Combat pushrod excess compensation?

Hobot · Mar 6, 2012

Combat pushrod excess compensation?

A most common short cut error Norton did occurs in the Combat pushrods not being shortened along with CHO head lowering. Pushrod length should center rocker on valve stem.

note:
I'm not asking how to optimalize rocker contacts, just if there was a poor rocker geometry in pre-'72's or if they were pretty good centered, so can use pushrod length to calculate what to term for known amounts of more milling or spacing of components.

so:
We know how much of the head was removed in CHO's but I've never seen how much the pushrods were off to restore good geometry. Did prior Cdo's have pushroad about right? If anyone has whittled on Combat pushrods - what's the expected ballpark removed?

lynxnsu · Mar 7, 2012

i have used shortened pushrods minus 3mm
they are maney ones to prevent flex

beng · Mar 7, 2012

Heinz Kegler had an interesting theory on Norton rocker-arm geometry that was pretty much his own if you do not mind me sharing it.

He said that when the cam was on the base circle, that the end of the rocker arm should be centered as much as possible on the valve tip and then as the cam moved the rocker arm it would sweep the rocker end towards the inside of the valve.

The reasoning behind this was he said that the most pressure and strain on the valve train was when it was initially trying to move and accelerate the valve off it's seat. He said later on once the valve was moving quickly and up over the nose and back down there was much less work or strain on the parts. So he said it was important to have everything centered up at the beginning of the lift cycle, but later on was much less important.

This is how he set up his bikes. He also claimed that when "Norton" lengthened the valves on the Norton twin engine for the Commando engine it was a mistake and made rocker arm geometry worse, that engine builders should convert things back to how they were on the early 650 and 750 Atlas engines.....

batrider · Mar 7, 2012

When I sent my combat head to Leo Goff I also sent along the pushrods in case he needed to shorten them. He did shorten the exhaust pushrods slightly he said. They must have been different amounts because he labeled them right and left. He also added some shims on all the rocker spindles to center the contact point - valve adjuster to valve stem.

He replaced my intake pushrods with a pair of good used ones he had around. He said mine were not genuine Norton and he could bend them by hand. Well I couldn't but he's bigger than me with bass string clamping hands. They were narrower than a stock pushrod but the ends looked right. I never realized this or had a problem even slightly passing 7000 rpm occasionally while accelerating madly through the gears. They came to me as supposedly genuine new pushrods from the old Custom Corners mail order shop in Rhode Island in the early 80s. Wonder what happened to him (Brian I think it was?)

So it sounds like a good question for Leo... He doesn't seem to mind talking on the phone either.

JimC · Mar 7, 2012

To paraphrase an insurance company add: You are in good hands with Leo Goff.

I've been dicked around by local machine (butcher) shops. Sent my head to one of the Norton suppliers that also does machine work and they said the seats were too hard to grind. Sent the head to Leo, got back an excellently prepared head. No whining, no problems.

comnoz · Mar 7, 2012

beng said:
Heinz Kegler had an interesting theory on Norton rocker-arm geometry that was pretty much his own if you do not mind me sharing it.

He said that when the cam was on the base circle, that the end of the rocker arm should be centered as much as possible on the valve tip and then as the cam moved the rocker arm it would sweep the rocker end towards the inside of the valve.

The reasoning behind this was he said that the most pressure and strain on the valve train was when it was initially trying to move and accelerate the valve off it's seat. He said later on once the valve was moving quickly and up over the nose and back down there was much less work or strain on the parts. So he said it was important to have everything centered up at the beginning of the lift cycle, but later on was much less important.

This is how he set up his bikes. He also claimed that when "Norton" lengthened the valves on the Norton twin engine for the Commando engine it was a mistake and made rocker arm geometry worse, that engine builders should convert things back to how they were on the early 650 and 750 Atlas engines.....

I have noticed that the greatest wear in the Norton cam and lifter occurred at a point just after maximum lift when the valve and lifter comes back into contact with the cam after being "launched " from the peak of the lobe. If you look at a used lifter you will see a line or dent across the center that lines up with the cam just after peak lift. Any non-rotating lifter will show this.
Here is a picture of a used cam graph. It is showing wear on the exhaust lobe just after peak lift. Notice the slight flattening of the curve just to the right of the peak. I would assume that peak loading on the valve tip is going to occur just after peak lift also. Jim

cash · Mar 7, 2012

Jim,
I wonder if backlash caused by a slack cam chain could be a contributor ?

Cash

comnoz · Mar 7, 2012

Cash,
I would expect a slack cam chain might change the harmonics a bit and move things around but the "crash" of the valvetrain is still going to be there after the peak.
I read something about this years ago in some Mercedes Benz literature. The finger followers in their OHC engines show the same wear line that they indicated was caused by the valve returning to contact with the follower after the peak lift. Jim

swooshdave · Mar 7, 2012

comnoz said:
Cash,
I would expect a slack cam chain might change the harmonics a bit and move things around but the "crash" of the valvetrain is still going to be there after the peak.
I read something about this years ago in some Mercedes Benz literature. The finger followers in their OHC engines show the same wear line that they indicated was caused by the valve returning to contact with the follower after the peak lift. Jim

I wonder if a gear driven cam would exhibit less of the harmonics?

comnoz · Mar 7, 2012

swooshdave said:
comnoz said:

Cash,
I would expect a slack cam chain might change the harmonics a bit and move things around but the "crash" of the valvetrain is still going to be there after the peak.
I read something about this years ago in some Mercedes Benz literature. The finger followers in their OHC engines show the same wear line that they indicated was caused by the valve returning to contact with the follower after the peak lift. Jim

Click to expand...

I wonder if a gear driven cam would exhibit less of the harmonics?

I have a half dozen gear drive prototypes here that I have been trying to get made into a good design for a Norton. The sever harmonics in the Norton valve train have caused some serious noise and gear wear that I have not fully overcome as of yet.
It would be a lot easier if there where only two gears needed instead of four.
The original stretchy cam chain in a Norton does a great job of damping the harmonics of the spinning cam. Jim

swooshdave · Mar 7, 2012

comnoz said:
swooshdave said:

comnoz said:

Cash,
I would expect a slack cam chain might change the harmonics a bit and move things around but the "crash" of the valvetrain is still going to be there after the peak.
I read something about this years ago in some Mercedes Benz literature. The finger followers in their OHC engines show the same wear line that they indicated was caused by the valve returning to contact with the follower after the peak lift. Jim

Click to expand...

I wonder if a gear driven cam would exhibit less of the harmonics?

Click to expand...

I have a half dozen gear drive prototypes here that I have been trying to get made into a good design for a Norton. The sever harmonics in the Norton valve train have caused some serious noise and gear wear that I have not fully overcome as of yet.
It would be a lot easier if there where only two gears needed instead of four.
The original stretchy cam chain in a Norton does a great job of damping the harmonics of the spinning cam. Jim

I vaguely remember seeing a design for a split gear that provided a little cushioning and perhaps it was quieter.

Perhaps like this:

Each camshaft gear is a split (scissors) type, consisting of two concentric, spring-loaded gears, set at a slight angle from each other. When engaging the teeth of the idler gear, the spring-loaded split teeth of the cam gear take up any backlash, ensuring smooth and quiet operation.

http://www.honda.com/newsandviews/artic ... 0707112298

http://www.ktm950.info/how/Orange%20Gar ... rhaul.html

Of course I can't imagine what it will do to the cost. :mrgreen:

comnoz · Mar 7, 2012

I have something similar to that running in my bike. Of course it took two of them. They are preloaded with a ball and ramp arrangement and the ramps are wearing out. Jim

Hobot · Mar 7, 2012

Educational as always to a novice like me, that 650's and Atlas 750's had geometry about right. What I want to do is run a Combat w/o a head gasket and adjust rocker geometry "towards" ideal by thickness of a base plate. Going by Leo' Geoff's concepts implies to leave push rod length alone and raise cylinder by a bit more than is removed by lack of head gasket. Provided the squish and valves don't clash w/o a gasket, end result would be rocker force applied straighter on stems when matters the most, at initial inertia lift off, then offset contact towards inside of valve/shorter side of rocker arc, and give single plane to seal combustion, moving the 2nd planar seam to the base plate that don't see such thermal and pressure spikes. So what's a good guesitmate of base plate thickness to do this yet not make the geometry any worse than is so common and may even improve it???

Gear or belt drive cam will never be used by me in plain ole Trixie Combat and is not yet adequate for a Ms Peel engine or more extremely expensive equivalents.

hobot, last deer-car strike sets back Norton work by days-wks + couple hundred bux just to get back to normal travel function, so nothing improved or advanced, just more spending to exist, ugh. 1986 grill in 1996 car fooled us on hi vs lo beam lamp sockets, so now get to switch those out to bring in zone to adjust for legal and useful lighting. Till Trixie smoker solved, better not use her either. Don't clutter with a response to this rant, just know we are not in full control of our life and times, so sharing the mood helps dilute it.

lcrken · Mar 7, 2012

I've always set up the rocker arm geometry by watching the path of the rocker arm tip as the cam opens and closes the valve. The idea is that as the tip sweeps out and back accross the valve stem end, the contact path should be centered on the end of the stem, not offset towards the inside or outside edge of the stem. A little machinist blue on the end of the stem helps see the path. I have a selection of different length pushrods to find the right length, but a better way would be to have a set of adjustable pushrods to find the right length without having to repeatedly pull the head to replace pushrods. Once you have it right, you cut normal pushrods to the right length. That's what Steve Maney does to set up his engines. So far, I've been too lazy to make up the adjustable rods. Maybe in my next life.

There are probably more precise ways of setting the rocker geometry up by making special tooling to check the angle between the valve stem and rocker arm axis, but I'm not sure you'd actually gain anything for the extra work.

Ken

comnoz · Mar 7, 2012

Here is another picture that shows the point of highest wear on a Norton cam. Notice the flattening between the two dots. It is more obvious when you look at the cam graph with the cam analyzer software but I can't post that directly. This is the point of maximum impact on a Norton cam. Just after peak lift.

Hobot · Mar 7, 2012

Ugh, hard to keep yoose scatter brained guys on point here : )
I guess I'm on my own again, so will stick some feeler guages around base plate seam and clamp down assembely decently then watch the magic marker'd rocker action then order up base plate thickness. I suspect right off the shelf plate may be about right off the bat. I want to correct geometry and seal better simpler in one easy step away from plain factory method while keeping ~Combat CR.

As to the most wear prone lobe/lifter contact, where would one place cam lobe oil exit for best effect, keepping in mind this smack down landing area has nothing to do with the pushrods which should go slack about then. Blame dam deer on my delay not to send Peel's cam in for processing this fine spring I'm missing out on d/t ground level chemtrails. Nitride might be last Peel cam beef up to go.

Hobot · Mar 7, 2012

Detailed forum discussion to help confuse me into Leo Goff camp on pushrod lenght on valve train life style. Clues on how to enjoy a bit over length p-rods.
Must take new look at what to do and end up with

http://speedtalk.com/forum/viewtopic.php?t=3731

comnoz · Mar 8, 2012

This is what you need to get your pushrod length right.
There is no "one size fits all"
Valve stem length and therefore the pushrod length depends on the lift of the cam in use.
This puts the rocker to stem contact point in the same position on the valve stem at closed and full lift. That minimizes the sweep of the rocker across the valve stem which helps cut down on valve stem and guide wear. Jim

Hobot · Mar 8, 2012

Hey thanks for the hand drawing Jim, but its not possible for rocker arc contact to be the same at no lift and full lift w/o some gimbal contact gizmo. Leo Goff's reference leaves my head cocked on implications. I thought I only had one question on posting how to retain or get centered stem contact.

a.) how to run Trixie w/o a head gasket - just a base plate, of a thickness to both "help" the valve geometry and not mess with CR or squish gap much?
I don't expect to get optimal this way, just retain ok geometry w/o smoking.
Removing gasket is same as lengthening push rods. Raising barrel base is same as shortening rods. Was hoping for standard amount to trim Combat p-rods, then could calculate base plate thickness. Will just have to check w/o base plate or gasket and go from there with feeler guages under cylinder.

Yet I stumbled on more than I thought I needed to know.. so...
b.) what is the optimal geometry for lift and endurance in a special like Peel.
best lift or best force alignment for narrowest contact?

Quote from Buddy Rawls:

"Pushrod Length- Incorrect pushrod length can be detrimental to valve guide wear. Most sources say that centering the rocker contact patch on the valve stem centerline at mid valve lift is the correct method for determining the optimum pushrod length. This method is wrong and can actually cause more harm than good. The method only applies when the valvetrain geometry is correct. This means that the rocker arm lengths and stud placement and valve tip heights are all perfect. This is rarely the case. To illustrate this, think of the valve angle and the rocker stud angle. They are usually not the same. If a longer or shorter valve is installed, then the relationship of the valve tip to the rocker stud centerline has changed. Heads that have had multiple valve jobs can also see this relationship change. Note, the rocker length (pivot to tip) remains unchanged, so the rocker contact patch will have to move off the valve centerline some particular distance for optimum geometry to be maintained.

The optimum length, for component longevity, is the length that will give the least rocker arm contact area on the valve stem. In other words the narrowest wear pattern. This assures that the relationship is optimized and the rocker is positioned at the correct angle. This means that the optimum rocker tip contact point does not necessarily coincide with the valve stem centerline, and probably will not. What is the acceptable limit for being offset from the valve stem centerline? That will depend on the set-up. A safe margin to strive for is about +/-.080" of the centerline of an 11/32 diameter valve stem. This means that no part of the wear pattern should be outside of this .160" wide envelope. As the pushrod length is changed, the pattern will change noticeably. As the geometry becomes closer to optimum, the pattern will get narrowest. If the narrowest pattern is too far from the valvestem centerline, then the valve to rocker relationship has to be changed. In this case, valve stem length will need to change."

comnoz · Mar 8, 2012

hobot said:
Hey thanks for the hand drawing Jim, but its not possible for rocker arc contact to be the same at no lift and full lift w/o some gimbal contact gizmo.

Better think about that. And read the link you posted again. Jim

quote from the link

Postby #84Dave » Sat Aug 12, 2006 8:11 pm
Ed...... your 2nd paragraph is a perfect example of 'over-arcing'. Valve guides take a tremendous beating with an over-arcing situation in the geometry. Your 4th paragraph explains proper geometry. -------Wherever the roller is positioned on the stem tip at CLOSED valve, that should also be the roller position on the stem tip at full OPEN valve, for proper geometry.-------- Swinging through the arc between those points will cause the narrowest sweep of the rocker roller across the tip toward the exhaust side, which imparts the most of the cam lobe 'command' across the rocker ratio to the valve. Minimum lost linear valve movement and about as good as it gets. Your comment on valve length? Another comment, which you're likely aware of. On my typical paved oval Chev engines with a stand/shaft system. I'll have about .700" NET intake and .660" NET exhaust lift. Half that NET is .350 & .330 (Mid-Lift). So there's obviously a .020" delta @ mid-lift. I always set the proper geometry by having the exhaust valve .020" shorter than the intake @ full closed. That's why pushrod lengths in .050" increments are a no-no for my use. If I used them in the above example, I'd re-introduce error back into the valve geometry. And finally...... I have a whole bag of extra .025/.050/.100 Jesel shims. When required, which is most of the time, I'll machine the thicker shims to get the proper stand heights. I try to get within .005" @ final installation.

Combat pushrod excess compensation?

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