250-500cc Overheating 360

My top end was in need of rings as they were pretty worn
replaced the piston and rings, the new one was .0018 larger, my guess wear
set squish at 2.67, book calls for 2.6mm, figure thats close enough
assembled added coolant, now it runs WAY hot, boiling radiator hot
are these engines that critical on piston size

any thoughts what I missed

Got coolant flow?

No my squish is half of what the book recommended, no over heating.
Did you add coolent or just reuse the old stuff?
It's unlikely that you've got an air lock.

Like shawry said you do have flow.

1.2mm would be the ideal, if the piston/ring have been heat cycled then i would recommend checking seals and piston.
Piston for scuff marks and seals for water/air ingress, with the engine running do you get air bubbles at the filler neck?.
Last thing would be crank seals and jetting new piston means higher vacuum so might be leaning out pulling air through seals or gaskets.
Just a thought but if you have an inline thermostat then remove it and recheck.

thanks for the replies
yes I had coolant flow
no it was new coolant
the spark plug was a bit dark but reasonable, so not a vacuum leak
no inline thermostat this year model
these are all good things to check,, so thanks

the power was ok when I first took off but faded after about 10-15 minutes
I stopped to see what was going on, it was hot, not riding hard, and on flat ground
checked the coolant and flow, started again, started up a little hill, within a few seconds it ran low on power
stopped let it cool, went back to my truck
another day tried it again,,, same results only sooner
coolant stays full, been sitting for 3 months, just getting around to it
it is baffling me for sure
George Earl did the engine about 14 years ago, I bought it right after, it has been super reliable and good power
so I looked it all over and refitted the original piston for squish check, almost identical, .004 less squish, not enough to change anything
the rings had an .027 end gap, .019 is the outer limit .003-.005 is fresh, so they definitely needed to be replaced

I know a guy that had this same problem, it turned out his exhaust packing was plugging when the exhaust flow increased.

theres something to consider
talked to George Earl today he said since he rebuilt it 14 years ago fuel has definitely changed
plan to reassemble, add a racing type fuel and probably check packing on sparky

Wonder if the original piston was cast and the bore done to suit minimal expansion, new forged with tighter clearance may be getting caught when fully up to temperature.

both pistons are OEM, same casting numbers

now to make matters worse took my 99 360 out riding and it needs some serious work
have a vibration and lack of power, might be tied but need to troubleshoot
Lectron acts like it's not getting fuel sometimes and has a vibration that numbed my feet, sounds like clutch area noise, pull the lever and it goes away
aaaagh, down to 2 bikes now, guess some serious maintenance or repairs are in my near future

cap tests fine

anybody ever have what seems like a fuel starvation issue with a Lectron

Grasping at straws same fuel in both? Low octane produces heat and the vibration on the second bike may also lead to aerating the fuel bowl mixture leading to a lean condition.

on the 99 360 I went riding with dirt dame last month and at the end of the ride it started
didn't think much of it,, figured I was low on fuel, turns out there was almost a gallon left in the tank
so they are separate issues, guess I should have started a new thread on that one
my apologies

Check reeds and stator /pick up before tearing into them, hope its something simple presume usual suspects have been checked (kill switch,ignition wiring connectors, spark plug, fuel filter, tank and carb vent lines).

yes I was thinking reeds too, ignition is recent, kill switch new, spark plug normal, fuel filter is in the petcock, bought a new one
tank vent is new and it's a Lectron carb so no vents as we think of them
that said pulling carb to check internal screen
all good things to look at,, thanks

The lectron does have two vent lines. Just check they are not gummed up with dirt or grease.
Sounds like a thorough going over the motor is required.
May find your exhaust is blocked, reeds gone and crank case is sucking in air.

Lol
Good luck.
Let us know your findings.