Merlin camshaft rocker pivots

[bathtub tom]

I've searched the forum to no avail.

Can anyone explain, please, why Merlin rocker pivots appear to be on a rotating shaft?

http://www.unlimitedsdetroit.com/images/RandyRoe/rr_merlin_valve.jpg

[H Peacock]

It does, as you say, appear that the rocker pivot shafts rotate, but they don't. These spur gears are driven by the camshaft gear-train but rotate freely on the rocker shaft, ie the shaft doesn't rotate. They are used to provide a drive to accessories such as a Heywood compressor or engine rpm pick-off. You can see a small cover plate held on with 4 bolts in-line with the rotation axis where these are fitted.

[bathtub tom]

Thanks for that. I couldn't understand why they appeared to have a rotational aspect (is that a sentence?).

[cockney steve]

Have not even looked at your reference and I'm not a Merlin Engineer or afficionado, but i'll have a guess .....
A valve-rocker has a reciprocating motion which, given that thrust from pushrod and valve are always in the same plane(angular, not aero)
the rocker-shaft would have a tendancy to wear on the thrust-face, thus becoming elliptical in the pivot-areas.
A rotating shaft would minimise this, but in turn, the pedestal-mountings for the rocker-shaft would be subject to wear.

As an aside, RR's 6.75 litre car-engine had the camshaft-lobes ground with a slight taper, the objectivebeing to impart a slight twist to the follower thus rotating it for even wear....why they didn't just set the lobes slightly to one side of the centre of the follower, I've no idea.

[Onceapilot]

H.Peacock is correct. Interestingly, your photo shows a cam drive without the compounded spur gear that drove the auxiliaries. I assume this is a Meteor?

[Linktrained]

OAP

That would be the Meteor engine, as fitted to the Comet ? (The proper one, with tracks and a turret, I mean !)

Some training for these was done at Farnborough, adjacent to RAE, in 1945 using a Ryper Simulator, which overlooked the R/W.

PS Other road users treated tanks with "L" plates with some respect but did not know that some pupils were not yet 18 and some Instructors were just 19.

Slightly different speeds, I recall, to something built by DH a little later and also seen at Farnborough !

[Onceapilot]

Linky, I suspect the pic is of an ex-tank Meteor engine fitted to a tractor (as in tractor racing) , judging by the generally non-aviation standard of pipes etc.
PS. Never argue with a tank, my father-in-laws stone built barn did and, came off worse-twice!

[slacktide]

Engine in the pic is most assuredly installed in an unlimited class hydrofoil racing boat.

[Ozlander1]

Engine in the pic is most assuredly installed in an unlimited class hydrofoil racing boat.


Yep, give the man a medal. :D

[Typhoon650]

Hydroplane, not hydrofoil. Huge difference. One traps air under it to go fast, one rides on foils in the water to go fast.

[Onceapilot]

Boat, Tank, Tractor?
Next prize goes for the best explaination of why the aux idlers remain fitted when their compound drive gear is not fitted?:)