Promoting Valve Rotation?

GRM 450 · Nov 30, 2010

Next question please,

What is the best way to promote valve rotation in a Mk3 head.
New guides are about to be installed, the old ones didn't last very long and the valve seats showed pitting and the stems have marks that show the valves were not rotating.
A suggestion is to use a .005" flat shim under the bottom spring retainer and lap the inner and outer of the retainer and the bottom of the spring so they can rotate easily.

Any one have a comment on this?

Desmo heads are easy as there isn't very much spring tension and the rocker can be offset slightly tp promote the valve to rotate. But I'm new to this valve spring thing,,,,

graeme

geo46er · Nov 30, 2010

Greetings,
Personally I have never heard of such a thing. Under the tension of the typical valve spring I seriously doubt that any rotation takes place at all. Could you provide some references regarding this???

GB

Hobot · Nov 30, 2010

Never heard of valve rotation provision in Norton, just slot like wear on stem tops by centered rocker geometry. Usually in engines its the flat lifters slightly tappered on cam contact that rotate, not the valve. Interesting if you can pull this off in Norton.

comnoz · Nov 30, 2010

There is no valve rotation in a Commando. Special spring seats or valve caps are required to allow a valve to rotate if you have offset in the rocker. Jim

splatt · Dec 1, 2010

NO :!: :!: :!: ,as for the offset rocker thats a standard commando feature

GRM 450 · Dec 2, 2010

Thanks,
The fellow who does machining for me (a perfectionist to the extreme) told me to lap the springs into the bottom and top spring retainers, and then lap the bottom of the lower spring retainer and install a .005" shim between the retainer and the head when I first built the motor.
I didn't do this because I thought it was a waste of time and I couldn't see how the spring could let the valve rotate.
Anyway 8000ks later, with the head off to have the exhaust thread repaired, I was amazed to see the wear to the guides, seats and valve stems. (the stems aren't so bad, but they obviously weren't rotating)
This time I will do as he suggests as it can't hurt? And time will tell if it makes any difference at all.
He does lots of English race bikes, so I will heed his advice.

graeme

comnoz · Dec 2, 2010

GRM 450 said:
Thanks,
The fellow who does machining for me (a perfectionist to the extreme) told me to lap the springs into the bottom and top spring retainers, and then lap the bottom of the lower spring retainer and install a .005" shim between the retainer and the head when I first built the motor.
I didn't do this because I thought it was a waste of time and I couldn't see how the spring could let the valve rotate.
Anyway 8000ks later, with the head off to have the exhaust thread repaired, I was amazed to see the wear to the guides, seats and valve stems. (the stems aren't so bad, but they obviously weren't rotating)
This time I will do as he suggests as it can't hurt? And time will tell if it makes any difference at all.
He does lots of English race bikes, so I will heed his advice.

graeme

I know most car engines with rotating valves used a spring cap or seat with radial needle bearings inside to allow them to rotate. I also know that 70's Ford motors with rotating valves suffered with severe valve recession problems when the switch to unleaded was made. Ford removed the rotators to help reduce the valve recession problem. I would be interested in seeing the result if you get the Norton valve to rotate. Jim

mike996 · Dec 2, 2010

I don't know if any modern engines are designed with rotating valves but in older engines the mechanism to allow valves to rotate is more problematic than any advantage gained by a rotating valves. Back in the 60's/70's several manufacturers tried it and dumped it in just a few years. The Norton valve train, like most other valve trains, does not rotate the valve and cannot be made to do so without totally re-engineering the valve assembly/rocker arm. The advantage is more theoretical than practical.

prmurat · Dec 2, 2010

If I look at the Panhard system it seems it was only possible because of the no springs configuration(torsion bars). I have difficulties seeing a system like this with regular valves springs.
Philippe

splatt · Dec 2, 2010

It's done quite easily, use valve retainers that touch each other,the valve is the free to spin happily, jump up and down and then eventually fall into the cylinder,Ford use this method on certain motors, but they use multi groove collets

comnoz · Dec 2, 2010

splatt said:
It's done quite easily, use valve retainers that touch each other,the valve is the free to spin happily, jump up and down and then eventually fall into the cylinder,Ford use this method on certain motors, but they use multi groove collets

And they still fell into the cylinder.

Hobot · Dec 3, 2010

Ms Peel's excesses and conflicting needs has taken me on wide ranging searches scratching at straws to spank elite moderns with biplane power plant. I've never come across valve rotation on purpose but have found various ways to get flat tappet lifters to rotate on the cam contact. Generally a combination of off centering of tappet on cam lobe center line or a slight bevel on tappet face. Requires liffers to be round in profile of course. Use of radius lifters and roller lifters requires some means to keep them from rotation, either in shape of by tying two lifters together with swivel bars.

Promoting Valve Rotation?

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