CB500 Four vs 550 engine case compatability?

[gioventures]

So after removing my kick starter assembly on my 72 CB500 Four, ive come to find two very infortunate hairline cracks on the bottom case where the kick start shaft runs through. My only two options are, remove the bottom half of the case and take it to a local welder to see if they can dremel out the cracks and fill them in, then smooth them out, or buy the bottom end off of a buddy who has a spare CB550 motor. Clearly it would be a cheaper and easier alternative to buy the bottom end off of a 550 how ever what i dont know is if my 500s bottome end case is exactly the same to the 550. My understanding is that theg gearing for the 550 is differeent from the 500 therefor the internals of the cases should be different. Does any one have any more info or experience on this? Please help! Anything would be useful.

 

[Hot500]

Part numbers for the 500 & 550 cases are different. The 550 motor had a lot of changes from the 500. The clutch engagement was on the opposite side of the upper case from the 500 and the clutch housing was bigger than the 500.

Also, Honda SOHC/4 motors had matched cases. You cant mix and match. If you have a look on the back of the cases you will see a series of letters, like ABBCA or similar. These are the main bearing sizes or color codes. Both cases must match. If either top or bottom case becomes damaged beyond repair, they are scrap metal. Go get another set of matching cases.

There are 500/4 motors everywhere on Ebay, however, with a competent welder and a lot of grinding, sanding and polishing, you can finish up with an invisible repair freshly painted good as new.

 

[gioventures]

Part numbers for the 500 & 550 cases are different. The 550 motor had a lot of changes from the 500. The clutch engagement was on the opposite side of the upper case from the 500 and the clutch housing was bigger than the 500.

Also, Honda SOHC/4 motors had matched cases. You cant mix and match. If you have a look on the back of the cases you will see a series of letters, like ABBCA or similar. These are the main bearing sizes or color codes. Both cases must match. If either top or bottom case becomes damaged beyond repair, they are scrap metal. Go get another set of matching cases.

There are 500/4 motors everywhere on Ebay, however, with a competent welder and a lot of grinding, sanding and polishing, you can finish up with an invisible repair freshly painted good as new.

Thanks for the tips Hot500. So what i gathered from this is that its going to be much more difficult to find a matching bottom end to fit my top end of the case due to the manufacturing batches from the castings even if its from another CB500. I found a bottom end case on ebay for pretty cheap however i have no way of knowing whether or not that case is compatible with mine. Ive looked all over my motor to find a number or letter configuration much like you described. The only thing ive been able to come across is hand written numbers on both the top and bottom cases. F488 is written on the inside of the Oil screen casting area as well as on the top portion of the outer case right underneath one of the cooling fins. Ive noticed that in the pictures of the ebay sale, there is a number configuration also written on the oil screen casting area "L215"....im not entirely sure of the significance of these numbers....any ideas?

 

[Hot500]

Have a look on the outside of the bottom case at the very back of the case. The letters should be stamped down near the bottom edge in the middle.

To find a matching case, it will need to have the exact same series of letters to the case you now have. Not impossible but a bit like winning the lottery.

Your best chance is to find a set of cases with an engine number as close to yours as possible. This should mean that the cases were bored at about the same time and may have an identical set of bearing sizes.

Probably a whole lot less hassle to just find another set of cases. Personally, I would be looking to buy a complete motor. That way I could be fairly confident I was getting a matching set, and not a couple of random cases thrown together.

 

[gioventures]

After some searching and grease removal i was finally able to locate and identify the casting code you were talking about. Mine reads BBCBB. I emailed the guy who has the lower case of a 72 CB500 Four for sale and asked him to identify his casting code as well. His reads BBBBB. I take it that they are not compatable..?

 

[Hot500]

No they dont match. Ask the guy where the top case is. He may still have it and be trying to sell it as well.

 

[gioventures]

No they dont match. Ask the guy where the top case is. He may still have it and be trying to sell it as well.

Thanks Hot500. I emailed the guy telling him that its a no go. I would ask for the top end of the case which I'm sure he has as well however im kind of keen on sticking to the original motor number which coincides with my frame VIN. I think it would just be easier for me to disassemble the bottom case and just have a local welding shop drill out the cracks, weld it up, and polish. Hopefully that'll do the trick even though i have a feeling that it will be pricey. If thats the case and push comes to shove, i might have to resort to some JB weld to fill in the cracks with as a temporary bandaid till i can find a miracle matching case or some one who will do the job cheaper. Id really like to use the kick start on this bike. Its the who reason why i went for a vintage bike. Granted it has electric starter which it would be smarter to use more frequently but still..im quite stubborn and want my kick start.

 

[Hot500]

As the cracks in your case have clearly been caused by the pressure exerted on the kick start lever, ask your welder if he can brace the area around that seal housing for a bit more support. Good luck.