No compression after HG change

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TwoHundredTeeDeeEue

New Member
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Morning all.
Replaced HG on my 200 TDI recently and put a 2nd hand head on (looks in decent nick, cleaned up valves and fitted new stem seals). I did balls it up and put gasket top-down initially (it was dark, that's my excuse..). Tried starting, sounded like low/no compression as turn over was really fast. Realised oil leak from front of cylinder 1 and the thickness marker on gasket was behind diesel pump so knew what I'd done. Took it all off again, refitted with new HG. I still have the same starting issue but no leaks this time. There was some coolant in the cylinders after my previous mistake.
Compression tests on all cylinders showing only 3-5 bar. Leak down results were pretty good, took rocker shaft off to ensure valves were sealing and they seem to be acceptable.
Any suggestions on what I might have done or what I do next? Main concern is I've bent the con rods and not getting compression due to reduced piston travel so I'll need to take the head back off to check that anyway. Seems a bit extreme that would have happened just turning it over from the starter for a minute or two though.
 
Pump and valve timing, that of course if if you touched it?
Adjusted the valve clearances?
Power to the inj pump stop solenoid?
I cannot see it being a compression issue, if all cylinders are reading the same.
 
lynall said:
Pump and valve timing, that of course if if you touched it?
Adjusted the valve clearances?
Power to the inj pump stop solenoid?
I cannot see it being a compression issue, if all cylinders are reading the same.
Click to expand...
Didn't touch the timing so hopefully that's still okay, unless it jumped a tooth when I tried starting it with coolant in the cylinders but not sure how likely that is on these engines.
We didn't do valve clearances yet, it is a different head so that is definitely worth a try. I assumed it would be a bit noisy and run a bit rubbish but should still start.
Checked pump solenoid, can hear it clicking so as far as I can tell, that is probably working. I was initially hoping that was the problem as it would have been an easy fix :) I did replace spill pipes too but bled the system all the way to the return pipe and can see no air and fuel is coming through.

I see, so if they are all reading around about the same, its not an immediate indicator of a problem? They just seemed really low but that's assuming the gauge I'm using is reading accurately...
 
You will definitely need to do the valve clearances especially as it is a replacement head the actual clearances themselves do not matter as long as it is some for initial starting
Do not forget to fit the valve lash caps as well
 
lynall said:
You will definitely need to do the valve clearances especially as it is a replacement head the actual clearances themselves do not matter as long as it is some for initial starting
Do not forget to fit the valve lash caps as well
Click to expand...
I'll give that a try then, thank you very much for the advice. I didn't think it would make that much difference initially so didn't bother with that step :)
 
Why was the work carried out in the first place?
Did you do the compression test with the rocker shaft removed?

3-5 bar is rubbish so you have done something really wrong or not doing it correctly.

New head? which rocker shaft not that that really matters You need to check the you have valve tappet clearance to start with .

J
 
lynall said:
Easy to do, just google rule of 9.
Click to expand...
Thanks for the advice, can't feel my fingers or toes after being out in the cold for an hour but it started up and sounds pretty sweet. Really appreciate it! Clearances were all far too tight so must have been holding valves open. We should have done the leak down test with the rocker shaft on and run through the cycles. I was expecting the worst and forgot the basic :)
 
marjon said:
Why was the work carried out in the first place?
Did you do the compression test with the rocker shaft removed?

3-5 bar is rubbish so you have done something really wrong or not doing it correctly.

New head? which rocker shaft not that that really matters You need to check the you have valve tappet clearance to start with .

J
Click to expand...
It's been blowing out the head gasket by the bulkhead for about 3 years but still perfectly driveable so decided winter was a good time to undertake the work. Assumed the head might be scarred from the exhaust blow so go a replacement to "save time". I started the job late November so time didn't really factor in the end 😀
 
TwoHundredTeeDeeEue said:
Thanks for the advice, can't feel my fingers or toes after being out in the cold for an hour but it started up and sounds pretty sweet. Really appreciate it! Clearances were all far too tight so must have been holding valves open. We should have done the leak down test with the rocker shaft on and run through the cycles. I was expecting the worst and forgot the basic :)
Click to expand...
Free fixes are the best.
 
Just a quick update on this. Test drive went okay, blew intercooler hose off but nothing catastrophic. Got a bit tappy when warmed up and wouldn't start when hot. Redid clearances and it was even worse, was missing and sounded like ****e. Inspected pushrods and, somehow, 4 were now bent. May have happened on first refit when cylinders got water in but I'm sure I'd have noticed 2nd time around. Fitted new pushrods, lash caps and adjuster screws (couple of them looked a bit warped but I can't be sure) and it sounds pretty good again. Fingers crossed I've fixed it properly now, on the umpteenth attempt. 😀
 
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