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Old Forks and Oil

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Suntan Sid
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Joined: 07 May 2009
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PostPosted: 13:12 - 06 Jul 2018    Post subject: Old Forks and Oil Reply with quote

I have just replaced the fork oil seals on my puny project bike, (show and tell update soon), here is a diagram of the fork internals:-

https://images.cmsnl.com/img/partslists/yamaha-gt80-1975-usa-front-fork-front-fender_bigyau0819c-4_c577.gif

On this particular bike there is only one fork spring, the other fork leg has no spring just a simple damper.
In the service manual it specifies the quantities of oil for each leg, 90cc in the l/h fork and 120cc in the r/h fork.
Logic dictates that I should be putting more oil in the fork leg without a spring and less in the fork leg with a spring.
In the service manual it merely gives l/h and r/h quantities but doesn't specify which fork has the spring in.
To confuse me even further, the previous owner had marked the fork legs "left" and "right" the right leg had the spring in.
So is my logic correct, do I put more oil in the leg with no spring?
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fatjames
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PostPosted: 14:08 - 06 Jul 2018    Post subject: Reply with quote

What bike is it? Although, I'm not sure I can google any better than you..
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Nobby the Bastard
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Joined: 16 Aug 2013
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PostPosted: 15:09 - 06 Jul 2018    Post subject: Reply with quote

As the exploded picture has the lhs exploded and displaying a spring, I'd assume the spring is supposed to go in that side.

Edit: If you look at the drain screw, it should be on the front, but it's on the back of the exploded view so RHS.

Edit 2: Do they both have as drain screw at the bottom?
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temeluchus
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PostPosted: 18:16 - 06 Jul 2018    Post subject: Re: Old Forks and Oil Reply with quote

Suntan Sid wrote:
So is my logic correct, do I put more oil in the leg with no spring?


No. The spring takes up some of the free volume in the fork, so I would think the smaller amount would go in that fork.
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Ed Case
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PostPosted: 18:42 - 06 Jul 2018    Post subject: Reply with quote

Been into bikes for decades but never come across front forks with only a spring in one leg, have you removed the fork cap on the supposedly 'empty' leg to check ?, I certainly would.
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Suntan Sid
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PostPosted: 20:32 - 06 Jul 2018    Post subject: Reply with quote

fatjames wrote:
What bike is it? Although, I'm not sure I can google any better than you..


The bike is a Yamaha GT50, you can see it in this thread:-

https://www.bikechatforums.com/viewtopic.php?t=323620

Nobby the Bastard wrote:
As the exploded picture has the lhs exploded and displaying a spring, I'd assume the spring is supposed to go in that side.

Edit: If you look at the drain screw, it should be on the front, but it's on the back of the exploded view so RHS.

Edit 2: Do they both have as drain screw at the bottom?


No there are no drain screws, the only way to drain the forks is to remove them from the bike and hold them upside down. unfortunately I can't find an online diagram for the specific model but, I know for a fact, (I have a hard copy of the Official Yamaha parts list that covers the 50cc and 80cc versions), that they are the same as the diagram, apart from the drain screws.

Ed Case wrote:
Been into bikes for decades but never come across front forks with only a spring in one leg, have you removed the fork cap on the supposedly 'empty' leg to check ?, I certainly would.


Yes, there is only one spring, that's the way it came from the factory!

temeluchus wrote:
No. The spring takes up some of the free volume in the fork, so I would think the smaller amount would go in that fork.


Err, that's what I was alluding to, less oil in the fork with the spring, for the reason you stated..
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temeluchus
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Joined: 01 Oct 2008
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PostPosted: 23:00 - 06 Jul 2018    Post subject: Reply with quote

Suntan Sid wrote:
Err, that's what I was alluding to, less oil in the fork with the spring, for the reason you stated..


Oops misread that entirely for some reason. Probably the heat.
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