Modified 90 shift forks???

[bandito90]

Upon tearing down the bottom end on my 90, I found worn shift forks and a few gears that are going to be replaced. I have tub of various 90 parts,I got with another stroker motor.
I found these shift forks in there.They appear to have holes drilled in them and have most of the rougher casting ground down. Any idea what the advantage or reason to do this would be.
The pics are kinda rough.

Thanks 147239147240

[Vealmonkey]

There would be a minimal weight savings, but I would think more for lubrication purposes. The gears should already be sitting in gear oil though, but it's the only thing I can come up with that makes sense.

[barrett8]

yes i have seen this done to blaster trannys it for smoother shifting and better lucubration as veal said some times they mod the shift drum too

[Vealmonkey]

Not only for lubrication in, but lubrication out as too much lube can cause some drag. It was a popular mod at one time long ago.

[bandito90]

Thanks,Those were the only two things I could think of.I'll have to take a better look at the shift drum,To see if its been modified.

[oscarmayer]

so was it really worth doing?

[Vealmonkey]

So you're asking if modding the shift forks is worth doing? Wether it made a difference, as long as the rider felt it did and gave him more confidence in the machine, couldn't hurt could it? I mean, you're not talking alot of work if you already have the cases split. There have been many mods throughout the ages the may or may not have made a marginal difference, but if it bolstered rider confidence, well then, all the better. Sometimes all the little tricks can make a ton of difference. But that's why they were called tricks. Every builder would do a little something different, usually within the rules, occasionally outside the rules to try and give them an edge. The difference is in the details. The lengths some guys would go to would be mind blowing to alot of people. It went far beyond just "blueprinting" an engine.

[oscarmayer]

lol yea i know about the racing stuff, but i was jsut curious on if this actualyl make a known difference or was it jsut done becuase it was thought too? if there was never any evidence that shows it helped, i would probebly not do the changes. I"m asking because i am about to redo one of my son's racing engines and we are doing a 4speed semi-shifter. so i was goig to split the cases, remove the 50cc cranka dn rod and isntall the 124cc stuff while in there i was thingk inf if ti makes a difference, I'd polish out th eparts, if not, then i'll leave them be.

[barrett8]

polishing is not your friend in this case as you want to hold the oil to the surface of the part for less friction. but there are some parts that are polished smooth for a reason. the holes in the shift fork is just one small thing that adds up to the big picture in most case the bigger edges are removed on the shift drum and rounding the points off the shifting star. i have also tried cutting a spiral grove around the shaft that the shift fork ride on to add more oil. i think it help but veal also has a good point it could be in my head but i do it for better oiling and hopefully longer life

[Vealmonkey]

What does it matter that a previous owner smoothed the outside of the shifter fork? You don't need to lubricate the outside of the shifter fork. You don't need less friction on the outside of the shifter fork, so that doesn't matter one bit. I'm sure since the person who added the holes, just did it cause it only took a couple seconds to do on a sanding belt or with what ever method he was using just to make it look nicer. Or he could have cleaned off the casting marks so the forks wouldn't hold as much oil on the outside. Barrett, the outside of the shift forks don't need to be lubricated or need to hold more oil, so why even post that? And oscarmayer, what is or isn't worth doing is up to you. Engine builders went to great lengths to do all kinds of little details that may give them the edge over their competitors. Wether it's worth doing for you is purely up to you.

[oscarmayer]

yea makes sence. thanks guys! :)

[bandito90]

The shift drum does not look to have been modified. I guess I'll find out if the the holes make any difference, When I put these in my motor.