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Author Topic: ESR exhaust flange O-ring size  (Read 192 times)

Offline wilkin250r

ESR exhaust flange O-ring size
« on: May 13, 2019, 11:32:08 PM »
So I wanted to look around for new o-rings for my ESR exhaust flange, and I found a whole lot of people talking about them, but I never saw anybody post any specific sizes.  It was almost like a government conspiracy.  Not that I have a problem with ESRs prices or availability, I just wanted to look for maybe thicker rings, or different (more expensive) materials.

So I'm going to share my thought and findings, because I couldn't find the information anywhere else.

The o-rings I got from ESR are a hair over 0.100" in width, and since 0.103" is a fairly common width for o-rings, I'm running with that assumption.  It's either that, or assume they are metric, and I just don't think they are metric.

It's kinda tough to get an exact ID and OD on o-rings this large, because they don't hold a perfect shape at rest, they're kind of an oval.  I tried measuring the largest diameter at rest, and the smallest diameter, and finding the average.  I'm coming up with about 1.866.  This is subject to a very high degree of error.  This would mean the OD is about 2.072" (by calculation, not measurement)

My calipers don't fit exactly in the groove of my flange, but I believe I'm measuring a diameter of 1.942".  I know I'm going to want my o-ring ID to be smaller, to ensure a tight fit.  The width of my groove is about 0.120"



So I went through charts of o-rings, with the basic assumption these are standard size.  3/32 is a common o-ring size at the previously mentioned 0.103" width, and looking for the ID and OD to match closest to what I was measuring.

The end result is I believe these are a standard size #134 o-ring.  Standard dimensions are 3/32 width, 1-7/8 ID, 2-1/16 OD.  Actual listed dimensions are 0.103" width, 1.862" ID, 2.068 OD.  These are just a few thousands off from my actual measurements, so I'm pretty confident.




Offline 2Nubs

Re: ESR exhaust flange O-ring size
« Reply #1 on: May 14, 2019, 12:26:59 PM »
I like this idea. The extra thickness might very well seal these pipes up without the need for RTV. My R is a splooge making machine right now. I had planned to use RTV, but I will gladly try to source some O rings for us to test out.
86 330

Offline The norm

Re: ESR exhaust flange O-ring size
« Reply #2 on: May 14, 2019, 01:19:49 PM »
I use orings and rtv to make a good seal
I had a BDT motor once.....It SUCKED!
Currently: Hybrid Engineering 310 stroker built by Pete

Offline wilkin250r

Re: ESR exhaust flange O-ring size
« Reply #3 on: May 14, 2019, 07:43:56 PM »
Based on their price and temperature requirements, I'd give it a 98% certainty these are standard hi-temp silicone.  Anything more exotic and high temp is significantly more expensive.  Kalrez o-rings around that size are about $50 per o-ring.  I'm actually not opposed to spending that kinda money, but not before I do some more testing.

McMaster has a large selection of 0-rings.  A standard #924 is a little thicker, but also smaller ID and OD, so I don't know if I want to stretch them that much.

A #225 o-ring might work, but it's a little thicker than I want.  It's listed as a 0.139" thickness, and the groove I have only measures 0.120".  That might be a tough squeeze.

Offline Hawaiiysr

Re: ESR exhaust flange O-ring size
« Reply #4 on: May 14, 2019, 11:41:10 PM »
A little unorthodox but I use tire plugs.

Offline hickwheeler

Re: ESR exhaust flange O-ring size
« Reply #5 on: May 15, 2019, 05:56:04 AM »
I buy the o rings for the KTM 300 and 250. They are thicker. I usually have to grease them to slip the pipe on. A little patience helps too. Seems to seal good with no rvt. You kinda have to stretch them over the flange
88 ESR 330 5mil stroke
88 ct350pv (BOF Build)
Puma coming soon

Offline 2Nubs

Re: ESR exhaust flange O-ring size
« Reply #6 on: May 15, 2019, 09:08:09 AM »
That is awesome info Gene. I think I will go that route.
86 330

Offline wilkin250r

Re: ESR exhaust flange O-ring size
« Reply #7 on: May 22, 2019, 12:24:58 AM »
I buy the o rings for the KTM 300 and 250. They are thicker. I usually have to grease them to slip the pipe on. A little patience helps too. Seems to seal good with no rvt. You kinda have to stretch them over the flange

Send me a link (or part number, or something) and I'll order a couple of those o-rings and measure them, I'll find out exactly what they are.

Offline wilkin250r

Re: ESR exhaust flange O-ring size
« Reply #8 on: May 22, 2019, 12:41:04 AM »
On a side note, a metric o-ring 3x47 looks to be a perfect size (3mm width, 47mm ID).  By the specs, it's slightly thicker than the #134, (0.118" vs 0.103") and nearly the same ID. 

Problem is, metric o-rings just aren't as common, and exotic materials even less common.  McMaster doesn't carry them in a silicone, but they DO carry them in a Viton, which has nearly the same upper heat range, and similar price.  I think I'm going to get me some.

My current experiment is running this 250r with no RTV, just new o-rings.  It previously leaked with o-rings and copper RTV, so we'll see what happens without the RTV.

Offline hickwheeler

Re: ESR exhaust flange O-ring size
« Reply #9 on: May 22, 2019, 04:53:57 AM »
88 ESR 330 5mil stroke
88 ct350pv (BOF Build)
Puma coming soon

Offline wilkin250r

Re: ESR exhaust flange O-ring size
« Reply #10 on: May 23, 2019, 09:07:25 PM »
https://www.motosport.com/oem-parts/part-number/0770440030

Looks like it is 44x3

And they look to be Viton.

I think you might be better off with a slightly larger inner diameter.  I measured right about 1.94 inches for my exhaust flange o-ring groove ID, and 44mm is about 1.73, meaning your o-ring is almost 3/4 inch too short for that length.  Not terrible, because you actually want it to stretch a little, but it means if your o-ring gets hot and cracks in one spot, you now have a 3/4 gap as it rips and withdraws.

McMaster sells Viton o-rings in 3x47 (1.85" ID), 3x48 (1.89" ID) and 3x49 (1.93" ID).  I might pick me up a set of each, package of 5 is less than $10.  Slightly more expensive than the silicone, but I'm certainly not going to complain about spending $6 instead of $4.50 for a set of o-rings on my exhaust.  And who knows, the Viton might hold up better than the silicone, even though the temperature specifications say it won't.

Offline hickwheeler

Re: ESR exhaust flange O-ring size
« Reply #11 on: May 24, 2019, 02:45:07 AM »
I have not had one go bad yet. They usually get messed up taking the pipe off. Because they get soft
88 ESR 330 5mil stroke
88 ct350pv (BOF Build)
Puma coming soon