Pushrod Sealing

Pushrod sealing is always a problem with Triumphs. Get it wrong & they leak like the Exxon Valdez! With care & the correct parts the sealing is robust & you should focus on 3 issues:

1. Use the correct parts; all of them!

Often owners will change parts from other years or leave parts out, sometimes through no fault of their own.

An example is that later 500 pushrod sealing uses a thin wall ring (often called a wedding band by their owners). Quite often these are discarded as a cosmetic part. But their function is to prevent the white square section seal from squeezing out. Once that happens then a leak is inevitable. To compound the issue the part is ommited from the parts book! However the 650s that use this arrangement do have the wedding band (Pt No 71-1707) in their parts book.

Since publishing the above statement I have had feedback that the parts book stipulates o rings top & bottom & no square section seal. Under such circumstances my only counter-arguments are 1 that the 650s use this arrangement & 2 that without the use of the square section seal there is no means to change the seal compression as described in section 2 below.

My sketch below shows a black o ring at the top but a red o ring can be used &, if as originally specified as a higher temperature component, would be preferable to the black o ring. Never use o rings from a plumbing store; they are designed to seal water pipes, not joints on ic engines!

2. Ensure you have the correct seal compression for your parts.

This has to be set for each individual engine. You will find that deviation from the factory parts may be necessary because for example the cylinder head has been skimmed. If the seal compression is not enough then the pushrods will leak, too much & you risk distorting the head. The aim is to get in the range of 30 thousands of an inch (0.75mm) to 40 thousands of an inch (1.0mm) compression set of the pushrod sealing system. There is a Triumph Bulletin (324) that specifies 30-40thou. The compression set can be adjusted by selecting one of the different thicknesses of white square seal that are available on the market:

Thin square seal= 70-3547(~2.5mm)

Medium square seal=70-4752(~3.2mm)

Thick square seal=70-1496(~5.0mm)

Additionally on the 500 unit Triumphs there are 2 thicknesses of head gasket due to a change of specification on '67onwards 500s which specified a thinner head gasket:

Thin Head Gasket=70-4675(~0.6mm)

Thick Head Gasket=70-4015(~1.2mm)

This obviously alters the cylinder compression ratio, rocker adjustment & space between piston & valve, so checks in these departments need to be considered before making the change of head gasket thickness.

CHECKING THE SEAL COMPRESSION SET

There are 2 methods you can use:

 1.dry assemble without the seals but with head gasket & pushrod

tubes, measure vertical float of the pushrod tubes in situ. The

white seal thickness is this measurement plus the 30-40thou compression minus the oring thickness (~2.5mm dia).

2.dry assemble all the parts including head gasket & seals, ensuring

the pushrod seals are fully seated. Measure the gap between head

gasket & head with feeler gauges

3. Don't be afraid to use additional sealants

Each owner has their preference, just be sure not to slop too much on that may break free & clog an oilway.