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Classic, Vintage & Veteran For Coventry and Meriden Models. Anything pre-Hinckley goes.

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Old 12-06-2012, 05:30 PM   #11 (permalink)
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Quote:
Originally Posted by Snakeoil View Post
They are not washers. They are tubular rings, like a napkin ring. I suspect this was the first attempt at restraining the expansion of the seals.

Rob
Rob,

According to a post by John Healy, the wedding band was not introduced until 1969 but many builders retro fitted them, quote:

"When the round section "O" rings where introduced in 1969:
a: The Buna-N (70-7310) "O" ring was specified for both top and bottom.
—After experiencing problems Triumph issued a service bulletin, mentioned by Paul above, introducing the wedding band and square section seal (70-3547).
—Triumph also introduced the Viton "O" ring (71-1283) to replace the Buna-N at the top. Viton will withstand more heat than Buna-N.
—Most engine builders have routinely started using the Viton "O" ring (71-1283) at the top and bottom.

b. The wedding band and square cross section seal was not installed.
—The wedding band was introduced into production for the 1970 model year.
—During rebuilds many mechanics adhered to the Triumph service bulletin and retro fitted the wedding band and seal.
—Although there is little published, THERE ARE two variants of the wedding band. If one takes the time to measure stock wedding bands one will find that there are two sizes.
c. In a 1965 service bulletin Triumph specified .030 to .040" for push rod tube crush. If there is too much crush you will bend the head and cause extrusion failure where the "O" ring deforms and is pushed out the gap between the head and push rod tube. Typical crush on a round section "O" ring, of the size found on the push rod tubes to affect a seal, is .010". The .030" to .040" assumes the use of at least one square section seal. In fact when this specification was given two were used. The square section seals will tolerate more crush than the harder round section "O" rings."

Henry

Last edited by henryanthony; 12-06-2012 at 05:34 PM.
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Old 12-06-2012, 08:20 PM   #12 (permalink)
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Thanks Henry. I've tried to run searches on the Britbike forum and it only results in frustration.

The crush spec aligns with what Mr. Pete has recommended in the past, specifically, no more than 0.040 inch.

The service bulletins seem to be the keys to the kingdom when it comes to Triumphs. I wonder if anyone ever published a full set on-line. I've never looked. Kim the CD man might offer them. I'd think they'd definitely be worth having if you are serious about keeping and maintaining a vintage Triumph in stock dress.

If I had to redesign the PRT and stay within the confines of the existing head design, I think I might use an aluminum tube with a thin o-ring grove on the face of the top flange and a double o-ring groove on the tappet block backed up by either the original square section sealing ring or maybe another o-ring groove on the face of the bottom flange.

Harley uses a similar square section ring on their spring loaded PRT and since them moved from cork to a polymer ring, they just do not leak. Maybe a spring loaded tube would work on Triumphs. At the very least, it would let you remove the pushrods and replace the seals should they start to leak without pulling the head.

I suppose the external PRT are to promote better cooling of the cylinder. But I really wish Triumph had followed BSA's path with internal pushrod passages.

regards,
Rob
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Old 12-06-2012, 10:26 PM   #13 (permalink)
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Rob,

Here is how I found JH's post:

First, go to Google, then type in: wedding bands site:britbike.com

Google will then search for any instances of "wedding bands" within the site of "britbike.com". You will have to wade through the varioius posts but you may learn more than you asked for.

Wouldn't hurt to try "triumphrat.net" too (my personal favorite).

You can search any site using the above pattern. The key is figuring out what terms to search. While the technical term is "sleeve" the common term is "wedding band" so it may take a few tries to find what you are looking for.

Regards,
Henry
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Old 12-07-2012, 07:10 AM   #14 (permalink)
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Rask Cycle also calls for 4 x 70-3547`s for 1966 650`s.
And 70-4746 cups.
I`d suggest fitting those and see what gap you have.
Press on the head to eliminate slack first.
I`m unable to find a Triumph Service Bulletin around that date.
But one of them states the gap between the head and gasket should be between .030" and .040".
Trial and error?
Best of luck.
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Old 12-07-2012, 10:06 AM   #15 (permalink)
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Quote:
Originally Posted by henryanthony View Post
Rob,

Here is how I found JH's post:

First, go to Google, then type in: wedding bands site:britbike.com...
Thanks Henry. I should take more advantage of the Google search capabilities. In this instance, however, I would never have thought to use the term "wedding band". Lance has been calling them napkin rings and that stuck. Most folks today are not old enough to know what a napkin ring is.

regards,
Rob
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Old 12-07-2012, 10:54 AM   #16 (permalink)
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Tricor make cnc'd alloy tubes that apparently seal a heck of a lot better
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Old 12-07-2012, 04:49 PM   #17 (permalink)
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I would expect the alloy tubes to grow a bit faster and a bit more than the jugs. This could be both good and bad. Good from a tigher seal perspective and bad from a repeated change in seal pressure. But then again, the jug will expand and contract so I guess I just talked myself out of the bad aspect.

I think if I ever build a Triton, custom PRTs will be part of the build list.

regards,
Rob
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Old 12-09-2012, 01:28 PM   #18 (permalink)
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Additional info

I posted this in my resto thread, but thought I'd mention it here as well. Turns out the PRT seal used on the bottom with the wedding bands is a larger OD. The seal used top and bottom on '66 is 1-3/16" OD where the one used with the wedding band is 1-1/4". The ID of the band is also 1-1/4". So, the old seal will not be properly restricted from extruding out from under the PRT by the wedding band. You need to use the cup and the seal from the same model year as they are intended to work together as a system.

Others have mentioned this point, but I wanted to confirm this part of it with actualy dimensions that I measured.

I would think that if the later model sealing rings that go with the wedding bands are the correct thickness to obtain the proper crush, then using the bands with those seal would provide a better seal as it would be sealing on the top, inside and bottom surfaces. With the cup, you only get a seal on the top and inside surface, which IHMO would make it more prone to leaking.

regards,
Rob

Last edited by Snakeoil; 12-09-2012 at 01:30 PM.
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