Busted Rocker Arm Shafts

[Bone_Digger]

I bought a non-running 1973 CB750 with good compression and have been disassembling it. When I took the rockers off I had a big surprise. The rear (longer) rocker arm shafts were broken in half at the pinch point where the rocker shaft arm mounting bolts hold them in place. Has anyone else experienced this, and if so what was the cause?

I have taken the whole engine down and have not noted anything grossly out of wack. However, I have not measured anything yet. Could it be that the previous owner simply tightened the mounting bolts down way too tight and snapped the shafts? Thanks for any insight you can provide.

 

[dirtdigger]

It does happen but normally only when used at high rpms in racing. Is it a stock camshaft? You can use any year sohc shafts. The early ones are a shaft with just the groove in the center, later shafts have the center groove as well as two small threaded holes. They are interchangable. The later model cam towers have corresponding holes to the threaded holes in the shafts and use small bolts to lock the shaft to the cam tower. It keeps them from coming out if they break but it also increases wear on the shaft and the rocker arms. There are no new shafts available (yet) so you will need to buy good used ones.

 

[Bone_Digger]

Thanks for the reply Dirtdigger. I believe the entire engine is stock. It has stock carbs, stock airbox, stock suspension, etc., so I assume the cam is stock as well. I'm away from home right now, but will check the cam measurements when I get back. Thanks or the info on the interchangeability between early and later SOHC rocker shafts. Do you know a sorce for used shafts?

 

[dirtdigger]

Ebay is the best place to find used 750 parts. You might want to put a wanted ad in the classifieds maybe someone on here has a couple.