T250 motor oil.

[daxman]

Kevin Cameron about ATF, 20-50 etc and highly effective gear oils (GL):
https://www.bilder-hochladen.net/i/bfqr-q4-0315.jpg" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

// You pay the same or even more for ATF, 20-50 or JASO MA specs. oil but receive inferior product (for lubricating transmission gears) compared to simple 80W90 GL4 gear oil.

That is interesting article in respect of race bikes that use dry clutches to put double the normal horsepower through a standard 'box... in the same article is says that gear oil will stuck a wet clutch together. Since I don't yet plan on racing my GT or fitting a dry clutch, if indeed that's possible, I'll stick to the liquid recommended by the manufacturer

[argo1974]

Stuck clutches might have been a special problem using hypoid axle oils back then. I've been using gear oils in my two strokes without any clutch related problems since I started riding motorbikes at the beginning of 90-ties. Why wouldn’t you take advantage of all that extra technology?

E. g. 1968 Suzuki T500 Cobra manual recommends Super Shell Motor Oil or Mobil Super Motor Oil among two stroke oils. Would I fill a four stroke engine oil into Posi Force tank today?
Furthermore, I'm pretty sure Suzuki recommended 20W40 for T250 transmission as it did for T500 Cobra.
The problem, engine oils contain lubricity additives which may cause clutch slippage and lack EP (extreme pressure) additives transmission gears need.

Racing conditions just accelerated otherwise slow but steady wear.

[daxman]

If there is any merit in using a specialist oil just for 2t wet clutch gearboxes then I suspect the benefits to the standard user are marginal - especially when you consider that most of the vintage machines here are used only for a few 100 miles a year and seldom in race conditions.

The benefits for not using it are convenience and cost. The 10W40 JASO (wet clutch) oil I use in the Yamaha 4Ts I have also goes in the GT250 box - in a pinch Id probably use it in the CCi too. It's £4/litre. and if do 500 miles a year for the next 20 years I don't think the box will complain.

If I was running a KR1 or an NS250R I might think differently.

[argo1974]

Just 3 more things to consider:

1) Suzuki started recommending Suzuki Transmission Oil in 1975:
http://www.ozebook.com/compendium/techb ... %201-5.pdf" onclick="window.open(this.href);return false;

2) Modern 2 stroke transmission oils, e.g. Motul 10W30 Transoil, Castrol MTX 75W140, etc. are API GL specs. oils. Not JASO MA.

3) Most modern motocross bikes take SAE 80 GL-4 as by user manual.
Also: https://motocrossadvice.com/dirt-bike-p ... arbox-oil/" onclick="window.open(this.href);return false;

[jabcb]

Learn something new everyday….

The 1975 GT380M owners manual highly recommends “Suzuki Transmission Oil”.
https://www.oldjapanesebikes.com/mraxl_ ... /index.php

A used vintage can of Suzuki Transmission Oil is available on eBay. It’s SAE 80.
https://www.ebay.com/itm/Vintage-Suzuki ... Sws-heu1BE

[daxman]

..I'll take my chances

[Alan H]

Me three. Just put 1500ccs of 20w50 in the gearbox and semi synthetic 2t oil in the tank. Someone needs to remember that they don't mix and '4 stroke engine oil' doesn't come into it.
I go with Suzuki recommendations. End of.

[dollydog]

having read the recommended lubricants section in every suzuki 2 stroke manual i've got - which is a lot - recommended lubricant for gearboxes, or transmissions if you like, is castrol gtx 20/50 or 20/40 engine oil on the odd occasion. one of them does indeed say to use suzuki transmission oil OR 20/50 engine oil. i think you'll find that suzuki transmission oil in the 70's was a completely different animal to what they call suzuki transmission oil in 2020. in the 70's suzuki transmission oil was normal, common or garden multigrade, as in 20/50. i've used it on ALL my gt's and t's since the year dot [1972 and onwards] and i've NEVER had a problem - ever. so i speak from a lot of experience
cheers, dd.