Daniel5691

Hello yet again,

I remember a couple of members mentioning the availability of dimensional drawings / stencils / images for flycutting S3 pistons for use with Euro S heads.

I'm ready to cut (well... the machine shop is...) and would greatly appreciate
any images that could be uploaded/ shared.

Again, thanks.

SMTCapeCod

https://rennlist.com/forums/928-foru...pistons-2.html

(22)

From several threads, looks like maybe Ducman82 or Lizard can amplify.

Ducman82

I sent mine to a machine shop down here. Greg brown users them. They have a jig made for this exact job.

Daniel5691

Thanks guys,
I am going to be using the plain-jane S3 "flat-top" pistons for the 5.0 bottom end, the ones that came with the S3 M28/44 block.
Tom Bell, at Bell Motor Service in Louisville, was just inquiring if there are any BTDT-type measurements for the relief cuts. I told him that several of the guys here had built hybrids very successfully and I would see if any drawings or images are out there. Seemed also like a couple of RL members had mentioned such drawings before. I am getting SUPER EXCITED about finally moving forward on this project, but I want to be as careful as possible, or at least as careful as necessary lol.

Dan

mark kibort

the valve relief depth is only .175" . you can forward that... position is from the euro pistons. I was using one of the top engine machinist around and even after he was done matching the pistons i gave him for a template, the reasult was being off by 1mm. so, i grinded off the 1mm by a dremel.

I have a drawing , stensil that i use.. ill see if i can find it and post it.

GregBBRD

I no longer do this, in house. My machinist has all my patterns and instructions.

The '85/'86 pistons were symetrical on the dome, but had offset on the piston pin. For some bizzare reason, the factory has the installation arrows pointing to the exhaust side. That puts the piston pin offset going one way on the 1-4 side and the other way on the 5-8 side. (One side of the engine has improved rod angle which makes the pistons noisier and the other side of the engine has way worse rod angle with quieter pistons.)

Makes zero sense.

This is a great time to fix this problem. All you need to do is pick out what you want: Better rod angle with noisier pistons, worse rod angle with quieter pistons. or leave it alone and pretend that having them facing opposite directions isn't one of the most absurd things, ever.

mark kibort

I dont remember the worse rod angle making quieter pistons, but of course, in greg we trust!
However, i remember this advice like it was yesterday. very gratifying to fix something that the factory did that was kind of brain dead simple to fix. however, we all know why they did it.. the pistons were asymmetrical and they tried to save costs and who would notice as they all were set up with the same valve reliefs. HOWEVER as you say its an easy fix and many thanks again walking me through why ...

(the S4 doesnt have this issue, because the valve reliefs are the same top and bottom, so the piston can be set up correctly for offset by the arrow pointing to the front of the engine.)

I did this mod and you just have to keep clear the side of the piston which has the greater offset.... as i understand it. you make one side of the piston banks so that they are normal. (no changes) and the other side, you spin the pistons around 180 degree and make the valve reliefs. i have details on my build on which side is which..

this way, you get more power, the engine will last longer and its done correctly.
you have a driver side set of pistons and a passenger side of pistons.

I remember Greg calling the Porsche engineers "cement heads".. that still makes me laugh today!

Daniel5691

Spinning pistons?
That makes my head spin ! !

Just my luck I would get the fore pointed aft and the aft pointed fore, and my poor engine would be noiser, shorter-lived, and make even less power. lol

Thanks for the help thus far.

Dan

GregBBRD

Just make them all point in the same direction....your machinist will understand.