SOHC.co.uk Forums > CB350/400
Smokey rebuilt 350
Laverda Dave:
Bad luck Roy. I second Moorey's suggestion. We use a similar method on train wheels prior to turning in a wheel lathe. Quick and easy, just make sure everything is as clean as possible to avoid any false results.
Good luck.
royhall:
Thanks guys. The stem seals were replaced and all checked for tolerance at the first and second build. Second time it was genuine Honda seals, no seals on the exhaust side as per 350F. Still smoked both times. I'm sure it's not anything to do with seals or wear this time, will be using the crack detection method looking for actual damage when I get round to it. At about 200 miles it started smoking badly all at once which would suggest something has broken or cracked. It will have to wait a while as it's Isle of Man time again on Thursday so will be away for 10 days. Hopefully when I get back someone will have stolen it (agreed value). ;D
royhall:
Sorry for returning to such an old thread but I thought it best to bring it to an end. You may remember I had a smokey CB350F that was refusing to be repaired.
After pushing the thing to the back of the garage under a sheet for nearly a year I thought I would have another go. This time around I am taking no prisoners so am removing all reproduction engine parts and replacing with genuine.
After stripping the top end I checked the barrels and liners for cracks with Dye-pen. They checked out okay. Unfortunately they were now at maximum bore with Cruzinimage pistons so they are unusable with NOS pistons. They are good though so I will sell them on.
Couldn't Dye-pen the head as the casting inside the ports (where it matters) is just too rough. After sending the head to an NDT specialist who checked it with something to do with Eddy Currents (pass) it came back with the problem marked. It appears that after changing the valve guides the casting had a small crack on No.4 inlet that had slowly propagated along until neat oil was being pulled into the cylinder. Bingo, problem found.
After weeks of looking I finally sourced replacement head, barrels, and pistons. The head was like new and required nothing but a clean up, painting, and valves lapped in. The barrels went off to Trigger (thanks for the great work Trig) who replaced some liners then rebored for the NOS pistons. All went back together with NE gaskets.
Only done a few miles on her, but the engine is smoke free and runs superbly. Guess it will have to wait until spring now to run her in properly. Thanks to all members that helped (or tried to help) with this problem. It can feel like a hopeless case but every problem has a cause, it just has to be found.
I treated her to a Spa day and polished everything to within an inch of its life. She looks a real lady now.
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hairygit:
So pleased to know it's finally sorted! I shudder to think how much time and hard cash this issue has caused you, but there HAD to be problem, it just took a while to find it. I think we should have a thread for saving some of these stories and ultimate solutions, there have been a few long suffering owners recently, and others can learn from the experiences. Well done for sticking with it and not giving up (plenty of people would would have done!)
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royhall:
On the hard cash front. This problem has caused me to break my self imposed limit that the finished bike shouldn't have cost more than it's worth. But what else can you do but sell it off cheap with a smokey pot. I'm not selling it anyway so doesn't really matter. However, this little problem ended up putting £680 onto the rebuild cost. Ouch.
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