T140V pushrod tube seals

Tigernut · Oct 3, 2022

I'm having problems with PRT seal squash / head clearance. I have some Wassell alloy PRTs. they look well made but they are too long - correct distance from the upper shoulder to the bottom face is 4.485" but these are 4.532"

When offering the head & gasket up, the gap is .088", ie: at least .048" too much. The thinnest bottom (white, box section) seals I can find are .097" thick. I don't want to use a thicker head gasket as I want the compression on this engine (I've fitted the barrels without a base gasket in order to gain compression and I don't want to lose it by fitting a thicker head gasket).

I'm going to see if I can get the PRTs turned down, but there isn't enough meat to get the whole .048" taken off. I will still need thinner section bottom seals (maybe around 2mm / .080"?) Any ideas or suggestions? Anyone know if extra thin bottom seals exist and if so, where?

Shelby-Right · Oct 3, 2022

Could they be shortened and remake the end they could be pushed together with silicon or a loctite product , they might need to be thin wall for clearance on the OD , or just get some made from free machining or 6061 T6 alloy . Cheers

Fast Eddie · Oct 3, 2022

Hate to ask the dumb question, but, why not just fit some stock PRTs ?

Tigernut · Oct 3, 2022

Fast Eddie said:
Hate to ask the dumb question, but, why not just fit some stock PRTs ?

It's a good question, I'm the dumb one! I thought exactly the same and bought a pair from a reputable retailer who told me they'd be good quality. They aren't. One is dented (I can live with that - just make it face the barrels), both had burrs that I needed to remove from the oil drain holes at the tops, and after doing that, I found that the bottoms are too large OD for the wedding bands to fit! By this time, I'm fed up spending money n all these pushrod tubes. If I can make the alloy ones work, by finding seals that will let me use them, I'll do that.

The crap 'standard' PRTs were made by MCA, by the way. I believe that LF Harris ones would be better, but as I said, I feel as if I've spent enough on pushrod tubes that don't fit to risk yet another pair...

Fast Eddie · Oct 3, 2022

Tigernut said:
It's a good question, I'm the dumb one! I thought exactly the same and bought a pair from a reputable retailer who told me they'd be good quality. They aren't. One is dented (I can live with that - just make it face the barrels), both had burrs that I needed to remove from the oil drain holes at the tops, and after doing that, I found that the bottoms are too large OD for the wedding bands to fit! By this time, I'm fed up spending money n all these pushrod tubes. If I can make the alloy ones work, by finding seals that will let me use them, I'll do that.

The crap 'standard' PRTs were made by MCA, by the way. I believe that LF Harris ones would be better, but as I said, I feel as if I've spent enough on pushrod tubes that don't fit to risk yet another pair...

Fair enough, we’ve all been there !

Frankie17 · Feb 22, 2023

there are two different types of tubes for T140 71-3329 / 71-7179 do you have the correct year tubes and cylinder head ?

i have a set of the Wassell alloy tubes 71-3329 Which measure 4.484"

acadian · Feb 22, 2023

I had a similar issue with my T140 rebuild last year and the alloy PRTs, I turned down the upper shoulder by about .020, used .125 square section rings at the bottom, and thin orings on the shoulder (1.25mm CS if I recall), this gave the correct crush clearance for my set up (copper head gasket). Main point, the range of bottom ring thicknesses is limited, but the range of upper oring thicknesses is not... look for your solution there

Tigernut · Mar 4, 2023

acadian said:
I had a similar issue with my T140 rebuild last year and the alloy PRTs, I turned down the upper shoulder by about .020, used .125 square section rings at the bottom, and thin orings on the shoulder (1.25mm CS if I recall), this gave the correct crush clearance for my set up (copper head gasket). Main point, the range of bottom ring thicknesses is limited, but the range of upper oring thicknesses is not... look for your solution there

I finally bought yet another set of PRTs (LF Harriss, from Monty's Classics). They are correct, though I still needed to de-burr a couple of the oil drain holes. On the O rings matter, I'm sure what you say must be right if you've done it and found it to work, but to my mind, as O rings are circular in cross-section, a smaller x-section ring will also be narrower when fitted - in other words, it won't reach the sides of the housing. Sealing may still be perfect if the face of the housing is dead flat and without imperfections, but I'd have thought that the ideal would be for the ring to completely fill the space when the head's clamped down?

acadian · Mar 9, 2023

Tigernut said:
I finally bought yet another set of PRTs (LF Harriss, from Monty's Classics). They are correct, though I still needed to de-burr a couple of the oil drain holes. On the O rings matter, I'm sure what you say must be right if you've done it and found it to work, but to my mind, as O rings are circular in cross-section, a smaller x-section ring will also be narrower when fitted - in other words, it won't reach the sides of the housing. Sealing may still be perfect if the face of the housing is dead flat and without imperfections, but I'd have thought that the ideal would be for the ring to completely fill the space when the head's clamped down?

True, smaller CS ring will not fill the ID of the PRT bore in the head, but if the contact surfaces on the tube and head are in good nick, and with a smear of copper RTV, they seal up good. Getting the crush height correct is the main concern, as you know, and I'm not certain how much sealing actually occurs at the distal contact area of the rings anyway.

Edit/; Another option I've not pursued would be to simply buy some sheets of silicone rubber gasket material, they come in a range of thicknesses, you could very easily make up a punch and cut your own square CS bottom rings