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Old 09-23-2008, 10:09 AM
dbeardslee's Avatar
dbeardslee dbeardslee is offline
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Join Date: Nov 2007
Location: Maineville, OH
Posts: 3,452
30 minute cam chain tensioner mod

Leave it to the Airborne to come up with a great mod for an XS. Tadracer (101st) had an excellent modification for a cam chain tensioner in a previous post. Unfortunately it involved machining a block of aluminum. I kept looking at it and wondering how I (2/75th) was going to turn a piece of aluminum down to make my own housing. Then I stripped my tensioner locking bolt, and suddenly it hit me - I already had a housing.

TADracer's mod is shown below for those who have a damaged OEM housing.
I took the existing tensioner, tapped the tensioner shaft tunnel and installed a 4" stainless steel carriage bolt with the face ground flat. The tunnel is the perfect size for a 3/8 16 tap with no drilling required. I know what your going to say - 'That ain't metric, you savage.' I looked high and low for a metric carriage bolt, but couldn't find one in the right size, so I just went with sae. My appologies. Make sure the tap you use has teeth that overhang the shaft such that you can run it all the way through - it's a deep tapping operation. I took one and ground the shaft down so that it would work.

I took a locking flange nut, held it with a deep socket, and ground the ridges off the face and installed with a fiber washer.

I tapped out the stripped locking bolt hole and installed a bolt with a neoprene washer. Filling it with JB Weld would work just as well, and the next time I have it off that's what I intend to do.

I cut a slot in the end of the carriage bolt to accomodate a flat-bladed screwdriver.

To tension the chain, set the timing plate to 'C', loosen the locking nut, turn the stem in finger tight, hold the stem with a screw driver to prevent it from turning and re-tighten the locking nut. Doesn't need to be too tight. If you're going to try this on a hot motor, I recommend using a screwdriver to adjust, turning with the shaft not the handle to avoid over tightening, and a crowfoot wrench for the locking bolt - unless you like muffler burns. Or just do what I do, and adjust it cold.

Edit: It was determined in later posts that an additional locking nut should be added to double-nut the adjustment for safety, so pick up a extra 3/8" nut.
Originally I wrapped the threads with teflon tape to avoid any possibility of leaks. It made it too difficult to turn by hand, so I took it off and reassembled without it. I doesn't leak at all, so the teflon tape wasn't needed. You want the carriage bolt to turn easily so you can get the correct tension on it.

This mod works GREAT. It doesn't slip, and it doesn't leak. Total expense was about $6, not counting tools.

As there may be some legs reading this post, I better add some pics (that was for your amusement, Mike Giroir)

And here it is installed:

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Here's the scratch-built version mentioned above...

I took a piece of 1" thick aluminum and cut out a body that would bolt on in place of the stock tensioner. I drilled holes for the mounting bolts and then tapped a hole for a 5/16" carriage bolt to act in place of the plunger. I ground the head of the carriage bolt flat to ride against the chain slide. An O-ring, flat washer and two jam nuts completed the thing.

I removed the valve cover so I could see the cam chain and I used the manual tensioner to adjust the chain until it had about 1/8" of play midway between the cam sprokets.

Chain noise is now minimal and it performs perfectly. Took about an hour to make and cost about $6.00 for the parts.

I think I have a loose screw behind the handlebars.

'79 XS11 Standard, Jardine 4/1, Dyna DC1-1 Coils, 145 mains, 45 pilots, plastic floats - 25.7mm, XV920 fuel valves, inline fuel filters, speed bleeders, Mikes XS pods, spade-type fuse block, fork brace, progressive fork springs/shocks, manual petcocks, 750 FD, Venture cam chain tensioner, SS brake lines

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