Rocker feed route

[marki]

Hi All.

  Looked at a friend’s 6 today after he had to change his rocker shaft, he has no oil feed to the rocker.

where does the feed come from ? I’m presuming a gallery up through the block and head to the rear of the shaft. He’s only just bought this car and he was told the engine was rebuilt a couple of years ago. Is it possible they could have fitted the head gasket the wrong way and blocked the feed ?

 Cheers Mark

[Nigel Triumph]

The feed to the rockers comes up through a drilling in the rear left corner of the block, from the rear camshaft journal.

There's a matching drilling in the cylinder head, so oil to the rockers does indeed need to pass through the head gasket. I'm not sure how the gasket could be fitted wrong to block the feed, they are marked to show which way up they should go.

Other possible blockages could be dirt, misaligned cam bearings (if fitted) and incorrect assembly of the rocker shaft components. All these errors would require a ham-fisted approach to engine assembly.

There are also blanking plugs in the ends of the rocker shaft. If those were omitted the oil would dribble out of the ends of the shaft without reaching the rockers themselves.

Nigel

[marki]

Thanks Nigel

 I did take out the screw in the end of the rocker hoping to see some oil but nowt there.

[ed_h]

Only one of rhe rocker shaft pedestals is drilled.  I think It's possible to put a non-drilled pedestal in the position where the oil feeds.

Ed

[TonyC]

Hi Mark,

just been through all of this in detail after having to change rockers and shaft due to badly worn rocker probably caused by blocked oil gallery at no 2 cyl position, this despite oil and filter changes every year i.e. 3-4000 mile interval.

The rear shaft pedestal has the oil gallery co-incident with the hole in the head. The oil is fed under pressure up through that gallery and into the hollow rocker shaft, which in turn has galleries co-incident with each rocker arm. As Nigel notes, there are plugs in the end of the shaft which if not fitted or loose will allow oil to leach out and starve the rockers of lubrication. One point to check is that the shaft isn’t in the wrong way round, which prevents the oil galleries in pedestal and shaft lining up once the tapered plug is fitted to secure shaft to back pedestal to stop shaft rotation. Unlikely as the feed for the rockers would be in the wrong place as well, but worth a check in case that hole in the shaft has been drilled in the wrong place when manufactured.

I used new phosphor bronze bushed rockers which make a little more engineering sense for longevity. A point to note and which I found a little surprising is that the oil bleeds out of the rocker shaft onto the rockers and doesn’t spray out as you might imagine and which is perhaps more usual on OHC engines. You can run the engine with rocker cover off and not get covered in oil. There are (should be) two gallery holes on the rockers themselves - one on the top allowing oil to dribble down onto the valve stem area and one at the back allowing oil to dribble down onto the push rod socket area.

Hope it helps.

 

TonyC

 

[Andy Moltu]

The rockers are fed via the cam journal, effectively reducing pressure so you wont get huge flow like an OHC engine.

The other thing to check is that the grub screw is in place or the shaft can rotate and the feed not align with the intended hole in the rocker shaft.

The can fit a direct feed that takes a feed from the oil gallery and feeds it to the head (into the existing rocker feed gallery via banjo bolt).

However this can deliver too much oil to the top of the engine and pour oil down the oil guides so many restrict the feed to 1-1.5mm by brazing and drilling the banjo bolt.

[john.r.davies]

As said above, the oil gets to the rocker shaft from the rear camshaft bearing.   The pressure in there won't really be enough under any circumstances to pump it up higher, so there is a flat and a scroll on the camshaft journal, to urge the oil onwards.    This is sometimes called a 'metered' oil supply.

The oil passage passes vertically from the camshaft bearing, through the block, the gasket and cylinder head.   But the rear rocker shaft pillar does not line up with that drilling, so a horizontal passage was drilled from the rear left hand corner of the head to connect them both.    You will find a machine screw there that seals the outer end of that passage.

Because the passages join at a right angle and are not smoothed, the junctions may trap particles, so when opportunity arrises, a probe with thin wire or a blow-through with an air line are advised.

John

Edited July 7, 2022 by john.r.davies

[marki]

Thanks for your replies gentlemen, the engine is now out on the way for a rebuild after I found lots of particles in the oil amongst other things. It’ll be interesting to hear back from the builder.

 Cheers Mark