750 SF2 clutch drum shims

murphus

murphus

Senior member
Location
Lost in the Midwest
Putting the clutch back together on my 74 SF2. When I took it apart it had one shim on the back side of the clutch drum and one on the front side under the circlip. Odd to me at least, both shims, front and rear, are the same thickness, 1mm. Checking primary gear alignment while putting it back together shows it's properly aligned with no shim on the back side, the clutch drum proud by 1mm with the shim in place. Does the shim serve any purpose beyond spacing? Does the bushing in the drum need to press against a shim and not against the abutment on the input shaft?
 
Laverdaparadies lists these shims in smaller sizes as well. To me it looks like the inside one prevents the bush from contacting the shaft that could potentially eat into it. The outer one to prevent the circlip being affected by the clutch drum. You may need to shim out the primary sprocket slightly.
 
If my straight edge is accurate, any shimming will take things out of alignment; what to do? Will a 1mm offset destroy the primary chain? The chain (which I'm replacing) looks perfect. I did not check alignment prior to disassembly. Could it have been this way when it left the factory? That said, judging by the seemingly somewhat mangled crank lock washer I'm pretty sure someone's been inside the primary before.
 
For whatever reason Tippie, you're comment didn't appear on my end until just now! I didn't see the shims listed on the LP site but will look again. And I'll look for primary gear shims, as well. Thanks.
 
Shims on the Paradies site are with the gearbox diagram.
I'm confused, what do you call the clutch drum?
And the bush? Are you referring to the bronze bush in the outer drum?

Paul
 
In stock form, the clutch drum is held in place by a 1mm shim inside and out. To get the chain run straight, it MAY be necessary to either move the drum OR the primary sprocket. The drum can be shifted by replacing one shim with a thinner one and adding another to the other side to attain correct axial clearance. In this case, be sure to use HARDENED shims, soft steel will be quickly chewed up. The primary sprocket can be shimmed outwards, soft steel is OK there. These shims do not show up in any parts books as far as I'm aware, but the factory installed them regualrly. The drum MUST have a couple of 0.1mm axial movement to allow lube to enter the drum bush.

Of course you can leave the chain run crooked, it's your chain... doesn't do much good for chain longevity, overall performance or primary drive noise though.

piet
 
There's plenty of sources for hardened shims in all European countries Thomas..

I still do not understand where there should be an inside shim to protect a bush on a 750 clutch?

Paul
 
Paul Marx said:
I still do not understand where there should be an inside shim to protect a bush on a 750 clutch?

Paul
Click to expand...
Due to the clutch being constantly engaged/disengaged, there will be axial movement of the clutch pack acting on the drum. Only in an ideal world will the chain pull the drum exactly straight. The unprotected bush rubbing on the end of the mainshaft splines won't last very long, not to mention the chain run going everywhere but where it's supposed to be.

Simple, basic engineering principle, guess there are a few simple rules that need to be adhered to in medicine as well...

piet
 
Problem solved, so to speak. My straight edge turned out to be not so straight after all, the primary gears are in fact in alignment. Lesson learned: I need better equipment. Thanks all.
 
I have also found that it is not very easy to check the alignment there due to the plate covering the clutch rubbers sitting a tad proud. I have also rarely found that they need shimming from the standard 1mm fortunately.
Thomas thanks for the link for shims. Sources of oddball items is a great resource for us. Here in Norway there are virtually no retail sources for lots of engineering type things, they only deal with account businesses, and enquiries lead to "get in touch with one of our account customers".
 
sfcpiet said:
Due to the clutch being constantly engaged/disengaged, there will be axial movement of the clutch pack acting on the drum. Only in an ideal world will the chain pull the drum exactly straight. The unprotected bush rubbing on the end of the mainshaft splines won't last very long, not to mention the chain run going everywhere but where it's supposed to be.

Simple, basic engineering principle, guess there are a few simple rules that need to be adhered to in medicine as well...

piet
Click to expand...
Now I get it. I needed to go and have a look. I didn't see the mainshaft splines going so far.

Paul
 
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