Piston Rings

[Michel3007]

I'm reopening this post to ask if anyone would have the exact dimensions (internal and external diameter and thickness for each of the three rings) for standard piston rings for a 350 Strada, so I can order some ? Mine are in my cylinders

The suppliers I have found are ready to make some for me but need the individual height of each ring, and also want to know if the cylinders are Nikasil coated or cast iron (I believe that for a 1973 Strada, they are cast iron, right?)

I have only ordered ready-made kits before so don't know really what I should make sure of ? Any advice is much appreciated.
Should I also indicate the piston gap to the supplier (0.20 - 0.30 mm according to the manual)?
One last question, is the spring under the oil contraol ring absolutely necessary ?

Cheers

[stradella]

The only question that I think I can answer for you is the Nikasil/cast iron cylinder question. I am pretty sure that the cylinders would have been/would be cast iron, not Nikasil. I have never heard of Morinis using Nikasil bores back then.

(I know Moto Guzzi used Nikasil, or perhaps it was a chrome (?) bore, on the 850T in about 1974-75. I had an 850T a while ago.)

Edit: would it be a good idea to contact Luzzi in Italy (Siena)? They are/were long-time Moto Morini people and could - perhaps - have some new old stock rings. (???) I don't have the contact details for them but I have seen other forum members, on this forum, who seem to have their contact details.

[norbert]

All 501 have Gilardoni/Nikasil coated cilinder and pistons from Gilardoni, as well as all 350 custom bikes and as far as I know all Darts as well. Also the last 350 Enduro X- Motors and probably the K2 motors as well (K1 I don´t know)

[MickeyMoto]

My 1981 K1 has iron liners.

The nikisil barrels have 'Gilardoni' cast in them.

[norbert]

Often is an easier way to explain some things with fotos and hope that this is ok for you. It doesnt´t help to find the rings but may help to distinguish the pistons.

Here are three 350 pstons
from le left: Strada, Sport (o,4 oversize),Gilardoni/Nikasil

k-20221205_121217.jpg (96.18 KiB) Viewed 3155 times

The upper surface of the Sport and Gilardoni cilinder (where the A of the Gilardoni one) are nearly 2 mm elevated compared toe the Strada, what makes the difference of compresion compared with the sport pistons . From the uppest point down to the lowest part in the center I measured a differnce of almost 2 mm (5 and 6,9 mm). (Take care when mounting a Sport piston in a Strada barrel. The rings will reach a bit higher so clean up carefully the coal at the top end of the barrel. this is nonsens, forget it!)

The Giladoni pistons do not have that expansion gap of the Sciam pistons. They are marked with the letter A or B and the barrels should wear the same letter. As far as I know that is the result of minimal differences caused by production. (a bit like the famous A, B and C cambelt pulleys are dued to tolerances in the production of the belts)

DSCI0092 [1600x1200].JPG (321.92 KiB) Viewed 3155 times

[Michel3007]

Thank you for your input Norbert. Mine are not Nikasil from your explanation and pictures.

[norbert]

I have to correct myself: The height of the rings distance to the gudgeon pin is the same with strada or sport pistons! I doubted about this and have had another look at it today. Sorry

But there is another thing to have in mind, concerning the oilring:
As far as I know only in the older motors there was a spring behind the oil ring only in the rear piston (please correct me to get out of doubts!). This ring is 4 mm high. I only have one of these pistons left, a Sport. All other pistons I have Sport or Strada have 3mm oil rings. I dont know if the first models also have a 4 mm ring without spring in the front cilinder, or if these pistons with 4 mm rings have been made exclusively for the old rear cilinder (I suppose for Strada and Sport the same). Obviously later Morini recognized that this was not necessary and mounted the same pistons front and rear without that spring and a 3mm oil ring.

I measured on the pistons I have the following heihgts of the rings beginning from the top in mm for 350 ccm:
Strada: 1,5 , 2 , 3 (without spring)
Sport: 1,5 ,2 , 3 (without spring) 4 (with spring)
Nikasil: 1,5 , 1,5 (with a step facing downwards), 3 (without spring)

I´m sorry for the mistake above. But hope that together we can find out how it really is, because these problems and differences show up from time to time and it´s always a puzzle to clear that things

[Michel3007]

Thank you Norbert, you have been extremely helpful !
I seem to remember that I had springs behind the oil ring on both pistons last time I checked them but you might be right.
I will update your measurements with mine as soon as I take care of these rings