sudden loss of compression

[olidaviesuk]

All,

Quick question - just stuck some new pistons in my cup, put together as per manual, checked liner protusion etc etc, compression tested all 4 at 150psi +/- 4psi ran okay etc.. head torqued up to 70n/m

Had a spark plug hole in the head helicoiled by the local enginnering shop who did it in situ, as the thread was fcuk'd... though not sure exactly what they did as wasn't there when they did it.. put all the pipes back on today and wouldn't start...

Checked everying, inc valve timing and all okay, decided to compression test the engine cos nothing else left to check, and all at 45psi.... :crap:

Anyone care to shed any light on what might have happened, having the head off tomorrow to have a look...

[RICHIE]

All,

Quick question - just stuck some new pistons in my cup, put together as per manual, checked liner protusion etc etc, compression tested all 4 at 150psi +/- 4psi ran okay etc.. head torqued up to 70n/m

Had a spark plug hole in the head helicoiled by the local enginnering shop who did it in situ, as the thread was fcuk'd... though not sure exactly what they did as wasn't there when they did it.. put all the pipes back on today and wouldn't start...

Checked everying, inc valve timing and all okay, decided to compression test the engine cos nothing else left to check, and all at 45psi.... :crap:

Anyone care to shed any light on what might have happened, having the head off tomorrow to have a look...


dont rush to take the head off. did you do the compression test with the throttle open.

[Markey Mark (BD)]

Was it just pistons you put in or pistons and liners?

If it was just pistons did you key up the old liners by honing them abit first before you put new pistons in?

[olidaviesuk]

yep, throttle wide open.... matched pistons and liners came out of a spare engine I was building.. all tested and ran ok before i had the head helicoiled, seems to have dropped the same amount over all 4 which is whats puzzling...

have checked the comp tester on another engine as well and is working ok...

have squirted oil in the bores as well and makes no difference...

[RICHIE]

are you able to do a leak down test. at all rather than a compression test. this will help diagnose if the compression is escaping and will help locate the problem rather than tking the head off.

[Adam 005]

Broken comp tester:agree:

[olidaviesuk]

heads off, loads of metal swarf over the place.. thinking looks like headgasket and valve seals... hmm im seeing an afternoon of lapping in valves and swearing at engineering shop..

not pleased!

[michael tierney]

u will get low readings if the engine is cold(6bar).also low if all ur rings are broken and low if ur exhaust is blocked or cam timimg out!!

[Os8472]

heads off, loads of metal swarf over the place.. thinking looks like headgasket and valve seals... hmm im seeing an afternoon of lapping in valves and swearing at engineering shop..

not pleased!

Sounds like you need to go back to the engineering shop and give em hell