Thanks Markus,

This is helpful, seems the same ring set works for both 2.5 and 2.7 cars, as I thought. Unfortunately the Mahle sets are out of stock everywhere I looked at. Now I think I`m gonna go with this:

https://www.ebay.co.uk/itm/183341980498?ul_noapp=true

It`s an SPD product, which I`ve never heard about...

Workshop manual: does such thing really exist??

In the price range of the eBay ones i would go with OEM: https://www.********************************************** **************************************.com/oem-parts/porsche-piston-rings-99610303302/?c=bT0x

Edit: uhm - seems to be a competitor of pelicalparts.

Shure, an official pdf workshop manual in english language for the 2.5 exits.

Yes, but it contains nothing about the engine internals. Porsche never intended techs in the field to work on these, so they never published anything.

Yes, I have the Bentley workshop guide, which is useless for engine rebuild, Wayne`s book, and a parts list with diagrams I found on the web. That`s all I have.

Markus, I`d go with that too if it was in the same price range, but that`s for one cylinder..

Markus, I`d go with that too if it was in the same price range, but that`s for one cylinder..

Rings can rotate during their life so there are no original ring positions. Always give a light hone before installing new or old rings to help bed them in. .

Cant find the link on running in a motor but if you are using old pistons, a few squirts on the accelerator with a back of is all that is required.

Have you ever see race cars do 10000 miles as slow speed to run them in ?

New pistons, new hone, 2 - 3 heat cycles and pedal to the floor.

Quite and old video of mine.

https://www.youtube.com/watch?v=PsEFKYULNDc

Cheers Wallace

Thanks Wallace,

Yeah, I meant the same rings to go back to the same cylinders.
What do you use for honing? Just a honing tool in a drill or you take it to a machine shop?

12500 rpm is not bad for a 4T single :cheers:. What can the CB125 twin do, if the singe can be spinning like this?

One of these will do, https://www.toolfactory.co.nz/products/ampro-3-jaw-engine-cylinder-hone-50-175mm-75mm?variant=39640318349&gclid=EAIaIQobChMIhN7U-pyL4AIVCSQrCh33Mg57EAYYAiABEgK7IPD_BwE

Quick hone (20-40 sec) with some cutting oil is normally fine. Just roughen up to help seal the rings.

Just think of it this way, take a sharp knife and draw it across and oil stone. Home many strokes does it need to sharpen, 6 or 12. Same with and engine, the stone tears the liner microscopically, a few slides of the piston rings beds them in .

Seen some aero engines documents where they 'lap' the rings in by hand with a piston lapping jig.

Have 2 CB125 twins and one is bored to 150 cc. I need to do my magic on the motor but that will be good for 14000+ .

Will do. Honing will also help keep oil film on cylinder wall.
I also like to play with vintage Japanese bikes, I have a TX750 Yamaha and a CB750 K1.