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#841063 02/25/21 3:53 am
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Does the seal only go in flush with surface of the case? Any special install procedures required?

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Yes and No.

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Well that's what I do.

There is some contention about whether the flat face faces toward primary drive or towards the middle of the crankcases. I've seen it written here that the flat face goes toward the centre of the crankcases.

The workshop Manual is obtuse and uninformative on this saying "with the knife edge always towards that part which is to be sealed"

I have always put flat face to primary, but I keep losing primary oil. As I run a crank-vent which probably generates a vacuum in the crankcases I'll be trying the flat face in next time around.

I always put a bit of loctite sealant on it as the seal is a bit loose in the crankcase, but this is probably futile I suspect.

People with more practical experience of this will chime in soon.

Cheers
Ray


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I install the drive side crank seal with the lip and spring facing the the primary. Works fine, Been doin it this way for over thirty years. If the timed breather is working properly the crank case should be below atmospheric pressure , as the primary case heats up it becomes positive with respect to atmosphere, it should be vented either with the stock chain oiler ,or if this is deleted, a drilled inspection cap.


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I have always installed the oil seal with the open end to the crank cases, the solid end to the primary. This is how the factory did it when I split the crankcases of a couple of engines from new bikes in the early 70's. This is so when putting the distance piece (part no 68- 686 or 68-687) onto the crank shaft and pushed into the oil seal it doesn't tear or catch the lip of the seal. I don't suppose it makes that much difference as a lot of the racing people don't put one in and use the primary to let the engine breath. If you have a parts book and look at the oil seal there you will see the picture shows the metal spring facing the crank shaft.

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the lip and spring should be toward the pressurized side (crankcase) so the pressure will tend to compress the seal against the shaft. if installed the opposite way, the pressure will tend to expand the seal slightly away from the crank allowing for leakage


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I was taught many years ago that the spring faces the oil you want to keep in.


VicCyclone

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Originally Posted by VicCyclone
I was taught many years ago that the spring faces the oil you want to keep in.

And when there’s oil on both sides?


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Originally Posted by triton thrasher
Originally Posted by VicCyclone
I was taught many years ago that the spring faces the oil you want to keep in.

And when there’s oil on both sides?

which way is the oil most likely to want to travel, from the higher pressure side to the lower


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Originally Posted by Thunderlizard
Originally Posted by triton thrasher
Originally Posted by VicCyclone
I was taught many years ago that the spring faces the oil you want to keep in.

And when there’s oil on both sides?

which way is the oil most likely to want to travel, from the higher pressure side to the lower

Agreed, if your building a bantam you want the spring side towards the crank, that way your keeping the Crankcase pressure in the engine. Its the air pressure against the lip that keeps it sealed.


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Either way round works, once your rings are knackered its best if the lip is towards the crankcase.
interesting that the factory had no faith in the timed breather and the WSM completely omits any mention of the seal orientation.


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Originally Posted by VicCyclone
I was taught many years ago that the spring faces the oil you want to keep in.

Totally correct ! . the lip faces the oil being retained ( in the crankcase ) , that is how "knife edge" oil seals work that is why the lip on them is on an angel ...thats what i did in 40 years in the engineering trade anyhow

best way to fit them is if you ca find a peice of tube around the right size so you can drift them in square , use plenty of grease on the od of the seal and the id of the hole it goes into


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