SOHC.co.uk Forums > CB750
Camshaft troubles
SandwichEnthusiast:
So I've taken the reins on a project 1975 CB750, which in my inexpert opinion seems in pretty good shape, and I'm hoping I can get it back into action for next season.
We popped the Cylinder head cover off, and the camshaft has broken under the third holder from the left, and kinda gored the holder up.
So it looks like I'm in for a new camshaft and a new camshaft holder.
So I'm looking for some sagely advice; http://www.crotchrocket.com is giving me a about $113 for a holder and $228 for a new camshaft (I don't even know where those parts are coming from)
Should I be assuming I need 2 new camshaft holders?
what does this mean for the rest of the engine? Is there going to be damage all the way through?
What did the previous owner do to screw it up like this?
I'm kinda resting on my laurels to clean out the garage to get some space to rip this bike apart, and am waiting to find out what this camshaft damage means I'm in for. Any advice/comments would be appreciated. Thanks.
BTW I'm in Canada, but this seems like a good CB fourm.
Dave M:
If the cmshaft snapped then you could also be looking at valve/piston damage if a piston has hit a valve.
I'm not sure if there's any clearance between an open valve and the psitons but I'm sure our experts will be able to offer some additional advice.
BassMan_720:
It's head off time, I'm afraid. An open valve will clout the top of the piston.
You should be able to replace only the damaged holder. These were supplied separately by Honda. Cam oiling was a weakness in early CB750s. I thought that they had sorted this by 1975 though.
I trashed a camshaft back in 1977. I traced a problem down to a blockage (suspected fibre from the paper oil filter) in the small metered hole in the head that feeds the holder oil way. This didn't snap the camshaft but it didn't do it or the holder any good at all.
Several of my mates (we all had CB750 at the time) with K0-K2s also had similar top end problems. I don't recall any of my mates with F1s having this problem. If you search through the CB750 forums you will find plenty of advice about regular oil changes to avoid this in future.
Fingers crossed that the damage is minimal. These parts are quite scarce. After a failed search over here, I've recently won similar items on eBay, from the states, for my restoration project.
Good luck
Steve
JonnyB:
I had to rebuild a couple of years a ago, on My F1 ('76) I had a "squealer!!" The cam had seized in the holder due to oil starvation. When I dropped the oil filter there was so much metal in it the oil looked like silver paint.
I've had two cams fail though oil starvation and I once bought an engine for spares and it had the same problem, but I've never seen a snapped camshaft, I'd like to see a pic of that.
To do the job properly and still have faith in the engine afterward, you really need to get a camshaft AND cam carriers from the same engine, you'll know then that the wear will be even.
I would, (and did) do a complete engine strip, and took the oppertunaty to check all the other bearings and clean the crank cases of any dirt.
As Steve said check the piston crowns, and valves for damage, a new pistons are around but cam holders and caps are a rare as rocking horse sh*t.
SandwichEnthusiast:
Thanks for the information. I've been assuming I'd need to tear down the whole thing, at least to look at it.
Somebody mentioned wanting some photos, and I have a bunch up at:
http://www.uoguelph.ca/~ibaran/
sorry for the low budget directory list,
DSC00066.JPG, DSC00068.JPG, DSC00070.JPG is the broken side,
and
DSC00067.JPG is the good side (im a little nervous about that wear in the center, should I be?) and DSC00065.JPG is the whole top end.
Anyone who would like to roll through them all and give me any comments on condition, or anything else for that matter I would really appreciate it.
could it have been as simple as overtourqing the camshaft holder?
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