Smoking Jup

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Keith Clements
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Smoking Jup

Post by Keith Clements »

Josephine has started smoking!
The symptoms are a puff at start up but then little emission until at normal temp when large clouds of smoke appear. My first thought was a head gasket but an endoscope on the cylinders showed they were oily.
Plugs too were oily. Both oil and water were low, but I cannot be certain these were certain indicators as there was a leak which I then fixed with some K seal. More investigation required.
Compression test showed 190 psi on 1 and 3 and 160 psi on 2 and 4. Once again I cannot be absolutely certain that this is a recent drop as I am not any good at record keeping. But is the drop caused by the gasket, a relaxation of the block or ring wear or breakage, valve seal or tappet clearance.
The endoscope should show a head gasket failure by showing clean areas where the leak occurs, but why are all four cylinders oily? I checked the pintel valve which was sucking, perhaps a little too much as the filler cap was sucked in and a hand over the oriface detected suction. I ran without the filler cap when there was no excessive blow back and the smoke did not decrease so unlikely to be the pintel not closing but still could be the balance pipe seals. The latter I do not think is the cause as the smoke is white and really only comes when hot.
The smoke did appear more to be steam than blue burnt oil.
I also tried my carbon monoxide test on the radiator by trying to bubble any exhaust gas in the rad water through the special detecting fluid. But no bubbles. I have modified a rad cap for this purpose.
So I have at the ready a set of pistons and liners and a set of head gaskets as I still cannot decide the cause, of course it could be both need doing!
Pictures follow of each cylinder showing what I think is excessive oil.
The engine sounds great, pulls well at 85mph and idles perfectly!! But when I stop at the lights the cars behind tend to hold back :oops:
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Nick Webster
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Re: Smoking Jup

Post by Nick Webster »

In the fourth endoscope picture down are we looking at a burn on the edge of the piston? A bit of a concern I would have thought. However,I doubt that has anything to do with smoke, unless a ring has broken. But If the oil is visible in all the bores it is suggesting something more general like a gasket or possible fracture. Surely it is not long since this engine was rebuilt. I know you like to seek extra power from your engines but what do you consider your maximum rev limit to be and at what compression ratio?

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Re: Smoking Jup

Post by alexander »

I had some thing similar and found the return oil ways in the head were blocked and oil was getting into the bores.
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Re: Smoking Jup

Post by Forumadmin »

If the return oilways are blocked the tappet cover fills up and oil will either be sucked in through the inlet valve stem or oil will get through the exhaust valvle guide into the exhaust.
Excess oil will eventually flow back through the push rod tubes.
You will see excess oil when you take off the rocker cover. Always check there is no condensation or water in the rocker cover as this indicates solder was not put under the head stud washers or the rubber seal is not properly fitted in the centre stud.
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Re: Smoking Jup

Post by Forumadmin »

Nick, the engine has done about 3000 miles having been driven to Italy with no issues. With overdrive I seldom take to max revs which on this engine is low at 4500rpm.
I agree I am concerned about the pattern around the liner and piston but there seem to be similar on all cylinders. This engine was one I bought from Wes and had new liners and pistons, which I did not check thoroughly and are not the usual ones I use.
Investigation will commence on Monday after watching the Jup race at Brands Hatch on Sunday.
I may first check crankcase depression with the vacuum gauge before taking the head off on 2 and 4.
Keith Clements
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Re: Smoking Jup

Post by Keith Clements »

Head off confirms a leaking head gasket. The endoscope showed the washed piston crown indicative of a gasket leak.
20210713_185125.jpg
20210713_182431.jpg
What caused it? Liner heights at 10 thou. But looks like some overhang on the gasket. NZ do two varieties with the larger diameter (yellow sticker) closer to the original (orange sticker).
20210713_185815.jpg
and this showing difference in variety.
20210713_185710.jpg
20210713_185227.jpg
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Keith Clements
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Re: Smoking Jup

Post by Keith Clements »

Hopefully together again tomorrow with the larger gasket.
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Keith Clements
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Re: Smoking Jup

Post by Keith Clements »

Seems to be not smoking now...having replaced head gasket with the NZ yellow sticker large diameter.
I suspect the problem was caused by there not being enough pinch because the heads were prepared for the larger pistons whereas these are standard Jowett ones.

I also polished the heads to get rid of some milling machine marks, so let us hope this lasts longer.

Will do a few miles tomorrow and then retorque the heads.
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