Topic: Cb350f fresh top end smoking like nuts!

[grcamna2]

Sorry for the long delay. I finished up the bike in June and stored it for the summer before starting it. I live in Phoenix Arizona and summer time is not when I'm spinning wrenches in the garage.

I fired up the bike this week and it doesn't smoke!!! Halleluiah!!! Turns out the piston to cylinder clearance created by the machine shop that bored the cylinders the first time was the culprit all along. This has been a long and very frustrating process (three top end tear downs searching for the culprit) and at the end of it I can confidently say that they key to preventing this from happening is finding the right machine shop that has experience boring these smaller cylinders. As I stated in my previous posts I had Utah Crankshaft and Shortblock rebore the cylinders using NOS Honda pistons at .75 oversize and I can't thank them enough for getting it right. The turn time was very quick and the price was reasonable.   

Thanks to everyone for your input and assistance. I wanted to circle back and post this solution to assist other restoration mechanics from going through the frustration of chasing down a problem that could have been prevented by using a machine shop that has experience with these smaller inline fours. 

Now it's time to log some miles on this little CB350F and seat the rings!

A great progress report on your CB350F top-end rebuild 
I have struggled with automotive type machine shops for years who have 'decided' that the correct specification for piston to cylinder clearance was "too tight"    I would like to have told them, 'I'm the customer,these are the specs:do your job' !    I have spent lots of $ repairing damaged jobs & getting cylinders rebored and getting new sets of oversize pistons and rings to say nothing of never-ending disappointing treatment;hey ! The losses to my trusting nature plus the price of that stuff adds-up.
I finally found a very good PowerSports Machinist(all he does is motorcycle parts w/ a few side jobs on other stuff once in a while)here in N. Cal. and been going to him for a few years;he's a one-man operation working out of his shop next to his house though so it does take time as he's very busy.
 Did you speak to someone over there at Utah Crankshaft that was able to make sure they followed all the specs and good communication? What part of Utah are they located in ?

[SquierA]

I found Utah Crankshaft on Ebay as they have a listing for pistons, wrist pins, rings and already bored cylinders for the CB350F for $899.99. The listing is still on ebay now.

I called them before I sent them my parts and explained my challenge and they measured the parts I sent them before reboring the cylinders. After they confirmed the out of spec measurements they rebored my cylinders and shipped my parts back in a timely manner and called me to let me know how the new bore measured. I was very pleased with their service. 

They are located in Springville Utah and their phone number is 801-702-8142.

[grcamna2]

I found Utah Crankshaft on Ebay as they have a listing for pistons, wrist pins, rings and already bored cylinders for the CB350F for $899.99. The listing is still on ebay now.

I called them before I sent them my parts and explained my challenge and they measured the parts I sent them before reboring the cylinders. After they confirmed the out of spec measurements they rebored my cylinders and shipped my parts back in a timely manner and called me to let me know how the new bore measured. I was very pleased with their service. 

They are located in Springville Utah and their phone number is 801-702-8142.

Thanks for that.