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Pushrod Tube Seals Help Wanted

13K views 20 replies 12 participants last post by  Code Man 
#1 ·
I'm working on a TR7 1978. I've looked at online manuals but they picture a different push-rod tube (two diameters at bottom of tube) and no steps on the lifter blocks. Also the tube has an orange ring on the inside. Here is photo's of the tube and block., along with the seals and o rings I got from EMGO.. What goes where and how and why?
 

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#2 · (Edited)
Pushrod Seals

The large white seal fits over the tappet block and the steel band fits around the seal. The base of the tube sits on this seal and when torqueing the head down the steel band helps prevent the seal from 'squishing'. Both my recent 'O' rings were black so not sure of the colour differential but one fits in the lower end of the tube and seals against the tappet block, the other fits over the top of the tube. The chances of the seals preventing oil leaks would be slim with the tappet block in that condition. The block needs to be removed to be cleaned up properly, or replaced with a new one.
 
#4 ·
The large white seal fits over the tappet block and the steel band fits around the seal. The base of the tube sits on this seal and when torqueing the head down the steel band helps prevent the seal from 'squishing'. Both my recent 'O' rings were black so not sure of the colour differential but one fits in the lower end of the tube and seals against the tappet block, the other fits over the top of the tube. The chances of the seals preventing oil leaks would be slim with the tappet block in that condition. The block needs to be removed to be cleaned up properly, or replaced with a new one.
Okay, I got the clear ring over tappet block to the base of the turned diameter, the band is around the clear ring. An o ring is in the tube recess and one on the top. I place head on an find a good 1/4 of an inch from head to head gasket. To me a red flag goes up. Too much to 'squish" What do you suppose is wrong or right?
 
#3 ·
Quite often,the seal that is hidden on the tappet block,only replaceable by removing the block,is the cause of a leak.
They tend to get forgotten and would require the tool for removing the block.I use the red one at the top.Fit the head a couple of times to see if that top seal pops out as it often will do.After a few dummy runs,it seems to stay put.It does need a bit of lubricant when fitting.Try and avoid silicone sealant on the O rings,that seems to make a leak even worse.
Careful assembly is the key as always.
 
#6 ·
These are the tubes that I removed. I remember it having a clear crunched seal in it. My original post shows the tubes and seals as questionable to me. It's my friends motor. I have taken the top end off to replace valve springs.
 

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#8 ·
Hi Red, In the photo, the clear lower seal looks too large of diameter, like it's for an earlier type eng. How does the prt fit with no seals top or bottom?

My motor is earlier, the tube is straight. They may have changed them later. I don't know one way or the other for sure.

I used to placed the wedding band on the cyl. block around lower white seal, then installed prt. I read a book where they gently install band on lower end of prt with a light weight hammer. I tried that last time. It worked quite well for me. I think better. Only put in on enough to hold it. Not more than 1/16". Some prt were made undersize on the OD & the wedding band fits loosely. That is no good & the band will migrate up, often going crooked, allowing the white seal to displace. The band should be a light press fit on prt.

Take a scotchbrite pad & a dowel or the like & polish the head bore & make sure there is no burrs or sharp edges leading into the bore. Clean well after polishing. Same w/tappet block surfaces, polish them & make sure no sharp edges. I use fine emery cloth for tappet block polishing. Triumph never did that & it led to many leaks.

When trial fitting head, leave wedding band off & make sure prt it fully seated in head.
Don
 
#9 ·
1/4" is too much gap between the head and head gasket. DO NOT torque the head down with that much gap as you'll warp the head. Good call on listening to your gut that something was amiss. As others have said, ensure you have the correct tubes but then also see if you can get a thinner white seal for the bottom as they come in different thicknesses.
 
#10 ·
Did this ever get resolved? I ask because I've come up against exactly the same issue on my T140 project engine. It seems that the O rings that fit inside the lower ends of the PRTs are too thick. They are the same thickness as the upper ones, only black instead of red. Offering the PRTs up to the tappet blocks without the sealing band, so I can see what's going on, it is clear that the internal O rings aren't going over the blocks (with the bands in place, this is hard to see).

I notice in the 1980 parts book and the 1976 parts book, that the earlier model had different O rings top & bottom, whereas the later model had the same part no. for all 4.

I've got a bag of O rings collected from Triumph gaskets sets over the years. Among them are some which are the same OD as those I was using, but they are about half the thickness. If I fit one of these, the PRT goes on easily. But it seems TOO easily - apart from a tiny amount of friction getting the PRT over the top of the shoulder on the block, there is no friction and the tube just drops the rest of the way.

I don;t remember ever having had trouble fitting PRTs before - anyone got any thoughts on what's going on, O ring-wise?
 
#12 · (Edited)
Hi John,

I notice in the 1980 parts book and the 1976 parts book, that the earlier model had different O rings top & bottom, whereas the later model had the same part no. for all 4.
Mmmm ... but have you also looked at the tappet blocks and prt? Different part numbers in '76 and '80; you aren't comparing like with like?

Fwiw, I never buy those half-arsed 'top end overhaul kits' and the like, never seen one that didn't have a confused and confusing number of bits, any number of which don't fit the given bike being worked on. :( Luckily, triples had far fewer changes to heads, tappet blocks, prt and seals, and I specifically chose the bits on my T100 that use the same seals. :thumb I keep a few of each consumable, so I can deal with a sudden prt leak anytime, then I use a trusted dealer that knows his arse from his elbow to replace the bits used.

The square / rectangular section rings are pretty consistent at .125" (1/8") height.
Mmmm ... but are they ~15/16" i.d. and 1-3/16" o.d.? If they are, they're 70-4752; they can be white or translucent.

Otoh, if they're more like 3/16" thick, ~15/16" i.d. and 1-1/4 o.d., they're 70-1496; these can be white or black.

Finally, there's 70-3547 - ~15/16" i.d. and 1-3/16" o.d. like 70-4752 but only 1/10" thick; can be useful when trying for the desirable seal 'crush' measurement when heads and rockerboxes are torqued.

Hth.

Regards,
 
#11 ·
OK, an update: Since my post of about an hour ago, I've measured all the O rings I've got and found a surprising variation in thicknesses. The square / rectangular section rings are pretty consistent at .125" (1/8") height. But the O rings vary by over .010". I have tried using a pair of the thinner red O rings in the bottoms of the PRTs and they go over the tappet blocks nicely - a good fit that I can imagine will keep oil in, but not requiring a huge amount of force to get them on the blocks.

All the O rings are out of various LF Harris gaskets sets. Obviously, they should all be the same. Yet another thing to check from now on!
 
#13 ·
Yidh(alab)! I think I've gathered from other threads on this subject, that the difference in the O ring part no.s was one of materials rather than dimensions (?).

I've just been messing around with a spare tappet block and various O rings in PRTs. Most of the black O rings can be shoved over the block but it takes more effort than I'd like. A couple (sod's law made sure these were the two I first picked when trying to fit the tubes on my engine!) won;t go over the block at all - not using hand pressure anyway.

All of the red ones fit easily. The smallest red O ring is .092" thick and the largest black O ring is .1035" thick. Quite a difference.

The fact that there are such differences could come in handy in some situations but it would be nice to be able to take a better level of quality control than this for granted.
 
#17 ·
Hi John,

I think I've gathered from other threads on this subject, that the difference in the O ring part no.s was one of materials rather than dimensions (?).
John Healy will likely supply any additional information on material but the dimensional differences are definite.

70-4752 is what's shown in every triple parts book; the ~15/16" i.d. fits over a 1" o.d. tappet block and prt top.

On the triples, the prt go into the rockerboxes; the additional o.d. of 70-1496 causes problems there - where they become mangled when the rockerboxes are fitted - and at the bottom - where they won't fit into the steel cups that stop them being squeezed out when the rockerboxes are torqued down.

The reduced thickness of 70-3547 is useful with skimmed heads and similar when aiming for the desirable 'crush' (~0.020"-0.025") per washer.

Hth.

Regards,
 
#14 ·
Another update: I've now got .025" clearance between the had gasket and the head, which is actually too little, so I need to find another 5 to 10 thou. This is a lot better than the 70 or 80 thou I started off with. For information, in case of use to others, I found variations in the lengths of pushrod tubes as well as in the thicknesses of PRT O rings. One pair of PRTs (what looks to be an original Meriden pair) are around .010" longer between the relevant points than my other 'spare' set (which have a much more angular design to the lower ends where the diameters change, making me suspect these are a pattern pair). With thin 'square section' bottom seals (opaque white), thinner O rings and shortest PRTs, I'm at .025" gap. If I revert to the thicker O rings I should be just about right. It's lucky I happened to have the selection of items to choose from - goes to show you can't have too much Triumph stuff!
 
#15 ·
Hi John,
I just finished installing my PRT's for the second time on my 76 T140V engine. First time top seals on both PRT's popped out without me knowing until I started the engine and major oil leak there and from the bottom of one of the PRT's. 2nd attempt I purchased new seals (viton) again and fitted the bottom interior o-ring to the PRT and noticed it slid up and down over the tappet block with no resistance. Tried the same seal in the other PRT and it fit perfectly. So, the two tubes that I had were different. I didn't want to screw around with them anymore so purchased new PRT's and wedding bands. Fitted the new PRT's with the same type of seal top and interior bottom and they fit into head and over tappet block beautifully (nice snug fit). Don't remember what thickness square o-ring under PRT's but know it wasn't the .125 because my head had been shaved and was using the .080 thick copper head gasket.

After I torqued the head down and before installing the rocker boxes I poured oil down both PRT's clear to the top to check for leaks and could see no leaks anywhere. So pretty sure I won't have any problems but I'm still not 100% sure until I get the engine started and drive it around for a while.....Gary
 
#21 ·
Hi Dave,
I'm sure you're right and hoping for the best when I get it started. I wish I'd filled them with oil the first time I installed the head. Unknown to me at the time, top o-rings on both PRT's had half of the ring sticking out the side of the tubes after installing the head. How that happened I don't know. I installed the tubes to the head before installing the head and must have bumped them some how while trying to fit the head over the center two studs and under the top of the frame.

That was only part of the problem. The bottom of one of the PRT's was distorted and the inside o-ring slipped over the tappet block very loosely. I think it was flared out for some reason because I couldn't get the PRT to slip into the wedding band and had to sand the outside edge of it to make it fit. I didn't realize the inner o-ring fit loosely at the time I installed the head and it leaked leaked like crazy.

This last time I pulled head and barrels. New rings, PRT's, viton o-rings, wedding bands, and tappet o-rings. Sure hope it doesn't leak.
Also replaced clutch rubbers and chain adjuster. For some reason the previous owner had a 650 cc chain adjuster on it. Probably all he could get at the time. Should have the thing completely back together by end of day....Gary
 
#19 ·
Hi John, I came across a similar problem when I rebuilt my engine a few years ago, and the problem was that a PO had fitted non matching tappet blocks, a mix of the two types, but used the earlier PRT's! I have now fitted the later type blocks without the oil feed and matching PRT's, and if I recall these only had the black O rings.
 
#20 ·
Before joining the forum I had issues with the prt length and seal thickness. I thought there were only two prt's, those with internal pushrod guides and those without. Some were missing the chrome ring, and various combos of seals were used, I wasn't sure why. Discussions like this clarify the issue for me. Thank you all.
 
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