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Gearbox pressure #775751 06/06/19 10:56 am
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Mike Baker Offline OP
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Kind of an issue that's not really been solved. I put a good amount of time on the 650 Triumph at NJ a couple of weeks ago so a primary service was in order along with switching out to a bigger front countershaft sprocket for Road America in several weeks.
Previously, I'd get a fair amount of gb oil coming out the little vent hole on the inner cover, made enough of a mess that I thought one of the pit out inspectors might pull my tech sticker. I added a vented plug and dropped back to 350cc oil and that seemed to solve the issue. Now I'm finding that I've got gear oil coming through the mainshaft into the primary. Seems the gearbox is still building pressure. Never had this happen on any other Triumph I've owned but I've not run one as hard as this one either.
I hate to add another hose but I'm thinking it may be time to make up some sort of substantial breather for the GB. Any retired or active Triumph racers experience similar symptoms?
Thanks

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Re: Gearbox pressure [Re: Mike Baker] #775753 06/06/19 11:20 am
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Allan Gill Offline
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whats the gearbox filling cap/dipstick like on those? my A65 used to do this until i cut a deeper groove in the dipstick.


beerchug
Re: Gearbox pressure [Re: Mike Baker] #775795 06/06/19 6:55 pm
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Mike Baker Offline OP
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Not sure what cutting a deeper groove means. Does that allow pressure to be relieved?
There is no dipstick on a Triumph, only a screw plug for filling.
Thanks for taking time to respond

Last edited by Mike Baker; 06/06/19 6:56 pm.
Re: Gearbox pressure [Re: Mike Baker] #775796 06/06/19 7:15 pm
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How sloppy is the fit between the mainshaft and high gear bushing? It’s not quite the same animal but I had this problem on my unit 500 that seems to be caused by a slightly worn mainshaft and loose ‘no ream’ bushings. I fit tight bushings and honed carefully to the low end of the clearance range and it helped a lot.

Chris

Re: Gearbox pressure [Re: Mike Baker] #775797 06/06/19 7:21 pm
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I don't see why, at least from a theoretical basis, you should have much pressure in a gearbox. Its not like the crankcase with the volume changing as the pistons go up and down. I wonder if the problem isn't simply a bad seal between the gearbox and engine. Another thought would be a crack or porous casting in the case between the engine and the gearbox.

Ed from NJ

Re: Gearbox pressure [Re: Mike Baker] #775801 06/06/19 7:56 pm
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You don’t need pressure to make the gearbox leak into the primary. It gets along the sleeve gear bush, as said above.

It’s not usually enough oil to matter very much.



Amateur Loctite enthusiast.
Re: Gearbox pressure [Re: Mike Baker] #775811 06/06/19 10:42 pm
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Mike Baker Offline OP
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Agree with you, Ed. Cannot imaging how this can be pressurized but the fact is that it pukes out oil. I'm going to replace the mainshaft clutchrod bushings and the high gear bush. Both items have some slop. The oil is not coming out the high gear bush, but rather through the mainshaft clutchrod drilling.
Have to think that a porous or cracked casting is a stretch but who knows? This motor is anything but stock, guess that opens all possibilities

Re: Gearbox pressure [Re: Mike Baker] #775827 06/07/19 6:30 am
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triton thrasher Offline
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Can you see the gearbox oil level?

If it reaches 1/3 of the way up the timing side end of the layshaft with the bike upright, that’s enough.

It just occurs to me- you’re not using automatic transmission fluid or somesuch runny nonsense in the gearbox, are you?

I’m not arguing against replacing worn bushes though.


Amateur Loctite enthusiast.
Re: Gearbox pressure [Re: Mike Baker] #775833 06/07/19 10:26 am
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Mike Baker Offline OP
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Not sure about where exactly 350cc puts the level. I'll pay some attention to that on reassembly. I did notice some evidence of lack of lubrication where the mainshaft rides the right hand bearing. Perhaps 350 isn't enough. I use Redline shockproof lightweight. I had considered whether or not it might be too thin. Plan to use heavy in it now.
This bike is very similarly built to Jake's.Main difference is the engine breather. He's using the stock late breather, mine is through the front mount. Wondering if I could be pulling a vacuum in the primary somehow that could suck oil through the mainshaft...

Re: Gearbox pressure [Re: Mike Baker] #775836 06/07/19 11:27 am
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Mike, what brand oil are you using? I might be reluctant to lower the gear box oil level...Maybe a 3/8 vent hose is a good idea...


79 T140D, 96 900M Ducati ....On a bike you can out run the demons..
Re: Gearbox pressure [Re: Mike Baker] #775840 06/07/19 12:14 pm
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Allan Gill Offline
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Originally Posted by Mike Baker
Agree with you, Ed. Cannot imaging how this can be pressurized but the fact is that it pukes out oil.



Not sure how hot it gets in a triumph gearbox but as it heats up the pressure will automatically increase... another thing to note is that IF there is too much pressure and there is presence of moisture then the oil will degrade until the additives fail, then it would have as much protection as water.... The process would be accelerated with engine oil because of the higher pressures and heat in certain areas but the princilpes are the same if there is a lack of ventelation.

As a note is the oil turning milky at all?


beerchug
Re: Gearbox pressure [Re: Mike Baker] #775842 06/07/19 12:47 pm
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Mike Baker Offline OP
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Redline shockproof lightweight, Tony. After seeing the bearing, I will run it with 500cc now.
Alan, the bike gets serviced regularly after races. There is no water in the gearbox. I too have considered the effect that heat has on a "closed" system.
A 3/8" breather has been cut into the inner cover.
The more I think about this, the more I lean toward going back to the stock engine breather. I initially modified things because I like to use lighter syn oil in the primary. But with a 1 way valve on the breather hose and the motor running a lot of rpm's maybe it's pulling enough vacuum in the crankcase to overcome the crank seal. Dunno. Big experiment.....

Re: Gearbox pressure [Re: Mike Baker] #775846 06/07/19 2:16 pm
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Do you feel the Shockproof is a good oil as in it gives better gear action?? Maybe try a Redline 85-140 GL4..?..


79 T140D, 96 900M Ducati ....On a bike you can out run the demons..
Re: Gearbox pressure [Re: Mike Baker] #775848 06/07/19 2:30 pm
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are you running a seal around the crankshaft sprocket up front? maybe it's messed up and the crankcase is pulsing in and out through the primary, which transfers the pressure changes to the mainshaft drillway. how are you venting the motor and the primary?

wait, you answered that.

i don't mess with timed breathers. i just run an open tube from whatever needs to be vented, long enough that the pulsing is a lesser volume than the hose.

run the motor with the primary filler cap off, and hold a piece of paper over the hole to see whether it gets sucked down. if it does, you've got vacuum in the primary.


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Re: Gearbox pressure [Re: Mike Baker] #775850 06/07/19 3:06 pm
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Is the gearbox breather hole in the upper front of the inner case open?

Re: Gearbox pressure [Re: Mike Baker] #777159 06/24/19 11:06 am
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Mike Baker Offline OP
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Update- All back together now, New bushings in the high gear and mainshaft clutch pushrod. Worn but I don't think they were the cause of the problem.
I think the gear oil migration was due to the crankshaft seal installed with the spring toward the crankcase. I think that with the Mike's XS valve and high RPM's that there was enough vacuum in the crankcase that the seal as installed didn't work. Created a vacuum in the primary, and emptied the primary and gearbox into the motor. Seal is now installed with the spring out. I've also opened up the old 71 style primary breather and added a breather to the gearbox. The hope is that now the only vacuum will be in the motor. 4 weeks till Road America and if the the stars align and the creek don't rise, Ginger Man the weekend after.

Re: Gearbox pressure [Re: Mike Baker] #777203 06/24/19 10:30 pm
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Keepin' our fingers and toes crossed for you. Shiny side up, and all that.


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