• Enter the March CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!

Wanted - CB750 DOHC Cam Caps

N0MAD

Traveler
Messages
1
Reaction score
0
Points
1
Location
Louisville, KY
Lucky me, tearing down the motor on my 79' 750k, 7/8 valve cover bolts snapped off inside the thread of the cam caps.

I'm looking to buy a whole set of them so I can replace them and get this build finished.
 
Here is some info from www.CB750c.com that confirms my suspicions that the cam holder caps are align bored with the head:

QUOTE:

The caps on the head are line bored as a unique set when the new head is machined. Caps should not subsequently just be swapped willy nilly from one head to another without measuring them for how well the bearing hole in the cap lines up with the one in the head. Some will line up OK and can be traded from motor to motor, but they are not all exactly alike, so there is no guarantee that an A cam cap from one motor will line up right on another motor in the A position, for instance. If it's off far enough, it can damage the head, cap, or even the cam if it's bad enough, and if it's just off a little, it can still ruin the oil cushion and cause excessive wear.

In order to see if it's possible to use a cap from another motor, you should do measurements and checks to the prospective new cap first with the cams removed. Or at least do machinist quality exact measurements of the new cap to within about .0005" accuracy to insure you won't have problems.

------------------------------------

The way I do it is bolt the trial cap on with dowels in but no cams. Then I check to see if I can hang a fingernail up at the seam between head and cap inside the bearing hole's surface, telling me that the front to back fitment of the hole in the head and in the cap matches well. Once have a cap that I like for that front to back fitment, then I put cams in, with no buckets so there is no spring tension, just the cams in the head with plastigage and the caps bolted on with dowels, to check for the proper vertical fitment per the Honda Shop Manual for each bearing, as they are not all spec'd the same. If I get the right clearance and fit with these tests, then I put it all together and run with the new caps assured that it will be fine.

------------------------------------

Q ) So they didn't just make a ton of "L" cam caps and put them on motors when they were assembling them???? actual question from member

A1 ) yes they did but then they bored the whole head at one time for the cams with the cam caps attached - Frank

A2 ) That's right, and that is why there are round cut outs on the sides of the top of the head for where the line boring machine had to go in to do the cut. They aren't just there for decoration, or to piss you off and make your valve cover seal leak.

All split bearings like that, that require accuracy and are made out of two parts that get put together, can't just be thrown together. It requires precision machining or the holes would never line up on axis or be the right size....

Same thing goes for the main bearings or rod bearings, but the tolerance is even more critical, about .0001" or less. With mains, you can't dare use the top case from one motor, and the bottom case from another. They are line bored and measured and the sizing is stamped on the cases to indicate how tight the cuts came out. You cannot use different case halves from different motors at all.

END QUOTE


Here is a link to the post, but I had to register as a user there to be able to follow the link:

http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&p=222549#222549


So you might consider extracting the broken bits from the caps you have:

http://www.secondchancegarage.com/public/671.cfm


I've gotten pretty good at broken bolt extraction, so if you don't want to fool with them I could probably be persuaded to do the repair for you at a reasonable cost if you can't find a local machinist to do it.
 
Hello, I am facing a similar problem. I have cracked my tachometer drive cam cap (dont ask how....). On inspecting thoroughly, I am confident that the bearing surface part of the cap is intact but the tachometer worm drive part is definitely cracked. Here are some images:

https://drive.google.com/open?id=1hetnumiigcpMO6GDf79qzTgGAQ1Nz0bU
https://drive.google.com/open?id=14LBd89HLg_YSZVITarZU16-txDVuoJzM
https://drive.google.com/open?id=1SrTBsymVKSD5orOvskTf3_em9M4GmsAU
https://drive.google.com/open?id=1BdVUGM2qs86wKgjijDfr17cuFpuUTpOU

I am thinking of getting these Argon Welded and using these (might cancel the tachometer drive altogether. Still thinking about that). What do you guys think?
 
Back
Top