2-Strokes 4-ever

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Eric Gore and/or Rich,

Considering this for a 125, and I lean towards RM's.

This bike will be woods focused so we're looking for low-end and torque. I remember reading somewhere that Eric thinks the idea of staying with a square bore and stroke may be a good idea. Have a friend with EG's RM144 Mo-better low-end... he loves it.
1- Where is the benifit of a stroked motor focused?
2- I'm guessing the stroked motor gets a new crank and cylinder spacer?
3- Top end longevity compared to stock?

Thanks
 

Backslayer

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I did a cr 125 with eg 144 kit and had the mid to top end porting, and I really liked it, you gain more low end over stock because of the bigger bore. And not shifting as much as stock. Now I don't know anything about the longevity of the stroker, but I don't believe I lost any with the 144 kit. Now I don't think you would have to stroke it if your wanting to go to a 144, I think the rm has to have case grinding but don't think it has to be stroked. You figure the formula, Displacement = Stroke X Bore. So if you stroked your rm to 144 you would have a longer rod and slightly bigger piston. Don't know if that would be better, than a just a bigger jug or not, Will be interested to hear what rich has to say about it though
 

Rich Rohrich

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2-Strokes 4-ever said:
1- Where is the benifit of a stroked motor focused?

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?

That's the way it is normally done.

2-Strokes 4-ever said:
3- Top end longevity compared to stock?

Thanks

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.
 
Last edited:

Rich Rohrich

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Wolf said:
FYI, I think Eric is out this week.

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

2-Strokes 4-ever

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