Bad Chain???

[jmd_forest]

Ever since finishing up the build of our 1980 XS400 (around 10K miles on the odometer) cafe racer in the late spring we've (my son and I) had an annoying problem: as the rear wheen spins the chain will vary from reasonably tight (a little too tight) to fairly loose (maybe a little too loose). It makes for a rough ride with constant "rou rou rou rou" grinding . Since I installed new wheel bearings and painted the sprocket during the build I was concerned the rear wheel/sprocket was "out of round" due to some stupid reassembly mistake. However, when I jack up the bike and clamp a marker to the swingarm alligned with the sprocket and spin the wheel I see no indication of out of round. I've also checked the front sprocket for out of round as well as play in the swingarm and see no out of round or play. The tightness occurrs when the chain, as measured by the position of the master link, is at the same spot and since it takes about 3 revolutions to line up the chain in that spot I believe the problem must be the chain since if it were the sprocket it would occur on every revolution, not every three revolutions.

Note: The sprockets seem in very good shape.

My questions for the forum:
1) Does my diagnostics seem logical or am I missing something?
2) What size and type of chain should I use as a replacement? Any specific recommendations?

Thanks for any info you may be able to provide.

 

[drewpy]

should be 20mm slack in the chain at its tightest point

other than that, are all the links lubed?

you need 530 chain between 98 and 110 links depending on the model

 

[jmd_forest]

Yes, the chain is well lubed. I soaked it in a container of oil for several weeks while rebuilding the bike. Is is normal for the chain to get tight then loose as the wheel spins?

As I recall the model is XS400 SG.

 

[Greasey Fingers]

Just replace the chain and go from there, theyre not expensive. Buy a chain break so you can size it up to your bike they usually come with 120 links. Ive used chains from the seller in the following link and the quality is fine, maybe there is a us distibuter for them you could msg them and ask: http://www.ebay.com.au/itm/530H-Mot...orcycle_Parts_Accessories&hash=item4842bd3a70

 

[jmd_forest]

Greasy,

Thanks, I think that is what I will do. Since there is no obvious (or non-obvious as far as I can tell) cause, the chain is the best guess. And for $30 or so its worth the effort.

 

[xschris]

New chain and sprockets if you do the chain do the sprockets also. Even with new ones you will have a little hi and low spots but it should be just slight.

 

[jmd_forest]

Put the new chain on today. During the installation I noticed the front sprocket nut was loose. The only thing keeping the nut from spinning off the sprocket shaft was the locking tab, I could actually jiggle it back and forth a hair with just my fingers. Luckily I have a set of 3/4" drive large sockets and one fit the sprocket nut perfectly. So .... I installed the new chain, tightened up the socket nut, and adjusted the chain. The chain now has very little variance in tension at any point in rotation. Took it for a ride and the "rou rou rou rou" grinding was gone and it now has a much smoother ride, more of what I remember of chain driven bikes (for the past 20 years I've been riding a 85 XJ700 with shaft drive).

I did not replace either of the sprockets since they seemed in near perfect shape.

 

[Greasey Fingers]

Probably didnt even need the chain Oh well a new chain never hurts anyway, good to hear it was a simple fix. Another story with a happy ending