Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board 70-3309 O ring for gearchange spindle

I bought one of these with other parts for my 1963-ish 3TA mongrel from a UK supplier (TMS of Nottingham). When I went to fit it its section was too big as was the overall diameter. I phoned TMS and they said there were 2 versios of the ring but all my parts books up to 1970 show the same part number.

Does anybody have the later part number or is my information incorrect?

Probably 2 different manufactures making them to 2 different specs

Maybe both wrong?

Mine come from Harris

Could be. I've managed to find something the right size (and free!) in my local bearing supplier.

I seem to remember two different depths of grooves, but equally could have dreamed it!

This may be a case of an o-ring with an identity problem...there are (4) part numbers loosely associated with this one- 70-3309, 60-3530, 60-2640, and 99-9956.
-Dave

Hi Ian, You are 100% correct!!! The groove on shaft is smaller. It demands smaller oring.

I don’t know when/if 500s went to fatter oring.


The 650 went to fat ring in 1970. I know this for a fact with personal observation.


The skinny oring is same as earlier tack drive body oring. Guess what?? The sellers sell the fat oring for this too!!

If you force shaft in with fat oring, the fit is tight enough to give enough friction to give erratic shifting. It will usually peel the oring OD.

Trust me I’ve been down this road twice new!

I have yet to find seller that sells the correct skinny oring.

Hopefully you will.


Taking shaft& outer cover to various hardware stores in USA nobody had correct size ring. I ended up going through my oring box of Mercedes orings. Found size that fit. No idea what part #.
You are not crazy! Parts sellers are wrong.
Don

As Ian seems to have found an O ring that works, that’s fine. Just to know there is an issue is important, but in all fairness to parts sellers, they do go from the parts books, which just don’t help.
Luckily, the oil level is such that a loose O ring doesn’t matter too much, though a fat one does.

Hi Mick, The parts book shows the part # E3309 (70-3309) for skinny ring is used up to 1971.

The 70s I had apart all had the fat ring. It’s possible they had later shafts??

The 1972 parts book changed part # to D3530 (60-3530). The 60-3530 ring was used on both right & left foot shift until very late years when shifter started using kick start shaft ring.

End of day the root problem is suppliers are not supplying correct ring under E3309. THEN PROBLEM IS PERPETRATED BY RETAILERS.
This is just nonsense!! It’s been going on for at least 5 years I know of. It should stop!! We need a E3309 oring of the correct dimensions.

The retailers need to rattle the suppliers cage & have them get the correct oring. I’ve spoken with several retailers. They say they can’t get the real E3409 oring. Ok, THEN QUIT PASSING IT OFF AS IT WILL FIT!

I know I recorded the dimensions of both shaft grooves. Can’t seem to find that page at the moment. I’m away from PC now.
I have spare later outer cover. I can pull shaft & measure later.

Mick, do you have early shaft & can measure?

Triumph used some odd ball orings not readily sold by oring suppliers.
The fat ring on late shaft is common size & most hardware stores in USA stocks it.
Don.

Hi Don and Mick, interesting discussion. Over on Hermits oring list we measured this oring to be a -15.

https://www.hermit.cc/tmc/parts/o-rings/triumph_o-rings.htm

Don, according to you would that be a fat or a thin one? If memory serves the -15 went into my 71 engine without problems.

Iansoady, did you measure the oring that did fit? Would be interesting to compare dimensions.

Cheers.

Hi Bigbars, The way I read it #15 is the fat one that all the hardware stores stock & sell.
Don

The O ring that I got from the local supplier was .060" thick (about 1/16") with an OD of 0.580 approx (9/16" or so). But this is really too small in diameter - the shop was out of stock of the next size up so I may pop back to get one of the bigger ones. Accurate measuring of these rings is tricky as they just squash so easily.

I take the point that losse is better than tight in this application....

Hi Ian, The fitting of orings is interesting. I've fit thousands of rings at work. Some are a tight fit on shaft, Some are just barely touching shaft.

The compression into bore can be the same. How can I describe the fit? I'd say ideal would be snug fit on shaft in the groove& sticking out above outside diameter of shaft maybe .010" ish... The rubber must touch inside of shaft, fairly tightly. Not have so much compression into bore that there is no place for rubber to go.

Rubber is like a fluid. It doesn't really compress. It distorts, but must have space to distort to. Meaning the rubber is in groove so there is hollow space between rubber the corner of the groove. The outside of ring sticks up above OD of shaft. When pushed into bore the top surface of ring is pushed down & the rubber under this tension is displaced sideways. So the ring has to be the right size such it has enough tension to seal. Yet enough room to displace.

The fat ring as I expect you found won't go in as the rubber is hydraulic locked in the groove. You pretty much have to really force it. Hard!! As the rubber tries to displace the top outer edge migrates & finally expands out the groove & is sheared off as you continue to push.

I'd put ring in groove. I ring it with a very skinny screw driver without sharp edges to remove any twist & to sort of equalize stretch. Then take a straight edge & place it over ring & see how much it sticks up above OD of shaft. If ring is too skinny it may not stick up at all or not enough. Finally if I lube all with oil or grease & push shaft into the bushing. Be sure to smooth lead in edge of bushing well with fine emery or the like & the surface where ring rides in the bushing is smooth as well. With practice you can feel the fit/compression of ring. You want a firm push to compress ring, & at the same time the shaft will rotate freely in bushing.

Reliable centering is key to good shifting. If shifter springs are rusted, weak or deteriorated in anyway renew them. I used to get late T140 springs which were much stiffer than normal springs under part #57-7051. They have thicker wire diameter & have a very decided curve to spring. I've not been able to purchase them for about 3 years now. The LF Harris ones often with a yellow tinge of paint on them are at least decent tension. Sold as 57-7051, but are NOT real 57-7051. Getting 100% reliable centering of shifter is what matters however you get it. So the friction of the oring is part of this equation.

If you measure your groove depth, width, the diameter of bore in bushing. There are many online oring calculator charts on what dimension of oring is best for rotating shaft.

Keep us posted on what you find. My hunch is metric oring will be best fit. The material will be what it is. Likely neoprene?? I've use those on my trans filler plugs etc. They are good for 4-5 years. Viton is material of choice, but that may not be possible to obtain.
Don

Thanks for that. I am new to Triumphs but not to O rings! The ones I have are just appreciably proud of the OD of the shaft when fitted. Given that my outer cover is from an older model and has no seal on the kickstart shaft I suspect that any leakage from the gearchange shaft will be minimal compared to any from the latter!

Very early days anyway but I'm doing trial assembly of various sub-assemblies to check compatibility. To my great surprise, the gearbox internals slid into place with no problem, although I did fit the sleeve gear to the mainshaft rather than trying to engage the layshaft gear with it as I pushed everything home. I was expecting a struggle getting the inner end of the layshaft and the selector spindle located in the shell.