I bought a Grom early this year and started racing it with friends. As bought, the bike has 7,000 miles and a header, pipe, PCV, tail tidy, LED signals kits, and a few other odds and ends. I installed Öhlins front and year, MNNTBX bronze swing arm bushing, sticky tires, and a few other odds & ends. Had a ball this summer racing and my bike is very evenly matched with my buddy's.


Last week while chasing each other around at high speeds (for Groms) my engine seized. Trailered home. Magnetic drain plug covered in shavings. No rattling when it went so I suspect bottom end. At this point I'm not sure whether the seized engine is worth rebuilding or if I should just go with a used engine (which I have a line on).


My Grom friends and I have come to a gentleman's agreement that big bore kits aren't allowed. Max displacement is 125cc. Help me spend my money to make this track-focused Grom make more power.

Recap: Bike has header, pipe, PCV with unknown tune, and a seized engine. I upgraded the clutch this summer.

So, I'm looking at your various heads, pistons, cams, etc. My goal is the most power I can make with 125cc displacement without decreasing longevity too much. I look at all the options and I have a hard time deciding which would be the best combination of everything.

• Which head? Or OEM head with maybe some home porting?

• Is a 4 valve head possible? Is it even worth it?

• Which piston? Is a piston even necessary?

• Which crank? Or, stick with stock crank?

• Which cam? Or, stick with stock cam?

• Does converting to an oil pump add power to the rear tire because the oil spinner goes away, or is it just to improve lubrication, or both, or neither?

• With a higher output 125cc motor is an oil cooler a good idea? I don't want to add unnecessary weight, but will if it's functional.

• I see that heavier duty starters are offered. Necessary or good idea for 125cc built motor, or BBK only?

• Any other things I should be considering?

Again, I'm looking for a balanced package of upgrades to do to my Grom engine for power for road racing while keeping 125cc displacement.