Topic: Damaged case on a CB 550K- Can I mix and match top and bottom cases?

[dleisch]

Greetings- I am wondering if OK to mix and match top and bottom cases in CB550K 1978.  I have one complete engine, with a damaged area on the top part of the case (could be repaired, not structural, big chip off the ignition case).  I have an extra set of cases (that are empty no guts inside).  They are both from the 1978 model year, casting numbers are only a few thousand apart.  Would it be OK to just swap out the top case and mate it to the bottom case on the complete engine?  (thus only moving the guts from one top case to the other top case)  These cases look to be interchangeable when from the same model year I would think.  Cheers, Dave.

[ekpent]

It is suggested by most not to use mismatched upper and lower cases from different engines.

[bryanj]

Definately a big NO

[Shtonecb500]

no, source new set.

[RAFster122s]

Cases are made as a matched pair...

[dave500]

the main bearing tunnel is line bored as a complete case.

[newday777]

Greetings- I am wondering if OK to mix and match top and bottom cases in CB550K 1978.  I have one complete engine, with a damaged area on the top part of the case (could be repaired, not structural, big chip off the ignition case).  I have an extra set of cases (that are empty no guts inside).  They are both from the 1978 model year, casting numbers are only a few thousand apart.  Would it be OK to just swap out the top case and mate it to the bottom case on the complete engine?  (thus only moving the guts from one top case to the other top case)  These cases look to be interchangeable when from the same model year I would think.  Cheers, Dave.

Welcome aboard Dave

As the others have said that is a no because of the machining of the crank bore being a matched pair.
Use your second set of cases. Is there a reason you didn't want to use the complete second motor?

[dleisch]

THANKS ALL!  Super helpful to know the cases are a matched set.  Now to decide if I repair the damaged case or switch all the guts to the other cases...cheers! 

[Stev-o]

Personally, I would just search for another motor and use the entire bottom end [they are typically bullet proof]

[pekingduck]

I would recommend repairing the original case, as it's non-structural, and you could even cut a section out of the spare case to match.  Any welding/fab shop should be able to do it. We used to do it fairly often (along with re-constructing fins) in the Seventies. It was even an accepted repair for insurance jobs.

[HondaMan]

I've had many cases repaired by welders. The worst one was an early (REAL early) K0 with the chain hole in the case. It took 2 trips to the welder and 3 to the machine shop, but in the end it didn't leak and ran fine. One 750 came to me with an electrical box on the top of the cases, drilled right into the motor and mounted with self-tapping screws. You can figure on what happened to that tranny...I changed that out (and primary chains and oil pump) and had the cases welded back up, worked fine.