Smokey rebuilt 350

[royhall]

Any ideas guys....... Rebuilt the 350/4 about 9 months ago and so far it has only done 240 miles...... At first it ran very clean but has slowly started to smoke on pots 2 &4....... I have checked all the usuals such as carbs, timing, points gap, valve clearance etc....... I thought at first that it may have been rebored to a too loose tolerance but having done a cylinder pressure check they all come out at 165psi dry and 210psi with a few shots of oil (hot engine), so I am ruling that out....... My thoughts now are with the Cruzinimage gasket set I used ie. non factory head gasket and cheap valve stem seals....... Also the plug out of No.4 is always wet when its pulled.......Any opinions before I pull the head back off..... Cheers.

[hairygit]

Is the plug wet with petrol or oil?

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[royhall]

Quite hard to say for sure Hairy. But its black and doesn't really smell of petrol, and its still wet an hour after coming out. So I would say it's oil.... No.4 is very smokey. Whats the opinion of the stem seals in those Cruzinimage kits?

[hairygit]

I've not used them personally, but those who have seem happy with them. I would give it a few more miles to bed in the oil control rings properly, as 240 miles is nowhere near run in yet. Try taking it out at least once a week, and put at least 50 miles a ride on it, then see if the problem is still there after 800-1000 miles, until then I wouldn't get worried about it. Keep a close eye on the oil level, it will drop if it's burning oil badly.

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[hairygit]

Thinking about it, the 350 does not have stem seals on the exhaust valves, maybe what you are describing is "normal" and the reason Honda fitted inlet and exhaust stem seals on the 400/4?

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[royhall]

It does have stem seals on both sides. https://www.cmsnl.com/honda-cb350f-four-1972-usa_model435/partslist/E++02.html#results Your probably correct about needing more miles. A thought just occured to me, maybe I should check the breather pipe hasn't got kinked somewhere pressurising the cases. Cant believe I didn't check that. DDOOOOUgh

[hairygit]

We all sometimes forget the most basic things and imagine the worst. Get out and ride it, enjoy it, and it might be a good idea to change the oil as well in spite of the low mileage, Honda used to specify X miles or months, whichever comes first.

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[royhall]

All that's bothering me really is No.4....No.2 is only gently smoking (you can barely tell) but No.4 fills the driveway with fog and it takes ages to stop doing it once on the road.

[Trigger]

Sounds like you have a little bore polishing going on. Hairy is right, take it out, get it hot and give it a few revs.

[royhall]

Sounds like you have a little bore polishing going on. Hairy is right, take it out, get it hot and give it a few revs.

Cheers Trig. What causes the bore polishing?

[Bryanj]

Riding it too gently and infrequently

[royhall]

Riding it too gently and infrequently

Too many bikes versus too little time. The age old problem.

[Clem2112]

My 400 smoked a bit from cold startups after its rebuild. This stopped after a few runs though.
I put this down to slight exhaust valve stem wear and there being no seals on the exhaust stems.
The green o rings (under the valve guides?) were not replaced either.

[royhall]

People keep mentioning there being no stem seals on the exhaust valves. When I stripped mine there were seals already on all the valves, there were 8 seals in the gasket set, my parts book shows seals on all valves as does the parts drawing on CMS. When I built it I replaced all eight. Maybe some of the USA models had them fitted and the very few sold into Europe (mainly Italy) didn't. Can anybody verify that.

[paul G]

Roy,

           Both the ones I have done did not have them on the exhaust and both gasket sets only had four in them.