1979 750 Engine Problems

[Bocephus]

1979 CB750 with 26,000 miles. I had a burnt exhaust valve in #3 so disassembled. Problems I encountered along the way.

• Several of the cam tower bolts snapped off. Any tried methods for removing? Drill and easy out? Will also need new bolts.
• Timing chain guide broken and chain wore a tiny hole through the block. So small that the only way I could tell was to blow air through it. I think I can repair this with JB Weld and a new guide.

Not sure if I would be better off repairing this engine or try to find a good, lower mileage engine. Are all 750 DOHC model years 79 - 83(?) the same and interchangeable? Looking for some help with this mess. Thanks, Jim

 

[brettp]

I would weld the hole, instead of jb weld.
I would drill out the cam bolts careful not to ruin the threads.
You can save that engine for sure.

 

[Loose Chain]

That's in pretty bad shape for only 26 thousand miles. That valve should be a reminder to others of what happens when you ignore valve adjustments.

 

[Bocephus]

Is it common for the cam tower bolts to snap off in the head? I had more than 10 break trying to remove them.

 

[Loose Chain]

Is it common for the cam tower bolts to snap off in the head? I had more than 10 break trying to remove them.

No it's not common. Was there any indication that the engine had been apart before.?

 

[Bocephus]

No there wasn’t. I was really surprised by this.

 

[brettp]

I wonder if a PO used loctite. I had some threads strip in one of my cam bolts, which are m6 size, so I drilled and tapped for an m8 and put in an m6 helicoil. Worked for me. Couldn't use a timesert or thread-lok (?) because the receiving end of the bolt (cam shaft tower? Lol) doesn't have a lot of width.

 

[Loose Chain]

It might be cheaper for you to find another head to rebuild. There is no doubt that the valve seat that had the burnt valve will need to be fixed, plus if you have to pay someone to extract all the broken bolts you will be into it for quite a bit of money. How do the cylinders look?

 

[Bocephus]

Cylinders look fantastic. I’ve already managed to bugger up the head so time to move on and find a replacement head. Will need to find one with the camshafts in the head. What should I expect to pay for a head?

Thanks, Jim

 

[brettp]

Look on marketplace along with other places. Prices on marketplace can be all over the place, though. Wish I was more help, but that's all I got.

 

[Loose Chain]

Cylinders look fantastic. I’ve already managed to bugger up the head so time to move on and find a replacement head. Will need to find one with the camshafts in the head. What should I expect to pay for a head?

Thanks, Jim

What did you do? Why do you need camshafts?

 

[Bocephus]

The cams are fine but since they don’t use bearings, they are matched or worn to that particular head. Right?

 

[Loose Chain]

No, the cams you can change but the caps have to go back on the same order as they came off. So what happened to the head?