Bottom end noise and the primary drive sprocket nut - The Sportster and Buell Motorcycle Forum

mrcfjf · #1 24th April 2007

I went on the forum ride the other day and on the way home I noticed a new knocking sound in the bottom end at idle. I thought the exhaust was loose or an engine mount came loose, but after listening to the sound at my house, I determined it was in the bottom end. It was a loud knock that coincided with the sound of the exhaust.

Upon reading some threads on here and the Sportster list, I determined that the most likely cause was a loose primary sprocket nut. This is frequently referred to as the compensator nut, but I don't think my bike actually has a compensator here. The torque spec on this nut is 210ft.lbs, but I was able to remove it with very minimal effort using a 1/2 in drive 1-1/8in socket. It was way too loose. The threads on the nut would be usable if the application were less critical. I'm buying a new nut so I don't have to risk this problem again.

I bought a new torque wrench so I can reinstall it properly. This post is just an FYI for everyone.. The bike was a recent 1200 conversion (in the last 1000 miles).

Chris

indyrednek · #2 24th April 2007

Red loctite as per manual.

TechRep · #3 24th April 2007

Quote:

Originally Posted by mrcfjf

The torque spec on this nut is 210ft.lbs,
Chris

The changed the torque with TT 211.

TT 211 – September 16, 2005
Sportster and Buell XB Model Flywheel Sprocket Shaft Nut Torque Update
The flywheel sprocket shaft nut torque for 2004 & later Sportsters and 2003 & later Buell XB models has been changed. The torque has been increased from 190-210 to 240-260 ft lbs. Remember to clean the threads and generously apply LOCTITE Threadlocker 262 (red) onto the threads of engine sprocket shaft.

mrcfjf · #4 24th April 2007

Thanks for the info. I make sure to torque it to the updated spec. There was no evidence of any loctite on this nut, but I'll put some on now. Hopefully, this won't happen again after that.

wildwill8 · #5 24th April 2007

I always put a Butt load of red and turn the Impact up all the way a Drive that Puppy Home I have never got the dang things to TQ with out everything turing on me.

TechRep · #6 24th April 2007

Quote:

Originally Posted by wildwill8

I always put a Butt load of red and turn the Impact up all the way a Drive that Puppy Home I have never got the dang things to TQ with out everything turing on me.

My concern with the impact on that sprocket would be knocking a magnet loose on the rotor. I have never seen it happen, but I did drop a rotor and broke one just by hitting the deck.
Just a thought...

wildwill8 · #7 24th April 2007

the impact I have is only good for 250 so it should be in the TQ specs.

ReddTigger · #8 10th June 2007

I don't have an Impact, BUt I got a good quality Torque wrench from Mac, goes to 250. I've fabricated a peice of plate steel to wedge into the primary drive sprocket to hold things in place.

grindbastard · #9 17th August 2008

My bottom end knock started yesterday after the 50 mile ride home from work. I adjusted the primary chain (per the Hero method) and it didn't help.

Looks like I get to pull my primary cover tomorrow and check things out. I left my manual at work...what size is that nut so I can procure the correct wrench?

Any other helpful tips or need-to-knows?

biknut · #10 17th August 2008

My 1988 1200 engine sprocket nut tq is 150-165 ft lb.

I've had it off many times. I never use loctite on it. It doesn't need any. When you got over 150 ft lbs of torque on a bolt you don't need no stinkin loctite.

It's important to lock the primary and torque it correctly. In 88 thousand miles I've never had one come loose.

Sometimes you can lock the primary by putting a board in the rear wheel, but if you're putting over 200 ft lbs on the sprocket nut you'll probably need one of these Jims Primary Lock Tools.