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Engine Specific Info and Questions => IDI Engine => Topic started by: wil892 on April 16, 2011, 05:27:14 am
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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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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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I trust the compression test was done on a thoroughly warm engine...
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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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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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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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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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Stick with the SB lump mate, they are uber cool and fairly rare over here 8) 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 ;D
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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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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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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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I always found that you had to spend good money for a good, consistent compression gauge, gas or diesel
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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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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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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... :o
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.... ;D
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Thanks mark, would it be possible to run with stuck rings for 15k miles then? I have run 5w40 synthetic for all those miles surely this would have unstuck them?
Ideally removing the head and pistons and honing would be much more cost effective than replacing the bottom end, something I think would be easy enough for me to do.
Are stuck rings common on these? I'm wondering if the other pressures are ok and it is just no3 cylinder with the stuck ring. As i mentioned the original honing marks were all clearly visible when I had the head off last and no ridge.
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Thanks mark, would it be possible to run with stuck rings for 15k miles then? I have run 5w40 synthetic for all those miles surely this would have unstuck them?
Ideally removing the head and pistons and honing would be much more cost effective than replacing the bottom end, something I think would be easy enough for me to do.
Are stuck rings common on these? I'm wondering if the other pressures are ok and it is just no3 cylinder with the stuck ring. As i mentioned the original honing marks were all clearly visible when I had the head off last and no ridge.
I believe synthetic is renowned for unclogging crud, and is definitely too slippery for decent break-ins. But does it remove genuine 'coked on' matter, I dunno.
Don't tell anyone, but I use multigrade Wilko special ;D which coupled with the worn out rings, probably contributed to the stuck rings.
When I first had the engine, they were all reading the same 300psi, so as I had no starting issues I had put it down to my homemade adaptor:
40000 miles later, and after only a month of intermittantly hard starts, the readings were 160, 200 200 and 270. But with those ring results maybe the readings were fairly accurate. :o.
Since August's rebuild I'm barely using any oil, the dipstick shows semi translucent, rather than completely opaque and the oil baffle is definitely nolonger 'greasy'. I'm running injectors out of a Ford 1.6, and they are set to 125bar IIRC
I've just done a run pure A38 stuff today. Half journey with family loaded and half ditto but with three 15ft dead apple trees on the roofrack chopped into 10ft lengths with all twigs on, 50 to 80mph going, and 50ish with trees and my mileage is.... 56.2mpg. 8)
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I think the reason the book doesn't advise the use of oil in diesel compression testing is the potential for hydrolock if you get a little overzealous with quantity. keep it small quantities and should be fine.
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The MK2 Bentley says that the reason not to use oil during compression testing of diesel engines is that it can ignite (just like diesel fuel does), damaging the compression tester, causing bodily injury, etc. etc. etc.
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The MK2 Bentley says that the reason not to use oil during compression testing of diesel engines is that it can ignite (just like diesel fuel does), damaging the compression tester, causing bodily injury, etc. etc. etc.
the starter would have a tough time bending a rod or doing any kinda damage from a hydro lock..
but, having a compression gauge blow up in your face would kinda suck..
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The MK2 Bentley says that the reason not to use oil during compression testing of diesel engines is that it can ignite (just like diesel fuel does), damaging the compression tester, causing bodily injury, etc. etc. etc.
the starter would have a tough time bending a rod or doing any kinda damage from a hydro lock..
but, having a compression gauge blow up in your face would kinda suck..
Sounds nasty, but unless you were cranking for ages, and even then I doubt it could happen. How do you hydrolock from a few ccs of oil when you have the large prechamber and the injector tester?
Perhaps limit the oil to half prechamber volume. Naturally, don't do it unless compresson results low anyway.
When cranking you should only need do it for say 5 or 10 revs, and watch the pressure rise as you are cranking, for comparison purposes.
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The MK2 Bentley says that the reason not to use oil during compression testing of diesel engines is that it can ignite (just like diesel fuel does), damaging the compression tester, causing bodily injury, etc. etc. etc.
the starter would have a tough time bending a rod or doing any kinda damage from a hydro lock..
but, having a compression gauge blow up in your face would kinda suck..
Sounds nasty, but unless you were cranking for ages, and even then I doubt it could happen. How do you hydrolock from a few ccs of oil when you have the large prechamber and the injector tester?
Perhaps limit the oil to half prechamber volume. Naturally, don't do it unless compresson results low anyway.
When cranking you should only need do it for say 5 or 10 revs, and watch the pressure rise as you are cranking, for comparison purposes.
but if you are taking compression readings on a hot engine, like you should, then it is COMPLETELY POSSIBLE for the oil to ignite in the cylinder, if you are using oil at all..
another thing, if you take a compression reading thru the glow plug hole, be sure to disconnect the power to the fuel solenoid on the top of the pump. then no fuel is injected (compression gauge wont blow up that way)
and even if you did have enough oil in a cylinder to hydro lock it, the starter would come up tight against the oil, the rods and bottom end would be fine. you can not bend a rod with a starter, unless its a starter from a tug boat or something..
even if you did get a hydro lock, you would just have to let the oil out, then start the engine and let it burn the oil out of that cylinder..
only way i see it possible to hydro lock an engine and damage it, is driving (hitting a huge puddle) down the road. or driving into the river/creek/ditch on accident, lol..
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Just had a thought. I thought I saw some years ago on here that the chinese 1.6 head castings actually had the 1.9 precups installed. does anyone know if this is true, if so it may explain why my compression is so low and my timing has to be set at 1.25mm to have the car running properly.
Thanks
Will
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as compression lowers, the engine wears, and needs to have advanced timing..
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warm, hot, draper, or harbor freight...those numbers are low. End of story.
As for rings resetting. Can't say I agree. That motor is just tired. I pulled a rabbit diesel out of field that sat for 18 years and it fired up with fresh diesel and a new battery.
Time for a replace or rebuild.
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After reading about putting oil in the cylinders to try to diagnose bad rings etc, i realized that i don't know if i've every personally done it. Good point about the hydrolock and/or igniting. Too many gassers i guess