Bored & Stroked

2-Strokes 4-ever said:

1- Where is the benifit of a stroked motor focused?

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Port time/area and the pipe dimensions determine the powerband, not the stroke length.

2-Strokes 4-ever said:

2- I'm guessing the stroked motor gets a new crank and cylinder spacer?

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That's the way it is normally done.

2-Strokes 4-ever said:

3- Top end longevity compared to stock?

Thanks

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When you increase the stroke length you increase the piston speed at a given rpm. You also change the rod angularity and the rod ratio (rod length / stroke). If the stroke is increased and the stock length rod is used the effective ratio becomes smaller which in most cases will increases the thrust face pressure on the piston. The combination of higher piston speeds and increased thrust face pressure tends to make rings wear faster in many cases.

Big bores tend to have wider exhaust ports which can increase ring wear as well, but usually to a much lesser degree.

There is no free lunch here, just better compromises.

If you want to increase the displacement on an RM125 I would suggest you do it with the bore only. It's an inexpensive, reliable and proven approach. It's my opinion that stroking it will show a poor return on your investment for the application you describe. Stroking has it's place, but what you describe seems best suited to a simple big-bore and changes to the port time/area (porting) to put the power where you want it.

Send Eric and e-mail ( ericgorr @ hotmail.com ) or give him a call. He can enlighten you further.

I hope this helps.

Wolf said:

FYI, I think Eric is out this week.

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You're right Wolf. I forgot he is on vacation for a few days.