Hi Everyone,

Is there a way of increasing the secondary compression on a mc21? I'm having my crank inspected as it has suffered water damage (long story) and as the crank cases were empty was wondering if its possible to raise the secondary compression i.e. reduce the crank case volume to something closer to a NF5. I've seen loads of 2 stroke cranks with additional material (stuffers) added to them and started thinking, if the cranks apart and the the bearings need replacing then I wonder if I could add some nylon inserts around the big end area?

I'm also having a straight cut primary and secondary gear made which will hopefully make the right side bearing last longer.

Regards

Dave

You're actually referring to the primary compression, not the secondary compression.

Consider filling in the space behind the reed valve stoppers. That's one area that gives good results. Then just tidy up the cases and get rid of sharp edges and what have you.

Remember that the water pump and 2T oil pump are also driven off the primary gears, so unless you're going to be running premix and an electric water pump then the waterpump shaft gear also needs to be considered.

Daveyb069 wrote:Hi Ever

I'm also having a straight cut primary and secondary gear made which will hopefully make the right side bearing last longer.

Regards

Dave

Dry clutch or wet clutch ? How many sets are you having made ?
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NSR300

Hi Matt and Neal,

This is a long term on going project for my track day bike and I'm having one set of straight cut primary gears made to trial. To clarify, he's making me one crank primary gear and one dry clutch drive gear. I will be disposing of the oil and water pumps and going electric. The bike's an original dry clutch so the gear noise will be no bother.

Finally got hold of a replacement crank for a really really good price i.e. not the ebay price!

I've started to fill the spaces behined the reed blocks, as per edetuckracing and swapping over to Vforce reeds. Just wondered if anyone has tried to modify the crank webs, by adding nylon stuffers?

The person making the gears, can also make a close ratio gear set. Though I'm not sure whether I should go down this route, as there's TT F3 gearboxes out there.

Regards
Dave

Good luck and keep us posted on progress
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NSR300