Combat pushrod excess compensation?

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OK thanks for setting me straight on this- ie: that if the head is constructed about perfect, then its possible the rocker arc trace line can intersect valve stem at its two travel postions. 90' mid range contact makes sesne to me as retains best leverage angles.

I don't yet know if my factory Combat or my special allow for this or not. Closest approach to your 90' constant point contact is the narrowest contact example. The bugaboo is where that lands on stem or lash cap.

All I really want to know, ahead of time, is if my Combat can get away with better sealing w/o a head gasket by juggling base plate thickness.
 
hobot said:
OK thanks for setting me straight on this- ie: that if the head is constructed about perfect, then its possible the rocker arc trace line can intersect valve stem at its two travel postions. 90' mid range contact makes sesne to me as retains best leverage angles.

I don't yet know if my factory Combat or my special allow for this or not. Closest approach to your 90' constant point contact is the narrowest contact example. The bugaboo is where that lands on stem or lash cap.

All I really want to know, ahead of time, is if my Combat can get away with better sealing w/o a head gasket by juggling base plate thickness.

If you can seal the head without a gasket you sure can make up the height with base shims.
I haven't had much luck with using no gasket. I have run them with thin copper rings or copper wire o-rings but have never been able to seal one for very long running just head to barrel. Jim
 
Ugh, but have ya tried Hylomar? I had best luck with real flamering, just didn't have any on hand when Trixie needed it. Still don't have a new gasket on hand, why would I after a few 1000 miles fine. Now I don't trust current copper one anymore, so encouraging its mechanically safe to try a Plan B in my ongoing lesion plan. I may have the points ignition set a weep bit advanced too, but only a hint of back fire rarely - so not by much. Will report back if it works out any better than yours did. Will order real flamering as back up.
 
comnoz said:
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. Jim

The impression that it is normal for a valve-train to have clearance between it's parts under normal operating conditions except when a solid lifter is resting on the base circle of the cam lobe would be wrong. When parts lose contact with each other while the lifter is on a ramp or lobe then you have valve float and are on your way to making junk.

Only a poorly designed cam, valve-train or valve float would let a valve-train be "launched" and have to land with enough force to damage itself, and I can believe that the Norton valvetrain with all it's disadvatages and faults will be the one to have problems if they are possible.

The Norton valve train has almost every disadvantage one could think of for an overhead-valve valve-train. The worst part of it is it's low rocker-arm ratio which is almost down to 1:1. This means that the entire valve action that is needed, acceleration and lift, has to be ground into the cam lobe itself, and that limits valve action a lot compared to an engine like a General Motors pushrod V-8 which has historically used rocker arm ratios between 1.5-2:1.

If someone moved the pushrod ball on a Norton rocker arm in towards the pivot to get the rocker ratio up to 1.3:1, which is a possible modification to the stock parts, the a cam could be ground on a larger base circle that is much stiffer than a stock cam. the cam could even be ground full-relief on a blank that is almost the size of the standard cam tunnel. This is because the higher rocker ratio would let the valve have adequate lift that would not all have to be ground into the lobe. The lobe could be far less radical than they have to be now, with much less and gentler movement of the lifter and pushrod than currently is used.

Also because the leverage advantage a high ratio would give to the valve spring in controlling the lifter-side of the valve-train, the same or even a weaker valve spring could be used for a given rpm.

The Norton engine is a real POS design for high-rpm work, but still a lot make it their hobby to try and get it to do the job of a short-stroke-OHC, multi-main-bearing engine.

A high rocker ratio would let the valve move faster and spend more time at a useful lift for any given duration, enhancing the only thing the Norton twin gets close to having as a strength, which would be making useful power at rpms below that which cause it to fall apart.

Instead of concentrating development on High Rpm power from an engine that can not stand it, and turning the engine into something completely different to what ever came out of any factory in the U.K., a high rocker arm ratio used to produce high lift with a moderate duration could squeeze mid-range torque out of a Norton that no one ever has before, and at an rpm level that would let it be done without completely re-manufacturing it into something alien.

Development in this area might let an engine with a re-worked standard head running high-ratio rockers, run in the mid-range like a Full-auto head with standard rockers and cam profiles....at much less cost.

Getting back to Heinz Kegler's idea of having the rocker arm contact the center of the valve while it is heavily loaded during the acceleration of the lifter up to the nose of the cam, the Nascar tuner Smokey Yunick agrees about that being the point of highest stress during operation.

Also there are two different kinds of loads possible in a poor valve-train like the Norton's. If you have a glass table you can gently set an Anvil onto it and it will hold it's weight with no problems, but you can drop a penny on the table from the height of a few feet and possible chip, crack or even shatter it. In a well designed valve train made entirely from glass, or maybe hardened steel, there are ideally no shock loads during operation, the springs keep everything together during the lift cycle and the cam profile accelerates everything while keeping below the limits of launches and drops.

What Kegler was concerned with was dealing with the maximum normal pressures and side-loads endured by the valve-train and valve guide during engine operation, which is something that is going to occur at any rpm from idle-speed on upwards. The sort of shock-loads induced by poorly designed lobe profiles, weak valve springs and high rpms were probably not what he was aiming his solutions and theories at.....
 
Gosh beng, I love it when ya talk like that!
So does anyone know if Combats are supplied with 'long' push rods that put rocker contacts a bit on the 'under arc' side to stem? How much off 90' do Combat rockers land with factory assembled items.

I know Nortons get damaged in rpm red zone. I'm cooking up a hi pressure slow roller hi gear'd torquer, but not Trixie Combat smoker.
 
Hi I'm a new member, been devouring posts for some weeks now. Been rebuilding my 1970 Commando for about a year now (so many tasks, so little time). I first built this bike from an accident-damaged basket case in 1983 ( the crankcases were in 5 pieces and I had them welded up). It ran nicely, except for the time when it swallowed a piece of Amal slide, but no real damage done. It ran sweetly on a run to Brisbane and back. Its had little use since 1988 but I wanted to give it a 40th birthday present by actually using it again. Unfortunately it had not appreciated being neglected and it complained bitterly. Hence the bare-frame rebuild started last year. I found I could buy parts from England far more cheaply and easier than local (unlike 1983) and I went a bit overboard. Regarding the issue of pushrod lengths, I didn't take enough notice of the rocker angles before dismantling but I THINK my pushrods are too long for best sweep/loading parameters. I can't get my head around the Heinz Kegler theory posted by beng; surely the more the valve opens the more the spring pushes back on the valve train, wouldn't this outweigh any inertia? Maybe if our Nortons had desmodromic valves....? Jim's post makes sense, that is, to centre the arc at half lift, to minimise the sweep across the valve tip. However, another of Jim's posts refers to measurement of peak loading occurring after the valve "launches" from full lift. Maybe, then, it may be better to err on the side of centring the arc slightly after half lift, that is to increase the sweep slighlty to relieve the valve train of some loading? Anyway, I'm on to the engine now. Forks, gearbox, vernier isolastics, frame, long sidestand done. Not long to go.
 
hobot said:
Gosh beng, I love it when ya talk like that!
So does anyone know if Combats are supplied with 'long' push rods that put rocker contacts a bit on the 'under arc' side to stem? How much off 90' do Combat rockers land with factory assembled items.

I know Nortons get damaged in rpm red zone. I'm cooking up a hi pressure slow roller hi gear'd torquer, but not Trixie Combat smoker.

If all other parameters are equal the Combat pushrods will be shorter to compensate for the factory shaved head, I have read that the difference is .040".

One of the Combats factory installed faults was coil bind. Dealers installed thiner bottom spacers/heat insulators to relieve this issue. Given the very closeness of coil bind after this fix and the concievable similarity with non-Combat valve trains wouldn't the potential for launch be quite limited? I have become a believer in radiused tappets for quieting the valve train; experts have told me that I am giving away horsepower, but don't have much to say when I tell them that reliability is my goal. I think that putting the valve train on a diet is the best way to gain function and reiability; my next Cdo engine will have JS Engineering's BSA tappet/pushrod modification.

In previous post by beng he speaks about increasing the rockerarm ration to permit a larger cam profile that would decrease the acceleration the tappet experiences so that the engine could make more useful power; great post!

So why does the Triumph run so well with a cam that has an acceleration ramp that has virtually no curve? They go from the base circle to an almost flat ramp; the tappets have a radius, the pushrods are short and light and the rockerarms have a ratio greater than 1:1. This would appreat to fly in the face of previous posts???

Great thread.

RS
 
hm, RS, I didn't know about Combat spring bind. My reason for asking about Combat push rod length is the quality of head gaskets now-a-days, so was hoping to go w/o a gasket or base plate, wondering if that would be in right direction and amount to comensate for the longer push rods in Combat with shaved heads. I've got a special that is a far away from Norton and still be considered a Norton by the unknowing, but hardly anyone could service Peel's parts as non have a factory parts number. I'm want to keep one Combat as Norton as possible, so how do I do it and not smoke and leak every season of mild normal use. Peel is the one I will mistreat to the max, not plain Jane Trixie.
 
In an earlier post Comnoz has a picture that shows cam wear on the back side of the lobe. He equates this to maximium loading on the valve tip. I just can't get my head around that picture. Could there be something else at play here?

It seems to me the intake might have initial high load overcoming inertia of the valve, springs and keepers but then the spring loading would build until it's open all the way and I just can't see how loading could go even higher on the back side of the lobe. The exhaust valve must overcome the pressure in the cylinder as well as inertia which migh cause very high inital loading but I can't see the backside loading here either.

Could the valve springs be expanding from maximum compression in less than a smooth action maybe even jaring the valve train like a jackhammer on the way down?

Is it possible that the high forces of peak lift with maximum spring compression on the lobe have actually reshaped the lobe pushing top of the lobe toward the back side rather than worn it off? If this were the case then it would explain why the leading side retains it's shape. I don't suppose you have a graph of the original profile to see if the lobe has changed other than the flat spot.
 
kentvander said:
In an earlier post Comnoz has a picture that shows cam wear on the back side of the lobe. He equates this to maximium loading on the valve tip. I just can't get my head around that picture. Could there be something else at play here?

It seems to me the intake might have initial high load overcoming inertia of the valve, springs and keepers but then the spring loading would build until it's open all the way and I just can't see how loading could go even higher on the back side of the lobe. The exhaust valve must overcome the pressure in the cylinder as well as inertia which migh cause very high inital loading but I can't see the backside loading here either.

Could the valve springs be expanding from maximum compression in less than a smooth action maybe even jaring the valve train like a jackhammer on the way down?

Is it possible that the high forces of peak lift with maximum spring compression on the lobe have actually reshaped the lobe pushing top of the lobe toward the back side rather than worn it off? If this were the case then it would explain why the leading side retains it's shape. I don't suppose you have a graph of the original profile to see if the lobe has changed other than the flat spot.

The wear on the backside of the lobe is caused by the impact of the valve train coming back in contact with the cam after the valve train is "unloaded" as it goes over the peak of the cam. On the opening ramp of the cam there is a loading ramp that opens the valve smoothly so there is no impact to break the oil film. Plus the spring pressure of the valve near the seat is low in comparison to the spring pressure near its peak - then you add the inertia of a falling valve and wear here is common.

Here is a better picture of the wear in comparison to an un-worn cam.

Combat pushrod excess compensation?
 
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