8 replies to this topic

[jonlad]

Hi folks, a quick and easy one for you engine builders out there...

 

Should there be a gasket on the bottom of the rocker post(s) in particular the one with the oil feed through it?

 

Sure enough there hasn't been on the engines i've stripped, and i can't find one advertised anywhere, it just looked a bit odd putting it together without one.

 

I guess it'd have to be all of them or nothing to keep the shaft perfectly straight...

 

 

I'm sure theres a good reason for it not to be there...?

 

Thanks

Jon

[Spider]

There's no gasket there, but a good idea to clean the bottom of the posts up on the oil stone and wash properly before fitting.

[jonlad]

Quick and helpful as ever thanks MokeSpider

[tiger99]

It was a really interesting question! There will be some small amount of leakage between post and cylinder head, which of course ends up back in the sump. At least one of my ancient engines had the base of the oil feed pillar machined with an annular groove to take an O ring. I don't think it was an A series, more likely a Triumph, but it would be an easy mod if anyone was seriously concerned about their rocker shaft oil feed being inadequate. But it would be better putting the groove in the head so gravity would keep the O ring in place during assembly.

[jonlad]

Thanks Tiger, it seemed odd to me on first inspection that there wasn't a seal, especially given the criticality of oil feed to the rockers.

 

The A series designers must have known what they were doing though!

 

I like the idea of an o-ring and hadn't even considered that. A counterbore would be easy to create, an annular groove might be beyond my backstreet garage ability

[minimans]

No gasket but you may find the odd shim under them if somebody's been playing with the rocker geometry.............

[nicklouse]

not needed as the pressure is low when it gets up there. what it does need is a clear path.  ie no misaligned parts. lack of locating grub screw allows the the shaft to rotate closing off the supply. leading to wear.

[tiger99]

That is a good point! The car where I saw the O ring had the flow restrictor at the rocker shaft end so the oil came up at significant pressure, hence the need for the O ring.

 

As for making the groove, it would normally be done on a lathe or milling machine, but as it is generally ok to use a flat bottomed groove it could me made by hand, with a normal drill, using a very small holesaw with the pilot drill replaced by a plain rod, or by a counterbore with some metal removed by grinding so that it left an unmolested ring around the hole, to prevent the O ring collapsing inwards during assembly.

 

By the way, in most applications a square O ring groove ideally wants to be 82% of the O ring thickess in both width and depth. That gives the correct amount of retention when dismantled, and compression when assembled. A very hard O ring material will need a bit more than 82%. At about 78% the O ring is squeezed completely into a square section, which is not good.

[Cooperman]

In around 70 years of the a-series engine, an O-ring has never been necessary.

There is no problem with the standard set-up.

I just built a Ford 2.1 Pinto OHC engine and there is not even a gasket between the oil pump face and the block. I was surprised, but it works fine at up to 7500 rpm with no loss of pressure.