CG Road to 250CC

[ego]

In my opinion the 4 valved head is too expensive for this build. That’s why I am planning to use a 250 polished and port matched head. Maybe I will use a custom camshaft too. My only question is, will the stock crank and gearbox handle it. Newer opened a case by before. Thats why I am asking these things. Will there be any overheating issues? Is an oil cooler necessary? What else do I have to upgrade to make it work reliable.
Last but not least which size carb do you prefer on this build?

[Megadan]

Originally Posted by ego

My only question is, will the stock crank and gearbox handle it. Newer opened a case by before. Thats why I am asking these things. Will there be any overheating issues? Is an oil cooler necessary? What else do I have to upgrade to make it work reliable.
Last but not least which size carb do you prefer on this build?

My Hawk is basically rocking a "stage 3" Motocult big bore kit, which is over 20hp at the rear tire, a 6-7hp increase from stock, which is nearly 50% more power. It has enough compression/cylinder pressure that you can feel it vibrate the ground at idle. Crank is just fine, so I wouldn't worry about that unless there is a manufacturing defect that can cause a problem.

I run a decently large oil cooler, and it doesn't overheat at all. I would say that if you do want to hop up the engine like this, an oil cooler is definitely a good idea. At the very least one of the 65ml coolers that uses the valve cover oil ports. This will drop cooled oil right on the valves and head, and will keep the rest of the oil at least a bit cooler too. I have a 125ml cooler that draws from the sump and sends the cooled oil straight into the pump to cool the entire oil supply. It's a rather large, but also very very effective cooler.

Side effect of a good oil cooler is that it also makes your oil last lot longer, and helps prevent clutch fade.