sigh- 82 dohc engine/gearbox demons

[my03]

Hi guys, I have a cb750 which i bought with the weisco 823 kit, I put on some cr 29 carbs and dyna ignition system.

So a month ago it just died on me like it was running out of fuel.

Turns out the plugs were fouled up and running really rich.

So I spent 900 bucks to get it all sorted and tuned on the dyno.

The mechanic told me that it's burning alot of oil. When I pulled out of the shop it was cylinder no 2 was not firing, we pulled out the plug and sure enough it was fouled, we cleaned it up and fine again.

Rode it home and all electrics cut out,. burnt fuese somewhere I suspect - yet to have time to have a look at it.

Anyway, the oil issue is of concern, perhaps a worn ring on the no. 2 piston? or old valve stem seals? Furthermore it keeps popping out of second gear and back into neutral. not sure why the problem is so imminet, perhaps its cause we topped the oil up with a different oil?

I really have limited mechanical expereince but I love my bike. I really don';t want to give up on it and wanted to get your opinions on how to get the bike running flawlessly.

Should I even bother taking the engine out and trying to find the problem? or should I start fresh and buy a rebuilt motor somewhere? Labour is really expensive in australia here.

Does anyone know reputable workshops that sell ready to go rebuilt engines for dohc cb750? or do you think the problems I mentioned are minor and can be ironed out?

I was thinking of doing an oil change to start, then keep my eye on the oil level and keep topping it up. But the second gear issue needs to be sorted.

Any advice would be greatly appreciated.

Thanks

 

[my03]

Anyone had a similar problem would you please let me know if it's a big fix?

Thanks

 

[dirtdigger]

More than likely the jumping out of gear is a worn dog on the gear in the transmission. Oil burning is rings or guides, in either case the cases will have to be split to inspect parts. I would look for a different motor.

 

[my03]

Thanks for the reply, is replacing a worn dog gear a big job? is it labour intensive? just want to know what I'm up for in costs. Where will I get the replacement gear?

As for buring oil, I assume that would be a total rebuild? Am I ok to keep my eye on the oil level and just keep topping it up?

Does anyone know any companies that sell rebuilt engine packages? I'm located in Australia and would need to get it freighted over here cheers

 

[dirtdigger]

To replace the gear you would have to split the cases to get to the transmission, it is fairly labor intesive. So motor would have to come out of the frame.

I guess you could just keep adding oil but there will be a point where you are replacing fouled spark plugs more often then you are riding it not to mention the cost of the oil you have to keep adding.

Honestly most people dont rebuild these dohc motors they just buy a used motor and swap it in, they just aren't as popular as the sohc motors are. All of the parts are available for rebuilds but I dont know of anyone that rebuilds them and sells them.

 

[my03]

thanks DD, ok I might consider buying a good condition motor for swap, which is a shame because the old engine has the 823 kit in it.

I have keihn cr29mm carb, and a dyna 3000 ignition modeul on there, will these parts be suitable for the new stock engine that isnt stroked?

 

[dirtdigger]

They should be fine. the 823 isn't a stroker it is just a 3mm bigger bore, common size for the dohc motor.

 

[my03]

Thanks for that

What other engines would be compatible? The dohc cb900 will fit won't it? Will the engine bolt straight on and be compatible with everything else I have on the bike?

Does anyone know a good source of spare engines for cb's?

Thanks greatly appreciated