Crankshaft seal question

10drum

10drum

Joined
May 10, 2020
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Greetings,

I have a question about the primary side crankshaft seal on a 72 750 Interstate equipped with a CNW starter and dry primary.

I replaced the seal as the old one was, when installing the starter and primary, and as shown in the parts book, with the spring facing out toward the primary. There has always been some oil seepage into the primary. With a wet primary it would not be noticed.

If the bike sits for a week or more and wet sumps, it'll puke oil some oil when started. Seems to me that if the seal was installed with the spring facing inward toward the crankshaft it would seal properly. To do that I'd risk damaging the seal on the crankshaft shoulder.

Has anyone installed the seal with the spring facing in, if so how was it done?

Thanks for all replies,

Phil
 
What crankcase breather arrangement do you have? A reed valve breather is excellent for reducing crank case pressure. Excess crankcase pressure will certainly cause blow by past the PTO seal.

Your bike obviously wet sumps… you should drain the sump before starting after sitting for a prolonged period if you want to give the PTO seal an easier life. A sump that’s full of oil puts immense pressure on that PTO seal.
 
10drum said:
Greetings,

I have a question about the primary side crankshaft seal on a 72 750 Interstate equipped with a CNW starter and dry primary.

I replaced the seal as the old one was, when installing the starter and primary, and as shown in the parts book, with the spring facing out toward the primary. There has always been some oil seepage into the primary. With a wet primary it would not be noticed.

If the bike sits for a week or more and wet sumps, it'll puke oil some oil when started. Seems to me that if the seal was installed with the spring facing inward toward the crankshaft it would seal properly. To do that I'd risk damaging the seal on the crankshaft shoulder.

Has anyone installed the seal with the spring facing in, if so how was it done?

Thanks for all replies,

Phil
Click to expand...
The spring goes towards the engine, not primary! I've never seen a Norton any other way! It's almost guaranteed to leak into the primary if the spring is towards the primary.
 
marshg246 said:
The spring goes towards the engine, not primary! I've never seen a Norton any other way! It's almost guaranteed to leak into the primary if the spring is towards the primary.
Click to expand...
I agree, however the parts books shows it installed the other way, and usually when a seal is to be installed over a shoulder that is not beveled a cone is used to install the seal. I could possibly have a cone made???

I am going to replace the seal & see if I can get it to slide over the shoulder hopefully without damaging it. I'l buy two seals just in case.

Thanks for the reply.
 
10drum said:
I agree, however the parts books shows it installed the other way, and usually when a seal is to be installed over a shoulder that is not beveled a cone is used to install the seal. I could possibly have a cone made???

I am going to replace the seal & see if I can get it to slide over the shoulder hopefully without damaging it. I'l buy two seals just in case.

Thanks for the reply.
Click to expand...
There is no problem fitting the seal over the shoulder.
 
10drum said:
I agree, however the parts books shows it installed the other way, and usually when a seal is to be installed over a shoulder that is not beveled a cone is used to install the seal. I could possibly have a cone made???

I am going to replace the seal & see if I can get it to slide over the shoulder hopefully without damaging it. I'l buy two seals just in case.

Thanks for the reply.
Click to expand...
The crankshaft has a taper (super bevel)! Nothing needed!
 
marshg246 said:
The crankshaft has a taper (super bevel)! Nothing needed!
Click to expand...
Seemed like a sharp edge, and since the one that was in there perhaps was backwards. I also ask an old-timer and he told me that's how he's always installed it. IDK I'm going try to install it this time with the spring toward the crank shaft.
 
10drum said:
Seemed like a sharp edge, and since the one that was in there perhaps was backwards. I also ask an old-timer and he told me that's how he's always installed it. IDK I'm going try to install it this time with the spring toward the crank shaft.
Click to expand...
This is not Norton specific.

Oil seal basics 101.
 
BTW, all Norton seals go with the spring towards the oil you want to keep in. Even the timing side camshaft seal in the timing cover which makes it difficult to install since you're pressing/hammering on the thin metal.

I would not be far off saying that ALL seals with springs go with the spring towards the oil you want to keep in.

If you're just relying on a "old timer", I like most here are "old timers" :)
 
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Reactions: TBW
L.A.B. said:
He wasn't a Triumph old timer by any chance.
Crankshaft seal question
Click to expand...
Ya, before they breathed through the primary, Triumph wanted the seal to keep the primary oil out of the crankcase. Of course, that still meant that the spring went towards the oil you wanted to keep in. I did it "wrong" for a long time and put the spring towards the crankcase.
 
Easy answer is spring side towards pressure. No need for "How could you get it wrong " etc. Keep trying, cheers Roy.
 
L.A.B. said:
He wasn't a Triumph old timer by any chance.
Crankshaft seal question
Click to expand...
Well yeah, I guess I'd be a triumph old timer as well. Triumph, Norton, BSA, Yamaha, Honda, dealership/shop since 1962. Carl Donnelson, Donnelson cycles in STL. I like that image, where is it from? I don't think I've ever seen it.
 
The yaki said:
Easy answer is spring side towards pressure. No need for "How could you get it wrong " etc. Keep trying, cheers Roy.
Click to expand...
Yes, I know that, 35years as a Industrial electrical-mechanical technician, built thousands of hydraulic cylinders. That's why thought it was strange the parts manual showed the seal the other way.
 
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