Topic: CB400f Engine rebuild into CB350f Frame

[A350- 4 me!]

Hey all I am fairly new to engine rebuilds and what to do.  I have  a 350F running condition and it is smoking like crazy, I believe it is due to the rings.  So I ended up finding a 400F motor on CL thats in pieces, the guy I bought it from builds the cb450? with the 305cc motors, he said the motor I have just needs new rings and new gaskets. 

So I am sorry if I started a new thread when I should've just searched, the information I've been looking for was not found. Should I rebuild up the motor completely or just quick rebuild so I can be riding.  I am on a budget but would to have  a solid running engine for maybe 5-10 years.  I am still in the process of locating the gaskets, timing chain and  tension;  basically the main question would be should I split the crankcase if I am on a budget but want a solid running bike for years to come that maybe taken to the track a few times.

[Triffecpa]

just do a top end rebuild on the current engine.  There is a guy on Ebay who was selling CB350F rings for about $45.  You need a top end gasket set.  Replace the cam chain while you are in there.  Use one of the ones that have a press together master link.  Just hone the cylinders and put it back together again.  It's unlikely that the bottom end of the engine needs rebuilding.  The small CB's rarely get run for 10's or thousands of miles.

Tracy

[A350- 4 me!]

cool thanks, I thought to use an endless  I will still need to split the crankcase, which in turn will require more parts to be replaced. 

[Triffecpa]

I use the ones with master links on my track bikes and rev the snot out of them.  Never had a problem.  If you can't find a 350F or 400F specific chain, buy one for a CB750.  They are the same chain only about 10 links longer and usually cheaper.

TR

[camelman]

For a budget build on a 350F I highly recommend replacing your valve stem seals too.  You'll have to buy a gasket set to get your head gasket, and the valve stem seals will come inside that gasket set.

Be careful with those cylinder head cover bolts too.  Only tighten them by hand with a 10mm screwdriver.  The manual states too high of a torque value for them.  Stripping them results in oil leaks.  Repairing them costs about $60 per hole at a machine shop.  They don't need to be very tight to seal the oil in.

Oil and filter afterwards and you are good to go.

Camelman

[A350- 4 me!]

Thanks guys for your input, I have stripped some of the bolts for the valve cover while replacing the valve seals with some viton ones. I think I will still rebuild the 400f motor but over a longer time period.  For the mean time I probably will find rings for the 350f and do a minor rebuild till the 400f is ready.

[Triffecpa]

Thanks guys for your input, I have stripped some of the bolts for the valve cover while replacing the valve seals with some viton ones. I think I will still rebuild the 400f motor but over a longer time period.  For the mean time I probably will find rings for the 350f and do a minor rebuild till the 400f is ready.

Buy a heli-coil kit and repair them yourself.  The kit comes with the proper drill and tap and a variety of lengths of inserts.  Costs about $35 and there is enough material to do a couple dozen holes.  The only thing that I would add is some aluminum thread cutting fluid (it's greenish)

I think that those cam cover bolts are 6mm, but double check.

TR

[A350- 4 me!]

Cool thanks, definately will do that.  After looking around for prices on rebuilding a 400f motor, I dont think I afford to do that on my budget.  Do you guys think it is doable to rebuild it myself without any engine rebuilding knowledge.  I am most afraid of the crankcase.