Broken Cam Guide

[Highlander]

Hey Guys. I got a 1980 CB750 K here a few weeks ago. Cheap......Then I had a guy put some rebuilt carbs on , and since the weather here is finally getting nice, for now, I was getting ready to go for a ride...Now to the good part.  Engine had a more then unusual noise...tried adjusting the cam shaft tensioners....Hmnnn....still noisy. I'm aware that the valves need to be adjusted as well when you do the carbs, pulled off the valve cover today,   what was left of the guide was laying on top of the cam/valves. I was wondering if anyone has had a similar problem,  I got the main  broken piece of the cam shaft guide out, any thing smaller should fall into the oil pan ..... ( Yes or No ) .......i'm hoping anyway.... Don't see anything in the cam chain valley, but the front chain has some  slack. Turned it by hand , doesn't appear to be anything stopping it.   I am going to drain the oil  tomorrow and see what I find... or do I need to pull it apart ?  Working on this in the back yard, so tearing it down there is not how I want to go about it...Always something.

[Lucky 1]

You could inspect for damage change the filter and look for pieces,
but the pieces could be all over inside the engine.

It is up to you if you want to tear the engine down.

I would inspect everyplace i could get to.

But you still have to replace the guide and that may
 only be possible by tearing the engine down.

[Highlander]

I ordered a new one ( cam chain guide )  from bike bandit this morning.  They are waiting on a new shipment , so it seems these are in demand. It  attach's on top of the cylinder, from what I can see. The front cam chain doesn't want to tighten, don't know if it has too much slop in it, or if its because of something else....like a broken piece of metal down there.   Odo says 33,000 miles. Well..i'll drain the oil and see what I find. If I have to split the case, might as well rebuild it. here we go.....

[seestheday]

You want to think about what broke the guide.

I'm guessing your chain may be badly worn and/or the tensioner is broken. The tensioner sits under the b cam chain. Well, there are two, but you definitely need to check the b chain tensioner. Fixing it doesn't mean splitting the case, just removing the head.

[Highlander]

I bet your right. The front cam doesn't want to tighten.  Definitely  don't want to mess the engine up. Got a shop manual off Ebay, and from what I can see , that tensioner runs about 125.00 bucks.  A guy had a engine    (1980 CB 750 ? )   on Ebay totally rebuilt....2000 bucks.  She'll kill me....

[seestheday]

I think I got my new tensioner from a honda dealership for about $110.

You might also need another B cam chain.  I would definitely check to see if it's badly worn.

Btw - have you downloaded the shop manual pdf's from this site?

Check out this thread on another forum: http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=12228
There are some good pics of where the cam chain guide goes.  The "B" chain is the one that joins the two cams together.

The "A" chain is what joins the exhaust cam to the rest of the engine.

There are two cam chain tensioners, one for each chain.  If the "A" chain blows up then your engine may be toast.  Thankfully it doesn't look like this happened to you.

You can replace the "B" cam chain and "B" cam chain guide with the engine still in the frame.  To replace the "A" guide or cam you have to pull the cylinder (and head), so the engine has to come out.

Here is a thread on how to re-install the cams if you do pull them: http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=12100

[Highlander]

I 've  been running it with out the valve cover on , can see its   an accident waiting to happen. Been trying to get it to tighten up, no luck yet. I got another guide from bike bandit, and can get another chain from vintage CB's...still haven't checked into the tensioner, and /or replacing it. If I have to take the head off, I might as well rebuild it. I just had a guy  put a set of really nice set of rebuilt carbs on , powered coated them and everything....since i like having two  ( or 3 ) of  things, I might just check around for another engine, and put the carbs on that..Never had a engine blow up on me ..and don't want to now...anyway, Thanks for the input guys...

[seestheday]

Running with the valve cover off?  Isn't that incredibly messy?  How is there not hot oil splashing all over you...?

[Highlander]

Ha...nothing wrong with the ports, or the oil circulating....I wanted to watch the exhaust cam chain..it definitely needs to be replaced. Going to take the head off, and see what's going in with the tensioner

[seestheday]

If the tensioner is broken it will be fairly loose. Only way to know if you need a new one is to measure it under tension.

You should also pull the oil pan to remove the debris.

Sent from my BlackBerry device

From: Highlander [via Honda CB750'S]

Sent: Friday, May 3, 2013 10:58 PM

To: seestheday

Subject: Re: Broken Cam Guide

Ha...nothing wrong with the ports, or the oil circulating....I wanted to watch the exhaust cam chain..it definitely needs to be replaced. Going to take the head off, and see what's going in with the tensioner

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[Hoosier Daddy]

seestheday wrote

.... You should also pull the oil pan to remove the debris.

^^That's what I was going to suggest.