Valve adjuster contact geometry

JRD said:

One of the reason of change in geometry is the seat recess.
When guide are changed , the seat is usually recut . Then the valve seat is a bit deeper in the head, the valve sits higher and the rocker arm is no longer in the middle of the valve stem.
Solution is to change seats , and avoid to recut seats when guide are changed (if possible)

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When I changed guides a few years ago it was necessary to cut the seats. I didn't take more the .010" off and the valves seem to sit up quite nice in the head. My geometry is off on that side a little but I believe in the range of exceptability.
I am in the process of obtaining a RH6 or RH5 and will probably offer this one up when the time comes.
It may need seats and has a broken fin as pictured but is basically a good head as it sits, but that's for another part of the forum.

rvich said:

Was the geometry improved on the Fullauto heads? Or just more accurate machining?

Russ

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Just more accurate machining.

It's easy to get a valve off center when replacing guides. Reamers don't necessarily follow the guide bore unless a jig is used to guide the reamer.
New guides with non-concentric bores are also pretty common from some suppliers. Jim

The roadholder article, i assume there is no copyright issue in posting this.

3000 miles? There must have been something wrong. Here's mine after 13K miles. Original setup.



Dave
69S

Well it appears my geometry is out of whack due to the fact that my valve height is .110 too high. .020.or even .040 might be acceptable but .110 has cause the rather new exhaust guides to to prematurely wear for and aft to the rocker action.

All this is because the valve seat are wore out. Some have suggested grinding the brand new stellite valve tip and use lash caps but lash caps are .080 which would mean the I would have to remove .180 from the tip. This is of course not applicable because the beehive springs are longer and the valve stems are already machined up closer to the tip.

My recourse is a valve seat and guide renewal or find a head with good seats and guide. I would hate to put that much money into this head. Although it's given years of good service, it seem to be a little tired.
Ahh, the thrill of the hunt. Crap!

Hey, you've still got about a month, maybe more in MI. Get on it.

Dave
69S

Another possible reason is that the valves are too long
There are exhaust valves that are 3.94" Long As Against 4.1" For Later Valves;

Ref;
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... RL:GB:1123

"New guides with non-concentric bores are also pretty common from some suppliers. Jim"
I find this hard to grasp. The process of manufacture pretty much forbids it.. I.D. and then O.D. are turned while chucked up, then parted off. :?: Tell us more of what you see....

concours said:

"New guides with non-concentric bores are also pretty common from some suppliers. Jim"
I find this hard to grasp. The process of manufacture pretty much forbids it.. I.D. and then O.D. are turned while chucked up, then parted off. :?: Tell us more of what you see....

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Non-concentricity is not generally a problem if the guide is bored in a modern CNC machine.

Many guides are made in a turning center or a screw machine and the hole in the center is created with a drill.

Take a piece of bronze alloy rod and put it in your lathe. Then try to drill a hole exactly through the center of it. The drill is going to want to wander off center as you drill. That is a common problem on some guides. Jim

comnoz said:

concours said:

"New guides with non-concentric bores are also pretty common from some suppliers. Jim"
I find this hard to grasp. The process of manufacture pretty much forbids it.. I.D. and then O.D. are turned while chucked up, then parted off. :?: Tell us more of what you see....

Click to expand...

Non-concentricity is not generally a problem if the guide is bored in a modern CNC machine.

Many guides are made in a turning center or a screw machine and the hole in the center is created with a drill.

Take a piece of bronze alloy rod and put it in your lathe. Then try to drill a hole exactly through the center of it. The drill is going to want to wander off center as you drill. That is a common problem on some guides. Jim

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This is a common issue when machining bronze and brass in general, and copper, my god, that's another issue all together.
Bronze and brass needs to be scraped, so to speak, with the cutter edge literally blunted and perfectly balanced. But actually, these should be bored then reamed to size. With a traditional cutter, even if new, and after a perfect center drilling, will help but tenandancy is to pull to one side, the more it grabs, the more it pulls to that side and there you have it, a seemingly good guide but only offering poor geometry. This could be why cast Iron guides were used, other than offering up black lung, a no brain-er to machine.
This being said, it is only one of many possible conclusions to poor geometry.

pvisseriii said:

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This could be a little bit of an optical illusion caused by the mushroom adjuster, but it looks like it would be nearly impossible to get the adjuster on the head of the valve where you want it just by cutting the valve down. The problem is that shortening the valve doesn't do anything to change the geometry and position of the rocker, it will be exactly where it was but the adjuster gets reset. That would bring it will be closer to the center, but it doesn't look like it would be that much.

But putting in a little longer pushrods would change the geometry of the rocker. It would bring the rocker down and the adjuster up. It would make a bigger difference in the alignment compared to just cutting the valve. Maybe the combination of longer pushrods and shorter valves can help you get it straightened out without doing the seats and guides. You should be able find custom pushrods and maybe valves that are the right length without needing to be cut down.

Heres an enourmous picture of the Allen Key type . which do not require three hands to adjust .

( actually Triumph ones , but UNF . ) http://www.google.com/imgres?imgurl=htt ... CEQQrQMwDA

Thinking if Yr heads planed away , SHORTER pushrods will bring the angle acoss the tips greater and the lenghtll get them centred - ish . Thicker head gasket d have the same affect . The mushroom head suckers are getting side contact afore face contact .

rpatton said:

pvisseriii said:

This could be a little bit of an optical illusion caused by the mushroom adjuster, but it looks like it would be nearly impossible to get the adjuster on the head of the valve where you want it just by cutting the valve down. The problem is that shortening the valve doesn't do anything to change the geometry and position of the rocker, it will be exactly where it was but the adjuster gets reset. That would bring it will be closer to the center, but it doesn't look like it would be that much.

But putting in a little longer pushrods would change the geometry of the rocker. It would bring the rocker down and the adjuster up. It would make a bigger difference in the alignment compared to just cutting the valve. Maybe the combination of longer pushrods and shorter valves can help you get it straightened out without doing the seats and guides. You should be able find custom pushrods and maybe valves that are the right length without needing to be cut down.

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re; But putting in a little longer pushrods would change the geometry of the rocker. It would bring the rocker down and the adjuster up. It would make a bigger difference in the alignment compared to just cutting the valve.

May I ask, would fitting a thick copper head gasket as opposed to a thin head gasket have any marked difference on this problem :?:

Yep Barnard every change of base or head gasket or of head or barrel milling affects the valve geometry gooder or badder. Example being the Combat Norton fitted with standard Commando push rods but with head milled the pushrods are ~.04" too long for best geometry. One generally sets up engine assembly first then fiddle the push rods. I've bought Maney steel p-rods for Peel but have not had them cut to size yet d/t not knowing which gasket I'll end up yet. There is some controversy on what is best geometry though, center rocker motions all across stem or get rocker contract centered at max spring compression loads...

I have found a head with, what would seem to be, factory fresh seats and guides. The contact points are so much better and would seem to validate the notion the the old seat were cut either too deep or too wide. I think it is more like the later. That is not to say that perhaps the guides in the old head were not machined right.

I have milled the head and am ready for assembly. My issue now is that I have sent my "C" head along with the new exhaust valves to JC to get the exhaust seats and guide replaced. Oh well, no big whoop, I'll see them soon enough.

I am excited to run the seemingly new modified RH1 and have 32mm to 30mm adaptors for the new 32mm premiers, not to mention the new powerArc in place ready to fire.

New,




Old,

It looks as though the guide might have been loose in the head and somebody reamed the hole and fitted an oversize guide, and in doing so got the guide out of alignment. If it came from the factory that way, it is pretty disgusting .

I found this recently,and it is completely wrong.

ntst8 said:

The roadholder article, i assume there is no copyright issue in posting this.

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It would work if the radius on the adjuster screw was part of of a roller which was free to rotate,but we don't have roller rockers.
The radius on the adjuster is approximately 3/8",and that's approximately the error you would have on valve length using this method.(The valve would end up too short).

The authors have confused rolling with scrubbing and side-thrust.Hold an adjuster in contact with a valve tip.Rock the adjuster through 20 degrees and watch it roll across the valve tip.With 3/8" radius and 20 degree swing,it will roll across the valve-tip approximately 0.131".This must happen between zero lift and full lift (the adjuster rolls across the valve-tip away from the rocker shaft) if the adjuster is not skidding on the valve and creating side-thrust.It won't happen exactly,but you can get it close.

By an accident of geometry,the least amount of total scrub/skid happens if you take a line off the valve-tip square to the valve stem and it passes through the centre of the rocker spindle at mid-swing of the rocker (which is a little under 1/2-lift).Then the arcing action of the rocker closely matches the rolling action of the adjuster.You would then get the amount of scrub calculated in this magazine article.Do the calculation as if the adjuster radius was part of a roller,and use the radius from the rocker spindle centre to the roller centre.Then calculate how far the adjuster radius must roll across the valve for the same angular swing.Calculate for full-lift and 1/2 swing.

In any case its better to have the square situation at about 1/3 lift,or even less for very high rpm,because at high rpm the forces are greatest at opening and closing acceleration.

Any comments?

On 5/26/2013 3:31 PM, Peter Charlton of Brit Iron list wrote:
> Not sure what you are trying to say Steve, but I was the author of the original part of that article, the more complicated maths/geometry and diagrams were added by somebody else. All I know is that originally my valve tips had deep troughs worn from one end of the valve tip to the other, and after only 3000 miles, and now, after shortening ny valves by the method I proscribed, my adjusters do not move at all across the valve tips, they simply lean from side to side as they open the valve, and the only mark left on the valve tip is a small circle bang in the middle.
>
> I did post all this stuff on the Brit Iron list quite some years ago, and seem to remember another chap here who had independently arrived at the same conclusion as myself, the Commando valve stems are too long.
>
> Pete Charlton

Like I said,the article in Roadholder is completely wrong,and it ignores the fact that tipping the adjuster through 20 degrees causes it to roll on the valve tip.The bigger the radius on the adjuster,the further it will roll IF THE GEOMETRY IS CORRECT.

Holding the adjuster central while it is trying to roll only causes it to skid and create side-thrust.It won't be good for valve guides,and it will cause concentrated wear at the centre of the valve tip.

If anyone were to try that method of adjusting geometry,I would suggest they use a dummy adjuster screw of zero radius (ground to a point where it contacts the valve-tip).The results will be completely different,by about 3/8" in valve length.The results will be more accurate,for reducing scrub/skid and side-thrust on a solid rocker (non-swivel,non-roller).

If the valve length is correct,changing the radius on the adjuster does not affect the amount of scrubbing/skidding.It only afffects the distance that the adjuster rolls across the valve tip.It can roll 0.130",but only skid by about 0.015" in the process.Between 1/2-lift and full-lift,the adjuster is rolling away from the rocker spindle but the skid/side-thrust on the valve-tip is pushing the valve toward the rocker spindle.

ONLY A ROLLER-ROCKER,OR SWIVEL-FOOT (LIKE PORSCHE) ,SHOULD BE SET UP AS DESCRIBED IN THAT ARTICLE.

Resurrecting this old thread since I've recently had reason to investigate this stuff.

I agree entirely with X-file, although nobody wants gouges in the tips of their valve stems from one edge to the other it is none-the-less evidence that your rocker/valve/pushrod arrangement is as good as it can be.

Although the spherical radius on the end of the lash adjuster is fixed the motion imparted to it by the action of the rocker is an approximation to true rolling across the tip of the valve.
Rotation plus translation = rolling.
Arrange things to minimize the translation and you are still left with the rotation of the adjuster spherical radius against the tip of the valve i.e. a grinding action.

You can't achieve true, zero-slip, rolling with a rocker because the rate of translation can't be fixed relative to the rate of rotation. but the stock arrangement likely limits average slip to about 15% or so (i.e. adjuster translating 15% faster or slower than it needs to, to keep up with the rolling action).

I'm going to be happy if the witness marks on the valve stem end and the lash adjuster are about the same length and reasonably centered.