Rookie Mistake ... CB500T Cam Chain Mystery

KnuckleBustingTwin

KnuckleBustingTwin

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OK ... so I'm a dumb a**! While trying to get the top end back on my engine a couple days ago, I realized that I forgot to reinstall the top end cam chain sprocket and am wondering if anyone else has done this and found a way to install it without having to pull out one of the camshafts?

In the midst of writing this note however, I uncovered another mystery, in looking up the parts fiche for the '75 CB500T, honda-cb500t-twin-dohc-1975-usa-cam-chaintensioner_bighu0233e5005_22f7.jpgI noticed that the diagram doesn't show a cam chain roller at the top of the cylinder head?
For the hell of it, I took a look at the '74 CB450k7 and sure enough there it was honda-cb450k7-1974-usa-cam-chaintensionerguideroller_bighu0029e6006_fdad.jpg... now I am wondering if I actually have a CB500T engine in the frame ...

Here is a pic of what I forgot to install ... Cam Chain Sproket.jpg

I just walked out to the garage and looked at my shop manual for the CB500T and it does show the top roller in the head as well (maybe CMSNL is wrong)

I also noticed that the cam chain seem's "tight" even without the cam chain tensioner installed ... obviously this could be explained, if in fact i am not working on a true CB500T engine ... this is the cam chain I bought after researching the correct one on the old Honda Twins forum last year (Timing Chain D.I.D. 219t128 with Lock Cam Chain) ...

Here is the serial # from the engine I'm working on ... Engine Number.jpg

Any advise would be appreciated ... Thanks Bill
 
The bottom end is absolutely a 500T, though that does not prove the crankshaft (where the extra engine size comes from since they lengthened the stroke to make it a 500) is from a 500T. That said, it's unlikely that anyone would have changed anything in the engine prior to you getting it. That guide/idler sprocket is a PITA to get in place even with the head apart, so I really can't imagine you doing it by pulling one of the cams but I suppose it's possible, I've just never tried it. Really, I've never removed that sprocket from a head before doing it on my red bike, only because they rarely wear out. The DID chain is the best one to buy and if you got the tip from either me or 76Twin then you probably bought it from twowheelsfrank in Germany. I'm guessing the fiche at cmsnl.com is just incorrect, I've discovered a few in all my travels there. I suppose the tensioner could take up the extra slack in the chain, especially with a new unstretched chain, so I wouldn't worry about that part... but you definitely need it in there.
 
The roller was used in the 500T engines . . . it's just shown in a different diagram to the one you've been looking at. And no, no idea why Honda shifted components about on the diagrams; it just happened from time to time.

It's part #9 on the camshaft/valve page of the microfiche:

honda-cb500t-twin-dohc-1975-usa-camshaftvalve_bighu0233e5004_5b89.jpg​

And no, you won't be able to install the roller without pulling out one of the camshafts; there's simply not enough room to manoeuvre otherwise. It won't add much tension to the chain by itself (i.e. without the chain tensioner being installed) because it's purpose it to guide the chain and stop it contacting the roof of the head.
 
ancientdad said:
The bottom end is absolutely a 500T, though that does not prove the crankshaft (where the extra engine size comes from since they lengthened the stroke to make it a 500) is from a 500T. That said, it's unlikely that anyone would have changed anything in the engine prior to you getting it. That guide/idler sprocket is a PITA to get in place even with the head apart, so I really can't imagine you doing it by pulling one of the cams but I suppose it's possible, I've just never tried it. Really, I've never removed that sprocket from a head before doing it on my red bike, only because they rarely wear out. The DID chain is the best one to buy and if you got the tip from either me or 76Twin then you probably bought it from twowheelsfrank in Germany. I'm guessing the fiche at cmsnl.com is just incorrect, I've discovered a few in all my travels there. I suppose the tensioner could take up the extra slack in the chain, especially with a new unstretched chain, so I wouldn't worry about that part... but you definitely need it in there.
Click to expand...

Thanks Dad ... I believe it was 76Twin who gave me that advice and I did buy it from twowheelsfrank out of Germany ... appreciate the help!
 
the-chauffeur said:
The roller was used in the 500T engines . . . it's just shown in a different diagram to the one you've been looking at. And no, no idea why Honda shifted components about on the diagrams; it just happened from time to time.

It's part #9 on the camshaft/valve page of the microfiche:


And no, you won't be able to install the roller without pulling out one of the camshafts; there's simply not enough room to manoeuvre otherwise. It won't add much tension to the chain by itself (i.e. without the chain tensioner being installed) because it's purpose it to guide the chain and stop it contacting the roof of the head.
Click to expand...

Thanks Chauffeur ... I suspected that would be the case, I guess I'll just have to pull a cam and hope for the best .... ugh ... I was so excited to have the engine behind me too! ... Oh well ... another day, another challenge! ... Bill
 
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