ST90 vs SAE30

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Hughieboy
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Fri Jun 14, 2019 4:10 pm

I'm sure this has been answered 1000 times but I can't find it...

I have recently built a small block GT186 motor, my first build and all is running well but the clutch slips a little when you give it the beans. It currently has a Surflex 4 plate clutch that's been in for a few years so I decided to upgrade to a Readspeed 5 plate clutch as they seem to get good reviews.

However, sitting on the side at after 4pm on a Friday (great timing) I currently have a new bottle of ST90 gear oil but Readspeed recommend SAE30. I'm not an oil expert, I guess this is to do with viscosity but of course being the weekend I want to get on with it and I doubt I will buy that in Halfords... plus I have the new bottle of ST90 already purchased, less what went in when the build was finished last week before discovering the clutch slippage.

Can someone more knowledgeable than I tell me whether this is just a recommendation or if it's essential to correct operation? I don't want to mess things up obviously but would prefer not to have to wait another week if it's not essential. Being a bit of a shed numpty spanner twiddler I don't fully understand or appreciate the difference/importance.

Thanks.

Mrnice71
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Fri Jun 14, 2019 8:32 pm

Firstly readspeed recommend Putoline SAE 90 , its says on the bottle special lambretta gear oil and l have found this to be by far the best gear oil , also make sure u give the plates a good soak in the oil preferably over nite , and ruff the steels also . What springs are u using ?

mick1
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Fri Jun 14, 2019 8:59 pm

Doesn't really answer the question .

Is ST90 a compatible replacement ?

Interesting, i'ld like to know as well.

Scooterdude
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Fri Jun 14, 2019 9:37 pm

ST90 and SAE90 are one and the same.

fairspares
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Sun Jun 16, 2019 3:41 am

ST 90 gear oil is ok to use with standard plates however it contains additives that are not suitable for race type clutch plates eg Surflex red and green , Readspeed red plates etc and if used will cause the plates to slip. A basic SAE 90 gear oil does not contain the additives that effect race type plates . Westways SAE 90 gear oil available on ebay is a good one to use with race plates but can be used with all other standard type plates also.
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rosscla
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Sun Jun 16, 2019 10:41 pm

Exol do a straight SAE90 non EP gear oil. Available also on EBay or from Lubetech.
"Our dilemma is that we hate change and love it at the same time; what we really want is for things to remain the same but get better."

warts
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Tue Jun 18, 2019 10:25 am

Anyone ever tried ATF? It works in a much higher stress environment than even the most powerful scooter. ie several hundreds of hp's and lbsft torque while gripping enough to move a couple of tons of slug like cars. Probably higher temps too.
Lots of wet clutch like action and gears too.

Different grades, some I think not suitable for brass like metals.

Warkton Tornado No.1
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Tue Jun 18, 2019 10:30 pm

warts wrote:
Tue Jun 18, 2019 10:25 am
Anyone ever tried ATF? It works in a much higher stress environment than even the most powerful scooter. ie several hundreds of hp's and lbsft torque while gripping enough to move a couple of tons of slug like cars. Probably higher temps too.
Lots of wet clutch like action and gears too.

Different grades, some I think not suitable for brass like metals.
I was deliberately staying out of this discussion, but.....the cat's out of the bag! As the result of owning a Mazda Bongo for a while, I bought more ATF than I needed so tried it in various engines, some without the owners even knowing.

(It does take some getting your head around it, as we tend to think ATF is designed just to slip, but it is also required to 'drive' when used in autos, as well as lubricate all moving parts within)

It works very well IMHO, tends not to deteriorate & stays 'clean' but is also cheap as chips. In fact, a torquey engine that slipped it's six plate clutch quite easily under power with ST90 no longer does so with ATF.

The Bantam racers have been using it for decades, as they have extremely high first gears, with their C/R three speed boxes, that they have to slip their clutches an incredible amount just to get off the line. Some of them actually use oil coolers in conjunction with ATF & steel on steel wet clutches! Then there are the MX riders that often use ATF.

In engines with high 20's BHP (can't quote the torque ATM) it has proved itself to me & a few others :D

warts
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Wed Jun 19, 2019 5:32 pm

Lots of MX people use it too - which was why I posed the question.
Most of the time , it seems they use the clutch as an infinite gearbox - "fanning" the clutch for much of a lap, lap after lap to keep high strung engines in the powerband. Atf is a popular choice for giving a smooth and controlable between slip and grip.
A modern 125 could expect to pop out 35+ HP, 250's approach 50hp.

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db67
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Thu Jun 20, 2019 7:25 am

(It does take some getting your head around it, as we tend to think ATF is designed just to slip, but it is also required to 'drive' when used in autos, as well as lubricate all moving parts within) -- what brand & grade is this oil ? would be interested in using it as an alternative to st 90 thanks ;)

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