Heavy lifters and valve bounce (2015)

Peel will have 600 watt 3 wire field coil 8 lb alternator so allows me to day dream of this...

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Jim Comstock has confirmed that the cam is flexing in sync with valve bounce. Now he is well on his way to a central cam support and other details - see his spintron post.

I suspect that the heavy stock lifter is a big part of the cam deflection and spring back problem. A good way to demo that would be to fill a stock lifter with lead and see how much the increased weight effects valve bounce (hint for spintron). Or take this as a given and move on to solutions.

I don't offer the central cam support but all the JS cams in stock are steel with hard lobes.

Hi Jim, as a purchaser of some of your internals including the JS2 cam, your website states that the JS2 cam is a copy of the PW3 with some changes, would those changes include a better off ramp profile to ease the potential of valve bounce?
Note the point on them being of steel and not cast
Regards Mike

Much as almost all of us agree lighter parts that still endure is way to go But research has shown the mass on cam side of rocker has the least effect than other side. But till the tests are done just speculating and limit intervals over red line. I wonder if cryo tempering might stiffen detectable? Its done to rifle barrels to help dampen their metal tube oscillations that move faster than the bullet - so can shove exiting bullet off target.

hobot said:

Much as almost all of us agree lighter parts that still endure is way to go But research has shown the mass on cam side of rocker has the least effect than other side. But till the tests are done just speculating and limit intervals over red line. I wonder if cryo tempering might stiffen detectable? Its done to rifle barrels to help dampen their metal tube oscillations that move faster than the bullet - so can shove exiting bullet off target.

Click to expand...

When calculating spring force vs inertial force in pushrod type valve trains the valve train mass is converted to "mass on the valve side" to address the different rate of component movement on the valve side (faster) and the cam side (slower) of the rocker arm. To quantify the mass contributed by each component of a stock CDO valve train, thought it would be interesting to assemble a table showing the mass of each component of the valve train and convert all the values to "valve side mass" to allow an apple to apple comparison of each component.

The table below presents the results, where all entries in the "cam side mass" column are actual weights of the components and where entries appear in both columns, those in the "valve side mass" column have been mathematically converted from "cam side mass" to valve side mass and reported accordingly. The data table shows that the lifter is the 2nd largest contributor to valve train mass, representing about 80% of the IN valve mass. Employing a BSA lifter would reduce the lifter mass "on the valve side" to ~ 30 g, thereby reducing the total valve side mass by ~ 13%. Overall I was a bit surprised to see that the "valve side mass" of the entire valve train is on the order of ~ 0.5 lb, which is considerably heavier than my initial intuition suggested.



I believe Snotzo has done similar conversions in 4stHead for the simulations he has run, so hopefully he will be generous enough to confirm that these numbers are in the same ballpark as his.

Brooking

The profiles are not exactly the same - the JS2 has more duration and less lift than the PW3 and that means that there is less lifter acceleration and a more gentile slope which could mean less bounce, but not a gentile as the JS1/Axtell 3. JS cams are steel instead of cast iron like the PW3 and that also makes a difference.

The lighter lifters and the lighter beehive springs make a difference. The JS2 grind was probably originally designed for BSA/Triumph lifters and what works for lightweight lifters may not work for heavy flat lifters.

Hobot

"mass on cam side of rocker has the least effect" refers to car technology where the rocker ratio is greater and only then when the cam side is moving slower is the statement true. The Norton is different with a 1 to 1:14 ratio. Everyone forgets that - be careful about transferring car tech to Norts.

WZ

The lifters I measured were closer to 75 grams. As you say - surprising what the total mass figures out - its too much. You should figure out what the valve side mass it is with the BSA lifters and Beehive springs and show comparisons.

Weights

Stock lifter 74 g.

BSA lifter 38 g.

Stock spring pair is 59.7 g.
Stock retainer is 16.1 g.
R/D Spring pair is 59.3 g.
R/D Ti retainer is 10.8 g.
Bee spring is 42.3
Bee TI retainer is 4.7

The table below presents the results, where all "cam side mass" entries have been converted to "valve side mass" and reported accordingly. The data table shows that the lifter is the 2nd largest contributor to valve train mass, representing about 80% of the IN valve mass. Employing a BSA lifter would reduce the lifter mass "on the valve side" to ~ 30 g, thereby reducing the total valve side mass by ~ 13%. Overall I was a bit surprised to see that the "valve side mass" of the entire valve train is on the order of ~ 0.5 lb, which is considerably heavier than my initial intuition suggested.

Image

I believe Snotzo has done similar conversions in 4stHead for the simulations he has run, so hopefully he will be generous enough to confirm that these numbers are in the same ballpark as his.


WZ507

Click to expand...

While some of the data tallies, there are a number which differ, mainly through the method of measuring, or the use.
Valve, retainer and keepers, and follower are identical.
33% of the beehive spring I measured is 14.5 grams.
The pushrod weight is the same, but should be shown only on the cam side of the rocker pivot.
The intake rocker I measured weighed 95.4 grams complete with adjuster
For calculation purposes the rocker inertia is first calculated, which was 52 Kg/mm squared.
The weight of the valve end of the rocker differed from the weight of the pushrod end by 12.1 grams.

While the data might not differ so greatly, it is the way in which it is processed within the program which is so very complicated.

Listed below are comparisons of weights and spring rates etc between various brands of valve train. The Conical springs that were designed for me by the makers of Comp cam springs came up with a spring rate of 310 lbs. The beehives have stronger oval wire (.142" x .180") and the conical wire was the same thickness height wise but is round (.142").

JS Beehive valve spring 42.3 g, TI retainer 4.7 g, rate 324 lbs per inch, Street seat pressure 90 lbs, Race seat pressure 130 lbs

RD racing spring 59.3 g, TI retainer 10.8 g, rate 318 lbs per inch, Race seat pressure 130 lbs

Stock spring 59.7 g, steel retainer 16.1 g, rate 280 lbs per inch, Street seat pressure 85 to 90 lbs balanced with shims.
100+ lbs shimmed for racing

BSA radiused lifter 38 g
Stock flat lifter 74.6 g

JS pushrod 31 g
Stock pushrod 32 g

The illustration above shows that JS's imagination has not let him down!
This is computed at 8000 rpm to show the separation more clearly, but it is occurring to a lesser extent at 7500 rpm.
I have omitted to indicate a third separation even greater than the two indicated,around the valve closing point.
The lightweight BSA followers also separate from the cam at 8000 rpm, but only just.

As my simulation is carried out for a single cylinder, the effects of the two cylinders running will inevitably modify this output to some extent.

That I have used a PW3 camshaft for my computations is because I have the necessary profile data. I do not in any way suggest that the PW3 is an inferior cam, on the contrary, it is an excellent cam when used for the purpose for which it was designed, namely, a performance cam for a long stroke Commando engine.

If anyone can provide me with S96 files for another cam I will willingly run a computation using that data

Here are the closing ramp details as measured on my cam mapping hardware.

Snotz

Its good to hear that the PW3 has reduced valve bounce (just barely) at 8000RPM with BSA lifters compared to using heavy flat lifters. But but since the profiles are not labeled on the graph its difficult (if not impossible) to distinguish the flat lifter graph from the BSA lifter graph.

Comnoz
My graph below may not be perfectly accurate but it shows the different ramps for the different cams I use. .100" lift is at the top of the chart and the ramps have been joined at .100" lift to make comparisons easier. The JS1 is the Axtell #3 and that ramp should be good. The JS3 is the D+ and it looks like that ramp has already been fixed compared to the early Norris D+ cam. The JS0 is the BSA spitfire cam and it looks to be the most gentile. The JS2 is the PW3 which is undergoing so much scrutiny. To have this cam redesigned with a more gentile ramp costs about $500 (current quote) and I could do it but I'm not sure its necessary if valve bounce is "just barely" at 8000RPM with the BSA lifters and Beehive springs as Snotzo suggests. 8000RPM is getting a bit high and rarely do racers buzz beyond that (over-revving to avoid shifting into a turn) and if they do then a little float is tolerable - hopefully their motors start to wheeze a little, run out of poop and self govern.

Is it worth it? I'm not sure but I'm checking into it. On the other hand - if you could get the valve to slam down faster with less ramp - like desmo action (and not break the valve) you would get more power where you want it.

I would like to test JS2 cam on my spintron and see how it looks. Jim

comnoz said:

I would like to test JS2 cam on my spintron and see how it looks. Jim

Click to expand...

Do you have one (a JS2 steel cam - not cast iron)?

If so - go for it. Might as well use the Beehive springs as well if you have them. I suggest you shim them to .050" from coil bind as in the instructions.

jseng1 said:

comnoz said:

I would like to test JS2 cam on my spintron and see how it looks. Jim

Click to expand...

Do you have one (a JS2 steel cam - not cast iron)?

If so - go for it. Might as well use the Beehive springs as well if you have them. I suggest you shim them to .050" from coil bind as in the instructions.

Click to expand...

I do not have a cam or springs. I do have lifters and blocks.
If you want to send Mike's cam to me I will spin it and send it on to him. He has OK'ed that. Jim

Here's a ramp comparison that I traced/copied/overlaid/magnified from a PW3/JS2 comparison graph that Jim Mosher (of performance Indian) made for me when he was putting together Fred Eikers 920 Nitrous land speed racer. Its a little crude but you can see the difference in ramps. Hopefully its enough of an improvement that valve bounce won't be a problem - it depends how high you rev it.

jseng1 said:

Here's a ramp comparison that I traced/copied/overlaid/magnified from a PW3/JS2 comparison graph that Jim Mosher (of performance Indian) made for me when he was putting together Fred Eikers 920 Nitrous land speed racer. Its a little crude but you can see the difference in ramps. Hopefully its enough of an improvement that valve bounce won't be a problem - it depends how high you rev it.

Click to expand...

Jim,
Thank you for the education on valve train physics. I've noticed that even with the Photobucket anti blocker add on for my Firefox browser, I can not view the image in this post or in

https://www.accessnorton.com/NortonCommando/heavy-lifters-and-valve-bounce.18975/page-2#post-283153

Can this be fixed?

I also have a question. How do the A65 BSA lifters differ from Triumph T120 & T 140 lifters? Is the Triumph radius incorrect, or perhaps the length? I ask, because Triumphs were "much" more popular. There are a lot more used Triumph lifters around, compared to BSA.

Charlie

Triumph lifters used to come in two different radiuses - the "R type' has the bigger radius. Most Triumph 650s will cop 8,000 RPM without blowing up - but not for long. It is still the situation where good mid-range torque is better than lots of top-end horse-power. And generally if you improve one, it is at the expense of the other. If you improve the mid-range, you can run higher gearing - then valve-bounce is not a problem. Once you have over-ported the head, you are stuffed.

I have a question. - When you fit the barrels to a Triumph engine, it is common practice to fit a piece of rolled-up paper between the stems of the lifters to stop them from dropping into the crankcases. How is this done with Norton barrels and BSA lifters ?

Pieces of hose pushed over the lifters.

Circlips in the groove at the top of the lifter are the stock BSA method.

Ken