Topic: Tonight's Episode of Mythbusters!!!

[Tommy Neimeyer]

In quite a few threads I have read that a CB500/550 cam cover can be used on a CB650 head.  Is there anybody who has ran a 500/550 cover on a 650 head?  It is a fact that it will bolt on and it looks like a close fit but, IMHO it has several spots where the gasket will not seal.

Paul,
  You have both in front of you, what is your opinion?

Inquiring minds want to know??

Cheers, Tom

[cb650]

One of the last pics of a "big bore 550" the rocker covers sure did look like 650s. Looked nice.




                   Terry

[Tommy Neimeyer]

Terry,
  I think you are right, they are 650 covers on a 650 head on 750 cylinders.

What I want to know is if the 500/550 cover will fit and SEAL on a 650 head.

Cheers, Tom

[paulages]

in the name of SOHC science, i'll break out the heads and covers and compare tomorrow. this is already in my list of items to check for compatibility, but i'll bump it to the top.

right now, i'm concerned with trying to make the 650 clutch work with the 550 cover, or the 650 clutch work with the 550 kickstart, but i haven't gotten very far. it looks like it would work, but the clutch plate lifter mechanisms are different between the two, and the 650 won't accept the 550 plate (which would allow the 550 cover). as far as i can tell, there doesn't seem to be any noticible diffrerence between the clutches themselves other than the gearing differences which were said to make the 650 clutch more reliable. more on this on my engine build thread when i make proper comparisons...

[kayaker43]

I've tried a 550 gasket on a 650 cover, and although the shapes are different, it appears there is some overlap everywhere so people are using it. Make sure to get the later 550 covers with the pinned rocker shafts. I would be willing to weld up and machine areas to get good gasket surface because I'm determined to run the old covers.

I also think you could artfully trim the 650 cylinder and head fins to make them look like 550's. Remove just enough so you don't lose too much fin area?

I'm also stubborn enough to think there's some way to fit an old clutch cover and make the 650 clutch work, I hope I'm right because that would finish the disquise. I'm glad Paulages is doing the autopsy comparison first so we can all nag him about interchagability 

[oldfart]

Terry,
  I think you are right, they are 650 covers on a 650 head on 750 cylinders.

What I want to know is if the 500/550 cover will fit and SEAL on a 650 head.

Cheers, Tom

Tom -- Believe it or not, I once was deep into a 750cc project out of a CB550.  Years ago.  Had all the stuff, including the 650 head.  I wanted to retain the 550 cam cover also, as you suggest.  I found that the cover will not seal, because the pattern of loops and curves is different.  Particularly right at the plug well areas.  I was planning on welding up the 650 head so that it would mate up.  That's how much I wanted to make the engine look like a sleeper 550.  Anyway, I had a heart attack and had to quit my job and move into an apartment, and all the stuff went.  All the parts -- cases, cylinders, head, 650 crank, spare frame and bike.  All of it.  So, no, the cover will not work unless one of the two (cover or head) is reshaped, and since the cover is quite thin, that leaves the head.