18T Counter Sprocket Ok?

[rwingsfan]

Those that are running the 18t countershaft sprocket, any problems? I have read through many threads here and there are in some cases a clearance and or other problems. I have a like new PBI 18T I was thinking about running. The PO had a 17T on it, but the shaft guard was gone anyway. With the 18T the chain clears,but not a lot. Advice?

 

[weekendrider]

There was a member on the old rider site that had to much slack in the chain. A power/motor brake threw all the slack up front bending his push rod.
He lamented not maintaining the chain adjustment with the 18T.

 

[rwingsfan]

Makes sense, but this would not happen with a 17T?

 

[weekendrider]

I suppose if you let it get floppy enough. I'm not going to test the theory though.

 

[bluebikerblan]

Watch out for O-ring chains......they're larger and more likely to cause serious interference with the push rod. Personally, I wouldn't even attempt using a 530 O-ring with 18T.

I like running the OEM 17T with either a 33T (dual purpose) or 31T (highway) rear sprocket with
a conventional (non O-ring). Reviewing Pete's spread sheet below, I see why. Blue

 

[pamcopete]

Here is a little spread sheet that shows MPH vs RPM for all combinations of sprockets, tires and gears, including MikesXS 5th gear.

You will find that there are other combinations of sprockets that yield the same RPM vs MPH using a stock 17 tooth drive sprocket.

MPH vs RPM

Example:

18/34 = 3888 RPM at 60MPH (18" rear wheel, sprocket ratio = 1.88888)
17/32 = 3874 RPM at 60 MPH (18" Rear wheel) sprocket ratio = 1.88235)

 

[rwingsfan]

Ya I ordered a o-ring chain, so I am thinking maybe just abandon the 18T and get a 17T. Just this one is a nice aluminum PBI. Oh well

 

[C-Los SD]

18T is fine with a 520 chain, you do have to remove the chain guide right below the sprocket for clearance.

 

[hutch08]

I will be running a 18 up front with a 530 o-ring... chainguide removed, its definitely close tolerances to the pushrod... but its on a rigid, so the chain will be fairly tight and i'll also be running a chain tensioner. I'll just have to keep an eye on it i guess.

 

[rwingsfan]

Actually mine is going on a rigid also,with no chain tensioner, but I still have not decided what course to take.

 

[pamcopete]

OK. I must be missing something here. What is the attraction to an 18 tooth sprocket?

 

[bluebikerblan]

OK. I must be missing something here. What is the attraction to an 18 tooth sprocket?

Me too! Without beating this up.... Pete's point must be (as would be mine) that converting to an 18T sprocket would seem pointless unless you're seeking ratios lower than those that are more conveniently obtained via stock 17T counter drive and 30T & up rear sprocket combo's.

"Steel Rear Sprockets - ( Standard 530 (#50) Pitch ) - Use in combination with fronts to increase or decrease torque or top speed. Smaller Rears & Larger Fronts move engine vibration away from Highway cruising speeds. 34 Tooth is the Standard rear sprocket size on all 1970-84 650's (USA Models). A very noticeable reduction in engine vibration is achieved a highway speeds when the rear sprocket is reduced to 32 teeth or less. Note: Rear Sprockets will be shipped Cadium Plated or in Black Finish, whatever is in stock." Mikes XS

What kind of ratio is being sought? Blue

 

[hutch08]

xsjohn always recommended the 18t front to help with vibes on the highway... If anyone knew much about the XS it was him

 

[gggGary]

I pulled the cover on a 78 with stiff clutch action, it only showed 8300 miles. The clutch push rod had a nice neat z bend in it and careful looking showed two marks where the chain had gotten it. I assume someone let the chain get real slack and she jumped the sprocket. I had a good push rod and swapped it in,, no other issues.

 

[rwingsfan]

Pete, I don't think you are missing anything other than there are always different ways to a mean. Some say having the larger front is smoother, even though the other combos SHOULD yield the same results. I suppose the same could be said for the Pamco unit as opposed to the TCI box, different avenue to the same destination. And like with anything else there are pros and cons. I was just trying to get some real world feedback on the 18T front, thats all.

 

[pamcopete]

rwingsfan,

Well, there could be some science to the issue. I have heard something to the effect that certain combinations of sprockets will or will not cause the same teeth to come in contact with the same links repeatedly and that has some effect on the wear pattern of the chain and / or sprockets, so my comment was not sarcastic. I am really curious.

 

[rwingsfan]

Pete, I am curious also, thus starting the thread. After some further research though I think I might just go 17-32. The 18T I have fitted real close with standard chain and I just ordered a o-ringer. They are a little larger yet?

rwingsfan,

Well, there could be some science to the issue. I have heard something to the effect that certain combinations of sprockets will or will not cause the same teeth to come in contact with the same links repeatedly and that has some effect on the wear pattern of the chain and / or sprockets, so my comment was not sarcastic. I am really curious.

 

[jay760]

I run 18's on both mine, one with an o-ring chain, with no problems at all, makes 1'st gear really long, certainly won't win a drag race with one but the lower revs at higher speeds it achieves is worth it.

 

[rwingsfan]

And no clearance issues? Hardtail or swinger? Does it tolerate even the slightest looseness in the chain?

I run 18's on both mine, one with an o-ring chain, with no problems at all, makes 1'st gear really long, certainly won't win a drag race with one but the lower revs at higher speeds it achieves is worth it.

 

[pamcopete]

jay760,

Well, as discussed above, you could have achieved the same results with a 32 tooth rear sprocket and a 17 tooth (stock) front sprocket, so why did you decide to go with a 18 tooth front sprocket?