1977 GS750 - Camchain tensioner problem

[Anonymous]

Hi,

I'm a newbie on this site, but a GS user of nearly 20 years (2 GS550s and a GS750 that I've owned for the last 13 years). This site is awesome - a goldmine of information and experience!

Anyway, the problem:

I'm running a 1977 GS750 with about 60,000 miles on the clock. The camchain is rattling around making the engine sound like a bag of bolts. When this started, my first thoughts were "check the if the camchain tensioner is working" (it's automatic on this model) or "buy a new cam chain".

So, I pulled the carbs off and took off the tensioner mechanism, cleaned it and oiled it, put it back on and adjusted it as per the Haynes manual. On starting the engine up, everything sounded fine - no more bag of bolts!

So, I took the bike for blast and a few kms later, the rattling noise was back.

I re-adjusted the tensioner again and the noise disappeared. Started the 'bike, blipped the throttle a couple of times and the rattling camchain noise came back.

So, with the 'bike on tickover, I slowly rotated the knurled wheel on the tensioner clockwise - and the noise disappeared again. I know the Haynes manual tells you not to do this, but I had to experiment a bit....

It looks like the camchain tensioner isn't functioning properly - does anyone have any idea of a "fix" for this? The tensioner looks OK - it just doesn't tension! The spring mechanism inside the tensioner appears to function OK ie. it pushes the plunger out to make contact with the tensioner blade. It just seems as if the plunger mechanism gets pushed back inside the tensioner body (and doesn't come out again) when the rear run of the camchain "pushes" against the tensioner blade.

Any help/advice will be gratefully received!

Cheers, Mark

[gs650gt]

Re: 1977 GS750 - Camchain tensioner problem

Hi,

I'm a newbie on this site, but a GS user of nearly 20 years (2 GS550s and a GS750 that I've owned for the last 13 years). This site is awesome - a goldmine of information and experience!

Anyway, the problem:

I'm running a 1977 GS750 with about 60,000 miles on the clock. The camchain is rattling around making the engine sound like a bag of bolts. When this started, my first thoughts were "check the if the camchain tensioner is working" (it's automatic on this model) or "buy a new cam chain".

So, I pulled the carbs off and took off the tensioner mechanism, cleaned it and oiled it, put it back on and adjusted it as per the Haynes manual. On starting the engine up, everything sounded fine - no more bag of bolts!

So, I took the bike for blast and a few kms later, the rattling noise was back.

I re-adjusted the tensioner again and the noise disappeared. Started the 'bike, blipped the throttle a couple of times and the rattling camchain noise came back.

So, with the 'bike on tickover, I slowly rotated the knurled wheel on the tensioner clockwise - and the noise disappeared again. I know the Haynes manual tells you not to do this, but I had to experiment a bit....

It looks like the camchain tensioner isn't functioning properly - does anyone have any idea of a "fix" for this? The tensioner looks OK - it just doesn't tension! The spring mechanism inside the tensioner appears to function OK ie. it pushes the plunger out to make contact with the tensioner blade. It just seems as if the plunger mechanism gets pushed back inside the tensioner body (and doesn't come out again) when the rear run of the camchain "pushes" against the tensioner blade.

Any help/advice will be gratefully received!

Cheers, Mark

Seems like the plunger getting stuck... have you checked that the slide surface of the plunger is even with no pits (the steel ball contact of the tensioner should roll smoothly on the slidind surface so the plunger will also move smoothly bacwards and forwards...). if there's a pit, the steel ball stops there and so does the plunger stop moving...

[saaz]

Years ago I had a similar problem. The angled surface of the plunger inside the unit had worn or lost its hardening. The plunger would push back when at higher revs/warmed up, but stuck put when it needed to apply more pressure when cold.

Try greasing the plunger well and making sure the surfaces are cleaned up, and that the spring on the knurled knob is not binding. If that does not work perhaps try smoothing the angled part of the plunger if unit looks a bit pitted.

In the end I replaced mine with a later one (had a plastic knurled knob rather than metal. That was about 20 years ago, workd fine today....

It could also be that the cam chain has worn to the limit and needs replacing. I replace mine at about 80,000 before it got bad, cos it needed a heavy duty one to handle the engine modifications.

Good luck. That was my experince

[Anonymous]

Maybe you could try hunting down a manual cam chain tensioner, the automatic ones can back off when the throttle is shut at high RPM, which can cause the cams to run out of time and could bend the valves.
I know they sell them for 1100's at www.schnitzracing.com and at https://www.cyclewareables.com/pages...tensioners.htm so you give them a call or something.

[Anonymous]

Guys, thanks for the advice!

OK, yesterday I pulled the camchain tensioner off the 'bike. The sliding surface of the plunger looks fine (no pitting), but there was a "dimple" worn in the surface of the chamfer on the plunger. I managed to clean this up by rubbing down the surface with an oilstone. However, I think that the problem is the bearing mechanism (part of the knurled wheel adjusting mechanism) that makes contact with the chamfer.

On my tensioner, there doesn't seem to be an easy way to pull the whole adjusting mechansim apart. I can pulled the knurled wheel and spring off without problems. The rest of the mechanism then disappers inside a large hexagonal nut before disappearing inside the cast body of the tensioner. Common sense says that there should be a way to separate this large "nut" from the tensioner casting, but I'm nervous that this "nut" is an interference fit inside the tensioner casting and applying brute force to try and "unscrew" it from the tensioner casting will just fracture the casting. Has anyone taken one of these things apart completely?

I'm pretty sure that the ball bearing (?) that presses on the tensioner chamfer is the culprit - I can see it inside the tensioner body but can't examine it in detail unless I can separate it from the tensioner casting.

If I can't fix this, then I'll have to get a replacement tensioner mechanism, which hasn't been easy so far (my experience has been that spares for GS' are getting harder to track down in Australia). Does anyone know if the tensioner mechanism from other models is interchangeable with mine?

[Anonymous]

Top End Noise-79/GS 850

Maybe you could try hunting down a manual cam chain tensioner, the automatic ones can back off when the throttle is shut at high RPM, which can cause the cams to run out of time and could bend the valves.
I know they sell them for 1100's at www.schnitzracing.com and at https://www.cyclewareables.com/pages...tensioners.htm so you give them a call or something.

I wonder if this is what happenned to me this morning.
I was travelling at higher R.P.M than normal and backed off to stop at the
red light.
At this time I noticed a louder than normal noise appear to come from the top end.
Fortunately I only had to travel another 100yds to park it.
I have to drive it 50 miles to get back home after work. Is there anything I can do to the tensioner if indeed it is the problem. The bike does not belch smoke and appears to idle so I am not sure what or where the noise comes from.
Please tell me that it is a simple fix as I love the bike and have been told that because of the year of it , it is not worth repairing. Local Dealer!!!

[saaz]

If the tensioner is working correctly, in normal road use it should adjust up any slack. It does sound like the chain tensioner was not doing this.

[Anonymous]

Guys, thanks for the advice!

If I can't fix this, then I'll have to get a replacement tensioner mechanism, which hasn't been easy so far (my experience has been that spares for GS' are getting harder to track down in Australia). Does anyone know if the tensioner mechanism from other models is interchangeable with mine?

Hi Mark,

Try either Brisons 9638 7140 or Penrith M/C Spares 4721 2116. I suppose it depends on where you are in Sydney.

Brisons tend to charge well but I'm told they are considered to be honest over the phone on the condition of used parts. Penrith Spares bought out Big Wheel M/C Spares a while ago and have lots of GS motors lying around the place.

When I was looking up prices for a set of barrels with pistons & rings for my GS1000G, Brisons were $350 and Penrith $300. On the other hand, Joe's Spares in Fyshwick ACT 6280 6703 were $150 for the same stuff. I've seen Joe's stuff, they have shelves of parts and lots of mostly complete bikes out the back, several GS of different sizes.

Kim

[saaz]

Joes are one of a few local wreckers for me. I can check out bits if needs be.

There is also Suzi parts over in Adelaide for new bits, but at new prices.

[Anonymous]

Top end noise

Hi;
I am both happy and relieved to say that my riding season has not yet ended.
I was able to ride home without any mishap. I adjusted the cam chain tensioner as per earlier suggestion and the noise is gone.
Thanks to all I can still ride with confidence.