Bike won't idle, poor compression.

[Roy Gavin]

Check the ring width on that Mahle set - Airhead top rings are an odd size 1.728mm or something.

Shouldnt be any problem getting your ring grooves opened out to suit a 2mm Total Seal top if they are wrong.

[Krauser4valve]

Getting ready to put the cylinders and pistons back on, any opinion on leaving the 2mm base shim on that someone had added, or leave it off?

[ME 109]

Getting ready to put the cylinders and pistons back on, any opinion on leaving the 2mm base shim on that someone had added, or leave it off?

I'd wait for a good answer before proceeding. The shim could greatly affect piston/head contact. I think.

[mattcfish]

Getting ready to put the cylinders and pistons back on, any opinion on leaving the 2mm base shim on that someone had added, or leave it off?

Like ME109 said. I bet Vanzen knows the answer. I don't know what the clearance is on K4 heads. Someone may have added the shim to reduce compression for low octane gas...or maybe bad things happen if you don't shim. An R100 didn't come with shims originally and has 99mm cylinder bases. /5 and /6 shims would not fit those cylinders. Your shims must have been custom made for some reason.

[Garnet]

There are 1 mm shims available for 99mm spigot engines. They are uesd, as Matt said, to lower compresion on late 70s engines.

Do a mock up with some modeling clay or wax and see what clearance you have in the squish band area. That will keep you busy till someone how knows better shows up.

[Krauser4valve]

Sorry, I mistyped the thickness, it's the standard 1mm compression lowering gasket-shim. The bike HAS had the cam changed to the later slotted style, but afaik wasn't swapped out for a 336 cam. At least I didn't pay for one.

[mattcfish]

There are 1 mm shims available for 99mm spigot engines. They are uesd, as Matt said, to lower compresion on late 70s engines.

Do a mock up with some modeling clay or wax and see what clearance you have in the squish band area. That will keep you busy till someone how knows better shows up.

Like he said...I never had an r100 (although my R90 now has 1000cc's). I thought all bikes built after 8/75 had o-ringed, 99mm spigots. R100 shims must have been available for adjusting compression only. That said, I know nothing about K4 valve and squish band clearances. I'll bet you don't need them, but you want to be sure.
Lots of Krauser info on this site.
http://www.beemergarage.com/literature.html
The K4 manual is on a PDF file. Not sure how to attach it.
The manual doesn't say anything about shims being required on an R100. It just says to seal with Dirko and avoid the oil passages on the upper studs. There are a bunch of other articles on this link. Read up. Hope this helps.

[mattcfish]

The Krauser manual states that compression with a 94mm bore would be 10.2:1. I suspect the shims are there to reduce compression so most pump gas can be used. 10.2:1 is pretty high. Premium gas only. Without the ability to dual plug, I wonder if pinging is an issue (as it is with stock heads and pistons).

Bad ring gaps and compression lowering cylinder shims, no wonder your bike ran like crap.

[George Ryals]

Put the cylinders on without the heads. Use deep sockets or sections of tubing as spacers so the studs can be snugged up. Bring the pistons up to TDC and measure the deck height. Compare the measurement to the squish area of the heads. Don't forget to consider the head gasket thickness.

Nobody can answer your question(without hands on the stuff) as to whether you can delete the shims or not. The cylinders could have been shortened, the heads could have been milled. Either put it back the way it was when it was running or mock it up and measure clearances and/or measure the combustion chamber volumne with a burrett (sp) to confirm staticcomp ratio.

Of course you could put it together without the shims and try it. If it pings or the pistons crash the heads or valves take it apart and put the shims back.

[Chuey]

For a tutorial on how to use the cylinder volume and deck height to determine compression ratio, you can check out a website called TheSamba. It's about aircooled VWs and Porsches. There will be something on there that tells how to do that operation and calculate the compression ratio.

If I knew anything at all more than the general principal, I'd be more help but this may be what is needed.

Chuey