tsoob
Part of things
Posts: 107 
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The motor in my E21 is showing its age, and it's... blowing a puff of smoke on start up.
Common M10 problem, oil seeps past one of the ageing piston rings, hence smoke.
Is this a MOT failure? I'm debating whether I keep the car all original as is, or if I put a known good M10 in its place... all may effect value as the car is original otherwise.
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I was under the impression it was very easy to pass for pre 92 cars. A puff of smoke just on start-up sounds fine.
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taurus
Posted a lot
Posts: 1,084
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A puff on start up shouldn't cause a problem, just depends what the emissions read once it's good and hot. Usually a weak valve stem seal.
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Unless it smokes like a modern diesel then the smoke itself isn't an issue, if the other emmisions are ok it will be fine.
Sounds more like valve stem oil seals than rings.
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tsoob
Part of things
Posts: 107
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Cyl #1's showing 90psi - Was told ring. Valve stem seal is a possibility, is there an easy way to check?
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Recheck compression then squirt some oil down the plug hole and recheck, if the compression has increased a significant amount it's the rings.
That's quite low -what were the others like?
Only smoking on start up or after prolonged idling is classic valve stem seal symptoms though.
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BT
Posted a lot
Posts: 1,772
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My truck throws out so much curse word on initial start up first thing in the morning it's sometimes impossible to see anything other than the smoke. However once warm it starts up with not the slightest sign of smoke.
So I take it to the MOT warm and no mention of it.
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my e21 320/6 smokes like a chimney on start up and under hard acceleration and passed the emission test no bother, as long as it runs with no misfires and a decent air/fuel mix it will be fine
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ChasR
RR Helper
motivation
Posts: 10,309
Club RR Member Number: 170
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Smoke and MOT.ChasR
@chasr
Club Retro Rides Member 170
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Old cars could smoke from startup and show a 'false' compression reading if the injectors are leaky. My Escort used to do this as many of the injectors would dribble fuel into the bores if the car had been turned off, to the extent the oil would begin to smell of petrol after a while.
But, it should pass if it has passed before.
I'd be tempted to do a compression test with the engine warm TBH. What injection system is it running?
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