Hope it's the Turbo !

Hope it's the Turbo !

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Discussion

annodomini2

6,334 posts

219 months

Friday 10th October 2003
quotequote all
plus if its been sat overnight dew can condense in the exhaust adding to the water level, just a thought.

Jap-Car

Original Poster:

473 posts

218 months

Monday 13th October 2003
quotequote all
Thanks for your thoughts. I ran the car some more at the weekend. As some of you guys suspected, the water turned out to be residual water in the system. It dissapeared after running for another 30 minutes.

Now the only symptoms are a pressurised sump and a some blue smoke (which is reducing, I guess as stuff burns out of the exhaust system). I believe this is probably therefore piston rings / bores, particularly as I did notice some damage to one of the bores when the head was off. (Although the compression test was good)

Question - has anyone come across this type of damage before? It is deep (2mm) erosion / pitting over the top 5 mm of the bore and for about half the circumference. I decided that it stopped just short of the top piston ring but maybe the damage was more extensive than I thought. The damage was in the cylinder where the head originally cracked which may or may not be coincidence. Thoughts?

Cheers,

Robert.

>> Edited by Jap-Car on Monday 13th October 09:57

Mr2Mike

20,143 posts

223 months

Monday 13th October 2003
quotequote all
Jap-Car said:
Question - has anyone come across this type of damage before? It is deep (2mm) erosion / pitting over the top 5 mm of the bore and for about half the circumference. I decided that it stopped just short of the top piston ring but maybe the damage was more extensive than I thought. The damage was in the cylinder where the head originally cracked which may or may not be coincidence. Thoughts?


Was the top of the piston ok? A chunk of broken piston ring etc. floating about tends to cause more damage to the piston crown than the bore, so not sure that's very likely.

If the engine has been stored and water has been allowed to get into the cylinder at some stage than this would certainly cause this type of pitting. If the engine was canted over at an angle only part of the bore would be affected, and of course the piston would have been at or near TDC.

Jap-Car

Original Poster:

473 posts

218 months

Monday 13th October 2003
quotequote all
Yeah, piston looked absolutely fine. when I rotated the engine by hand with the head off, everything seemed nice and smooth. I don't think the engine has stood for very long with water in the bore but it's possible I guess.

I wondered if it was due to either erosion as water / steam entered and exited the cylinder or perhaps water encourages pre-detonation (I'm out of my depth on that subject).

Obviously, I wish I'd measured the bore but I didn't. Is there anyway of telling if the problem is with the rings or the bore without a strip down?

Mr2Mike

20,143 posts

223 months

Monday 13th October 2003
quotequote all
Jap-Car said:
I wondered if it was due to either erosion as water / steam entered and exited the cylinder or perhaps water encourages pre-detonation (I'm out of my depth on that subject).



Water actually supresses detonation, which is why water injection is popular on turbo cars running silly amounts of boost.

said:

Obviously, I wish I'd measured the bore but I didn't. Is there anyway of telling if the problem is with the rings or the bore without a strip down?


A wet/dry compression test will show up badly sealing rings. Take a compression reading, then put a teaspoon or so of oil into the cylinder and take another compression reading. Any significant variation between the two readings points to a ring sealing problem.

>> Edited by Mr2Mike on Monday 13th October 13:11

Jap-Car

Original Poster:

473 posts

218 months

Monday 13th October 2003
quotequote all
Thanks Mike, but how does the wet / dry compression test tell me it's rings rather than bore?

Cheers,

Robert.

Mr2Mike

20,143 posts

223 months

Monday 13th October 2003
quotequote all
Jap-Car said:
Thanks Mike, but how does the wet / dry compression test tell me it's rings rather than bore?


Unfortunately it dosen't. All it can say is that you have a ring sealing problem, be it stuck rings, worn rings or worn/damaged bore. As the head will need to come off anyway (if the test shows an issue), you can measure the bore and ring gap (after dropping the sump and undoing the big end etc.) to determine exactly the cause of the problem.

The other way to do this is to perform a leak down test by pumping compressed air into the spark plug hole (via a special adapter) with both valves closed. The rate of pressure loss gives you an idea of ring and valve sealing efficiency. However, it still wouldn't point the finger at the exact problem. Sorry, but I can't think of any other way that dosen't involve stripping it down

Jap-Car

Original Poster:

473 posts

218 months

Monday 13th October 2003
quotequote all
Thanks,

I wonder if I could do a leak-down test at TDC and also at Bottom Dead Centre (or are one or the other valves open at this point?). My logic is that by comparing leak-down at top and bottom and across the cylinders, I might be able to tell.

I know that bores don't generally wear near the bottom and the volume of gas would be larger and therefore leak-down rate would be different. However, if say leak-down at top and bottom was markedly worse on one cylinder then that would imply rings. Whereas if leak-down is only worse at the top then this implies bore.

My reason for wanting to be sure before removing the head is that if it is the bore, I might just leave it as this would effectively mean a new engine which is a lot of work and money.

Is the inlet valve still open as the piston reaches the bottom of its stroke?

Mr2Mike

20,143 posts

223 months

Monday 13th October 2003
quotequote all
It seems like a reasonable theory to me anyway!

The inlet valve would still be partly open at BDC on the inlet stroke, and the exhaust valves would be starting to open at the bottom of the power stroke (depending on cam duration). However, you may be able to slacken off the valve clearances enough to prevent this if you have manual adjustment rather than hydraulic followers.

Jap-Car

Original Poster:

473 posts

218 months

Tuesday 14th October 2003
quotequote all
Mike thanks again for your thoughts. I think my valve clearances are set by shims beneath the cam so back to the drawing board! I guess I could try and hold the engine in place half-way down the power stroke and make a leak-down test there.

I guess I'll try for an MOT first and decide what to do depending on if the emissions test is OK or not.

Thanks everyone.