Worn Camshaft Drive Questions on Repair

TheodoreVH

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I have a 1978 Honda CB750K. When I was idling the bike, the camshaft drive chain sounded like it was loose and hitting something. The Cam chain tensioner had already been completely tightened and the sound persisted. I pulled the engine and took a look at the Cam drive to find that that the tensioner roller (the small on) has chain grooves... which I'm assuming means its pretty worn? Furthermore the chain cover on the valve cover has a large piece missing from it and looks like the chain had been rubbing against this and wore it away (see the pictures). What I am curious to know is what I should do going forward... I know that the Cam chain guide roller probably needs to be replaced as well as the Cam chain (using a master link technique) but I was wondering if I should check or need to replace the Crankshaft Cam Drive sprocket? First I don't know whether I can even check the Crankshaft Cam Drive Sprocket without pulling the bottom end apart which I want to avoid. Does anyone know if they wear easily? Similar question with the main drive chain (just curious)? Also because there is now a piece/pieces that possibly have gone through the engine... is there anything I should check or inspect to ensure that the engine is okay?
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Here you can see on the Valve cover the part the chain wore away. Its not too bad. I'll probably just have it welded
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In this picture you can just see the Cam Chain Guide Roller and see what I mean by the grooves in it

My main question is... How easily do the Crankshaft Cam Drive sprocket wear? Are they pretty resistant? Is this a common issue and how do most people fix it? Thanks
 

dirtdigger

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That roller is gone, you need to replace the tensioner and both wheels and the guide may be hard and deteriorating. Very common with the age of these bikes. The sprocket will be fine. I am not a fan or master link chains because I would never go back together with anything but a heavy duty chain.... they are a week point in the 750. The primary chain tensioner wheal is probably just about as bad and the chains are stretched. You will need to replace the valve cover because of the wear, I would just go on ebay and buy a used one so you dont risk warping the cover when welding. In my opinion with the amount of metal and material that has been worn away you need to at least take the oil pan off but I would be afraid of how much circulated through the engine.
 

TheodoreVH

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Thanks for the reply! A Master link isn't my preferred method of replacing the Camshaft Drive chain but it's a doable option for me. I'll make sure to spend the money on a good chain and master link and since I'm keeping everything stock it should last. I'm not 100% sure but I heard using a master link that is riveted is a much stronger and durable option... especially if you say that its a weak point on the 750. Luckily I know one of the best welders who is excellent. He's done some impossible welds on engines for me and my buddies so I'm not to concerned about warping... although things do happen. Checking the oil pan is an excellent idea. Honestly Ill keep my eyes open for damage but at the end of the day it is what it is and it was running decent before so fingers crossed haha
 
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