New clutch still slipping

[scott s]

Just got my '75/'78 combo bike back together. The engine is from a '78. Friction clutches are new.

I've adjusted the clutch several times and it still seems to be slipping. The tach is sticky from sitting for so long (years and years), so I can't tell at exactly what RPM's it starts to slip, but it's not very high. I'd guess ~3-3.5K, going by ear.

I loosen the cable so it's completely slack, adjust the screw until I barely feel it touch, then back out ~1/4 turn. Then I readjust the cable. I can get it into gear smoothly, find neutral every time, shifts VERY nice. It just slips.

I tried really bottoming out the adjustment screw. I tried barely making any contact with the adjustment screw. I've tried several places in between. If I adjust it the way I know how...the way that's always worked for me...I can get it to shift and go into all gears and into neutral no problem. It just slips.

I had some top end work done on the bike so I had the shop install the clutch discs. If the "dot" on the basket isn't lined up like it's supposed to, will that cause it to slip?
What else could be the problem? Weak springs? I rode this bike home a couple of years ago and don't remember it slipping.

 

[scott s]

The discs are new from MikesXS. I recently heard that some aftermarket discs are nearly out of spec from new. Anyone had trouble with these?

 

[5twins]

It's probably the springs if they're the originals. Maybe they weren't quite weak enough to slip a couple years ago but it sounds like they are now. And it doesn't matter if they measure correctly to spec (34.5mm), they can still be weak.

 

[scott s]

I have two sets of friction discs and plates in my parts pile. One set is used but measures correctly, the other is new and as such, measures spot on.

I also have a set of stock springs and a new set of Barnett Racing heavy duty springs. I think I'll check 'em out...rig up a way to measure the strength...and have all that ready to go for the first oil change. Take a look inside and see what's going on.

The only leak on the bike is from the starter cover, so that will be a good time to install a new gasket there, too.

 

[5twins]

I've heard the Barnett springs are really stiff. You might want to use only 3 of them with 3 originals or the lever pull may require Tarzan's help.

 

[scott s]

That was the plan, actually. How are the springs measured (lengthwise)? I've checked my manual and the "free" length of all my springs is longer than the specs in the manual, even the new springs.

The manual says 34.6mm. All of mine are 41.xx. It says "free length", but are they measuring them installed in the basket or something?

 

[5twins]

Springs are measured out of the bike with no tension or compression not when mounted and compressed. Because of the 41-something length, the ones you found in your clutch are some sort of aftermarket, not originals. But, all aftermarket springs are not created equal. Some are actually weaker than the originals even though they are longer. Have a look here .....

http://www.650motorcycles.com/ClutchSprings.html

 

[scott s]

I was at Pep Boys and my local shop today (getting the oil changed in my car) and had a chance to read the Pennzoil bottle.

Even though I've used Pennzoil automotive oil with good success in the past, I noticed today that the bottle now says "energy conserving" or something to that effect. I think that means that it has friction modifiers in it to make it real slick for increase fuel mileage.
I bought some motorcycle oil today and may try just changing the oil and see if that helps.

 

[Ghetto]

I was going to ask what oil you are using but you already answered that. I bet the new oil will be the fix. I run Shell Rotella in all my cycles. Never a problem with clutches.

 

[scott s]

I hope you're right. Worse case scenario, it's a $12.50 experiment ($4.99/L).
It's not THAT big a deal to go into the clutch cover, but I hate taking stuff apart after spending all year putting it back together.

 

[grizld1]

To answer the question in your first post--yes, misalignment of the pressure plate will cause the clutch to slip. You might want to check that before installing the fresh oil.

 

[scott s]

Well, tried the oil today and that didn't work. Still slipping. I took the opportunity to check/clean the filter (looked good. Some very, very small dirt and shop rag lint) and adjust the cam chain and valves.

I went through my clutch friction plates and found 7 that all measure 3.0X mm. I also found 4 metal plates that measure stock or above. Of all the other plates/discs, they were just slightly under new...2.98 or 2.96, etc. Nowhere near the wear limits, but I wanted the pick of the litter, so to speak.

I plan on pulling the clutch basket and see what's going on in there. I also have a one piece pushrod that I'd like to install. I'll also check the worm gear on the left side cover, even though I can't imagine what that could be doing to cause this problem.

I'll check/measure the plates/discs that are in the bike now when I pull the basket. I'll find enough steel plates to make up one good basket of "new spec" or better parts.
I'm also working on a homemade spring tester setup; something similar to the link posted above.

 

[scott s]

And just to clarify, a '78 engine should have 7 friction and 6 steel plates, right?

 

[retiredgentleman]

Yes, for a 78 you are correct.

 

[scott s]

My Dad took the springs I had to a race shop today and had them test them on their spring compressor/tester.
The stock springs measured 48# and the Barnett springs measured 60#. The stock springs had some variance in them, but I picked out three that were exactly 48#. The Barnett springs were all the same. Dead on 60#.
I plan on using 3 of each when I pull the basket.

How do those rates sound?

 

[5twins]

They don't really mean anything unless you give the height they were measured at, and they should be measured at the stock installed height.

 

[scott s]

Sorry, yes....they were measured at the stock installed height. Whatever the manual lists (don't have it with me right now).

 

[XSLeo]

I have seferal manuals. I can find the installed height for the valve springs but not the clutch springs. What is the installed height?

 

[XSLeo]

I have several manuals. I can find the installed height for the valve springs but not the clutch springs. What is the installed height?

 

[5twins]

According to the link above, .950".