marcjagman
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| posted on 13/10/06 at 08:04 PM |
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Low compression
Okay chaps, and ladies if there are any here, I have a small problem, no not that an engine problem. Nothing to do with a locost but I am hoping that
someone will still give me their opinions anyway. I have a 3 litre Supra non turbo Mk3 1989. Bought it as seen, drove it around for a little while and
decided to drive it home. After 115 miles a leak occured and subsequently ground to a halt, but not seized. There was a bit of a rattling noise and it
changed down a gear (auto) before the engine died. When I got it home and checked the compressions all but one were low, 60psi, number 1 cylinder was
almost zero. So what I am looking for is opinions on, head gasket gone or cooked rings? Any sugestions, except gallon of petrol and a ligher, are
welcome.
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MikeRJ
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| posted on 13/10/06 at 08:21 PM |
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Firstly when you tested the compression did you make sure the throttle was wide open? Common mistake to just turn the engine over with the throttle
closed wich gives low readings.
If not, then I hate to be the bearer of potentialy bad news but the Mk3 Supra are renowned for head gasket failures. Have a look at
http://www.supras.com/06/techcenter/display.php?QID=8
How hot did it get? If it was really badly cooked the piston rings may have broken or lost their tension causing bad sealing, but if it got that hot
the head gaskets a gonner anyway IMO.
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marcjagman
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| posted on 13/10/06 at 08:40 PM |
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I never actually noticed how hot it got, silly me. I know they are prone to HG failure but it was running fine for 115 miles. I know you are
supposed to open the throttle but the difference would only be about 20% the comp. should be around 160psi. It's not that bad changing the head
gasket once you have removed all the ignition/injection crap out of the way. head sets are quite cheap, £50ish. Thanks for your input though, I am
stripping the head of and just wondering if any one has a definitive way of checking rings without a strip down. Head is still attached but will be of
tomorrow (Saturday) afternoon to check the gasket, it just seems strange that 5 cylinders are all the same compression, 60psi and one is almost zero.
The engine spun like it had no plugs in it, quickly, and sounded like there was no compression. Oil is okay, all plugs clean with no signs of oil or
water and all look quite new.
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MikeRJ
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| posted on 13/10/06 at 08:57 PM |
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Are the cams belt driven? If so check to make sure it hasn't slipped. This could give low compressions, or zero if any valves met the pistons.
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marcjagman
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| posted on 13/10/06 at 09:12 PM |
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That I did check, all okay. Belt driven. First thing I thought of when I heard it rattle before it stopped. Rattled for about 5 seconds.
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Chippy
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| posted on 13/10/06 at 11:12 PM |
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Easy way to check if the rings have gone, is to put a few squirts of thin oil, or parafin, on top of piston. If it just runs through, then I think you
know what comes next. Hope that helps. Ray
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marcjagman
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| posted on 14/10/06 at 07:57 AM |
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Thanks, I knew there was a way I'd just forgotten. Must be my time of life.
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oliwb
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| posted on 14/10/06 at 10:44 AM |
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Do a second compression test with the oil in as well. If the compression is up is a sign of new piston rings needed! Oli.
If your not living life on the edge you're taking up too much room!
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marcjagman
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| posted on 14/10/06 at 07:19 PM |
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Oh dear, never seen it before but the gasket has blown on every cylinder. Put veg oil in all the cylinder bores and it drained on number 2. There is
zero wear on any of the bores except very slight marks on 2, which will hone out. Looks like the engine was reconditioned badly as some of the head
bolts were very tight and soon almost loose. All the pistons are clean, almost shiny. I am pressuming rightly or wrongly that it has had a rebore as
all the pistons have a 2 on them. Number 2 piston appears to have melted a little. Now to the question, does anyone know where I can buy 1 piston with
rings?
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gazza285
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| posted on 14/10/06 at 08:50 PM |
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A common thing on LDV 2.5 engines was to have the gasket go, have the head skimmed and then put it together. The head bolts would torque up fine, but
most of them were bottomed out in their holes due to the skim (even mild skims would affect torque settings) and the gasket would blow all over the
place after two weeks. Don't know if Supras are the same, but it something you could check.
To cap it all the LDV used to drop its back liner when it overheated as well, it must be the worst diesel engine Peugeot ever made.
DO NOT PUT ON KNOB OR BOLLOCKS!
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david walker
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| posted on 14/10/06 at 08:55 PM |
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It is unlikely that the bolts were loose as a result of a previously poor build. It is common to see loose head bolts on an engine that has overheated
and the head gasket failed. You'll need rings for all the pistons as a minimum, and probably more than one piston - look for grey scuffed flats
on the side of the others. If they are there they will need changing.
Dave Walker, Race Engine Services - 07957 454659 or 01636 671277
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marcjagman
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| posted on 14/10/06 at 09:12 PM |
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Got it stripped and every thing looks fine except the one piston. On they duff piston even the rings look good. If I can get some pistons/rings at
right price I'll get them failing that another engine. Seems a shame as this has only done 89000 genuine. Any ideas for cheap pistons?
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marcjagman
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| posted on 17/10/06 at 09:35 AM |
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Chepest plave so far to buy one piston is Toyota of all places, £42 inc.VAT. Wood Auto Factors, however, will sell pistons and rings at £46 each, BUT
you have to buy them in sets. 01924 291414 very helpful people if you ever need any bits.
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02GF74
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| posted on 17/10/06 at 10:14 AM |
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quote:
Originally posted by marcjagman
All the pistons are clean, almost shiny.
a sign that water was getting inside the engine - the same effect you would get if you were steam cleaning the pistons.
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