Tough technical questions

1. The application is to install a rotary shaft oil seal in an aluminum
housing. The configuration of the seal is with a rubber coated outside
diameter. The fit in the bored housing is a light push fit. I suspect the
seal will work loose on its own during service. What is the best way to
install this seal? Options I've considered include replacing this seal
constructed with a metal o.d., but this is not normally recommended due to
the high coefficient of expansion. A more promising solution is to "glue"
the seal in with Loctite 495, cyanoacrylate adhesive. Will that work?

2. The problem is installing a chain sprocket onto a keyed tapered shaft
which is then secured with a retaining nut. What is the best practice:
Install on clean and dry taper, install on greased taper, or apply a high
strength Loctite 272 to the taper before assembly? The idea is to make a
good assembly but be able to disassemble with no more than a puller without
heat. Am I correct in assuming that the key is designed for indexing but
the torque is taken up by the taper? If the taper is greased, removal is
easy, but the torque might be passed on to the key and cause localized
stress and failure. Clean and dry I think is the standard way of assembly,
but Loctite application may be in common practice too.

 

Loctite 609 would be a better choice, IMO. 495 is just common super glue,
and would probably not be suitable for use on oil seals.

Yes

If the taper is greased, removal is

I agree with the "clean and dry". If you are worried about it loosening on
the shaft, you could always heat the sprocket in a pan of water before assy,
then immediately torque the nut down. A little 242 on the threads would keep
the nut from loosening.
H

 

I would clean the parts and then add a thin layer of grease. Then torque
the bolt to specs. Even with gease, you will need a puller to get the
sprocket off. Because it is a tapered press fit the sprocket will still
move a bit up the taper.

 

I don't have an answer for the specific application, but from a
design/engineering standpoint, I would follow the written procedure as
far as grease or no grease. I say that because, unless there is a
positive stop (a step), the stresses on a tapered fit will go up maybe
an order of magnitude or more for the same bolt/nut torque, possibly
stretching or breaking the sprocket if it was not designted for that
stress (i.e., if it was designed assuming no grease).

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')

 

FYI....."cyanoacrylate" = Super Glue. while superglue bonds a lot of low
stress applications, I do not think that the brittle properties of that
adhesive will accomplish your desired task.

As far as I know the dry taper and the keyway is all you need. As long as
the keyway fits snug into the shaft, part of it's purpose is to prevent
rotation.

 

I suppose a seal with a slightly larger o.d. is not available? that
would be the ideal option. The seal ought to need to be pressed or
lightly hammered in to have any hope of reliable retention.

FWIW the standard practice for dealing with tapered-end rear axles
with separate hubs (commonly used on Studebaker, AMC and others) is to
install them clean and dry. They require a lot of force to separate
when torqued to spec, so no worries there. I have heard tell of
people lubing the tapers and subsequently splitting the cast iron
hubs.

nate

 

Precisely the point I was making.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
adddress with the letter 'x')