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Crankcase Pressure Cause Of Black Smoke


Best Answer ads7 , 15 January 2019 - 09:17 PM

The engine was just steam cleaning itself. Refit the breather to the carb.


Done thanks Go to the full post


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#1 ads7

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Posted 05 January 2019 - 08:45 PM

Recently fitted an unrestored 850 engine which drove really well for about thirty miles. I then revved it a bit under load uphill (around 55mph in third) after half a mile I returned home and black oily smoke now belches out continuously both at idle and on the move.

I'd assume an oil control ring problem? Oil is splattered on whatever the exhaust tip is near to.

Before taking the car on the road I did remove the head to inspect the bores which looked in excellent order. I hadn't got around to checking valve stems or stem seals.

There did seem to be higher than usual pressure coming out of the oil filler/breather.
I also stupidly routed the breather pipe into a catch can which wasn't vented adding to the pressure no doubt - could this have affected the rings?

Thoughts please

Edited by ads7, 05 January 2019 - 08:48 PM.


#2 ads7

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Posted 05 January 2019 - 08:55 PM

I'd add the mixture seemed good. Light brown deposits on plugs

#3 cal844

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Posted 05 January 2019 - 10:27 PM

Do a compression test anything under 120psi needs investigation. Also anything more than 10 psi difference will need to be checked

#4 Rorf

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Posted 06 January 2019 - 04:49 AM

Burnt oil does not give black smoke, but an over rich carb certainly does. 55mph in third up a hill in an 850 nothing wrong with that engine :D

When last was the engine oil changed?



#5 DeadSquare

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Posted 06 January 2019 - 10:04 AM

Recently fitted an unrestored 850 engine which drove really well for about thirty miles. I then revved it a bit under load uphill (around 55mph in third) after half a mile I returned home and black oily smoke now belches out continuously both at idle and on the move.

I'd assume an oil control ring problem? Oil is splattered on whatever the exhaust tip is near to.

Before taking the car on the road I did remove the head to inspect the bores which looked in excellent order. I hadn't got around to checking valve stems or stem seals.

There did seem to be higher than usual pressure coming out of the oil filler/breather.
I also stupidly routed the breather pipe into a catch can which wasn't vented adding to the pressure no doubt - could this have affected the rings?

Thoughts please

 

 

Check the black splatter from the exhaust on a bit of brown wrapping paper to see if it is oily or wet.

 

How much soot is in the exhaust from the previous engine?

 

Try the engine with everything that is vented from the engine being re burnt through the carb and then compare it when everything is vented down to the road.



#6 ads7

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Posted 06 January 2019 - 12:18 PM

Thanks for the replies everyone I'll try everything you suggest tomorrow and report back here cheers

#7 nicklouse

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Posted 06 January 2019 - 01:19 PM

excess crank case pressure is caused by worn rings. worn rings may also indicate worn other parts. strip down time.



#8 ads7

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Posted 07 January 2019 - 04:44 PM

Today's findings -

Was soot coming from exhaust. Changed needle from AAA to AAU to lean out mixture, car then started ok then it decided to blow out white smoke instead, no smell of oil thankfully.

Turns out that the cheap eBay head gasket has failed between cylinders two and three, water was shooting out of spark plug holes. Combination of over rich fueling and water resulting in wet black sooty emissions from exhaust.

It doesn't end there though .. compression test gave poor readings of 115 on both cylinders one and four. No point checking two and three obviously.

So head is coming off checking valve stems and lapping them in then new head gasket. Then check compression again. I suspect that ring dealing isn't great and I'll end up just getting the car fifteen miles back home and just using for very short local trips.

I'm not going to spend time stripping an 850. Frankly I've had it with the a series, already placed a wanted ad on 16V mini forum for complete Micra conversion and prepared to sit and wait for the right one to appear.

Thanks everyone for your help much appreciated

Edited by ads7, 07 January 2019 - 04:50 PM.


#9 ads7

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Posted 07 January 2019 - 04:53 PM

I meant ring sealing not dealing! doh!

Edited by ads7, 07 January 2019 - 04:56 PM.


#10 ads7

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Posted 15 January 2019 - 08:02 PM

Had a good result today.

Removed head, lapped in valves new seals etc used payen copper head gasket properly torqued down to 45ftlb with oiled head studs. let it go through one heat cycle then re checked torque settings.

Result! car now runs perfectly really lively for an 850.

There is a downside though compression is low at 125 across acylinders 2,3 & 4 with 115 on no 1

I'll continue to run her for as long as I can like this.

overall really chuffed with how it turned out considering I only paid 80 quid for the engine and box

Thanks everyone for the sound advice

#11 Dusky

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Posted 15 January 2019 - 08:46 PM

The engine was just steam cleaning itself. Refit the breather to the carb.

#12 ads7

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Posted 15 January 2019 - 09:17 PM   Best Answer

The engine was just steam cleaning itself. Refit the breather to the carb.


Done thanks

#13 DeadSquare

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Posted 16 January 2019 - 09:49 AM

Had a good result today.

Removed head, lapped in valves new seals etc used payen copper head gasket properly torqued down to 45ftlb with oiled head studs. let it go through one heat cycle then re checked torque settings.

Result! car now runs perfectly really lively for an 850.

There is a downside though compression is low at 125 across acylinders 2,3 & 4 with 115 on no 1



overall really chuffed with how it turned out considering I only paid 80 quid for the engine and box

Thanks everyone for the sound advice

I'll continue to run her for as long as I can like this.

 

 

 

I had a friend who commuted in a second hand 850 Mini Van with 2 cwt of BAE castings, 75 miles each way from Bromsgrove to Filton (Bristol)

 

It had well over 1/4 million miles on the clock, so you might die before your engine does.



#14 ads7

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Posted 17 January 2019 - 10:45 PM

Wow. Good to know.

I'm enjoying the car more now than when it ran a 1293 which suffered from vibration at certain revs and tended to overheat.

The 850 is such a smooth running little motor. It'll also be interesting to see how high I can push the mpg




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