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ddiggerr
03-03-2015, 08:39 PM
I am trying to find out if there are any differences in this gear between certain years

211505

The part numbers are almost identical except for the first three digits ....

YT175

'82 = 5V7-16111-00-00
'83 = 20E-16111-00-00

YT125

'80 = 4FU-16111-00-00
'83 = 4FU-16111-00-00

I am trying to figure out if I purchase a gear from an '83 YT175, is it going to fit my '80 YT125 ?

I don't have another gear to compare to, so I thought someone might have come across this in the past.

Thanks

dgm635csi
03-04-2015, 11:27 PM
I do not know the answer to your question with absolute certainty, but I am pretty sure that the primary reduction gears are quite a bit different between the yt125 and yt175. Here is my reasoning:

I've done quite a bit of clutch research lately for my yt175, and some interesting information has presented itself. The yt125 has 16 thrust weight ball bearings inside the clutch assembly, and the yt175 has only eight. The reason the 125 has 16 thrust balls, is because the clutch assembly in most likely spinning quite a bit slower in the 125 even though the engine probably revs higher than the 175. The centrifugal force on the balls is less due to the slower rotation, so in order to make sure the balls produce adequate pressure on the clutch pack for the auto clutch to work and eventually stop slipping as revs climb, they just used more thrust balls in the 125. The reason the clutch assembly rotates slower in the 125 is probably because primary reduction ratio is lower, meaning the gear on the crankshaft is smaller , and the gear on the clutch basket in larger when comparing the yt125 to the yt175. This way they could use the same transmission between both models even though the 125 produces less torque at higher rpms.

Most likely the gear from the 175 would not fit unless you bought both primary gears for the 175, and then your overall reduction ratios would not be well suited for the power characteristics of the 125. Also, you would have to change the clutch, and experiment with removing thrust balls to get the engine to idle in gear and engage properly.

Duncan

ddiggerr
03-05-2015, 02:11 PM
I do not know the answer to your question with absolute certainty, but I am pretty sure that the primary reduction gears are quite a bit different between the yt125 and yt175. Here is my reasoning:

I've done quite a bit of clutch research lately for my yt175, and some interesting information has presented itself. The yt125 has 16 thrust weight ball bearings inside the clutch assembly, and the yt175 has only eight. The reason the 125 has 16 thrust balls, is because the clutch assembly in most likely spinning quite a bit slower in the 125 even though the engine probably revs higher than the 175. The centrifugal force on the balls is less due to the slower rotation, so in order to make sure the balls produce adequate pressure on the clutch pack for the auto clutch to work and eventually stop slipping as revs climb, they just used more thrust balls in the 125. The reason the clutch assembly rotates slower in the 125 is probably because primary reduction ratio is lower, meaning the gear on the crankshaft is smaller , and the gear on the clutch basket in larger when comparing the yt125 to the yt175. This way they could use the same transmission between both models even though the 125 produces less torque at higher rpms.

Most likely the gear from the 175 would not fit unless you bought both primary gears for the 175, and then your overall reduction ratios would not be well suited for the power characteristics of the 125. Also, you would have to change the clutch, and experiment with removing thrust balls to get the engine to idle in gear and engage properly.

Duncan

Great I formation and thank you.

Now, I bought another primary gear from eBay from a Yt175 of an unknown year. It was cheap enough so I purchased. The engine I have has Vin which indicates it is an '80 yt125g. The top end is from a yt175 as it has markings showing engine size.

The whole thing looks pieced together and I couldn't begin to guess what came from where or what.

I am just hoping it runs. It has 16 balls in clutch assembly and a few other differences I cannot determine e what they are from


I will know in a few weeks when parts arrive