Scooterotica

corrado wrote:

soosh wrote:Maybe someone can come up with some proper scientific proof.
There's bound to be someone who's read a book on it.

replaced by scientifically accurate forums in the process.

Containing scientifically accurate opinions?

I've discussed this with a lot of dirt bike guys for years. They always say run in time is 1 hour, 1 tank of gas, or 3 start ups(cold to full temp, then back to cold). From all the two stroke theory i've read, it seems to be more a case of the rings and the piston in relation to the bore. Hard acceleration and/or high speeds push the rings harder into the bore. If they get pushed too hard into the bore too early they can scuff the sealing surface of the rings and bore, leading to poor ring sealing. That can mean less power and less cooling efficiency, or if the piston expands too far into the bore it just seizes(especially with iron barrels!).

One way to reduce run in time is to start with big clearances. 4 thou piston to bore and a bit bigger ring gap. You still may lose ring sealing efficiency, but the piston won't be able to expand into the bore and seize it early. Whether you would have a noticeable drop in power i couldn't tell ya, but starting at larger clearances will wear the top end out earlier. For long life you'd probably be best to start tight, then run in for a longer period. I believe that's where innocenti's tight 0.0015-0.0018" piston to bore clearance came from.

(WARNING-PURE OPINION!)...After reading the heat treatment section of the machinery's handbook and the various temps and cooling rates that can come into play(sometimes very low temps over long periods of cooling time for example), i wonder if the initial heat cycles of expansion and contraction don't have a sort of "heat treating" effect during run-in. Perhaps the expansion rates at given temps of the piston and rings change over repeated heat cycles making it safer to climb to higher temperatures for longer periods with little change in wear clearances.

Muttley McLadd wrote:

soosh wrote:There's bound to be someone who's read a book on it.

Waiting for Nelson..

How very dare you!

My take on "running in" (cast barrel) was for the heat generated to gently case harden the wall sides. This leaves the barrel with a hard wear resistant finish but underneath a "soft" core which allows for expansion and heat dissipation.

If you didn't run it in the heat generated (more heat) would not properly case harden the barrel

i was told heat it up let it go cold 3 times then start at 40mph for 125 mile 50 mph for 125 mile 60mph for 125 mile then ease the last 125 as it feels using your gears ie go around town not sit at 40mph for say 50 mile on a open road.

or when i had the t5 malossi built i just give it some out of the box never run it in and its still performing great 6 years on lol

ducksta wrote:i was told heat it up let it go cold 3 times then start at 40mph for 125 mile 50 mph for 125 mile 60mph for 125 mile then ease the last 125 as it feels using your gears ie go around town not sit at 40mph for say 50 mile on a open road.

or when i had the t5 malossi built i just give it some out of the box never run it in and its still performing great 6 years on lol

Would that be 60mph on your speedo or the 40mph equivalent on my GPS ?........ :biggrin: