Gearbox/transmission Oil

Hey there,


I'm new to this whole "bike mechanic" thing and I'm trying to slowly learn. I have a friend that works on bikes a lot, and is very helpful, but he also have 3 kids. So, since it's 10pm I figured I'd ask on here. It might be kind of a stupid question, but that's how I'm going to learn.


It's my understanding that I need to check/change the Gearbox oil from time to time. The Yamaha RD350 Owners manual lists it as a necessary maintenance step; however, I'm not finding out in there any more specific detail than that.


I guess first off, is "gearbox oil" and "transmission oil" referring to the same thing? It seems to be. If it's not, what's the difference, and do I need to check/maintain oil levels for both of them?


It's the little cap on the right side of the engine near the kick starter... at least, that's where you "check" or "fill" the oil when it's needed. From my understanding to check the oil level, you should start the bike for a few minutes to let it warm up, then let it cool down and wait for a few minutes before checking the oil. The dip stock is not very helpful either. It's black, has a a couple lines on the very bottom w/o any words. Now, I'm assuming between those two lines is where you want to be.... then again, it's sorta confusing because the space between the lines isn't very big, and it doesn't go up very high on the dipstick.


I guess I'm just looking for more info on maintaining the proper oil levels outside of the premix I'm running on my RD350. The info in the manual isn't seeming to give me what I need, or I can't find it. Anyways, any information on maintenance for the RD350 oil levels would be very helpful. As this is my first bike, and I want it to stay with me for a long long time, I'd like to have a very clear understanding of how to take care of it. Thanks in advance for any information.

I did find this, and this is at least a good picture, and gives me the proper oil type: http://home.mchsi.com/~xen-uno/RZ-YPVS-RD350-OilPumpAdjust.pdf

Place bike on level ground
Remove dipstick and clean it
Insert dipstick but don't screw it in.
Remove dipstick and look for oil on teh bottom of teh dipstick.

No oil = fill time
Oil higher than the cross hatched area or lines means too much oil.
Oil on that bottom bit only = perfect.

Low oil on an RD = burned dogs and selector forks

Transmission = gearbox. Same thing

If the bike is new to you, drain the oil and refill with 2 stroke trans oil. Some people still use auto oil and that's OK. Try to avoid oils with friction modifiers which are not good for wet clutches. My preference is Honda oil for CR 2 strokes. It's rated at 80/85wt which is roughly the same viscosity as a 20W50 multigrade.

Under the motor there are two main large bolts. One is the drain bolt and the other holds the detent spring in place. try to remove the correct one.

My favorite transmission lube for a two stroke is Mobil 1 75W-90 gear oil. A good higher viscosity engine oil is OK too. 15W-50, or 20W-50 is fine. You can use a non-synthetic gear oil, too. It's not too picky. Back in the '70 when I was racing 2-strokes, I found that 90 wt gear oil gave me better clutch hook-up than motor oil in the tranny.

As was mentioned, avoid any oil labeled as "energy conserving." They may cause clutch slippage because of the molybdenum friction modifiers.

Oil level is not very critical, and under normal conditions it does not change level once filled. The only place the oil can go is if it leaks out, or the crank seal between the primary pinion gear is leaking, and sucking transmission oil into the engine. Either condition should be noticeable, so the level rarely needs to be checked.

A good synthetic gear oil in the transmission is good for 10,000 miles, and there should be no change in oil level during that time.

Oil threads are always amusing. My race bikes all get Motul or Silkolene when I can get it from the Silkolene store in TX.

I do have some ZERO weight trans oil here that we used in a TZ with no ill effects. I have no idea where it came from but it's clear golden oil and "feels" thinner than the Honda red lube but not excessively thin.