Cam chain usable life expectancy?

[Guest]

Hello everyone, my first post on the forum and I'm looking for some advice...

I just purchased a 1977 Suzuki GS400 "barn find". The bike was last registered in 1989 and has 24K miles on it. So far I've torn apart the carburetors and cleaned them (I have not replaced any parts yet as the carbs cleaned up nicely and I could not see any significant signs of wear on jets or needles). Once I bench synced and reinstalled them on the bike, I was able to get her running (still not idling smoothly yet). With the bike running, I'm noticing the cam chain tensioner "rattling", which brings me to my question. Is it possible that the tensioner has reached it's mechanical limit and rattling because the chain is worn that badly? What is the normal life expectancy of a cam chain?

Appreciate any help/insight from the group...

Thanks in advance,

Bernie

[bgauweiler]

Here's a video of what the tensioner is doing

https://vimeo.com/288375283

[Cipher]

mine does that
btw dont touch it while its working
the manual should have the stretch limit specs for the chain I think you count links
simple enough to access the topend for inspection

[fbody_mike]

Set the valves (if you haven't already) and sync the carbs. You can get a lot of weird rattles and such at idle if the carbs are really out of balance.

[bgauweiler]

Set the valves (if you haven't already) and sync the carbs. You can get a lot of weird rattles and such at idle if the carbs are really out of balance.

By "set the valves" do you mean set the tappet clearance?

[fbody_mike]

Correct, you need to make sure the clearances are within spec before setting the carb sync. I have had carbs out of sync before, and it actually made the mirrors on the bike unusable because of the vibrations.

[Steve]

Yep, adjust the valve clearances, sync the carbs, make sure the cam chain tensioner is set properly.

While the valve cover is off to check your valve clearances, you can measure the distance between the number of pins specified in the manual.

My guess, after watching your video, is that the tensioner has not been installed properly. And, by the way, do NOT touch that knob while the engine is running. Hopefully you have not made the situation worse. Just as a precaution, you should also check your cam timing when you check your clearances.

So much for the good news, time for the bad. To access your cam chain tensioner to make sure it's installed correctly, you will likely have to remove the carbs.

And then, AFTER lunch, ...

.

[John Park]

My suspicion is that there may not be enough tension on the knob spring. As I recall, there should be a full turn of preload; read up on camchain tensioner service. Someone may have undone the nut that holds the knob on and lost the windup on the spring, or it may have vibrated loose.

Cam chains last pretty much indefinitely on these motors, mostly due to the sophisticated tensioner mechanism.

Probably, you still have the original points ignition. Uneven running is often due to inaccurate ignition timing. Carb sync is not very critical on the twins; they're inherently unsynched by two [missing] cylinders anyway. A bench sync is all you need. Make sure the ingnition advance mechanism is lubed and moving properly as they rust up over time.

Valve adjustment is mandatory when putting these bikes back in service. Way easier than valve replacement.

The good news is that it still runs - after 41 years. You have to like the price.

[bgauweiler]

I appreciate everyone's input and feedback. I took the cam chain tensioner off, removed the plunger, cleaned and lubed everything, reassembled and reinstalled the assembly, and now no more rattle (from the tensioner). I ordered a better feeler gauge set and shim removal tool and will adjust the valves, and check/set my timing next.

Again, thank you to everyone for your help!

Bernie

[John Park]

Don't bother with the shim tool; once you've used the zip tie method the tool becomes irrelevant. I don't have a link to it but it's on the site.

I prefer using new GS500 shims, which are readily available and inexpensive and better made, IMO. Beware of non Suzuki shims and the 29mm ones that look the same but are from something else; the originals are 29.5mm. There's a shim exchange service on this site which is more economical, but there's only four shims on a twin.

Valve cover gaskets may be pretty scarce for the old roller bearing twins, but ebay should have one if the dealers come up dry. Cleaning off the remains of the old one is a lengthy task; grease the new one well and it will come off intact and last for many inspections.

Sounds like there was enough crud on the plunger to hang it retracted.