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'66 T120R pushrod tube seal cups

5K views 17 replies 7 participants last post by  Snakeoil 
#1 ·
On my '66 T120R, I found two rings at the base of the pushrod tubes instead of the cups shown in the parts book, part E4746. I looked at the '65 parts book and it has nothing there, just the seal. I cannot find a parts book that shows rings instead of cups.

I'm about to install my head and noticed that the rings are very loose and really only rest on the tappet blocks. I assume that the seal at the bottom will expand as I tighten down the head, but not 100% confident it will expand enough to hold those rings in place.

Should I use the cups instead? Or will the rings work once the head is down and the seals compressed?

Thanks,
Rob
 
#11 · (Edited)
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
 
#4 · (Edited)
Hey Rob, I am not sure about the '66 but the ring on my 76 pushrod tube base is referred to as a sleeve in the book. It doesn't have a bottom- just sides and the seal is large enough to expand and lock it down ( with a little silicone) You could try a dry run to see if you are happy with the squish.

were they leaking ?
 
#5 ·
Thanks Dave. Never thought to look to later model years. Thought the ring was an earlier design.

I just looked at my '76 parts book and it also shows an o-ring in conjunction with the seal. Does the o-ring go between the seal and the pushrod tube or around the seal such that it is positioned between the OD of the seal and the ID of the sleeve.

And yes, it would appear that I have the later design sleeve. Yet I found no o-rings when I disassembled the engine.

regards,
Rob
 
#6 ·
Hey Snakeoil,

You'll see from the '76 parts manual that the bottom of the pushrod mates with an O ring - part number 70-7310, which then sits on a thick plastic sealing ring - part number 70-4752, all of this is retained inside a metal sleeve - part number 71-1707, which slides over the tappet block and is compressed when you bolt down the head.
 
#7 ·
There are two O-rings.
The top one fits over the PRT.
The lower one sits inside the lip of the base.
The tube sits on the white sealing ring, which is over the tappet block.
The base of the tube and its seal is constrained by the sleeve.
Fit the sleeve and the white seal over the tappet block first.
Then offer up the head and tubes, complete.
 
#8 ·
Cauky,

I'm trying to understand the positioning of that lower o-ring. I suspect I'm struggling because the 750 motor PRT is different. Are you saying that the o-ring fits inside the PRT and the ID of the ring seals againd the OD of the upper half of the tappet block? That would indicate that the bottom of the PRT is formed channel rather than a simple flange like it is on mine. That would also say that the o-ring is the first seal and the PRT white rubber seal ring is the second seal.

If my understanding above is correct, then I'm limited to just using the sealing ring and the napkin ring to restrain the sealing ring from extruding out from under the PRT.

There is another slight variation for these older motors. The front (exh) PRT needs to be installed in the head before you present the head to the jug with the engine in the frame. The rear,(inlet) needs to be installed on the tappet block.

regards,
Rob
 
#9 ·
Snakeoil
Forget my previous post.
Sorry for the mis-info :eek:
There were several arrangements over the years.
After doing a bit of research, I found the following:
`65 (and earlier?) 650`s have 70-3646 tubes. (alloy head)
70-1496 lower seal, black rect. section (thick)
70-3547 top seal 2.5mm thick
No cup/sleeve.

`66 to `68 had 70-6000 tubes
70-3547 top seal, white 2.5mm rect. section.
70- 4752 lower seal, white 3.5mm thick rect. section
70-4746 cup

`69 to `73 had 70-9349 tubes.
71-1707 sleeve
71-1283 top O-ring
70-7310 lower O-ring (fits inside the tube)
70-4752 bottom seal

You might like to view these:
http://www.classicbike.biz/triumph/Parts/1960s/65Triumph650ccPartsManual.pdf `65
http://www.mapcycle.com/parts-finde...inder-and-head-tr6/cylinder-and-head-tr6.html `68
 
#10 · (Edited)
No sweat, Caulky. I knew you were talking about a T140 config.

But, I will argue with your finding regarding the seals used on a '66. My manual shows the E3547 2.5mm seal used top and bottom (qty 4). So does the manual for the '66 on the Classicbike site. But for the '67, the manual on the Big D site shows the 3.5mm lower seal and the 2.5mm upper. Yet Classic bike '67 Tiger manual shows the 3.5mm , E4746, top and bottom.

How's that for British clarity at it's finest?

So, somewhere between DU24875 and DU44394 the PRT seals went from 2.5mm up and down to 2.5 top and 3.5 bottom to 3.5 top and bottom. Then in '69 it went to E7310 which is an o-ring.

I need to measure the amount of crush to be sure I'm using the correct seal rings.

It would have been so much simpler if they had simply cut a doube o-ring groove in the tappet block and put a square sealing ring at the bottom.

regards,
Rob
 
#12 ·
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
 
#13 ·
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
 
#15 ·
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
 
#14 ·
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.
 
#17 ·
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
 
#18 · (Edited)
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
 
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