Throttle Shaft Seals

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thesameguy
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Throttle Shaft Seals

Post by thesameguy » Mon Feb 18, 2019 6:05 pm

A long time ago, someone posted on some XR4Ti forum (maybe this one!) about the SKF 3970 as a replacement for leaky throttle shaft seals. At the time, I knew I had a leak looming so I bought four of them. They sat in a box until about a month ago, when I actually installed a pair of them in a throttle body. Of course, it worked.

During the installation I blew it on my first attempt as the seal is a Tight Fit, but the second (and third) try it went smoothly. Unfortunately, that leaves me with one spare seal and a second throttle body that needs attention.

This SKF seal is basically NLA. The OE application is the '96-99 Isuzu Oasis and, I think, an off-brand Chinese motorcycle. There are a couple places that claim stock, but both canceled my order.

The SKF 3970 is 10x18x6 (IDxODxH) but I think the factory seal is probably only 5mm tall.... the SKF seal protrudes a fair amount on the "front" side of the TB. I'm wondering if anybody has any more recent experiences with this seal before I try a seal that varies by some dimension.

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Re: Throttle Shaft Seals

Post by Ed Lijewski » Mon Feb 18, 2019 8:32 pm

Jeff Herson of Merkur Parts Midwest usually has XR new TB shaft seals.

YMMV
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Power Tryp
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Re: Throttle Shaft Seals

Post by Power Tryp » Tue Feb 19, 2019 12:34 am

If you have the dimensions, why bother hunting for an skf specific item?

https://www.bearingscanada.com/mobile/P ... x?id=55418
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Re: Throttle Shaft Seals

Post by thesameguy » Tue Feb 19, 2019 12:42 pm

Ed Lijewski wrote:
Mon Feb 18, 2019 8:32 pm
Jeff Herson of Merkur Parts Midwest usually has XR new TB shaft seals.

YMMV
Well, that would have been useful to know. :|

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Re: Throttle Shaft Seals

Post by thesameguy » Tue Feb 19, 2019 12:55 pm

Power Tryp wrote:
Tue Feb 19, 2019 12:34 am
If you have the dimensions, why bother hunting for an skf specific item?

https://www.bearingscanada.com/mobile/P ... x?id=55418
Short answer is because I don't know enough about seal construction to determine whether "generic NBR seal" is suitable for use in a throttle body pressurized to 20psi. The SKF part is (I'm virtually positive) acetate based and has a specific lip design, but I can't find much documentation on this seal since it's NLA. I don't think the choice is just about dimensions.

BUT, I did order what I suspect are those same seals from AVX yesterday. I won't know anything about them for years since I'm going to rebuild a spare throttle body. The alternative was some FPM seals - which would have been more desirable - from 123bearing.com... but that would have been $30 in shipping from France. Lame!

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Re: Throttle Shaft Seals

Post by Power Tryp » Tue Feb 19, 2019 4:20 pm

And that's reasonable. I just took waaaay to much time looking into this and without being a seal expert I can say I wouldn't hesitate to use the AVX seal in my own application.

Below you can see the profiles, HMS4 is what the 3970 is and while AVX doesn't list according to SKF nomenclature their TC seal looks virtually identical to the HMSA7.

Image

Also because SKF doesn't list a material for their 3970 I am going to assume it is Nitrile, especially at the low cost they were at.

Of course, I'm committed (or committable take your choice) I'm going to order in a couple AVX seals and try them on for size myself and report back once I have installed to see how well they go.
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Re: Throttle Shaft Seals

Post by thesameguy » Tue Feb 19, 2019 5:21 pm

Yeah, I found the HMS4 cross-section, but the 3970 is HMS48 which I could not find. I'm guessing it's a spec that has been replaced for a long time, because I can find no reference to it anywhere.

I highly doubt the 3970 is nitrile. It could be, but the OE purpose is inside a transmission and I don't think nitrile would be suitable for those temperatures. Hard to say though - I do agree with your point about it being cheap. OTOH, 123bearing's FPM seal was about the same price...

I've got four of each of the AVX seals coming, four with a 6mm height and four with a 5mm height. I really think the 5mm height is preferable to the 6mm of the 3970, but probably barely. I won't find out for years (fingers crossed) if this was a good decision, so let me know if you find anything sooner. :)

If you do order from AVX, you can use giveme5 for a $5 off coupon.

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Re: Throttle Shaft Seals

Post by Power Tryp » Tue Feb 19, 2019 5:31 pm

Well if 123bearing has them priced that low then I feel there's either a material error or a pricing error but anybody in France should jump on it if it's a pricing error, just for comparison sake my local supplier has the 6mm height seal in FPM and it's crazy and would be overkill for our application.

http://www.sealsonline.com/flabca/en/tc ... 0tc-v.html

Thanks for the coupon code!
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Re: Throttle Shaft Seals

Post by thesameguy » Tue Feb 19, 2019 5:47 pm

I don't think there's an error, I think they have low prices. :)

https://www.123bearing.com/section.php? ... &preview=0

(hopefully that works)

You can see:

Rotary shaft seal Double lip OAS-10X18X6-FPM - 10x18x6 mm = $6.42

and

Rotary shaft seal Double lip OAS-10X18X6-NBR - 10x18x6 mm = $0.94

I would have ordered a bunch of both were it not for the $30 shipping floor. Maybe I should have inquired about a group order.... :D

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Re: Throttle Shaft Seals

Post by Power Tryp » Tue Feb 19, 2019 5:59 pm

Huh I'll be damned that is incredibly cheap. Then they get ya on the shipping. Typical...
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Re: Throttle Shaft Seals

Post by thesameguy » Tue Feb 19, 2019 7:22 pm

Well, they are in France... They advertise a New York number, but I'm pretty sure I read they ship from France.

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Re: Throttle Shaft Seals

Post by thesameguy » Sat Mar 02, 2019 7:45 pm

I got my order from AVX very quickly, but then sat on the seals because of life.

Today I went ahead and rebuilt the other throttle body I have using the AVX seals... here are my impressions:

1. The AVX seals are much easier to install. The rubber surround on the seal shell is much less substantial than the SKF seal, no doubt because they are intended for a different purpose. From an installation perspective only, I like the AVX seal.
2. The 5mm AVX seal is a better fit than the 6mm SKF seal. The 6mm seal protrudes quite a bit from the throttle body on the cam side, and might drag a bit on the cam. The AVX seal fits essentially flush like the factory seal.
3. The AVX seal I ordered is a double-lip design vs the single-lip design of the SKF seal. I feel now this might have been a mistake. The AVX seal drags quite a bit on the butterfly shaft, and while the butterfly does close, it does not snap shut like I probably want it to. It may be okay in practice and may get better with a little use, but I won't find out for (hopefully) a long time. It's possible an 11mm ID would be better, but I don't think that exists. Just based on my gut, I think a single-lip 10mm ID seal is the better option.

All that said, something odd developed on my car, which is that following seriously heavy rains the TB doesn't seem to quite close reliably. It gets REALLY close but sometimes doesn't quite close. Symptom is a 2000rpm idle *randomly*… if I stab the pedal the springs will pull it closed, but slowly backing off the throttle it sometimes sticks slightly open. I don't know what's up with that, but will investigate when it stops raining. I have a couple ideas. Anywho, point is, I may try my spare TB sooner rather than later. I sure do love resetting TPS & base idle & using up throttle body gaskets. :D Hard to get mad when you bring that frustration on yourself though. :p

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