piston questions

hombre · Post by **hombre** » 18 Jun 2006 15:52

Hi all,

Just wondering if anyone can help...

I have recently bought a 3 1/2 engine which has two rearpistons fitted. They look alright, but can I use them in this setting?

Also is there a difference between pistons for Nikasilbores and the traditional ones? I.e. can I use the Nikasilversions in older bores?

and last but not least: how can I tell the difference between Sport and Stradapistons?

Thanx in advance for the answers!

Guest · Post by **Guest** » 21 Jun 2006 12:57

If the piston`s are both rear`s i would say no they wont work properly like that m8ty

The whole combustion process take`s place in the piston`s on the morini if im correct? So surley if they are both rear`s the combustion chamber on the crown wont be in the correct place?
Im a newbie here m8 so learning about these bikes myself but im sure a pro will be along any minute

lee

Post by **SteveMRC** » 22 Jun 2006 18:32

Maybe I'm being a bit stupid here, but how do you know they are both rear pistons?

I thought they were the same but turned round 180 degrees, but it has been a long time since I looked inside my engine. According to the manual the two half moon shapes should be at the front and rear of the engine when viewed from above.

Found this on the NLM site which show how to identify sport/strada pistons.

"Let's look at compression first. There are three levels to the piston crown. The top level which surrounds the valve heads and sparking plug, has a new moon shape adjacent to the plug and a peaked shape opposite.

It is the height of this level that determines the squish clearance and compression ratio. In the Strada the clearance (from the cylinder head) is 3mm, giving a compression of 10 to 1. In the Sport the clearance is only 2mm and the compression 11 to 1.

The next level (2mm lower on the Strada, 3mm on the Sport) is kidney shaped under the valve heads. A further 2mm down, the bottom level is circular, not quite in the middle of the crown. "

Steve

hombre · Post by **hombre** » 25 Jun 2006 13:15

The difference is that the rear piston has a 'cut' in it because it tends to get warmer in the rear. According to the german forum there doesn't seem to be a problem to use them in the front cylinder as well.

Thanks for the reply on the Strada/Sportpiston.

By now I know you can use pistons intended for Nikasil in older cylinders as well, but they need to be measured very accurately because they have less play. The whole story is (in german, but translatable with babelfish) to be found here:
http://baseportal.de/cgi-bin/baseportal ... =1&Pos=993

Greets from Amsterdam!

Steve Scott · Post by **Steve Scott** » 25 Jul 2006 13:25

I'm pretty sure both pistons oughtta have a slot cut in the skirt because the pistons run hot in a Heron head design. The difference between front and rear pistons is the wrist pin offset, which is different on the front piston to minimize piston slap noise caused by the fact that the cylinders intersect below the crankshaft centerline.
Having said that, unless piston slap really bothers you don't worry about it!