Hello all, I have a question regarding the Piston Ring End Gap for the Top Ring.

I've bored my W11B16 block to 77.5mm (3.05") and I'm using Wossner Pistons and matching +0.5 rings

Ive read the BMW TIS and Bently manuals which state the Piston Ring End Gaps for the W11B16 top ring should be within 0.20 - 0.36mm which seems a bit tight for SC? is also stated in another post link,

The install docs for Wossner, CP Carillo, JE Pistons suggest a minimum end gap for supercharging to be 0.0055" (or higher) per inch of bore diameter, which for a 77.5mm bore works out to be 0.016" (0.42mm)...?

I have two old STD blocks and they both have readings above 0.40mm with the old OEM rings.

Are the figures in the manual correct for the W11? Or should I follow the installation guide from wossener and go a minimum of 0.42mm?

Mod mini uses OB JE pistons in his rebuild and goes 0.015" on his top rings which is 0.38mm.

Can anyone shed some light on this?

Cheers,
Steve

 

Follow the installation recommendations for your new Wossner pistons. A gap of about 0.015” or so sounds correct to me, maybe even a little tight for a supercharger. My knowledge is general however, I don’t have specific experience with the TriTec. But that’s where I’ve kept it on American small block V-8’s.

The Bentley gives the specs for the stock pistons and rings. Is there any wear on your standard size block and rings? That would explain the wider gap. It doesn’t take much wear to increase that end gap past spec.

 

Thanks for taking the time to respond Dan, very much appreciated.

So after much research, I've come to the conclusion that fitting oversize forged pistons requires different gaps than the OE spec, so ill take your and industry advice and use the Specs provided by Wossner.

Cheers

 

I just did my 77.5 mahle at .016

 

Thanks for that info, I went with 0.016 also.