How long to run a new piston and rings?

[Donnie]

gp200 cast iron. Replaced the piston and rings only. Original cylinder and all clearances good.

Now if it was the whole setup I'd be saying 800 - 1000 miles.
Rings only 100.

But what about the new piston?

I'm still of the mind of 100 miles as the piston shouldn't be in contact with the barrel due to the film of petroil? Or am I missing something?

[eden]

I wouldn't run it in at all, the running in process is to remove the sharp peaks in the barrel which are produced when its bored.

see this pic





the glazed illustration is a result of babying the run in process!

[rosscla]

How about if you've roughed it up a bit with a light hone / glaze buster to remove some seize marks and a couple of minor scores?

[Donnie]

Interesting!

[onthelam]

For Motorbikes there is a whole series of articles about high load short period runs, with cool down in between, for break-in. Apparently the first 20 mins of running, or less, is the key. The theory being that high combustion pressure is required to force the rings against the cylinder wall so they get seated and not just rub up and down and get polished.

By post count you will see I'm a newby oldie who is just getting back into Lambrettas but much of what i have gleaned over the years probably still applies. As the barrel in question is cast iron.

[Donnie]

Good man and welcome back!

[shocky]

It might be worthwhile giving the piston a few blasts up and down the road then allowed to cool and repeat same for rings as tuis should normalise the grain structure in them
edens pic is good example of what can happen if you dont ride it hard enough or yoh use an oil that is prone to gumming up normally an oil designed for high revving motox bikes ...... I always run in on mineral oil for this reason and it helps colour the plug better for plug chops

[bristolmod]

+1 for Shocky.

[Jazzy]

Nice tip about plug colouring on mineral oil.
Ta.