Synthetic gearbox oil

[Johnhenry]

I've just drained the mineral oil from my MZ ETZ251 and re-filled with Fully synthetic gearbox oil and I must say after a few rides the gearbox and gearchanges feel much smoother.
The clutch doesn't slip as I was told it would and I may now do the same with my ETZ125.
I always use fully synthetic two stroke oil in my MZ's - and Jawa and Kawasaki Triple - and Super Unleaded fuel with an ethanol stabiliser.

[Puffs]

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[Blurredman]

Ta for sharing your experience.
I just saw that I had put synthetic 10W/30 Gear oil in my YZ, but I cannot remember any significant difference with the previous oil. At least not with those boots.

Indeed, I have seen some warnings that synthetic oils can promote clutch slippage, and I also use/have used synthetic engine oils in 4 strokes, with a common sump for engine/gearbox/clutch, without clutch problems. I think those warnings are unfounded, and I'm not sure if the synthetic production method really leads to oils giving significantly lower friction than oils produced by the conventional refining process. The rheology might however be less temperature dependent, depending on the specific oils you compare.

What I use also depends on what oil I can suitably buy. Further to what I said in the other thread on 2T Oil (http://mzriders.com/viewtopic.php?f=5&t=9279), I have, in the past, run my ETZ251 on a fully synthetic 2T oil for about 20k miles, and I still lost the small end bearing. So using a fully synthetic 2T oil does not guarantee you won't get engine failure. Maybe it reduces the risk, and maybe it reduces wear, but that you pay more is a certainty. And that you get less carbon too, IMO. In my old two strokes (ETZ251 + 634) I currently use a semi synth I could cheaply buy a batch off, and that seems to work fine too (& also little carbon). In my 2T MX & enduro bikes I have always run a fully synthetic. There I choose to do whatever I can to prevent a DNF & costly repair, hang the expense. If it really helps is another matter.

OP: How old and what grade was the old oil?


Puffs: I don't think semi or fully synthetic oils create slippage either. Which leads only to the additives. That being said- I always use 20w50 Mineral oil in my Honda, because I am sure not to get slippage.
Previously to owning the honda, I could normally stickthe same 10w40 semi i put in my car, into my bike- no slippage. I did that to the Honda.. Slippage. Perhaps the old clutch plates were of dubious age, and also the springs themselves. I have never however put anything but 20w50 for fear of ruinning the clutch, despite my replacement parts and increased strength springs.

In reality, you should really replace oils twice a year, as has been recommended on vehicles since the dawn. But who does that these days? - And.. I never did..

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[Blurredman]

I agree. You must stick with manufacture recommended, unless you know best of course

My Honda's original spec was 20w50 in 1978. Which, to be honest- was one of only a handful of oils you could have easily got. Others being SAE30 etc.

Interesting theory about the lower viscosity oil reducing slip. I only use 20w50 because I know it would work.. The engine's on 83k miles now, and at least the last 30k has been on 20w50, in my ownership. Perhaps I should put 10w40 in though? I can't decide.. When the engine is cold- and- I have to bump start it (perhaps the battery is dead), the clutch drags very much so. Infact- The clutch biting point is significantly different cold than warm- The clutch is hard and stiff when cold- light and soft when warm


My Mz's clutch slips a bit mid-rpm full throttle occasions. But.. it is due an oil change- And- seeing as I currently have 20w50 in it. I do have 80/90SAE ready to go.


As for 4t re-use over 2t. Surely 4t oil would have a lot of soot and particules extremely fine in it, perhaps that is why it doesn't split for you. After all- that's what makes it black, surely? Blowby?

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[Blurredman]

The original specs when it came out stated 20w50, 10w40, 15w40