Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board 3TA pushrod seals?

Digging through the pile of assorted bits I've come across the pushrod covers. These don't seem to match up with what I've read, especially here: https://sites.google.com/site/rightfootshifterspages/home/test/pushrod-sealing

My tubes look like the ones in the parts book with an enlarged diameter for the bottom inch or so which has what looks like a sealing rubber sleeve inside. Also on my engine (but not in the parts book) are white seals on the top of the tappet block. I have red seals in the cylinder head.

The rubber sleeves (p/n 70-3758) seem to be unobtainable. Any suggestions?

If you look at a picture of a 3ta gasket set on eBay you can see the rubber sleeves in there so they must be available. I then typed in "3ta pushrod seals" and they came up straight away.

Dave

Thanks Dave. I'm a bit reluctant to get gaskets from ebay as I've had bad experiences in the past. I have discovered that TMS list the seals however. But I'm still not sure whether I should also have the white seal and the "wedding ring" as these are in place on the tappet blocks I have - which may of course not be original 3TA items....

Have a look at the 350/ 500 tubes at the bottom of this page.

https://www.jrcengineering.com/tech...triumph-tappet-blocks-and-pushrod-tubes/

Dave

Many thanks Dave, that's a really useful site and explains (probably almost) everything.

I'm still struggling a bit here. Doing a dry assembly with the barrels & head on the bench, and fitting the pushrod tubes without the lower seals as they don't affect the height of the tubes. With a "thick" head gasket (measured at .041") and no upper seal but some plasticine in the recess the plasticine is compressed to .020". The white seals I have are .100" thick approximately. This would give a crush of .080" which is about twice what I've seen recommended - the seals would be squashed down to one quarter of their original thickness. This doesn't sound or feel right to me.

The parts were supplied by Feked in the UK.

Any thoughts?

Despite having mismatched crankcases from different years not to mention different capacities, the bottom end and timing gear has all gone together remarkably well. There's no perceptible step between the case sides at the barrel face and the crank and camshafts all spin easily. So I'm hopeful about that side.

Less so about the notorious pushrod tube sealing which has had me scratching my head for ages. There is an annular seal at the bottom of the tube which fits over the tappet block and a Viton ring which sits in the head to seal the top flange of the tube. The book and the experts here I've consulted say there should be .040" - .060" "crush" on this top ring when the head is bolted down. However, assembling with no seals at all leaves the head floating .040" or so above the barrel face - which coincidentally is close to the thickness of the head gasket. I measured this using plasticine in the joint and tightening the head down with no gasket.

Obviously, putting seals in would mean that there would be no clamping force on the head gasket at all. So after much thought I've decided to turn .060" off the bases of the pushrod tubes to allow them to sit further down and get this crush. What can possibly go wrong? More to the point, why do I need to do this? My only theory is that the head face has been skimmed at some point. Remember that this engine is being built from a fairly random selection of bits which someone else has discarded after selecting better ones.

Just looking at the photos I have to make sure that the reduced portion of the tube won't catch on the tappet block. And of course I will have to deal with any effects on valve / pushrod geometry if as I suspect the head has been skimmed.

Some photos:

This is the barrel after tightening down the head showing the flattened plasticine.

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This shows how the pushrod tube sits on the tappet block.

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Another view showing the flange at the top of the tube and the (annealed) head gasket - which by the way was rock hard when it arrived.

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This is the recess in the head that the flange fits into.

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The first pushrod tube in the 4 jaw chuck - it's too big for the 3 jaw.

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And this is the Viton sealing ring which is .090" thick uncompressed.

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There are three types of tappet block for 350/ 500 unit Triumphs. I don't know what the difference is but maybe you could try a comparison.

Dave

Yes I suppose I could but that would mean spending money and I'm notoriously parsimonious. Anyway, I think I now have a solution which will work for me.

I think the pictures tell all! If you go back to the posting that refers to to the JRC article, the tappet blocks with the tubes you have should be 70-3736, which have a very small diameter flange that fits inside the pushrod tube. You have later tappet blocks with larger flange diameter, so that can't happen. Shortening the pushrod tube may well work, as long as the bottom of the tube is not hitting the top of the flange when the bottom seal is fully compressed. You'd better hope you have a slight oil leak, as the bottom of the pushrod tube will rust where you have broken through the chrome!