Fork and oil pump questions

[kshields72]

Hello all,
I just bought a PW50 project and after a weekend of work I have a few questions...

First, it appears that it has forks from a PW80 installed on it. How do these compare travel length, and spring rate. The obvious difference would be the addition of damping over just springs. Also piston diameter. Are they the same? If not and I decide to swap back to 50 forks I would have to replace the steering stem which could get pricey.

Second, does the oil pump just power the oil injection sysyem, or does it do anything for transmission lube? The case had a freeze plug in it and would rather run premix if it has no other function. Does the transmission lube itself with the lower part of the gears sitting in the oil?

[lon12]

not sure about the forks but the tranny has its own oil. pump is just to get the oil the carb to lube the piston and crank.

[kshields72]

Thanks for the reply. After some more searching I figured the oiling systems out. The trans lubes itself like a differential with the lower gears sitting in the oil and the oil injector pump runs off engine speed and throttle position to adjust for the correct oil fuel mixture. So they are completely independent of one another.

On another note I have been able to find PW80 fork specs but not 50. I was able to have a friend measure the pistons on his. The 80 forks spec at 26mm diameter and 4.3" travel. The 50 forks measured 22mm diameter and approx 4" travel. There are a few fork seals for sale on eBay that have me questioning this though (only slightly but still) because they are 26mm and claim to be effective for both 50 and 80's of nearly all years. It will be a few weeks until I can measure mine to verify the piston diameter.

My grand plan is to get all new PW80 bearings and races for the stem since the previous owner just "assembled" it as is with cracked races and no bearings. The only issue I see is I'm not positive the frame neck inside diameter was the same on the 80 and 50. Hopefully I can find a Yamaha dealership with both sets of races in stock to measure and compare. Otherwise I will just have to order a new set and hope for the best. And if all else fails I'll just weld the new races to the neck. Either way when I'm done I'll post my results in case anyone is interested in the possibility of larger diameter (read stronger and less likely to bend) forks with damping not just springs.