What causes the usual idle-to-first thunk?

Transmission, clutch, chains and belts
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ArizonaMike
Posts: 45
Joined: Thu Oct 18, 2007 1:19 am

What causes the usual idle-to-first thunk?

#1

Post by ArizonaMike » Thu Jan 24, 2008 9:58 pm

Description: Was wondering what happens inside the transmission and/or clutch that causes the usual "thunk"

Post by Mike Colaizzi Pgh PA on Apr 30, 2006, 1:28am

Hi,

Was wondering what happens inside the transmission and/or clutch that causes the usual "thunk" (sometimes causing a mini-lurch forward) when we shift to first gear from an idle. Any way to adjust this to a minimum? Thanks in advance for responses.

Mike Colaizzi, Pgh PA

Post by Mbskeam on Apr 30, 2006, 4:26am

sounds like the clutch is dragging a bit and is letting you "FEEL" the drive train slop being taken up.

mbskeam

Post by caschnd1 on Apr 30, 2006, 7:33am

Yep... like mbskeam said... clutch is dragging. Lots of possible causes for this:

* Clutch is not adjusted correctly
* Engine and transmission are not aligned properly (especially with belt drives)
* Clutch hub studs have grooves worn in them where the friction plates ride
* Clutch basket drive dogs have grooves worn in them where teh steel plates ride
* Bent clutch hub studs

I'd pull the clutch apart and give it a good inspection.

-Craig

Post by Mike Colaizzi Pgh PA on Apr 30, 2006, 10:05pm

Thanks Craig

I knew there were grooves in the shafts, but didn't know they'd contribute to the "thunk". Guess I have to get a new one. What's a good aftermarket brand to look at?

Mike

Post by caschnd1 on Apr 30, 2006, 10:18pm

Mike,

Yeah, the grooves in the clutch hub studs can contribute to dragging. What happens is you pull in the clutch and the pressure plate moves outward, but because of the grooves the friction plates don't want to move away from each other. They stay put and you don't get a good release. Another thing to look at is the engine/transmission alignment especially if you have a belt drive. Remove the outer primary tin and start the bike. Pull in the clutch lever and watch the clutch basket. If it moves outward as you pull in the clutch, then things arent' aligned right. When the clutch basket follows the pressure plate you won't get a good clean release.
There are a couple ways to address this problem. 1) Align your engine and transmission. 2) Install a Ram Jett Retainer or a Clutch Tamer kit. Both of these kits will help a lot if your problem is related to the clutch basket walking. Both are also very easy to install if you are already swapping the clutch hub.
As far as clutch hubs go... I'm currently running a 5 finger hub on my panhead. If I was going to go and buy one today, I'd save the money and buy a 3 finter. After riding with a 5 finger hub for about 20K miles, I haven't found any advantage long term advantage.

-Craig



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