Boxerworks.com

Looking for a good source to buy 1st over oem R90s pistons. They appear to be N/A at USA dealers.

thanks,

RPG

RickR90s wrote:Looking for a good source to buy 1st over oem R90s pistons. They appear to be N/A at USA dealers.

thanks,

RPG

http://www.motoren-israel.com/product_i ... 15f66b7a89

Better than the originals. Excellent quality. Cheaper!

Also Motobins http://www.motobins.co.uk/displayfinal. ... &model=R90

Gentlemen, thanks so much,

RPG

I'm currently running the Wossner pistons from motoren Israel on my R90/6. They are nicely run in with around 5500 miles since April, off to Spain in a couple of weeks. No problems and the engine is very smooth (it was balanced). I can't remember what the nominal compression ratio is, I think that it is either 9.5 or 10.0. The bike runs nicely even at low revs (twin plugged, lightened flywheel, minor gas flowing)

Chas, so you'd recommend the forged pistons? how is the oil use after the rebuild?

I have reservations only because I know the stockers are cast aluminum and I believe BMW engineer's (even from 1974) had their reasons for using them. I seem to recall that forged pistons used to require looser tolerances but maybe not so anymore. Some of the older V8's that I grew up listening to had noticeable piston slap with forged racing pistons.

Just thinking out loud.

thanks,

RickR90s wrote:Chas, so you'd recommend the forged pistons? how is the oil use after the rebuild?

I have reservations only because I know the stockers are cast aluminum and I believe BMW engineer's (even from 1974) had their reasons for using them. I seem to recall that forged pistons used to require looser tolerances but maybe not so anymore. Some of the older V8's that I grew up listening to had noticeable piston slap with forged racing pistons.

Just thinking out loud.

thanks,

I don't think it's forged or cast that's the issue but the alloy used. Venolia pistons are famous for slap because of the alloy. They are more durable, but slap when cold, and require more bore clearance to accomodate the extra expansion.
Venolia only makes custom pistons for our bikes, so you need to ask them for a quote.
Another option for you is the Motoren Israel (Siebenrock/Wossner) 1000cc kit. That's what I have. The pistons are designed to work with your 90S heads. 9.5:1 compression. Mine aren't even fully broken in yet and I've got no oil consumption or slap issues. http://www.motoren-israel.com/product_i ... -1975.html for pre 1975 and http://www.motoren-israel.com/product_i ... -1980.html for models built after Sept. 1975. Not only do these have Lighter and bigger pistons, but you get the added advantage (better cooling and indistructability) of Nikasil jugs. Paint the jugs black, and few will know they aren't stock.

Pistons are fine , oil consumption has gone down after break in, no noise issues. I might have also gone for the seibenrock piston+cylinder solution but the coats of the project were mounting up. On my other bike, a R90s replica, I used the seibenrock 1070 kit and had the cylinders powdercoated black, they look and work fine.

In general terms there is stuff out there which is made to much closer tolerances than what was available 35 years ago. (Excluding the cheap stuff made in wherever)