SOHC.co.uk Forums > CB350/400
Smokey rebuilt 350
kevski:
Well from what i have read up on this particular subject the main problem seems poor quality gasket sets in particular the two rubber rings at either end of the head, does this same problem occur with the 400, if i eventually have to do mine i can see modifications coming on.
Nurse Julie:
I fitted extra 'O' rings around the end studs on my 400 rebuild, as suggested by Trig.
K2-K6:
I've read through that thread on net site, and something they are missing which may have a parallel here is those ring markings vertically in the bores.
That says to me that the piston rings are not round when compressed into the bore, else the ring's ends would not protrude further than their outside diameter (and make the marks you can see) that is not right. His question about black ring coating, and should it wear, shows that the rings are not touching the bores where the coating remains. They are, in effect, elliptical in shape. That will not seal the bores either oil going up, or compression going down. It should be getting to something like 175 psi, it's nowhere near.
Leakdown testing is only going to show efficiency in holding compression, it'll not show oil retention ability as that's the opposite direction.
Exhaust valve guide leaking doesn't usually affect combustion chamber as it's introduced after the cylinder. It'll smoke yes, but just from passing oil into a hot exhaust system.
Inlet guides leaking usually show with throttle shut on overrun, inlet vac goes high and pulls in oil, when you get back on the throttle it'll puff out a single-ish cloud of blue smoke.
Looks like the rings aren't working as they should, whether they'll bed in if they're not touching in the first place I doubt it. You'd, in effect, have to wear all of the "touching" parts of the ring down first before that process could even start to take place.
But as the first example of massive ring gap, that's what you'd get by the time you had achieved the above. There's lots of evidence in that thread but it's not being connected.
royhall:
--- Quote from: Nurse Julie on March 15, 2018, 01:23:51 PM ---I fitted extra 'O' rings around the end studs on my 400 rebuild, as suggested by Trig.
--- End quote ---
More information if you would Julie. Cheers
Nurse Julie:
If you look back through my engine rebuild thread Roy, there is a pic etc on there. I'm laying on the beach in India so defo not thinking of anything made of rubber in this heat !!! :o
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