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Cam Chain Tensioner Adjustment and Conflicting Instructions

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1965_dreamer Member
Posts: 3
Joined: Sun Oct 27, 2019 3:23 pm
Location: SF Bay Area

Cam Chain Tensioner Adjustment and Conflicting Instructions

Post by 1965_dreamer » Sat May 27, 2023 8:02 pm

There seems to be conflicting information regarding adjusting the timing chain on the 305's.

The not very helpful CL77 owner's manual says:

1. Loosen the lock nut and then loosen the adjusting bolt and the chain will be tensioned automatically

2. Tighten the lock nut firmly after adjusting the chain

Of note, the owners manual does not indicate the rotor position where the timing chain should be adjusted.

The slightly less unhelpful Honda 250/300 Shop Manual (1970) says:

To make sure tightness of chain, it is favorable to adjust putting the crankshaft at the bottom dead center.

The Chilton's Honda Repair and Tune-Up Guide (1966) says to adjust the chain while the engine is running:

For the adjustment of the cam chain, allow the engine to run at a speed of 3000RPM, loosen the adjusting bolt, and then re-tighten.

And then there is this thread viewtopic.php?t=7636177 on this forum where Loud Mouse says:

This is what HONDA says to do to adjust the cam chain.

Per HONDA Service-Repair-Handbook, 250-305cc Twins- All Years.
Page 37, Fig. 17.
11. Refer to Figure 17 and loosen the tensioner adjustment bolt. Rotate the crankshaft until the generator rotor "T" mark is 180 degrees from the stater indicator mark and tighten the tensioner adjusting bolt. This automatically tightens the cam chain to proper tension.

Lastly, a Honda service bulletin we found here ... 1659105755 says the adjustment should be made 90 degrees clockwise past T where all valves are closed (i.e., all rocker arms have free play).

In our service notes we found that we last adjusted the timing chain with the rotor at the T mark with the right cylinder at top dead center and the valves on the right side loose. So we did the same thing, but will likely re-adjust at 90-degrees past T per the service bulletin.

Also, at what point does the timing chain tensioner position indicate the timing chain should be replaced? Ours still has several millimeters of adjustment before it "bottoms out". But not sure if it's good to wait that long.

Thank you.

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Tim Allman Member
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Joined: Tue Dec 02, 2014 9:25 am
Location: Guelph, Ontario, Canada

Re: Cam Chain Tensioner Adjustment and Conflicting Instructions

Post by Tim Allman » Mon May 29, 2023 10:13 am

You want to find a place in the engine cycle in which the chain is not stressed by the cam, rocker arms and valves assembly. Essentially this means that you want a position where all the valves have tappet play. So, any place where you can slide the feeler gauge into all of the valve clearances will work.

Something you might want to check is the condition of the rubber wheel on the tensioner. If it's original it is probably hard, chipped and in need of replacement.

deuce_7 Member
Posts: 131
Joined: Sun Mar 18, 2018 10:36 pm
Location: California Central Coast

Re: Cam Chain Tensioner Adjustment and Conflicting Instructions

Post by deuce_7 » Tue May 30, 2023 9:39 am

Tim has offered some good suggestions.

I think these 305 motors can run just fine with some cam chain slack. By the time a cam chain has stretched to the point where the tensioner is no longer effective, it's probably time for a motor overhaul anyway.

The engine must be removed and disassembled to replace a cam chain.
1967 CL77 305 Scrambler

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