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Compression Results for GTD :(
by
wil892
on 16 Apr, 2011 05:27
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Hi
Bought myself a decent draper compression tester a few weeks ago. Anyway the car has been in the garage for a few weeks but battery ok. removed injectors and pipes and did a compression test. The car was running before this but was a little smokey and wasnt great in the mornings.
Results
No1: 200psi
No2: 200psi
No3: 100psi
No4: 200psi
Firstly these must be undereading otherwise I doubt the car would have run. But this is what the tester showed. The injector holes showed no excessive carbon build up and looked fine. Assuming the tester is undereading there is still a 100psi difference between No3 and the others which I guess would explain the miss it has when its very cold outside. TBH i really wasnt expecting these poor results though. Anyone got any ideas on what to do next. The engine had a new cast head 20k miles ago with new injectors. Im wondering if the 1.25mm advance I have been needing has been due to the low compression?
Will
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#1
by
the caveman
on 16 Apr, 2011 08:27
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That's all pretty low, even as you say if the tester is off by 100 lbs [ !] .
It would explaining all the other things you mentioned -timing etc. Looks like you need a complete rebuild unfortunately.
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#2
by
TDIMeister
on 16 Apr, 2011 08:33
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I trust the compression test was done on a thoroughly warm engine...
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#3
by
the caveman
on 16 Apr, 2011 08:50
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I trust the compression test was done on a thoroughly warm engine...
I agree that it SHOULD be done on a warm engine, but if it's that low even when cold, it's still way too low
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#4
by
wil892
on 16 Apr, 2011 08:52
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Test was done on a cold engine. Engine hasn't been run for a few weeks actually. Cars battery was charged but I also boosted it from another car while collecting the results.
One thing I dont understand is how the compression adapter can get an accurate result when the actual adapter and line for the tester acts as extra air volume. The hole in the adapter is quite big I can only think this is reducing the reading a lot.
However I retook the readings and got
No1: 210psi
No2: 205psi
No3: 120psi
No4: 220psi
Compression builds within 1 or 2 strokes. I do think the engine must be worn with those numbers though. It uses quite a lot of oil, has a lot of advance, is fairly smoky, and is noisy and misses a bit when the temps are freezing. However it starts up fine when its hot and uses no glowplugs. It also has good power and has been doing 40-45mpg.
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#5
by
the caveman
on 16 Apr, 2011 09:50
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You could try cranking the engine over for a few minutes get the rings to reseat if the engine has been sitting for a while. I would also drop a little motor oil in each cylinder to help diagnose whether it's the rings. But if the engine has big mileage it may just be too worn.
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#6
by
wil892
on 16 Apr, 2011 10:23
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Rings might need reseating yes, though the engine has only been off for about 6 weeks. Previous to that it was doing motorway miles and town miles with plenty of power.
When I had the head off about 20k ago the bores had their cross hatches on which would suggest the bores are within spec.
This compression tester annoys me because it cannot be giving an accurate result. It is made by draper and has a good reputation. The bore of the adapter just seems to big too give an accurate indication of the compression. I would have thought a diesel compression tester should have barely any bore to it otherwise it just introduces volume to the cylinder.
Having said that looking at cylinder 3 it is about 100psi less than the other cylinders.
Im not entirely sure on the mileage but I wouldnt have thought it stupidly high.
Car was starting fairly ok with two glowplug cyles when it was -5 celcius so the actual compression cannot be too bad. To test it I actually started it without glowplugs when it was -3, it took about 10-15 seconds of cranking then fired fine but a cloud of unburnt diesel came out the exhaust.
I expect I will put the engine back together and rebuild a block I have sitting in my garage, its very tempting to get a TDI in there but I would like to keep the car stock as it is quite a rare version of the 1.6td and everyone seems to just get rid of these engines over here in the UK in favor of AAZ or TDI. Which i do understand to an extent powerwise, but having an orignal stock(tweaked) GTD may still be pretty cool.
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#7
by
adi
on 16 Apr, 2011 10:28
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Stick with the SB lump mate, they are uber cool and fairly rare over here
And with a few tweaks can be GTI eaters. Mine has a stock intercooler (soon to be mounted up front), shimmed governor, MBC, 18psi and it will see any 8v GTI off with ease, and its not even set up properly yet! Its more fun beating GTIs when you're literally "smoking" them
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#8
by
the caveman
on 16 Apr, 2011 10:43
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While the head was still on, did you ever turn the crank by hand with a key or ratchet/socket. If the compression was good, there would have been a little kick back as each cylinder got near TDC
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#9
by
wil892
on 16 Apr, 2011 10:51
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haha yeah will be sticking with the SB lump, its a great engine.
caveman the head is still on the engine just injectors and pipes off it at the moment. When I get new heat shields I will put it all back and check that. As far as I remember it gets pretty difficult to turn just before TDC but will check for kickback. There is obviousely compression as if I disconnect the injector pump electrics and turn it over it sometimes spins back the other way if the TDC isnt quite reached, kick back I would say.
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#10
by
wdkingery
on 16 Apr, 2011 11:35
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yeah i had a poo poo tester from PROTHE and it also gave strange, low readings. starts and runs fine. over 40mPG. its pushin oil out the dipstick at an increasingly alarming rate. im kinda sad about this. but what to do? rebuild? idk..
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#11
by
the caveman
on 16 Apr, 2011 22:54
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I always found that you had to spend good money for a good, consistent compression gauge, gas or diesel
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#12
by
burn_your_money
on 17 Apr, 2011 00:32
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Were you testing with a heatshield installed? I can't see an engine running at 100 psi...
Like caveman said, try a small amount of oil in there and see what happens. With that low of pressure I wouldn't worry about the oil igniting
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#13
by
wdkingery
on 17 Apr, 2011 07:59
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i think the book says like a teaspoon of oil in the cylinder (obviously for gas as the book says not to do this on diesel but .. i didn't think it would be a big deal either)
my half cents says ... if you were just doing your comp test for an arbitrary reason then i'd ignore the results.. that's what i did haha
EDIT: oh and check yer valve clearances
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#14
by
Mark(The Miser)UK
on 18 Apr, 2011 02:11
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I made my own adaptor with an injector body. I left the needle in, but the spring out.
I also filled all the gaps with little coils of lead. Do this with your pro adaptor.
These engines will run with low compression. Search my pics out. I suspect that you have stuck in rings...
I had 7 yes that's correct seven out of 12 rings stuck in with gaps up to 160 thou, and it had still passed the MOT with 0.5% smoke... 
Pre rering it was fairly consistant at 45mpg [UK] now it is getting around 50mpg in town, and approaching 60mpg on the motorway.
All I did was pay for new rings $22 [$56 P&p] and £6 for a new head gasket off Ebay. Honed with some wet and dry stuck to a Robinson's barley water bottle....