l got a 2005 enfield bullet 350CC.thinking of re-boring the cylinder wall for 1st oversize.what will happen.will the life of engine be at stake?yes ,it is a cast iron engine.

rebore produces more power.

so consider high wear & tear on con rods or replace them with after market like Carillo con rods.

crankshaft bearings will take harder knocks..consider high quality cermaic bearings.

OEM head gasket thicknesss may be too high compression with overbore..depends on how much bigger u r making? u may need a slightly thicker gasket.

if u want perfection, cam profile will have to be changed. cos more gas flow in & out of engine.

might also conisder some porting.

Rebore only if cylinder bore damaged, or over-worn or too much taper-measure abt 1cm below top of stroke and at cylinder base, across and inline with c'shaft. Any rebore shortens the number of rebores left in the cylinder,& unless the new power overloads the old crankshaft etc, all will be well.

A properly done re-bore wo not effect the life of the engine. If u r thinking about doing it for an increase in displacement, do not expect much if u r just going for the next stock oversize. If u r talking about doing something like going to a 500, then that is a different story. The lower end of that engine may or may not be able to handle that level of power, & since the engine is not counterbalanced, it may vibrate more too.

This is a question for an Enfield expert. l am sure they have their own web community somewhere.

Good luck!

If you're going .010'' or .020'' over, u can expect less oil use & possibably easier starting & fuel mileage. Other wise, as long as the crank & rod bearings r servicable & in good shape, u do not have a thing to worry about. If it has replaceable shell bearings, I'd go ahead & replace them if u have it that far apart just for good measure. If the rod is the bearing & it is within specs, reassemble it & forget it. If ur bike has roller or ball bearing crank, then do not worry.