ausmini :: View topic - Brainstorm, lots of smoke

Right, Been fighting with the mini for various reasons for a few days now and each symptom seems to come at the exact wrong time.

It's a 998 bored +0.040, flat top pistons, lightened and balanced everything, 12G295 head, twin 1 1/4" carbs and a Wade 104 cam.

It seems to be blowing excessive amounts of smoke particularly at idle, here's whats been checked:

- compression - good on all cylinders and even
- plugs - no excess build up or wetness on any one plug.
- head - just been replaced with a known good 12G295 with new gaskets and all seems to be seated nicely
- mixture - not dead on but pretty damn close
- two different loads of oil (different oils as well) didn't smoke for a little while and then started again.

This motor has only done about 2 - 3000 k's since new.

At the moment we're thinking either:
(a) a broken oil control ring which would allow oil through the rings but the compression rings would keep the compression up
(b) a crack in the block near BDC of the pistons allowing oil in but not having any effect on compression.

Any other ideas? I'm going to strip it down and see what I can find but my brain is out of any other reasons for the oil burning. Thought I'd see if some fresh minds have any thoughts.

Author:	Mister White Keys [ Wed Apr 01, 2009 9:20 pm ]
Post subject:	Brainstorm, lots of smoke
Right, Been fighting with the mini for various reasons for a few days now and each symptom seems to come at the exact wrong time. It's a 998 bored +0.040, flat top pistons, lightened and balanced everything, 12G295 head, twin 1 1/4" carbs and a Wade 104 cam. It seems to be blowing excessive amounts of smoke particularly at idle, here's whats been checked: - compression - good on all cylinders and even - plugs - no excess build up or wetness on any one plug. - head - just been replaced with a known good 12G295 with new gaskets and all seems to be seated nicely - mixture - not dead on but pretty damn close - two different loads of oil (different oils as well) didn't smoke for a little while and then started again. This motor has only done about 2 - 3000 k's since new. At the moment we're thinking either: (a) a broken oil control ring which would allow oil through the rings but the compression rings would keep the compression up (b) a crack in the block near BDC of the pistons allowing oil in but not having any effect on compression. Any other ideas? I'm going to strip it down and see what I can find but my brain is out of any other reasons for the oil burning. Thought I'd see if some fresh minds have any thoughts.

Author:	9YaTaH [ Wed Apr 01, 2009 9:27 pm ]
Post subject:	Re: Brainstorm, lots of smoke
Mister White Keys wrote: Right, Been fighting with the mini for various reasons for a few days now and each symptom seems to come at the exact wrong time. It's a 998 bored +0.040, flat top pistons, lightened and balanced everything, 12G295 head, twin 1 1/4" carbs and a Wade 104 cam. It seems to be blowing excessive amounts of smoke particularly at idle, here's whats been checked: - compression - good on all cylinders and even - plugs - no excess build up or wetness on any one plug. - head - just been replaced with a known good 12G295 with new gaskets and all seems to be seated nicely - mixture - not dead on but pretty damn close - two different loads of oil (different oils as well) didn't smoke for a little while and then started again. This motor has only done about 2 - 3000 k's since new. At the moment we're thinking either: (a) a broken oil control ring which would allow oil through the rings but the compression rings would keep the compression up (b) a crack in the block near BDC of the pistons allowing oil in but not having any effect on compression. Any other ideas? I'm going to strip it down and see what I can find but my brain is out of any other reasons for the oil burning. Thought I'd see if some fresh minds have any thoughts. You seem to have thought of most of the reasons...except maybe rings not yet bedded in...go do some more driving and keep the oil up to it

Author:	simon k [ Wed Apr 01, 2009 9:40 pm ]
Post subject:
differential diagnosis 'eh do you have a PCV on it Steve? I've had the problem a couple of times with excessive oil coming out of the breathers and into the PCV, causing a lot of smoke... the excessive oil coming out of the breather was caused by the rings being worn out, giving blowby into the block. Still had good compression both times so... pull a breather off and see how much is coming out when I first rebuilt my current motor about 7 years ago, it just smoked and smoked, I put another head on it, and it stopped smoking, then I put the old head back on, and it didn't smoke again - never figured it out

Author:	Leighton [ Wed Apr 01, 2009 9:43 pm ]
Post subject:
sounds stupid and simple, but maybe valve stem seals?

Author:	Mister White Keys [ Wed Apr 01, 2009 9:44 pm ]
Post subject:
9Y, if the rings weren't bedded in by now, I'd be very surprised. As some people know I like to explore the rev range Simon, There is a lot of fumes from the breathers, no PCV on it so it wouldn't be blowing oil into the motor but the blowby is very likely. Although it shouldn't be worn rings after only a small amount of k's.

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Brainstorm, lots of smoke https://www.ausmini.com/forums/viewtopic.php?f=2&t=51753	Page 1 of 2

Author:	frednutz&co [ Wed Apr 01, 2009 9:50 pm ]
Post subject:
will you be coming on the alpine run

Author:	simon k [ Wed Apr 01, 2009 9:53 pm ]
Post subject:	Re: Brainstorm, lots of smoke
No on the PCV - gotcha Mister White Keys wrote: It seems to be blowing excessive amounts of smoke particularly at idle, after the rebuild 7 years ago, my car was actually consumed by it's smoke cloud at idle - a slight breeze coming from behind when it was sitting at the curb - the poor little thing just vanished! I re-ringed a motor for dad a couple of years ago, and it had an idle smoke problem as well - swore I'd never re-ring a motor again (till I did it a few weeks ago). The smoke has cleared up now, after a couple of thousand k's of running around. I figure the bores glazed a bit, and coupled with old pistons & not ideal clearances, took a while to bed in. When I discussed it with my guru, he said it was the rings not sealing properly - the explanation was that because it's happening at idle, there is full vacuum in the combustion chambers - the engine tries to suck air from anywhere it can get it, as much as it can through the (blocked) carbs, but also from below edit: basically what I'm suggesting is that blow-by can also be suck-by, maybe your old head didn't seal as well as it should, and the new head seals a lot better, showing up weaknesses elsewhere 2nd edit: what you need to do is a "leakdown test" - can be done with a rag and your compressor air blower, but better with a proper kit - screws into a spark plug hole, and has a pressure gauge - you'll be able to borrow one I'm sure

Author:	simon k [ Wed Apr 01, 2009 10:08 pm ]
Post subject:
bump for my edits to the above post

Author:	simon k [ Wed Apr 01, 2009 10:13 pm ]
Post subject:
check this out... good option for you I reckon Steve http://vmaxoutlaw.com/tech/leakdown_tester.htm

Author:	david rosenthal [ Wed Apr 01, 2009 10:29 pm ]
Post subject:
what type of oil rings are fitted 3 different types 1 cast iron slotted rings 2 3 piece rings , center wavy with top and bottom thin rings[look like a circlip 3 same as above but they have a expander fitted behind the center ring Some sets with the 3 piece type the top and bottom rings fit into the center wavy ring,but the ring groove is a little wider and they slide over the wavy ring. They do not have enough tension and will suck up oil flat out

Author:	guna mk1 [ Wed Apr 01, 2009 10:30 pm ]
Post subject:
A leakdown test is designed to test where cylinder leakage or compression is leaking. ie through rings ,valves, blown head gasket etc. You can have a motor with very little leakage but still burns lots of oil due to worn / faulty oil rings. It could help with your diagnosis but you will still have to weigh up all your options where the oil is coming from.

Author:	Mister White Keys [ Thu Apr 02, 2009 12:53 pm ]
Post subject:
Couple more bits of information, the engine has definitely been run in without any sign of oil burning so it isn't a matter of rings that aren't bedded in. We have performed a rudimentary 'leak down' test by compressing all four cylinders at BDC and listening to the leak past the rings, nothing excessive and the same on all 4 cylinders. The oil control rings are the 3 piece wavy type with the spring behind the wavy part to press the ring against the bore. I like the theory Simon, but I'm not too keen on driving it as is for any length of time on the offchance that it might clear up, I think a fine from the EPA is more likely. Well I shall be stripping it down soon and hopefully the problem will reveal itself.

Author:	AWOODY [ Thu Apr 02, 2009 3:27 pm ]
Post subject:
You only live in hope that it will clear up but it doesn't , I just had to rebuild an engine using another block to get rid of the smoke and it had only done 9000 miles ! most likely dud pistons , rings and bore . What type of pistons are they , are they low compression type , mine too had consistant pressures across all 4 cylinders but used oil and soiled itself after going down hills and it was not the head as it was checked by 2 very reputable places and I am running it on the new engine with excellent results.

Author:	drmini in aust [ Thu Apr 02, 2009 4:14 pm ]
Post subject:
Maybe it was given too much piston clearance when it was rebored- I've seen this happen before.

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