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Hi DavidP,

"So, does that chart have any correlation with O rings which are available to mere mortals, or is it just what should be used under ideal conditions?"

All the O-rings I have indicated so far, are the nearest AVAILABLE size that is reasonably optimised for a particular groove. The only issues are, that to know exactly what you are getting, with regard to size, material and hardness, is to source from an industrial O-ring supplier*. Even if you measure it, you certainly cannot do anything more than guess the material and hardness is just by examining an O-ring. Buying this way, the down-side is that there are usually minimum quantities that they will sell, as well as minimum order values - as is normal in dealing with industrial sources. That said, the unit costs of the O-rings are not particularly high. You may end up with a lifetime supply, but you CAN share them around! smile

* In the UK, one such supplier is Polymax and to quote pidjones for the US, earlier in this thread, "Signal Industrial Products is the Parker distributor in Knoxville. http://www.signalproducts.com/o-rings.html When I care about quality, I go for Parker. Available world-wide in imperial and metric. Used them for very critical applications at ORNL and Siemens".

When specifying a suitable O-ring size for our bikes, you are up against what looks like variable tolerances allowed by Triumph for the machining of the width and depths of the grooves. However, on a positive note, To find an O-ring that will fit, the design parameters specified by the O-ring manufacturers are not hard and fast and there is a reasonable amount of leeway, with the exception excessive gland-fill. If the volume of the O-ring is more than the volume available in the groove, with rubber being effectively in-compressible, it stands to reason that there will be difficulty in trying to squeeze it in, which is the EXACT problem that so many have experienced for decades when supplied with the wrong (oversized) rocker shaft O-rings.

"My measurements are suspect due to the elasticity of the object under measurement. ID could well be 13mm? What do you pros use, the world's smallest bore gauge?"

I have long experience as an engineer, but I would not call myself a Pro on this subject, All, many of us have available at home is a Vernier Caliper. For ID, the nearest I can get is to slowly increase the span until I can just manage to pick up the O-ring in two planes 90 deg apart. The cross-section is easier, just enough pressure to pick up the O-ring and hold it without it falling out of the jaws. Its very subjective and an approximation is as close as we can hope to get..

As you will have no doubt have found, picking a loose O-ring and trying measure accurately is not easy, but as in your case with the 12.8 x 1.3 O-rings, if you got reasonably close with your measurements, its possible to see that they will work. In fact, since you have already used them, its something you already know. So it seems your supplier/dealer is on the ball!

I don't know how far back some sort of engineering design standards with regard to O-ring and groove sizes may go, but with the oddball sizes of the grooves on our Triumphs, I sometimes wonder if it was before any guidelines or standards existed. Perhaps Triumph even got O-rings manufactured to their own dimensions.

At the end of the day, all we want to do is find an O-ring that will fit easily, seal effectively and give a good service life. Using first principles and doing a few calculations gives us a way to achieve that.

Terry


Bike History: Jawa 50 1956, Bridgestone 50/90 Sport 1967, Triumph T120 Bonneville 1970, Yamaha 125 DT125 Scrambler 1974, Kawasaki 125 KE125 Scrambler 1978, AJS model 18 500 Single 1964. Current bike Triumph T100R Daytona 1972.
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You can find just about any size O-ring at theoringstore.com. They have 13 x 1.3mm in Buna-N, $0.38 each, minimum quantity 3. $5 minimum order.
Not in Viton though.
They have a groove information chart for basic applications. For 1.3mm the groove width is 1.8mm and the depth is 1.05mm.
They have an "APP" that will measure O-ring sizes using your phone camera. A grid has to be downloaded and printed. They have calibrated grids for sale.
It could be that BSA had O-rings made to their own specifications.

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DavidP, give these guys a call and see if they can help. Probably want to sell quantity, however. Amazon (or ebay) may be your best bet.
http://www.signalproducts.com/About-Us.html


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I bought the recommended 13 x 1.2 mm Viton o-rings off Amazon. I installed them last week. They went in like a breeze. I also followed the suggestion to use the threads on the other end of the shaft to slowly pull the shaft in instead of tapping it in wit a punch. No sheared o-ring! Started it up today and ran it for 10 minutes or so. No sign of leakage! I am stoked. Hope it lasts. One question for the group: when I had the rocker covers off, there was noticeably more oil in the intake side. Not overly so, and the lesser amount on the exhaust side was not alarmingly less, but there was a noticeable difference. Thoughts? By the way, after completing the job, readjusting the valves and charging the battery, the bike started right up on the second kick after a 6 month hibernation. It would have started on the first kick, but it wasn't a good kick on my part.

Ed from NJ

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Could the slight difference in oil levels between intake & exhaust sides be due to the positioning of the pushrod tube drain holes? If the exhaust side's holes are nicely aligned with the drainage channels, but the intake side holes aren't, it must make a bit of difference?


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I used the rings from a standard gasket kit and drew them in using a spacer on the end of the shaft. Maybe a sliver or rubber. Won't know until I put boxes on and start the engine.


Keep your head up and your stick on the ice.

72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"

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Originally Posted by edunham
I bought the recommended 13 x 1.2 mm Viton o-rings off Amazon. I installed them last week. They went in like a breeze. I also followed the suggestion to use the threads on the other end of the shaft to slowly pull the shaft in instead of tapping it in wit a punch. No sheared o-ring! Started it up today and ran it for 10 minutes or so. No sign of leakage! I am stoked. Hope it lasts.
Ed from NJ

The problems many people have been having for decades is simple to explain.

If the o-rings supplied are oversized, you will have great difficulty getting them in, with the inevitable sliver left behind from trying compress the rubber. It means that there is insufficient material left to form as effective seal once they have been forced in.

These issues are well known! All the attempts with different types of sealers to substitute for a correct fitting 0-ring are just bodges attempting to get around the fundamental issue.

If you do as edunham has done and fit appropriately sized o-ring it goes together easily and simply works! My Daytona has done over 15000 miles now since fitting correctly sized o-rings and not a hint of a leak!

13 x 1.2mm Viton* for B-range bikes and 12 x 1.2mm Viton for C-Range bikes. *They need to be Viton because of the high temperature.

Terry


Bike History: Jawa 50 1956, Bridgestone 50/90 Sport 1967, Triumph T120 Bonneville 1970, Yamaha 125 DT125 Scrambler 1974, Kawasaki 125 KE125 Scrambler 1978, AJS model 18 500 Single 1964. Current bike Triumph T100R Daytona 1972.
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Hi, The orings I buy from Steadfast Cycles in USA are viton & are not oversized. I've had very good results with them. If you buy these & it's peeling or leaking, it's not the ring's fault. Something else is wrong.
Don


1973 Tiger 750
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