SOHC.co.uk Forums > CB350/400
Smokey rebuilt 350
hairygit:
Was your gasket set a genuine one Roy? I'm not certain but maybe Honda modified it part way through production ( like they did with the 750's) and CMS may have the later parts diagram on their website, and any pattern gasket set would contain enough seals for the later models.
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royhall:
The gasket set was a Cruzinimage item and to be honest not the best. Doubt the spec would have changed as it was only a two year model. Mine was an early 1972 bike and it had all eight seals fitted. To be honest the engine did not look like it had been apart before either.
royhall:
Sorry this has taken so long to resume, been busy building a Suzuki GS1000....... The story so far, my rebuilt CB350F has done 272 miles and pot 4 was smoking so badly I had to take it off the road.
Now the GS1000 is out of the way I decided to strip the top end to have a look, and I'm glad I did.......I stipped it down to the crankcases to look at the pistons. When the head came off all four piston crowns were covered in oil. On checking the gaskets and mating surfaces there was clear evidence of head gasket failure. There was hard burnt on oil deposits behind the head gasket metal sealing ring on all four pots and the gasket was very oily.
I had initially suspected that when the rebore was done it had been bored to a loose tolerance. On measuring the bores and piston skirts the clearance is 0.0008" which is bang on the money for Cruzinimage pistons. Checked the top rings in the bores and the ring gaps are between 6 &8 thou which is also spot on. The new bores appear to have run-in well with a slight glaze but the honing still visible. Strangely each bore has some light vertical scoring that appears to be from the ring ends as they are spaced about 120 degrees apart. Is this scoring normal, its not deep and can barely be felt with a finger nail. I have a new set of plus 1mm Cruzinimage pistons on the shelf, that due to a wrong delivery I got for free, and am toying with the idea of having it bored again just to be sure.
On the head, I tested for valve leakage with the old fill with petrol trick and all is good. That said though, whilst the head is off I am going to replace all eight valve stem seals again just to be sure, and also re-check the valve guides for wear whilst they are out. I solved the mystery of the exhaust stem seals, they had all eight fitted for the first 9 months (approx) of production then further models had the exhaust seals removed. Mine is a very early 1972 model hence the 8 seals. I have checked both barrel top and head for flatness (they were both skimmed at rebuild) and they are spot on.
The questions are how far do I go putting it back together, and clearly I won't be using any more Cruzinimage gasket kits. I have an Athena set for the rebuild (not sure how good the quality of those are) but now I have found that the head gasket was the culprit, should I search for a genuine NOS Honda head gasket? Also what about the rubber seals around the dowels, are they up to the job. I am assuming they are the same items on the 400/4. And how much should the honing be glazed, and what about the vertical scoring is that the cheap Cruzinimage pistons or is it normal.
There are quite a few documented head gasket failures on the USA site but these are mainly leaks to the outside from the edge of the head gasket around the oil control jets. Mine appears to be similar but leaking into the cylinders instead. I had no show of oil at all on the outside of the engine.
Sorry about the long post and the endless questions, just don't want to have to go down this route again. Cheers all.
Bryanj:
There is a post on the US site where he has had a lot of trouble with burning oil on an overbored 350 and has not yey cured it
royhall:
Have you got a link to it Bryan. Cheers.
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