rebore question

[elliottles1]

hi all,

i have just finished building a tzr125 engine to install in a honda nsr80 chassis for a bit of fun. my question is this, it is rebored to 2mm over and i was wondering whether anyone would advise increasing the combustion chamber size for this bore, to avoid possible problems with detonation? by my calculations the engine has increased in size from 125 to 133cc.

cheers
les.

[Czakky]

Can you check squish?

[m in sc]

that's a big jump. id def make sure it matches along with the head gasket.

[elliottles1]

hi again,

i can measure the squish in the next couple of days but it will be standard, i was thinking that if i did not reduce the squish and left it as standard then at lease the compression would be on the "good" side??

the head gasket is a multi-sandwiched alloy type that holds water as well, so it is not easy to modify for increased size. on top of that they actually sell big-bore kits for these that use the standard head??

whats the thinking out there?

cheers
les.

[m in sc]

WELL, CHECK THE bore hole on the gasket. some makers take the allowance to have the gasket to clear the biggest bore. taking .040" the inside of a gasket isn't hard at the fire ring if you need to either.  but having it hang into the bore would cause a hot spot.

also check the edge of the head bore. if there's a sharp step into the bore, just radius it a bit.

[elliottles1]

hi,

m in sc.

both of those i will do. many thanks.

les.