Topic: 3 questions about cb750 engine...

[la ca fe]

I have questions about 1978f motor:

Engine is stuck, what is the best lubricant I can put in the cylinders to unlock it?

Could I use a 74 cb750 head and jugs on a '77f motor?

Is there a good way to estimate it's mileage?

Thanks a lot.

[Stev-o]

I used a 50/50 cocktail mix of Acetone/ATF to "unstuck" my K7. Let it soak for a day or two and then rock it in 3rd gear (if motor is still in frame).

Yes.

Not that I know of.

[madmtnmotors]

Could I use a 74 cb750 head and jugs on a '77f motor?

Only if you use the early (flat top) pistons too.

[brandEn]

pro tip-
use the 50/50 mix of acetone and trans fluid but make sure to cover the engine with a towel or rag. When that motor breaks free all the fluid that's in the cylinder will SHOOT out the plug holes and make a mess out of the ceiling and everything 20 feet away.

[Johnie]

And how would you know that Branden   Good tip!

[Stev-o]

pro tip-
use the 50/50 mix of acetone and trans fluid but make sure to cover the engine with a towel or rag. When that motor breaks free all the fluid that's in the cylinder will SHOOT out the plug holes and make a mess out of the ceiling and everything 20 feet away.

Hey brandEn......I have the record, it is 17 feet! 

[la ca fe]

Thanks for the tips. I will give the 50/50 mixture a try.

[brandEn]

Yup I learned that one the hard way! Good thing my car was not in the driveway or it might have ruined the paint.

[calj737]

I'm a big fan of the 50/50 mix too, but if that doesn't work, try a vinegar soak. It eats the rust lickety-split. You absolutely do need to drain the motor and replace with some oil once it breaks free though. Even if tearing down...