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ST90 vs SAE30 gearbox oil

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

ST90 vs SAE30 gearbox oil

Postby Hughieboy » Fri Jun 14, 2019 5:14 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.
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Re: ST90 vs SAE30 gearbox oil

Postby Scooterdude » Fri Jun 14, 2019 5:26 pm

I run a Readspeed 5 plate on ST90 no problem.
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Re: ST90 vs SAE30 gearbox oil

Postby Hughieboy » Fri Jun 14, 2019 5:43 pm

Scooterdude wrote:I run a Readspeed 5 plate on ST90 no problem.


Thanks, you’ve made my day :D . What motor are you running?
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Re: ST90 vs SAE30 gearbox oil

Postby Scooterdude » Fri Jun 14, 2019 6:30 pm

Hughieboy wrote:
Scooterdude wrote:I run a Readspeed 5 plate on ST90 no problem.


Thanks, you’ve made my day :D . What motor are you running?

RT 225
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Re: ST90 vs SAE30 gearbox oil

Postby rossclark » Fri Jun 14, 2019 10:03 pm

Same
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Re: ST90 vs SAE30 gearbox oil

Postby ToBoldlyGo » Fri Jun 14, 2019 10:33 pm

I'm using Silkolene medium gear oil in a couple of my engines. Works very well. I don't think it's quite so viscous as the ST90 and you can feel the difference without compromising the performance.
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Re: ST90 vs SAE30 gearbox oil

Postby Hughieboy » Fri Jun 14, 2019 11:20 pm

Think I’ll go with the ST90 for a few hundred miles until the kits run in then maybe change to the SAE30.... I can’t just waste it and it’ll need an oil change then anyway...
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Re: ST90 vs SAE30 gearbox oil

Postby Scooterdude » Sat Jun 15, 2019 8:59 am

Hughieboy wrote:Think I’ll go with the ST90 for a few hundred miles until the kits run in then maybe change to the SAE30.... I can’t just waste it and it’ll need an oil change then anyway...

SAE30 is to thin for a Lambretta. Also you will be surprised how thin the ST90 goes once warm.
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Re: ST90 vs SAE30 gearbox oil

Postby Fast n Furious » Sat Jun 15, 2019 8:01 pm

Scooterdude wrote:
Hughieboy wrote:Think I’ll go with the ST90 for a few hundred miles until the kits run in then maybe change to the SAE30.... I can’t just waste it and it’ll need an oil change then anyway...

SAE30 is to thin for a Lambretta. Also you will be surprised how thin the ST90 goes once warm.

That's because the weight ratings of these 2 oils are at different temperatures.
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Re: ST90 vs SAE30 gearbox oil

Postby Scooterdude » Sat Jun 15, 2019 9:14 pm

Fast n Furious wrote:
Scooterdude wrote:
Hughieboy wrote:Think I’ll go with the ST90 for a few hundred miles until the kits run in then maybe change to the SAE30.... I can’t just waste it and it’ll need an oil change then anyway...

SAE30 is to thin for a Lambretta. Also you will be surprised how thin the ST90 goes once warm.

That's because the weight ratings of these 2 oils are at different temperatures.

Yes that’s right.
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Re: ST90 vs SAE30 gearbox oil

Postby Hughieboy » Sat Jun 15, 2019 10:26 pm

Thanks fellas... I’ll stick with the ST90 and see how it goes :P
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Re: ST90 vs SAE30 gearbox oil

Postby Kev Fox » Mon Jun 17, 2019 9:44 pm

Scooterdude wrote:
Hughieboy wrote:Think I’ll go with the ST90 for a few hundred miles until the kits run in then maybe change to the SAE30.... I can’t just waste it and it’ll need an oil change then anyway...

SAE30 is to thin for a Lambretta. Also you will be surprised how thin the ST90 goes once warm.

I put SAE30 in my Model D which is correct I believe. In a GT186 I would use ST90 as suggested.
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