R75/5 Siebenrock

Hi All-

Just purchased a Sieberock 1000cc Kit for my ‘73R75/5 LWB. I recall reading somewhere about the use of two base gaskets below the jugs as a way to lower compression, etc. I’m not inclined to do it, but just curious as to why some have chosen this method and whether it does seem to have merit.

Thanks for your comments!!
Tom

Tom -

I did a Siebenrock replacement for my R100/7, so not a displacement upgrade, but there was an increase in compression ratio with the new parts. I got my kit from Ted Porter. We talked about this. The CR went from stock around 9.1:1 to about 9.5:1. I felt that was too much of an increase and didn't want to consider dual plugging. So, Ted suggest I install a base gasket that was meant for the R60 series...it was 0.67mm thick as I recall. He indicated it dropped the CR to around 8.9:1. That was good enough for me.

The stock R75/5 was 9.0:1 so you would be in about the same situation. The /5 part number for the R60/5 was 11111257092. Check with your provider for something if you want to go this direction.

Siebenrock Kit

I believe the Siebenrock kit uses the same pistons as Motoren Israel sells.

I installed the Motoren Isreal forged pistons (1st over) on my high mileage R90s a few years ago. They were advertised as stock, 9.5:1 pistons. But I decided to measure all the volumes of the heads, cylinders, etc. and came up with 9.0:1. Sometimes, you have to do your own verifying.

RPGR90s

I lowered the compression on one of my R75s - it lost a little bit of power (not a big deal when you're just touring on an R75...), but the engine got a little smoother and it was a LOT less fussy about what gas I put in it.

Anyone know of a good resource on where to learn how to install a Siebenrock Big Bore 1070cc kit on an R100? I have an 83 RT that I am trying to restore. I'd like to turn it in to a old airhead hotrod. I've watched tons of youtube videos but no one discusses how to do the entire 1070cc kit. I've seen plenty of videos on how to upgrade/replace the cylinders and push rod seals but nothing discussing how to replace a camshaft or discuss what else is involved in this project. Thanks in advance for your input.

I want to put an 860 kit in my R65 LS. Time and $$ as always.