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Blue smoke on overun

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ratty
V4 Fanatic

United Kingdom
340 Posts

Posted - 10 Jan 2019 : 14:01:15

Engine was completely rebuilt about 15000 miles ago. Everything seemed fine until fairly recently. Have stripped engine to try and find the culprit but nothing is showing that is obvious. Piston rings are ok all were new, valve stem oil seals all good. Anyone else experienced this and found a cure? The smoke is bad, will even fluff a plug temporarily. Just looking for ideas. Just checked brake servo and pipe no oil any where.

melle
V4 Guru

United Kingdom
3833 Posts

Posted - 10 Jan 2019 : 21:42:10

PCV/ hose clean as well?

www.saabv4.com

ratty
V4 Fanatic

United Kingdom
340 Posts

Posted - 10 Jan 2019 : 22:12:28

clean as a whistle!

Derek
V4 Guru

United Kingdom
2191 Posts

Posted - 11 Jan 2019 : 12:30:59

I think I would still point the finger at the valve guide seals if you're sure the servo isn't getting brake fluid into it. Brake fluid tends to give a very big cloud of smoke and is more blue-white that the greyish oilsmoke which isn't usually so obvious. You really need someone following you to diagnose it. I replaced the seals on my car, the engine had under 40k from new on it and found a few broken. I used the pukka Saab hook tool to do the job. The new seals seemed to go up and down with the valve rather than staying fixed against the guide but it didn't smoke after I'd replaced them. If the seal stays up the guide when running I'd think that some oil can get underneath and get sucked through if the guides are worn. No actual guides in the V4 I think unless they have been retro fitted.

ratty
V4 Fanatic

United Kingdom
340 Posts

Posted - 11 Jan 2019 : 13:49:28

The engine is out and stripped. This engine is the one out of my trials car which I had specially built with a Kent High Torque cam 224 but the engine does not pull as well as the my other one which is bog standard. So am putting standard cam back in. Will be checking valve guides seals all are fine. But still haven't found a definite as regards the blue smoke.

GeoffC
V4 Mad

United Kingdom
507 Posts

Posted - 11 Jan 2019 : 17:30:44

If it's valve guides it's usually oil smoke on start up as oil drains through when the engine is switched off. Smoke on overrun is usually due to piston rings - did you do a compression test before stripping the engine?

ratty
V4 Fanatic

United Kingdom
340 Posts

Posted - 12 Jan 2019 : 12:13:54

Ok so on that basis it is more likely to be piston oil control ring or rings. Didn't do compression check only pulled one piston so far that was fine and all clearances were within tolerance. Carbon build up on tops of pistons and inside combustion chambers were ok,evidence of burning oil and running rich. Very black in colour. I have been trying to get a +40 thou. set of rings but they are as rare as rocking horse s--t! Plenty of standard around. If I could get hold of a set then I would renew them even though seem ok. I think that has covered the subject unless somebody has any other ideas? Will be fitting some Malbrad big heads and the 28/36 is going to be replaced by a new 32/36 from Fastroadcars. So hopefully with a standard cam engine will run a lot better and should pull a lot better than my other one. We will see.

Woody
V4 Guru

United Kingdom
2764 Posts

Posted - 12 Jan 2019 : 13:16:47

We’re the piston and oil control rings alignment in the piston grooves as they should be?

ratty
V4 Fanatic

United Kingdom
340 Posts

Posted - 12 Jan 2019 : 18:25:48

Excuse my ignorance but what do you mean by alignment? How could they be misaligned? Have only pulled one piston.

melle
V4 Guru

United Kingdom
3833 Posts

Posted - 12 Jan 2019 : 18:38:29

See Saab Workshop Manual 216-5 (Download here if you don't have one: http://saabv4.com/index.php/saab-factory-manuals/saab-v4-factory-workshop-manual-english/)

www.saabv4.com

ratty
V4 Fanatic

United Kingdom
340 Posts

Posted - 12 Jan 2019 : 18:42:14

Thank you will have a look. When the engine was rebuilt approx. 7 years ago engine was rebored and new + 40 thou pistons fitted. The blue smoke is a recent new problem. Although the engine is driven flat out often with lots of valve bounce whilst trialing it is only for approx. 3 minutes per hill.

ratty
V4 Fanatic

United Kingdom
340 Posts

Posted - 12 Jan 2019 : 19:56:31

Ok have had a look and yes they were in that alignment near enough. How far out have they got to be to start burning oil on the overrun? If they were completely out of alignment would there be other problems?

Derek
V4 Guru

United Kingdom
2191 Posts

Posted - 13 Jan 2019 : 13:54:30

Going back to the OP, does this happen when trailing or on the road? Thrashing the nuts off it up a steep hill and just coming off the throttle, perhaps down a hill are a bit different. Thrashing up a hill could cause excess oil to pool at the rear of the heads and then be sucked into the rear guides, good or bad seals. Oil can also go to the back of the pan and then much more of it will be thrown up the rear bores. I think that scenario was mention in a post some time ago? If it smokes at a reasonable speed on the road on a fixed throttle that's another thing.

ratty
V4 Fanatic

United Kingdom
340 Posts

Posted - 13 Jan 2019 : 16:33:09

No it only smokes on overrun after going down a longish hill, the higher the revs the worse it will be but I understand what you are saying Derek.

RhysN
V4 Fanatic

United Kingdom
411 Posts

Posted - 13 Jan 2019 : 20:35:23

That, on other engines is usually valve stem seals. I could be wrong with these engines though.

melle
V4 Guru

United Kingdom
3833 Posts

Posted - 13 Jan 2019 : 20:48:21

Would also be my first thought.

www.saabv4.com

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