Nicasil 49mm Bore; Noob? Dubh?

[808BMW]

Your local 2 stroke performance shop ; Whatever they charge

[Bear45-70]

and yes, a polini is not more forgiving at all.. correct break in on a polini is about 5 to 10 tanks, no stress on the motor.
the best ones to buy is used ones since they have gone thru alot of heat cycles. I always buy seized ones for cheap because it seems to be broken in already hehe!

5 to 10 tanks for break in? That's like 400+ miles. That's longer than I even broke in a motor, including several $7000 1 liter 2 stroke race motors. Seat the rings within the first 1/2 to 1 hour, then run that sucker like you stole it.

[burnt_toast]

and yes, a polini is not more forgiving at all.. correct break in on a polini is about 5 to 10 tanks, no stress on the motor.
the best ones to buy is used ones since they have gone thru alot of heat cycles. I always buy seized ones for cheap because it seems to be broken in already hehe!

5 to 10 tanks for break in? That's like 400+ miles. That's longer than I even broke in a motor, including several $7000 1 liter 2 stroke race motors. Seat the rings within the first 1/2 to 1 hour, then run that sucker like you stole it.

but most people are not racing these scooters. these motors you built for race, how long did they last?

the recommended interval for a corsa breakin is indeed about 10 gas fills with many heat/cool cycles, it has been proven and shown to greatly increase life this way on scooters specifically.

for this alum kit, I would say 5 fills ought to be enough. and for me personally my breakin: first 15min rings seat, vary throttle lots then continue to vary and push closer to wot through miles till 100mi, then can try holding wot.

[Bear45-70]

and yes, a polini is not more forgiving at all.. correct break in on a polini is about 5 to 10 tanks, no stress on the motor.
the best ones to buy is used ones since they have gone thru alot of heat cycles. I always buy seized ones for cheap because it seems to be broken in already hehe!

5 to 10 tanks for break in? That's like 400+ miles. That's longer than I even broke in a motor, including several $7000 1 liter 2 stroke race motors. Seat the ringstos within the first 1/2 to 1 hour, then run that sucker like you stole it.

but most people are not racing these scooters. these motors you built for race, how long did they last?

the recommended interval for a corsa breakin is indeed about 10 gas fills with many heat/cool cycles, it has been proven and shown to greatly increase life this way on scooters specifically.

for this alum kit, I would say 5 fills ought to be enough. and for me personally my breakin: first 15min rings seat, vary throttle lots then continue to vary and push closer to wot through miles till 100mi, then can try holding wot.

My stocker race motors lasted up to 3 to 4 years but were rebuilt because the compression had dropped 5 to 15 PSI, not because they were actually wore out.

The full blown race motors would last a season, but then a 5 PSI lose of compression could cast you a race.

I never experienced an engine failure during a race.

I find your personal break-in procedure to be reasonable.

Nikasil is a different ball game.

Your thinking on used cylinders is right on. Used will work and last longer than new.

[Arnadanoob]

Polini bores are incredible. People used to contest my break in procedures but some are really hard pressed with myths. I still have about 10 customers that have over 50k miles on the bore that ride everyday and the bore is in very good condition with hardly any measureable wear.

Contrary to belief, you are not physically wearing in the bore or rings during break in. If it were to wear that much in such a short time your rings wouldn't last more than a couple of months with daily riding. What's important like some of you said is the heat cycling. This accomplishes 2 things, first it aligns the molecular structure of the metal so that it improves in strength which is important to have when dealing with such high air-cooled temps. The second is to help conform the bore and piston to each other during the cool-down cycle. The bore will try to squeeze around the rings (which will compress) and add pressure to the piston. If you have the correct amount of oil (32:1) and are using the correct kind of oil (use a very good quality oil during break in with a high film strength, not cheap crappy oil folks!), the oil will remain suspended between the metal surfaces to allow the heat cycling to do its job without allowing metal to metal contact.

This is a little extreme for most but on our race prepped engines with radical race porting and super high compression, we ensure that the engine is running on the center stand with no less than 2 temp probes for the first few heat cycles before we put it on the road, the jetting is set very rich to the point it will start to sputter. When the engine approaches 200-220F we shut it down making sure the piston is at the bottom during the cooling period. What this does is it allows the bore to contract fully without the piston holding anything back.

Just remember, more heat cycles > all. The point is to get the engine gradually (slowly) up to operating temps with as little load as possible. Then turn off the engine and let it cool down all the way. Then as you continue the heat cycling process all you're doing is gradually increasing the time in which the engine remains at operating temps before you shut it down to cool down completely. You shouldn't use more than 1/2 throttle for much of anything and vary the throttle often when you ride. Avoid hills and don't carry any excess load during this period.

Remember to recheck your torquing of the bolts and nuts after a few rides. Check for leaks around the head, spark plug, base gasket(s) and exhaust flange.

[808BMW]

Nice, I gave my bike a half crank with the kicker every minute or so during cooldown on my first ~10 heatcycles, can't really tell when it's at BDC though, I'd guess you just barely turn the motor over.

2 heat probes, are they different? like CHT and EGT or just 2 different locations on the bore?

[Arnadanoob]

You can feel the intake/compression on the kicker, you should be on the downward stroke when you feel when the engine rotates easily (usually during the power/exhaust cycle).

You've guessed correctly my friend, CHT and EGT.