Long stroke crank case cut out info

[Grumpy225]

Putting a 62/110 crank in my RT190 and need the dimensions (depth, width and height relative to the seal plate) of where the cut out needs to be to clear the big end of the crank.

The original plan was to run a 60/110 crank but I was sent a 62 by mistake. Already had work done on the rod so no sending it back. Besides, now it will be a 205ccish motor.

I've seen the photos before but can't seem to find them now.

[RManson]

There are a few pics in my water cooled thread that show that trench I machined in my cases for a 64mm crank. I just started in the center and slowly worked it until the crank fit.

Hope this helps!

http://scooterotica.org/forum/viewtopic ... 7&start=90

[Grumpy225]

I ended up just measuring it all out and running it through the mill. Took a couple of tries but in the end it was good. I'm surprised the measurements aren't really published anywhere. It would seem like a 62 or longer conversion is pretty common.

Great build thread, I like the use of swivel joints on the shift linkage. Played with that idea for a suicide shift on a chopper project years ago.

[Knowledge]

Hi Mike,

I had plans for a 250 using a big webs (99mm) and machined out the whole of the crankcase (through the mag flange hole) to take the bigger crank. To be honest, if I was in your shoes, I'd do the same even though you are probably using standard sized webs.

Unless you are a strict adherent to the high primary compression school of thought, and plenty of people don't, it won't adversely affect your performance.

I suppose much depends on how good/cheap your machine shop is.....

[RManson]

That was the biggest challenge when I did mine; how to cut a larger hole inside a smaller hole. In the end I did it very carefully freehand, checking as I went. I thought about what you said Martin, but I wasn't certain enough that the primary compression wouldn't suffer as a consequence. Now that you mention it, I agree that it would probably be a non-issue and I would tackle it that way as well if it ever comes up again.

As far as the dimensions being published, I would imagine it would depend on the conrod as well. For example, the same 62mm crank with different make rods would require a different amount of machining.

Have you checked the amount of material left in the trenched area? Just curious. I know for my crank it broke through the original case material in a few spots so they're pretty thin, hence all the welding that's necessary on some builds.

Good luck with your build and post some pics!

Ryan

[Grumpy225]

Hi Mike,

I had plans for a 250 using a big webs (99mm) and machined out the whole of the crankcase (through the mag flange hole) to take the bigger crank. To be honest, if I was in your shoes, I'd do the same even though you are probably using standard sized webs.

Unless you are a strict adherent to the high primary compression school of thought, and plenty of people don't, it won't adversely affect your performance.

I suppose much depends on how good/cheap your machine shop is.....

I used a standard dimension crank. Wanted to limit the amount of extra machining needed. In fact the original plan was to just run a 60 stroke but I got sent a 62 and didn't find out until I had a bunch of work done on the crank and was trying to install it! This is a LPC motor, lots of extra material was removed from the crank case (like a RD350 block).

Fires up 1-2 kicks every time, running about 122psi compression at 1.4mm squish and so far has a great spread of power. Should be ideal for the kind of long haul riding I am planing on doing with it.