Topic: CB750 cam chain guide interchangeability?

[02z06dave]

I am in the rebuild process of a 1970 k0 right now. I ordered a new cam chain guide without really thinking about it and got the later style guide. Is it ok to use the later guide in the k0 engine or do I need to order the early guide?

[PeWe]

I have used the later (taller) with K1 cyl and head.
You might need to file a little to widen the upper part of cam chain tunnel where it will stick up. The mold is not square.
I had to do that on K6 heads that must have been shipped with the earlier, shorter.

The pins on the glider it hangs with are thicker on the later. Less rattling sound.

[MauiK3]

I never thought about this before.

[02z06dave]

I have used the later (taller) with K1 cyl and head.
You might need to file a little to widen the upper part of cam chain tunnel where it will stick up. The mold is not square.
I had to do that on K6 heads that must have been shipped with the earlier, shorter.

The pins on the glider it hangs with are thicker on the later. Less rattling sound.

Thanks. I have test fitted it and it seems like there are no problems. But I didn't want a problem that I don't foresee

[bryanj]

Normally if a newer part wont replace an older one Honda will keep both in production and change some of the part number

[02z06dave]

Normally if a newer part wont replace an older one Honda will keep both in production and change some of the part number

I don't know if that rule wpuld necessarily apply in this case because the older part wad also used on the CB350. Ot could have been kept in production for that model in particular

[HondaMan]

In those early sandcast/K0 engines with the shorter camchain guide, the chain makes a slight 'jump' to the upper sprocket in some of the later heads if the newer guide is used: I ran into this (the opposite way) with a sandcast engine when I tried to drop in the newer guide - just because I had it on hand at the time. The guide's top seemed like it was too far forward by a little bit (like only 1-2mm of distance difference) so the chain would deflect when entering the top of the guide. When I got the 'correct' shorter guide it sat slightly further toward the rear of the engine, and the line of the chain from the front of the cam sprocket was a straight-down shot, no deflection at the top of the guide.

So, I think the later guides might be slightly offset toward the front of the engine via their locating pin boss(es), and/or the cam's bearings similarly in the head? I don't have a sandcast head to go measure, but that's my hypothesis at the moment? I have a K0 head from a near-sandcast engine (like 80 past the sandcast era) somewhere around here, might have to go see if I can find it, now that I'm a-wonderin'...