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Discussion Starter #1
I had the misfortune to sieze my engine during a race in Utah. I believe the camshaft journal on the timing side is friction welded (due to lack of oil?). The engine was so hot when it slowed and stopped that the solder on the points melted.

I have removed the cylinder head cover and the tach side cover and only one rocker arm pin. There is substantial evidence of severe overheating. The engine crank and cam cannot be rotated at all. Of course, they are connected by the cam chain. The cam is in a position to depress one valve on each side so there is considerable pressure on the whole system.

I wonder if anyone has dealt with problem previously and what the solution might be to proceed with disassembly.
 

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Sorry to hear about your problem. Sounds like you have some major repairs to deal with. If it were my race engine I would be looking at complete overhaul, top and bottom before next season anyway, so I would take a dremel tool and grind the rivets flush on the top link of the cam chain flush with the side plate and break the chain. Then pull the rocker box off with the cam intact. If you can't get the and bearing off and the cam out then I guess the parts aren't usable anyway. I suspect if you generated that much heat the cam and rockers are scuffed beyond use anyway. Time to dig an engine out of the pares pile. You do have a spares pile for a CB350 race bike don't you?

Do you have any idea why it overheated so badly? I have never had a CB350 race engine overheat like that. Just on speculation, I would suspect that you had a bearing failure on the left cam bearing and that generated the heat, rather than the heat causing the failure. What kind of oil were you using? Is it a stock motor with stock valve springs? Heavy duty valve springs do increase the bearing load on the cams plain bearings and be a party to failure if other clearances or oil, or oil flow is marginal.

Ken

AHRMA 412
Vintage racing - old guys on old bikes
 

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CB350 cams sit in plain bearings, right? Maybe time for roller bearing conversion in the next engine. Will give you a larger margin of error.

Wonder if a oil passage got blocked or if the oil pump failed. I'd cut the cam chain and starting examining the oil passages to the head and the oil pump.
 

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Discussion Starter #4
Thanks for the advice. I figured the cam chain had to be cut but I just wanted to hear it from someone with experience. This will be my first rebuild of a cb350. I actually have 3 engines I want to fix up for racing. As far as I know, this engine was completely stock. No evidence of having been disassembled previously so valve springs should be original. I was using Honda GP4 oil 10w-40. The problem reared it head a few times before it finally siezed altogether. Excessive heat was evident but misdiagnosed as a fuel delivery problem. It would operate correctly and then just slow down like it was just bogging down. This happened several times over the course of two days before the complete siezure. Now that I se what was happening, I'm amazed at the toughness of these engines.

I have the Megacycle catalog handy. It's just money.[8:]
 
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