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750T: Broke plastic knob on tensioner assy - now what?

DimitriT

DimitriT

Forum Sage
Past Site Supporter
While replacing a leaky valve cover gasket on the 750T, I noticed the cam chain had alot of slack (compared to my 550). Thinking that the PO probably never adjusted the cam chain tension, I tried to twist the plastic knob and broke it off the assembly (without too much effort - as if it had been glued on.. hmmmm). Now I am left holding my knob, so to speak.

I checked for a replacement on bikebandit, but it appears the microfiche doesn't have it. My question: what is the purpose of the whole knob/spring thing anyway. Is it enough to loosen the locknut and just push the whole thing in? I've never adjusted cam chain tension before (never had to). So how do you know if the chain is too loose?
 
grab a

some



and kick back

....till someone who knows sumthin scrolls bye...


humour bump is all I can offer m8 - soz...:confused:
 
The radial (circular) spring tension is what drives the tensioner against the chain.This keeps the proper tension in the chain. If your plastic knob thingie was the outside spring holder for keeping the spring tensioned, then DON'T ride it until you get that spring tensioned again. DON'T push it in & lock it there, the chain will rattle around in there with no tension on it & break pretty damn fast. The spring is not very strong, but it's force gets multiplied a little by the mechanism, and that little bit of spring tension is absolutely necessary.

The knob on my bike is aluminum, so it won't break.

Now we wait for someone who knows what to do about it on your model comes along, but I thought I would chip in with the don't's so you won't break anything.
 
A plastic knob? That's a new one on me. Can you post a photo or three?

FWIW, here's all the gory details on the metal knob variety, as fitted to the GS850 and many other models. Yours likely functions exactly the same internally, although it looks different on the outside.

Maybe this will help you, maybe it won't:
http://bwringer.com/gs/camchaintens.html
 
West said:
DON'T ride it until you get that spring tensioned again.
Click to expand...

Now you tell me :)

Well, as it turns out the tensioner was completely siezed up. The lock screw wouldn't budge, nor would the adustment nut. I don't know how long the bike was ridden with the cam chain flopping around but I put 200 miles on it since Teusday. This may explain a few of the more interesting sounds coming out of that motor.

Fortunately the 550 (which is waiting for a master cylinder part) has the same exact unit so I swapped it (I was meaning to replace the 550's tensioner gasket anyway), replaced the gasket too. Fired it up in the garage to make sure I didn't screw up te carbs or something, but it's too late to take it out. I'll test it out on tomorrow's commute :)
 
Glad you caught it. You can't go by the screw lock and nut on the LH side (opposite the spring side) - under normal circumstances the lock screw is backed off and locked in that position by the nut - it had nothing to do with the tensioner working properly. You just use the lock screw to fix the tensioner rod when removing the tensioner so that the tensioner rod does not pop out into the crankcase. Then you use it again when you refit it, then back the lock screw off & lock it in place again & don't touch it until the next time you remove the assembly. So if that was frozen in the backed off position, no big deal, as long as you are careful not to drop the tensioner rod into the case - I am guessing that you were lucky (and/or cautious) enough to avoid that little pleasantry.

Since you have it out, if the tensioner rod itself (when unlocked) moves freely, the rod & mechanism is probably OK & all you have to do is fix up the spring tensioner part.

Good luck on your morning ride.


Thanks for all the nice instructions & pictures, bwringer.
 
Last edited:
Here's a picture of the plastic knob which broke off. With a little persuasion I got all the screws and bolts off it and I think I can repair it. I found a flat washer which fits well in place of the plastic (it's on the there in the picture). All I need to do is drill a small hole of the spring. All the gaskets and seals are shot and will need replacing too, ofcourse.

DSCF0457.JPG
 
Plastic adjuster

Plastic adjuster

I also have a plastic adjustment wheel. It has cracks in it. I am almost afraid to touch it. I do know that I need to make a tensioner adjustment. Wishing that I had one of those aluminium ones on there. If you guys (and girls) really want a pic of one I will gladly post one. What do you all think I aughta do about that? Is there somewhere to get an aluminium one?
 
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