May introduce a spurt of compressed air by using a rubber cone-tip blow gun (rubber air nozzle) held into the spark plug hole. And of course keep holding it in position to keep air from coming back out the spark plug hole while listening for escaping air at other places. The air compressor should not be running while listening because the noise will likely drown out any sound of escaping air. Or just use a portable compressed air tank.

Air heard escaping from exhaust port indicates exhaust valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from carb intake indicates intake valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from crankcase breather indicates loss of compression past rings into crankcase (perhaps worn piston rings or cylinders).

Air heard escaping from head gasket area indicates loss of compression past head gasket (perhaps due to a blown head gasket).

A leaking valve may sometimes be resolved by adjusting the clearance to within specs.

A leaking head gasket may sometimes be resolved by torquing the head fasteners when the engine is stone cold (such as after sitting overnight).


Good Fortune!

KZB2 650 wrote: Be sure to read the "how to set valve clearances" thread...... all 125 comments first. :lol:

swest wrote: . . . Did he test drive it before he gave it to you. Was he a HD mechanic by any chance?
Steve

Good Fortune!

dimanya wrote: . . . backfiring back into the carbs. . . . .

Indicates failure of the intake valve to fully seal (for whatever reason) when it's supposedly closed.
Often, but not always, remedied by adjusting clearance of the intake valve to bring clearance within spec.

What happens is that part of the combustion inside the cylinder escapes through the leaking (not fully sealed when supposedly closed) intake valve and goes out backward through the intake port and into the carb.

As known:






Good Fortune!

A common mistake by an uncaring or just incompetent mechanic it to set the cam timing wrong. If he doesn't have the tool, he will remove the cams then put them back in wrong. I'd first check the clearances. If you're lucky, you can adjust them yourself.
Steve.

swest wrote: A common mistake by an uncaring or just incompetent mechanic it to set the cam timing wrong. If he doesn't have the tool, he will remove the cams then put them back in wrong. I'd first check the clearances. If you're lucky, you can adjust them yourself.
Steve.

Where less lucky, may have resulted in a bent valve due to contact with the piston when the crankshaft was rotated.

Good Fortune!

Already getting the tool. Don't want to take cam shafts off and on.

Timing is perfect done by the book (though book is fkd up sometimes). When cams tied in place all 3 marks line up. Could not confuse cam shafts ether I marked them on the other side before taking off. He was regular mechanic just some guy that I know.