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Discussion Starter · #1 ·
Hey all!

I'm running into a strange issue and I'm wondering if anyone has any ideas. It seems like cam chain on my 78 CB400T is losing tension after only about 20 miles of riding.

I adjusted the valves and cam chain in that order following the FSM this spring. When I did the valves, I pulled on the cam chain and there didn't seem to be any play. The month or so after I only rode it short distances while I sorted out a fuel issue.

In May, I rode down to my new place and made it OK, but noticed more engine noise when I arrived than when I had left. I figured maybe I screwed up adjusting the cam chain the first time and readjusted it a week later after a trip to the grocery store - short trip, enough to warm things up. Next trip was across the metro to get the carbs tuned (PS, for anyone in the Twin Cities metro, Bruno is a super swell dude!). With the bike idling during the carb adjustment, it was obvious the engine was loud, a lot louder than when I left; after adjusting the cam chain, the engine sounded perfect. But by the time I was home again, the volume was back. The last time I went out to start it up was a few weeks ago, and while idling I could hear an uneven slap/slide of the chain, like it had too much slack. Maybe I'm being too picky, but I didn't like the sound of it and haven't rode since.

I don't know if the tensioner is stuck, because loosening and tightening the adjuster nut at a hot idle has quieted the engine. It's just the engine volume returns after a few miles, almost like the tensioner isn't keeping tension. The lock nut is snug, the washer is present. The valves don't seem to be the source of the noise, given how quiet the engine is after the cam chain is adjusted.

I'm unfortunately limited at the moment with what I can do; I moved from a rental house with a garage to an apartment that has underground parking and a lease policy against mechanical work. My closest friendly garage is 1.5 hours away.

I was looking through other threads and didn't see anything exactly like this in the SOHC section except this post about the nut bottoming out on the bolt and not the case. Adding a washer seemed like something to try that was not very invasive - I couldn't find copper, so I bought a brass washer. Stupid questions because engines are intimidating - should I add the washer with the engine off, or on and hot idling? Is removing the lock nut all the way going to cause any potential issues? Any other ideas on what the issue may be? Thanks!
 

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The lock nut can be removed completely BUT not with the engine running, too much chance of the T bolt coming loose and falling inside.
This fiche shows you the tensioner and assorted parts OEM Honda Parts, New York | Honda Parts for ATVs, Scooters, Motorcycles. Located in Mamaroneck near Yonkers. Shop our online catalogs.
The tensioner is held in place by bolt #10 to the cylinder. The spring attaches to the bottom of #4 to pull down on the slide that #6 pin is inserted into at the top. This causes the blade #3 to flex outward tensioning the chain.
I'm wondering if maybe the bolt #10 is actually securing the tensioner, that could allow things to move around. There was an instance 4-5 years ago of that happening on an engine, can't remember the details though.
 

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Discussion Starter · #4 ·
Did you try physically pushing the slipper down, with like a screw driver, then tightening the nut?
Also have you adjusted your balancers?

Edit: see post #3
http://www.hondatwins.net/forums/62...m-chain-tensioner-unoffical-manual-450-s.html
I haven't tried the manual method since it's against my lease; I have not adjusted the balancers. But I did find a good video on YT showing the procedure for adjusting the cam chain tensioner during a valve adjustment. If I can get to a friend's place this summer, I can try it yet.

The lock nut can be removed completely BUT not with the engine running, too much chance of the T bolt coming loose and falling inside.
This fiche shows you the tensioner and assorted parts OEM Honda Parts, New York | Honda Parts for ATVs, Scooters, Motorcycles. Located in Mamaroneck near Yonkers. Shop our online catalogs.
The tensioner is held in place by bolt #10 to the cylinder. The spring attaches to the bottom of #4 to pull down on the slide that #6 pin is inserted into at the top. This causes the blade #3 to flex outward tensioning the chain.
I'm wondering if maybe the bolt #10 is actually securing the tensioner, that could allow things to move around. There was an instance 4-5 years ago of that happening on an engine, can't remember the details though.
Thank you for the description of the parts themselves, helps me to make sense of things. Spatial reasoning of any sort is not my forte. If I'm understanding correctly, I want the #10 bolt to be securing the tensioner and not providing play to the tensioner within the case.
 
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