About time for the spintron

billet · May 21, 2015

comnoz said:
I got a package from JS today. He sent a JS2 camshaft as made by Megacycle along with a couple different springs to try. He asked that the springs be set at .050 from coil bind.

Here is a graph of the JS2 vs the PW3. They are very similar but the JS2 has the advantage of being made of steel.

Here is the JS cam in the spintron.

The beehive spring at .050 from coil bind gave 142 lbs of seat pressure. That ought to close the valve.

To me it seems that it has not been taken advantage of the beehive springs itself.
I`ts an awfully high spring pressure.
Maybe too much spring pressure can make the valve bounce?
Would be interesting to see the JS 2 cam tested with your conical ovate spring.

Sten

280 lbs at full lift.

Here are the spin results.

[video]https://youtu.be/ol5Pp2_FA3o[/video]

Spring number 2 was .035 shorter at coil bind. With an additional .035 shim It gave 150 lbs on the seat

It gave 285 lbs at full lift

Here are the results

[video]https://youtu.be/MBq_VLYpVVA[/video]

cjandme · May 21, 2015

This is an amazing thread, thanks for posting it Jim :mrgreen:

jseng1 · May 21, 2015

Yes the PW3 is about the same as the JS2 and they both have the same abrupt closing ramp. To be fair you need to compare the PW3 with the best (Honda) springs Comstock could find (upper vid), to the similar JS2 cam with the beehive springs etc (lower vid). Note that the seat pressure is about the same with either spring setup (only 2 lbs diff). At 7000RPM you can see that the JS2 setup is doing much better. The PW3 intake is described as having “severe” valve bounce and the exhaust valve is bouncing as well. At 7000RPM the JS2 setup shows no valve bounce on the exhaust and the intake is not bouncing as much as with the PW3. So according to the spintron tests the Beehive springs and the lighter lifters make a significant improvement.

[video]https://youtu.be/L0_pud6vcuw[/video]

PW3 cam above
JS2 cam below

[video]https://youtu.be/ol5Pp2_FA3o[/video]

See the comparison of the JS0 JS1 JS2 and JS3 ramps below. The JS2 (copy of PW3) has the most abrupt ramp of the group by far. I didn’t really want to send this cam in for testing on the spintron because it is presently being redesigned for me by Megacycle so it will have a smoother closing ramp. I plan on splicing on the more ideal ramp from the JS0 cam which looks like the smoothest of the four JS ramps. I also have a JS2 cam coming from Webcam and will see if it has a smoother ramp than the Megacycle version.

What I need is for you (Comstock) to send me an accurate clear image of the 86C ramp so I can compare it to the JS0 and JS1 ramps. You sent a screen shot of the 86C but I need a better and more precise image with even readable duration increments and lift (at .1") scales. The PW3 is one of the most popular racing cams and splicing on a smoother ramp to get rid of the valve bounce would make it very attractive.

comnoz · May 21, 2015

jseng1 said:
What I need is for you (Comstock) to send me an accurate clear image of the 86C ramp so I can compare it to the JS0 and JS1 ramps. You sent a screen shot but I need a better and more precise image.

All I can send from my cam analyzer program is a screen shot.

I can send you an S96 file but you will need a cam analyzer program to use it. Jim

comnoz · May 21, 2015

Here is the best I can do with a screenshot.

jseng1 · May 21, 2015

comnoz said:
Here is the best I can do with a screenshot.

Yes
That's exactly what I need.
Thanks

Also I think you mentioned that your spintron is using big valves. Most people reading this forum are using stock valves. The heavier bigger valves are going to bounce at a lower RPM - the intake bounces sooner than the lighter exhaust for this reason. Comparisons have already been made and its too late to change that but people should know if their lighter stock valves are going to fair better than what is shown in your spintron tests.

Snotzo · May 21, 2015

Jim,
would you advise what followers you used for the spintron tests with the JS cams ?

With regard to using the PW3 for comparison purposes, this cam was designed for use with the flat Norton followers. Using radius followers may alleviate the bounce problem, but will be at the cost of some loss of area under the valve lift curve, but at normal (7000 absolute max) rpm, any performance short fall would hardly be a big issue.

For out and out competition use, a new valve lift design would be the ideal way forward, but the requirement would first need to be clearly defined.

comnoz · May 21, 2015

Snotzo said:
Jim,
would you advise what followers you used for the spintron tests with the JS cams ?

With regard to using the PW3 for comparison purposes, this cam was designed for use with the flat Norton followers. Using radius followers may alleviate the bounce problem, but will be at the cost of some loss of area under the valve lift curve, but at normal (7000 absolute max) rpm, any performance short fall would hardly be a big issue.

For out and out competition use, a new valve lift design would be the ideal way forward, but the requirement would first need to be clearly defined.

Snotzo,
The followers used with the JS spintron test were NOS -BSA followers. Right out of the package. Jim

jseng1 · May 22, 2015

What intake tappet clearance did you use for the JS2?

comnoz · May 22, 2015

jseng1 said:
What intake tappet clearance did you use for the JS2?

.004 inch

jseng1 · May 22, 2015

If your spintron is using an oversize intake valve then you should tell us how much it weighs. If its a big valve then you could put in a thick walled seat and return it to stock size valve and weight.

A stock intake valve is about 66 grams. Oversize valves weigh about 72 to 76g and this will make them bounce at a lower RPM.

A lot of PW3 cam owners are reading this thread and most of them are using stock valves. If there is a RPM valve bounce difference between stock and oversize valves then they should know how much that difference is.

comnoz · May 22, 2015

I am obviously doing this research for my own development of a race engine. It is certainly going to include big valves as there is much more to be gained in the cylinder head than with a big cam.

I do have a stock valve cylinder head I can mount up and see how much difference it makes when I get some extra time. I am sure there will be a difference but I doubt it will be a big one. The difference in valve weight is less than 3 grams. Jim

Brooking 850 · May 22, 2015

I am running 0.006" for the intake and 0.008" for the exhaust with my JS2 cam, should I be running less?
Regards Mike

motorson · May 22, 2015

I am running 0.006" for the intake and 0.008" for the exhaust with my JS2 cam, should I be running less?
Regards Mike

The spintron shouldn't be getting very hot so the pushrods and everything aren't going to "grow" and take up a bunch of clearance. The specified clearance on any engine should go nearly to zero when the engine is at operating temperature. Maybe a tiny bit for oil and a bit for that extra hot temp reached sometimes.
Dan.

comnoz · May 22, 2015

Brooking 850 said:
I am running 0.006" for the intake and 0.008" for the exhaust with my JS2 cam, should I be running less?
Regards Mike

The literature JS supplied with the cam stated a running clearance of .004. I don't add to that figure since there is little heat involved. Jim

motorson · May 22, 2015

I might be confused here but I always thought that the clearance specified in any engine manual is designed to make sure the valve can still close even with everything all up to operating temperature. In a push rod engine you obviously have the lifters, push rods and valves which will all grow a bit when heated. Some of that is going to be balanced by the growth of the cylinder, head and even the block. All added together you come up with the final clearance you want to run at when everything is hot. How would JS get away with a lower clearance when they are pushing the same push rods, lifters and valves in the same engine?
Dan.

comnoz · May 22, 2015

motorson said:
I might be confused here but I always thought that the clearance specified in any engine manual is designed to make sure the valve can still close even with everything all up to operating temperature. In a push rod engine you obviously have the lifters, push rods and valves which will all grow a bit when heated. Some of that is going to be balanced by the growth of the cylinder, head and even the block. All added together you come up with the final clearance you want to run at when everything is hot. How would JS get away with a lower clearance when they are pushing the same push rods, lifters and valves in the same engine?
Dan.

JS gives a "running clearance" meaning it will be set when everything is up to temperature. Then depending on the materials used for pushrods and barrels the clearance may be more or less when checked cold. Jim

CanukNortonNut · May 23, 2015

comnoz said:
At the urging of Snotzo I decided to try some tests with asymmetrical ground lifters. What an improvement.

Here is the offset ground lifter I am using.

Here is the graph showing the curve produced. Note the fast opening rate and the easy closing rate with the big closing ramp.
Here it is compared to the PW3. The 86C has a little more lift.

Here it is showing the acceleration spikes that is causing the problem at higher rpms with the PW3. You can see the 4 big spikes from the PW3's opening and closing ramps.

]

Here is the wear pattern obn the lifters after 20 minutes run time at 5500 rpm. The cam contact area seems to be safely contained in the lifters area.

Jim
Regarding your asymmetrical ground lifters. How are these profiled? Is it a smaller radius leading edge going to larger radius trailing edge on the profile? Would this work with a 12a?
Thanks,
Cheers.
Tom
CNN

comnoz · May 23, 2015

Jim
Regarding your asymmetrical ground lifters. How are these profiled? Is it a smaller radius leading edge going to larger radius trailing edge on the profile? Would this work with a 12a?
Thanks,
Cheers.
Tom
CNN[/quote]

These are a simple 3 inch radius offset .250 toward the leading edge. They would work with a 12A but you will loose some effective duration. Depending on the use -that may not be a bad thing.

I am also experimenting with a flat leading edge going into a 3 and 4 inch R. trailing edge. This is looking good for the 12A grind as it looses less area under the curve yet revs with no bounce.

These mods also move the peak opening point about 8 degrees closer to the point of maximum piston speed/airflow demand. Jim

jseng1 · May 23, 2015

Brooking 850 said:
I am running 0.006" for the intake and 0.008" for the exhaust with my JS2 cam, should I be running less?
Regards Mike

I've adjusted my clearance figures a couple thou.

Its best to adjust them hot with .004' intake and .006" exhaust clearance. Then measure cold and keep records so you can always adjust cold. But 1st you want to check hot because cold measurements will be different with alum or iron barrels. Personally I've been running mine at .003 and .005" and I haven't noticed it changing. Its quieter and easier on the valve train.

.002" looser won't hurt anything and I've run them this way as well (but looser will add high RPM valve bounce).

When I worked at a BSA shop we used to adjust them as tight as possible (no feeler gauge) with the slightest amount of play that you could barely feel and still never burned a valve.

Jim Comstock - It would be good for you to verify if tighter tappet clearance really means less bounce. It could just as well be that the cam flexing and bouncing back is causing the valve to bounce and a lot of clearance (such as .015" or .020") might eliminate the rocker arm from pushing the valve open and causing it to bounce. If it worked then this would be an easy fix.