Enlarging a Neoprene Hole

[J Tiers]

You are not telling the whole story. Was this seal exposed to oil for 2 days? Have you removed it, checked for dimensions and compared them with new seal measurements?

This^^^^^^^^^^^^^

No info, no answer.

[Spindle]

Yes, it would be nice to find out what the seal looks like now, compared to when it was put in.

The seal was a "new component" (so was the rod), so presumably it is an OEM part, or an "aftermarket" part. There must be some history about it, from various M/C forums, possibly "reviews" of the product itself (I tend to disbelieve all reviews, they are totally uncontrolled).

If this is a common problem, then it will show up somewhere.

They're all aftermarket which is a major problem. I did make an inquiry at an antique motorcycle site but received no response.

[Spindle]

You are not telling the whole story. Was this seal exposed to oil for 2 days? Have you removed it, checked for dimensions and compared them with new seal measurements?

Yes, oil for 2 days, I don't have any dimensions and it is a new seal.

[mikey553]

Yes, oil for 2 days, I don't have any dimensions and it is a new seal.

So get it out and measure it. What are you waiting for? Aftermarket seal can be made from who knows what.

[Spindle]

Interestingly, some manufacturer sources suggested "neoprene" was very compatible with oils etc, suggesting no issues from the combination. But "neoprene" is not one material, there are apparently many varieties, with different properties.

While yes, I realize Mcmaster's listing is not an authoritative source, it is certainly an indication, and one that is quickly findable. Other sources strongly disagree. I found the following, and other similar information in a short search looking for industrial sources (not peripheral sources such as wetsuit companies, etc, of which there are dozens):

The Timco rubber site has this to say about Neoprene: "Neoprene’s properties, such as high resistance to oil, flames, and even damage caused by oxygen and ozone, make it the perfect material for a range of heavy-duty applications."

The Process industry Forum site suggests: "Neoprene is also popular due to its strong all-round chemical resistance as it remains unaffected by a range of chemicals including solvents, oils, and petroleum-based fuels"

So according to these and other sources, the possibility of swelling etc seems not to not be an issue.

What did the OP find after he extracted the seal from it's location? Did he find swelling, or adhesion of the neoprene to the rod?

Most importantly, does the seal or the rod turn when the engine is running?

The simplest explanation seems to be that the hole is too small. Most shaft seals I have dealt with are not that tight, and have relatively short contact areas. If the rod or the seal turn relative to each other, the tightness and possibility that oil may be excluded might cause a problem.

The rod and the seal both turn with the shaft bore they're in. The rod doesn't turn within the seal. Won't be able to get the seal out intact..

[Jim Stewart]

A standard lip seal that would have all the correct dimensions to fit with everything else?

Sure. There are millions of sizes - talk to someone at a bearing supply house.

-js

[Doozer]

Use O-rings.
Make up a thick washer or bushing thingy.
Bore the inside for an O-ring sized to fit the pish rod,
machine the outside for an o-ring sized to fit the bore
of the spline shaft. Set your squeeze between 10% and
20%. Maybe 10% on the small push rod so it glides and
20% on the outside to keep it static in the spline shaft recess.
This way you have only an O-ring to deal with, not some
special obsolete seal. And you control the fits to achieve what
you want. And you are not trying to size rubber. Bang done.
If you have the room, make it thick (long) and use a few O-rings
to seal the ID and OD of the bushing. Just maybe.

--Doozer

[chipmaker4130]

What would be a reasonable interference fit for just a disc seal?

For a thick, flat seal at that diameter I would shoot for .005", and that's after accounting for compression from insertion of the seal. In other words, .005" final interference with the rod.

[Spindle]

I found another seal kit in my archives, the seal OD is .784 vs .813 for the problematic replacement. I like the Doozer seal, but this one works perfectly, I just have an out of spec replacement.

[Spindle]

For a thick, flat seal at that diameter I would shoot for .005", and that's after accounting for compression from insertion of the seal. In other words, .005" final interference with the rod.

Thanks, that sounds like a reasonable fit, my current setup has @.003 interference and feels good.

[Jim Stewart]

Does it strike anyone oddly that this push rod is 6mm diameter in a Harley 45? (Well, .004 under 6mm.)

-js

[Spindle]

Yes Jim, it also strikes me oddly that the spark plug threads are 18mm x 1.5.

[Spindle]

Thanks to all of you for you generous response and input, it has been a great help as usual.

[Jim Stewart]

Yes Jim, it also strikes me oddly that the spark plug threads are 18mm x 1.5.

Far as I know, all sparkplugs are metric. Well, maybe not back in the '20s or thereabouts. There's gotta be a story there somewhere...

-js

[J Tiers]

Yes Jim, it also strikes me oddly that the spark plug threads are 18mm x 1.5.

Spark plugs are specialty and have been mm threads for a long time. A French invention, or at least first made in volume by Frenchmen.

Pushrods for a Harley are extremely surprising if mm sized. I would suppose H-D would say "you can't measure that in mm", just like our woodshop manager did. If they knew it was metric, they'd have a heart attack.

Maybe it's just way undersized for a 0.250"....... More likely that size is what fit.

Maybe the original problem is the bad seal is oversized (nearest metric size made in china?) and that squeezed it down to be too tight. seems reasonable.