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GuyGraham

Gearbox Sprocket Oil Seal

13 posts in this topic

WR450F 2008 model

Mines just failed the second time 5500 miles and about 250 hours

First time, was in the middle of a race and only discovered it at the end, and there was only about 200ml of oil left in it (Mid 2010 - approx 50 hours) :jawdrop:

Replaced it with Gen Yam seal and spacer even though there was no visible wear on the spacer

Just discovered its started to leak again today

No oil loss this time, as looks like its just started to leak, as its oily around the sprocket which isn't chain lube

At £20 for a pop for the seal I expect better from Yam

Looks also like I will be replacing it every year now, as an oil seal failure results in the engine oil leaking out (as the oil is under pressure behind this seal) and that'll end in tears!

Last time it failed, I also bought some off the shelf oil seals of the correct size as I had intended to use them if it ever failed again, but when the Gen Yam seal arrived, I noticed its not a normal oil seal - its got direction arrows moulded into to show direction of rotation, and ribs moulded onto the lip at 45 deg, plus the lip is longer.

With so much at stake if it fails, I never tried the off the shelf seals

Anybody else had any failures, or using just a bog std off the shelf oil seal with success

Edited by GuyGraham

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I have never seen one of these fail that was not a result of a too tight chain. I am always surprised to see so many improperly adjusted chains when I go riding with a group.

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There should not be any significant pressure behind the counter shaft oil seal. That's the purpose of the crankcase breather.

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Next time you fit a seal- put RTV silicone around the OD of the seal. This helps to keep em sealed.

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I have never seen one of these fail that was not a result of a too tight chain. I am always surprised to see so many improperly adjusted chains when I go riding with a group.

I run 50mm chain slack (measured with a rule, not guessed)

everytime I adjsut the chain I also take the lower shock bolt out and confirm the chain is not to tight all through the suspension movement, by moving the rear wheel up and down whilst checking the tenison

Done this again, and got 10mm lsack at the tightest point (ie mid travel)

I am absolute 100% that my chain is not too tight

There should not be any significant pressure behind the counter shaft oil seal. That's the purpose of the crankcase breather.

I don't think you understand the lubrication system of the engine

Oil comes under pressure, from theoil pump to the cavity behind the oil seal (the oil seal and the bearing form a cavity), the under then passes through the notches in the spacer and into the output shaft where it goes along and lubricates the gears.

Take you sprocket off, and start your engine - the oil pressure will pop out the spacer that the seal runs on

Next time you fit a seal- put RTV silicone around the OD of the seal. This helps to keep em sealed.

Good tip, but they leak from the ID, not the OD

After extracting the seal, I found grit trapped in it, presumably from all the times its been caked in mud and dirt has got in and caused the leak, much like leaky fork seals cause by dirt trapped in them, which can be rectified by the the feeler gauge trick to remove the offending grit and then the seal stops leaking until the next time dirt/grit gets trapped in it and they leak again

Must admit I don't take the sprocket off to clean around the seal lip and riding in the mud, when its becomes absolutely caked solid around the sprocket, but I think it may be worth while doing this rather than relying on the jetwash and a rag to clean it out

Edited by GuyGraham

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Being a dry sump engine what you're saying makes sense but I still can't believe there is that much pressure on that seal.

One of these days I will try your experiment. Not today though.

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Mine was broken four months ago as the cover plate was torn and too much dirt get in between the cover plate & the seals. I went to the auto part store and find the same seals (in specifiactions) for a Suzuki truck, only $5/pc. So far, no leaking, eventhough I haven't changed the cover plate yet.

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Are you running the stock countershaft sprocket that has a rubber seal glued to the sprocket? Or, an after market one that's just plain steel?

I hear the OEM ones can actually trap more dirt behind them than they repell.

Edited by DrFeelGood

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Running a JT front sprocket which is just plain steel with no rubber bushing

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i know my 99 WR400 is a lot old than yours. but someone on this thread my be able to help me. My front sprocket seal is leaking. and i was wondering if anyone know what the part number is so i can order one , or the dimensions are so i can buy an off the shelf one. 

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7 years of muddy/sandy/deep water crossings and I have yet to have ONE seal fail on my bike. I'd be inspecting the shaft for burrs/wear, seals should not fail like that.

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Being a dry sump engine what you're saying makes sense but I still can't believe there is that much pressure on that seal.

 

 

There is the full pressure of the lube system under that seal, yes.  Also under the seal on the clutch arm. 

 

To the OP, sounds like a dirt related problem.  Be sure that the seal cover, PN 2S2-17471-00-00 is in place (item 34 on the transmission page).  It's a sheet metal cover to help keep the mud balls and trail weeds out of the output seal. 

 

And don't adjust your chain too tight.

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grayracer - had another fail this year. Metal cover is in place.

 

 

 

Sussed it out that its dirt related  or rather dried mud - looks like I need to remove sprocket and clean it well after riding in muddy clay conditons coz it just gets jam packed tight in there with mud and gets under the seal causing it to leak

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