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Blue Exhaust Smoke


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#1 MacFreuden

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Posted 22 May 2020 - 11:51 AM

Hi all,

So rebuilt the engine and slowly but surely it has started to burn oil, I'm a novice and have never done it before so kind of expected some issues, just trying to pin down what it might be due to its characteristics though....

When I change up a gear I get a puff of smoke and it then clears and doesnt smoke whilst under constant load, if I'm sitting idling for a few mins and I then drive away there is much more smoke than a puff but again it clears under constant load. It is quite a lot of oil as it spits it out over the boot lid after about a 10 or 15 mile drive.

I've been advised that this is indicative ofthe valve stem oil seals however I put four new ones on (intakes), and a machine shop put 8 new bronze manganese valve guides in with four new inlet valves for me. He then cut all 8 in.

Wondered if it could be the valves need re-lapping? New head gasket is needed? Or piston rings? Anything else?

Am going to do a wet and dry compression test this afternoon and so will update soon with results...

Cheers jonny

#2 MiniMadRacer

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Posted 22 May 2020 - 01:48 PM

Does sound like valve stem seal / guide issues... do the compression tests then come back to us



#3 Cooper Mac

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Posted 22 May 2020 - 02:22 PM

Sounds like the valve stem seals to me, but there should be 8 of them, one on each valve.



#4 MacFreuden

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Posted 22 May 2020 - 03:07 PM

Okay I have done them and are as follows...

Dry -
1. 125
2. 127.5
3. 125
4. 128

Wet -
1. 131
2. 132.5
3. 130.5
4. 135

Am I right in thinking that these are a bit low but don’t show any issues with the piston rings as they are all near each other and near enough constant?

Where I previously said it was clearing under load, I’d change that now after using a long piece of wood on the accelerator and standing there watching the exhaust, it clears a little (not as thick/heavy) after the first blip however it does continue to come out blue when I held the revs up to and at 3000rpm for a short period.

As for the stem seals I thought I should have had 8 as well but rang minispares and they said I should have 4 and just on the inlet, as that’s all that came in the pack... think I will put an extra four on when I next take the head off though just to be sure

Edited by MacFreuden, 22 May 2020 - 03:11 PM.


#5 cal844

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Posted 22 May 2020 - 06:09 PM

In my opinion the compression readings are low, imo theres enough of a rise in the wet readings so it could be piston rings.

I'd also have fitted 8 MPI spec valve stem seals.

Were the valve clearances done after you rebuilt the motor?

Someone with more knowledge will be along soon

#6 MiniMadRacer

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Posted 23 May 2020 - 07:46 AM

Those readings are low on a newly built engine to be fair...

 

How did you take the readings.. all plugs out throttle wide open I hope...and battery fully charged

 

Seems to me the engine may not be "run in" properly or incorrect initial startup....

 

What oil is in it ?



#7 MiniMadRacer

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Posted 23 May 2020 - 07:49 AM

The thinking on the oil seals is in my opinion flawed

 

The general rule is 4 on the inlets only and they are not needed on the exhausts as there is no inward suction on them.

 

But that still doesnt stop the oil dripping past them once the engine is off.

 

I think the 4 is more a cost cutting form BL than a real "guide" as such.

 

I always fit 8...

 

Also silly question but did you buy the correct ones for your guides



#8 Dusky

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Posted 23 May 2020 - 09:27 AM

Nothing wrong with those compression readings. Dont let some people get into your head.
If you really want to check the ring sealing you need a leak down test.

#9 mini13

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Posted 23 May 2020 - 09:57 AM

As above,

Psi readings are variable due to engine spec, low copression ratio or a long cam will reduce the psi, also we don't know how accurate the gauge is.

What seals were fitted? if std rubber ones they can harden up, personally I'd always fit Viton ones where possible, and to all 8 valves on a non turbo engine.

#10 MacFreuden

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Posted 23 May 2020 - 10:27 AM

I’d love to say what stem seals were fitted but it was just what came in the cylinder head gasket pack from minispares I may ring. And find out Monday... some say you’d fit MPI ones or Viton ones - what is the difference?

I didn’t have the accelerator open come to mention it, it’s a carb model how does this affect it? Just lets it breath better or? I think I will carry out the test again, does the engine need to be hot or warmed up as well? Battery was fully charged though

Oil is Castrol 20w50 and the CR is 10.37, the cam is the 998-1380cc from minispares, for use with standard rockers, they say it’s similar to a Kent megadyne 286 but has a smoother idle and is more powerful below 5000 rpm but less over this, yet to see a graph with a direct comparison though

What would be the effect poor valve lapping in terms of exhaust smoke?

#11 MacFreuden

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Posted 23 May 2020 - 10:28 AM

In my opinion the compression readings are low, imo theres enough of a rise in the wet readings so it could be piston rings.

I'd also have fitted 8 MPI spec valve stem seals.

Were the valve clearances done after you rebuilt the motor?

Someone with more knowledge will be along soon

  

Those readings are low on a newly built engine to be fair...
 
How did you take the readings.. all plugs out throttle wide open I hope...and battery fully charged
 
Seems to me the engine may not be "run in" properly or incorrect initial startup....
 
What oil is in it ?

  

The thinking on the oil seals is in my opinion flawed
 
The general rule is 4 on the inlets only and they are not needed on the exhausts as there is no inward suction on them.
 
But that still doesnt stop the oil dripping past them once the engine is off.
 
I think the 4 is more a cost cutting form BL than a real "guide" as such.
 
I always fit 8...
 
Also silly question but did you buy the correct ones for your guides

  

As above,

Psi readings are variable due to engine spec, low copression ratio or a long cam will reduce the psi, also we don't know how accurate the gauge is.

What seals were fitted? if std rubber ones they can harden up, personally I'd always fit Viton ones where possible, and to all 8 valves on a non turbo engine.



I’d love to say what stem seals were fitted but it was just what came in the cylinder head gasket pack from minispares I may ring. And find out Monday... some say you’d fit MPI ones or Viton ones - what is the difference?

I didn’t have the accelerator open come to mention it, it’s a carb model how does this affect it? Just lets it breath better or? I think I will carry out the test again, does the engine need to be hot or warmed up as well? Battery was fully charged though

Oil is Castrol 20w50 and the CR is 10.37, the cam is the 998-1380cc from minispares, for use with standard rockers, they say it’s similar to a Kent megadyne 286 but has a smoother idle and is more powerful below 5000 rpm but less over this, yet to see a graph with a direct comparison though

What would be the effect poor valve lapping in terms of exhaust smoke?

#12 gazza82

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Posted 23 May 2020 - 11:55 AM

Not having the throttle wide open will show lower results ..

Poor lapping will give lower results too but shouldn't show blue smoke ..

Edited by gazza82, 23 May 2020 - 11:56 AM.


#13 cal844

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Posted 23 May 2020 - 12:01 PM

Repeat the test with wide open throttle and with the spark plugs out.

You'll also want to do it wet and dry.

Edited by cal844, 23 May 2020 - 12:02 PM.


#14 MatthewsDad

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Posted 23 May 2020 - 01:03 PM

... And engine warmed up to normal operating temp. Interested to see results.

#15 Dusky

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Posted 23 May 2020 - 01:37 PM

Repeat the test with wide open throttle and with the spark plugs out.

You'll also want to do it wet and dry.


Youre Only testing the strenght of the battery and starter that way. Absolutely pointless.




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