Topic: Cringworthy camshaft

[Rydog400f]

Feast your eyes on this bad boy. Needless to say I'm in need of a new camshaft and holder set. If I purchase a "good" used camshaft and holder, should I purchase new rocker arms as well? They seem to be in good shape. BTW I bought the bike like this.

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[PeWe]

If head is stock with no port job invested, replace it if there is a problem with oil restrictor fitting.

The huge hole where oil orifice (restrictor) should sit  is drilled wide open or is it just a missing restrictor? Compare with other side. This model is usually easy to lift with a nose plier.
Here  a part of the reason for lack of oil pressure ruin the cam. Dirt might have clogged the oil holes in cam holder too.


There are good heads for around $100US on eBay. Maybe in need of valve and seat job. Ex guides might be actual too.

Service investment your old head most likely needed anyway.

Remove oil filter, is there a spring and washer inside the filter sitting in cover? This is important, if not dirt from oil tank will pass up to the head.

Sure that the chromed surface on rocker arms is OK?
Rocker arm shafts too? Feel underside, no ridges were arms digs into the shaft due to metal dust, no oil.

I should invest in a complete top end with head and everything on it. Check eBay.
Maybe reuse valve cover

[ekpent]

Yep its toast but looks like someone caught it early and quit riding. I have much worse from a 750 here that shed a ton of steel and aluminum. Did you see any signs if silicone sealer anywhere when you were taking the engine apart ?

[bryanj]

Seen a lot worse when it was my trade.

That engine needs to come completely apart and be cleaned out of all debris then carefully AND CLEANLEY assembled.

[Rydog400f]

Yep its toast but looks like someone caught it early and quit riding. I have much worse from a 750 here that shed a ton of steel and aluminum. Did you see any signs if silicone sealer anywhere when you were taking the engine apart ?

Yeah it looks like the po tried to rebuild the top end. Tons of red rtv and the head nuts were only finger tight.

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[Rydog400f]

Seen a lot worse when it was my trade.

That engine needs to come completely apart and be cleaned out of all debris then carefully AND CLEANLEY assembled.

It currently is. I've just finished buttoning up the bottom end. Everything looked good considering.

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[Rydog400f]

Can anyone chime in on camshaft interchangeability? Mine is stamped with R1. If I purchase another R1 (if I cant find it) and holder set, is it OK to use my right holder (which is in good condition)? I know that the camshaft and holders/ rockers wear together. Thanks!

edit: This is a 1978 cb750f.

[robvangulik]

 Those R numbers aren't important at all, any 500 and 550 cam will fit (or 650, will give some more power too)

[Rydog400f]

Those R numbers aren't important at all, any 500 and 550 cam will fit (or 650, will give some more power too)

Are you saying any year of those models will work? Why would the 650 cam give more power?

[HondaMan]

Any 750 cam will work. There are some small differences in models, though. Yours appears to be the F2/3 head: is the engine that same type? Their cams are a little different from the others, but any F0/1 or K7/8 cam will be real close, should you not find one of the F2/3 cams.

RTV has torn up more top ends than anything else I have seen in these engines.
Don't use it...

[Rydog400f]

Any 750 cam will work. There are some small differences in models, though. Yours appears to be the F2/3 head: is the engine that same type? Their cams are a little different from the others, but any F0/1 or K7/8 cam will be real close, should you not find one of the F2/3 cams.

RTV has torn up more top ends than anything else I have seen in these engines.
Don't use it...

Ok that's good to hear. It's an F3 with the 410 head. I'm pretty sure that pushed in rubber seal is what did it in. I wonder how it even happened. The front of the engine was absolutely covered in oil leaking from above the spark plug.

[Rydog400f]

Any 750 cam will work. There are some small differences in models, though. Yours appears to be the F2/3 head: is the engine that same type? Their cams are a little different from the others, but any F0/1 or K7/8 cam will be real close, should you not find one of the F2/3 cams.

RTV has torn up more top ends than anything else I have seen in these engines.
Don't use it...

Ok that's good to hear. It's an F3 with the 410 head. I'm pretty sure that pushed in rubber seal is what did it in. I wonder how it even happened. The front of the engine was absolutely covered in oil leaking from above the spark plug.

How bout a camshaft from a Hondamatic?

[bryanj]

If you are that far in remove the head and valves and check for valve guide wear the 77/78 are notorious for wearing them out quickly

[jakec]

Ok that's good to hear. It's an F3 with the 410 head. I'm pretty sure that pushed in rubber seal is what did it in.

I had to reopen my bottom end when I was rebuilding, and when i took the freshly rebuilt oil pump off I found it had sliced one of the rather thick O rings in half. I caught it because I went back in for a totally unrelated reason. Your thread combined with another from a guy a couple weeks ago (also top end problem from oil starvation) are keeping me up at night.

[Rydog400f]

If you are that far in remove the head and valves and check for valve guide wear the 77/78 are notorious for wearing them out quickly

Definitely doing a valve job. Not gonna do a crank up rebuild with a crappy head.

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[Rydog400f]

Ok that's good to hear. It's an F3 with the 410 head. I'm pretty sure that pushed in rubber seal is what did it in.

I had to reopen my bottom end when I was rebuilding, and when i took the freshly rebuilt oil pump off I found it had sliced one of the rather thick O rings in half. I caught it because I went back in for a totally unrelated reason. Your thread combined with another from a guy a couple weeks ago (also top end problem from oil starvation) are keeping me up at night.

Dang that sucks. I get so nervous about forgetting something when putting cases back together. This is my third crank up rebuild so it's getting a little easier on every new project.

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