Gp 150 piston/cylinder clearance.

[mikeveslam]

I have got a New s.i.l gp 150 cylinder with a Mahle piston from scooter restorations. For my li 125
(Was Going to put a casa 186 on when funds permit) the piston/cylinder clearance is 0.0020" checked with feeler gauges.
Ring gap is 0.25 mm( can't measure piston. Clearance in mm as my gauges don't go that small)
Are these gaps ok for trouble free running in??
Cheers mike

[handofdave]

i like my piston clearances in air cooled machines a touch larger than .002 but run it in steady and it should be fine
dave

[mikeveslam]

That's all I needed to no. Cheers dave

[Grumpy225]

.002" is too small. I like to have everything set up to .0035" for cast iron (with correctly chamfered ports). Been doing it like that for about 20 years, no problems.

The big problem is the way you are measuring your clearance. You really need proper inside/outside micrometers and measure the parts in the correct places. Feeler gauges are great for measuring points gap and end plate float but no good for measuring piston/cylinder clearances.

[handofdave]

rapido race kits come in at .002"

[YAMLAM]

rapido race kits come in at .002"

Harry Barlow done my Rapido classic and put it to .004.

[Muppet]

2.5 thou perfekt for 57mm pot

[chris2470]

If you half the piston diameter and use this a guide you wont be too far out. i,e:
225; 70mm /2 = 35mm so use 3.5 thou
200; 66mm /2 =33mm so use 3.3 thou
150; 57mm /2 = 28.5mm so use 0.28 thou
etc, etc.

[Special X]

I'd go with

225 4 thou'
200 3.5 thou
186/175 3.2 thou
150 3 thou
To avoid seizure.

[mikeveslam]

Thanks for the above info lads, had it done to 3 thou & is now up and running again,
It's run in time
Cheers mike