8 replies to this topic

[bajean]

Another day another problem.... So my mini sometimes desides to puff out some blue smoke on heavy acceleration, and after reading several forums about this problem i've concluded that it might be the valve stem seals ( and being the original ones in the head and the engine being set in a garage for 20 years, i think they are the problem ) what do you guys think ? If this is the case i am in the process of rebuilding a 12g940 a plus head off a metro ( good clean " de coking ", re-lapping the valves, and new valve stem seals ), this might alleviate the problem and also give a bit more performance as it uses the bigger valves. Sorry for the huge paragraph, and thanks in advance.

[cal844]

That sounds like a good build, what I'd say though is to check the valve guides for wear too

[Stevie W]

Blue smoke on heavy acceleration can also be worn piston rings, might be worth a leak-down test or compression test.

 

If doing a compression test, carry it out with the plugs removed and the throttle wide-open. Pour a little oil down the bores and repeat the test, a slight improvement in compression results means worn rings.

 

Worn valve guides usually shows as a puff of blue smoke on opening the throttle, especially after a long overrun.

 

Cheers, Steve.

[bajean]

Il be using another head from a metro1275 lump ( the head that i am rebuilding), i checked the guides already and they are smooth with no play to be seen, so thats all good. I also thought that it might br rings, but it doesn't puff out smoke all the time even under acceleration which makes me think its the stem seals rather than rings ( not excluding them as it is an old engine after all ). Thanks for the info.

[sonikk4]

Smoke on the over run would be more indicative of worn rings unless of course you have a constant pall of smoke.

Blue smoke on initial start up would be a sign of valve stem seals / worn guides.

But as mentioned even with you using a good replacement head the problem could still be within the block so as mentioned a compression test / leak down test will give you a better idea of what is happening piston ring wise.

[bajean]

Agreed 100%, thing is it doesn't smoke on overun, only when on the accelerator. I''ll try and get a hold of a compression tester and see where its at, if the rings are indeed done, i have another engine that im having built professionally ( with a bunch of med / swiftune goodies and a completely overhauled sc gearbox ) il just wait for that to be finished and put in the fresh engine. Il rebuild it at a later date. Thanks all for the info i greatly appreciate it !

[gazza82]

If this is the case i am in the process of rebuilding a 12g940 a plus head off a metro ( good clean " de coking ", re-lapping the valves, and new valve stem seals ), this might alleviate the problem and also give a bit more performance as it uses the bigger valves. Sorry for the huge paragraph, and thanks in advance.

What engine is it going on? A 1275 or small bore?

[bajean]

Its a 1275 off a austin 1300.

[bajean]

Just thought i'd give an update on the mini. I just installed the new overhauled head today, and it seems to have done the trick, doesn't smoke on startup, acceleration or overun !

Edited by bajean, 12 May 2020 - 06:37 AM.