RD250 to 350 questions,

[Tommo]

Right I get that, but this is going directly to the track. I would like to have some sort of baseline to start with.

[m in sc]

I measured the pistons and they seem really tight.  IIRC it's supposed to be .5mm clearance? 

.0025-.003

[RDnuTZ]

this is a very interesting discussion to follow  Seems like there are 2 people with competing visions, goals and budgets for this project.

The opening post seems focused on putting together a budget track ready racer who buys a cheap runner 250 and is willing to go with budget top ends, etc. vs. later comments focusing on precision like measuring weights of pistons and bore tolerance and contemplating upgrading to known quality pistons like Pro-X without even installing the kit and trying it out? Also wanting a baseline to work with.

Curious to see which side wins the day here, but I suspect the vision of closer tolerances, and upgrading pistons immediately might not be satisfied without a complete tear down of the motor to verify everything is in good usable condition for a baseline before getting in too deep 

[1976RD400C]

I think you mean .05mm clearance, .002"

[m in sc]

i forgot to put the " in my call out.

like ive said, ive run mine for years and beat te snot out of the pistons no issues