Case Port Matching

[Zman]

I am freshening the bottom end of my 2000 XC327, with a crank rebuild and new main bearings. I figure it may be worth doing some case cleanup while I have it apart. Does anyone have experience with cleaning up the GG cases for better flow/performance and is it worth it? If so, can you share some details.

The case transfer port areas are pretty rough and floor of the reed cage is uneven. I hear that it is bad to remove too much material from the cases because it increases volume and reduces the compression in the lower end of the engine. I started putting some Sharpie marks where I thought I would do some grinding and smoothing.

Any input would be welcome.

 

[(F5)]

It might keep you amused but you won't feel anything more than placebo. What is more likely to yield a small result is the sharp edge at the transfer to bore.

But you cant do that without risking the plating, so it's a replate time exercise.

On race engines I've cleaned things up, just because, but . . .

 

[SS109]

I always match the cylinder to the cases using the base gasket as my template for both. Inside the cases and cylinder I will only remove casting flash, larger bumps, and grind down edges where the cases halves meet but that's it. Anymore than that and you really can affect the flow through the engine and not always in a good way. Like F5 said, more than likely placebo but my engines have always run strong.

 

[Zman]

Thank you both for the input. I will probably spend a little time "cleaning and smoothing" before I put her back together. I am building a 1999/2000 GG mostly from spare parts so I will not have a before and after comparison. I had a 250 top end that needed a replate so for a few dollars more I am doing a big bore 265cc. It should be fun when I am finished.

 

[farmerj]

Is it a counterbalanced engine? If so, when you're done do report!

Jeff

 

[Zman]

This one is not counterbalanced but we have two 1998 EC250 unicorns in our riding group. They are amazingly smooth and linear.

 

[Zman]

I did some touch up polishing and made the case transfer size/area more equal from side to side. I tried to create the same margin relative to the base gasket. The floor of the reed cage area was uneven so I tried to level that out a bit too.

This is the original bottom end from my 2000 XC300. I learned the older engines have bigger crank bearings, 6306 C3 and the clutch side crank seal is bigger too, 30x52x7.

Putting in the clutch side crank seal in this engine was NO FUN! The older engine does not have an inner sleeve that the crank seal rides on. This seal rides directly on the crank which is no big deal but when installing from the outside with the bottom end assembled, the inner and outer seal edges come in contact at the same time. It boogered up 3 seals before I figured it out and got the 4th one in straight and clean. The first and 3 tries, the inner lip caught on the crank shaft lip and folded out. The 2nd try went in on an angle and snagged viton on the outer shell and wadded it up. While that was in I was afraid the seal would not be concentric and would wear unevenly or not seal correctly.

On the 4th try I created a spacer driver to use the crank nut to drive in the seal evenly. I also used some plastic film to create guide so the seal would slide onto the crankshaft without damaging the inner seal lip. Fun! Fun! Fun! 3 hrs later I got it finished.

The bottom end is together and I am waiting on some parts.

 

[SS109]

Looks like you did good on it. Bummer about fighting the seals though. Sometimes something as simple as a seal can really test your patience!