Comstock valve springs and cam wear

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Comstock - Here are the exact spring pressures you sent to one of your customers:

height lbs
1.350" 120

1.250 153

1.150 189

1.050 222

0.950 260

Here is the exact recommended installation height you sent to your customer:

"recommended install 1.370 to 1.4"

******************************************************

So then (after calculating) 1.400" install height would be approx 103lbs (add .320 lift = 215 lbs)

1.370" install height would be approx 110lbs (add .320" lift = 222lbs)

The numbers you provided to your customer do not match the numbers in your video above. Something is wrong.

In the "Worn PW3 cam" thread you say (referring to your springs) “Actually, the added pressure over the nose helps improve the cam life”. (post #30). If this is true then why are you now suggesting that lower spring pressures are better than higher spring pressures? And how did your springs have higher over the nose pressure then but lower over the nose pressure now?
 
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The results are consistent to my findings though. New standard springs at fitted height should be about 108 lbs, giving roughly 223 lbs at max valve lift with a 06.1084 cam. Some consider this way too high, but can't give a figure backed up with evidence of what would be a good figure to use.
I am currently running a cam and radiused followers and will be at Austria with it if all goes to plan, this, on the FA head is 59 lbs fitted, not what I wanted or predicted but happy to go with it for test purposes, and 199 lbs at max valve lift of 11.24mm. This set up will be inspected in the Autumn. So far it is running really well.
Nice to see some physical testing, just need the miles on them now, as the baseline is established the results after say 30,000 miles help to see if what has been seen on the spring tester translates into ideal figures.
 
Madnorton said:
The results are consistent to my findings though. New standard springs at fitted height should be about 108 lbs, giving roughly 223 lbs at max valve lift with a 06.1084 cam. Some consider this way too high, but can't give a figure backed up with evidence of what would be a good figure to use.
I am currently running a cam and radiused followers and will be at Austria with it if all goes to plan, this, on the FA head is 59 lbs fitted, not what I wanted or predicted but happy to go with it for test purposes, and 199 lbs at max valve lift of 11.24mm. This set up will be inspected in the Autumn. So far it is running really well.
Nice to see some physical testing, just need the miles on them now, as the baseline is established the results after say 30,000 miles help to see if what has been seen on the spring tester translates into ideal figures.
Click to expand...

Have you checked for valve bounce?

I don't know what your cam is and that will definitely have a big influence , but when running a stock cam and stock springs with heavy valve caps I see valve bounce in the normal operating RPM range when the springs are down to 75 or less on the seat. [IE < 6000 rpm]

Seat recession becomes a big problem when there is bounce. Jim
 
comnoz said:
Have you checked for valve bounce?

I don't know what your cam is and that will definitely have a big influence , but when running a stock cam and stock springs with heavy valve caps I see valve bounce in the normal operating RPM range when the springs are down to 75 or less on the seat. [IE < 6000 rpm]

Seat recession becomes a big problem when there is bounce. Jim
Click to expand...

A bit of a gamble I know, but I will check clearances prior to Austria trip nearly 1000 miles on it now and no noises of concern. No dropping of air flow at the moment, so assume all is well. Above 4000rpm it still takes off like 2 stroke, the only problem is tyres, the roadriders don't last, the current tyre is about to be swapped out in less than 2000 miles, it will be a steady trip to the rally site on the new one.

The cam has been compensated for radiused followers, so hopefully the run down to the base circle should be kinder and the compression can help hold the valve shut to avoid valve bounce - I hope, seems to working so far. With 199 lbs on the nose hopefully the follower will not be lofted at high rpm, the nose of the lobe again is not so pronounced in shape as the standard cam, despite the lift, so hopefully this will also help there. With nested standard springs resonance should not be an issue either. Time and miles will tell. The valve stems were re-ground to accept the collets higher up the stem to avoid coil binding but using the FA head it seems I could have used standard valves as the fitted height on the inlets is pretty generous and thus the 59 lb rate. Had I used a standard head the predicted seated pressures were calculated to be 99 lbs and 240 lbs on the lobe, and very close to binding - this was a concern I was prepared to try, but it did not work out that way.
 
Good luck.

I gave up on Roadriders years ago. I now use Avon Cobras. Probably not as sticky and maybe not legal in the UK as they are front tires -but I can get 6 to 8000 miles out of a pair.
 
Remember, if you’re using Universal Roadriders on the rear, you would get a 3rd more mileage if you used a dedicated rear tyre...
 
The way I read this, Comnoz is providing in the video figures that indicate what will happen if you just swap out standard set of springs/seat and retainer to his conical spring seat and retainer, same cam, no shimming of springs. Just install. Just like the real life situation of a guy who decides to install a non standard spring with no further modification. This is not a high rpm race motor.

A baseline, no further change. A useful apples for apples comparison. As I understand it, Comnoz is saying no more than: in this case spring pressure is reduced. He is further saying this is compensated by reduced spring/seat/retainer weight and the set up still maintains follower to cam contact.

I wouldn't argue with it personaly as I have no basis for such an argument, and personally I assume Comnoz has backed up this assertion with Spintron testing! I don't think it is just opinion.

As soon as we mention a high lift cam and spring shimming, we must be expecting to use different figures that will be suitable for the application! And in such an application we would expect to be more particular about the installation. We would need installaion guidance.

Apples and Oranges!

Is it a suitable spring for a PW3? Consider that AN and Norman White/Mick Hemmings advise that a standard spring set up to be a suitable set up for a PW3. This might be a high performance road motor, or a race motor not intended to run over 7000rpm, say a 920 or 1007. So it seems to me likely that this spring set up would be OK for a PW3 as well as a standard cam. My assumption, assuming mainly a road motor or race motor constrained to 7000rpm

It might be interesting to see the spring pressure with a high lift setting, but assuming it does not become coil bound, but why would we expect a higher pressure than a standard spring seat and retainer set up?

Simple logic (not always a good guide!) would suggest a reduced pressure at this increased compression compared to standard springs.

But, I might also expect to be advised to adopt a higher install pressure for my particular application above 7000rpm in an attempt to further maintain follower to cam contact at these higher rpm!
 
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SteveA said:
The way I read this, Comnoz is providing in the video figures that indicate what will happen if you just swap out standard set of springs/seat and retainer to his conical spring seat and retainer, same cam, no shimming of springs. Just install. Just like the real life situation of a guy who decides to install a non standard spring with no further modification. This is not a high rpm race motor.

A baseline, no further change. A useful apples for apples comparison. As I understand it, Comnoz is saying no more than: in this case spring pressure is reduced. He is further saying this is compensated by reduced spring/seat/retainer weight and the set up still maintains follower to cam contact.

I wouldn't argue with it personaly as I have no basis for such an argument, and personally I assume Comnoz has backed up this assertion with Spintron testing! I don't think it is just opinion.

As soon as we mention a high lift cam and spring shimming, we must be expecting to use different figures that will be suitable for the application! And in such an application we would expect to be more particular about the installation. We would need installaion guidance.

Apples and Oranges!

Is it a suitable spring for a PW3? Consider that AN and Norman White/Mick Hemmings advise that a standard spring set up to be a suitable set up for a PW3. This might be a high performance road motor, or a race motor not intended to run over 7000rpm, say a 920 or 1007. So it seems to me likely that this spring set up would be OK for a PW3 as well as a standard cam. My assumption, assuming mainly a road motor or race motor constrained to 7000rpm

It might be interesting to see the spring pressure with a high lift setting, but assuming it does not become coil bound, but why would we expect a higher pressure than a standard spring seat and retainer set up?

Simple logic (not always a good guide!) would suggest a reduced pressure at this increased compression compared to standard springs.

But, I might also expect to be advised to adopt a higher install pressure for my particular application above 7000rpm in an attempt to further maintain follower to cam contact at these higher rpm!
Click to expand...

At the 95 lbs of seat pressure my spring will be far from coil bind at full lift. There is a lot of room for increasing the pressure. The pressure near coil bind would be too high for anything but a drag race motor or a Bonneville bike.

With a mild performance cam like the Webcam 312a I generally suggest 100# to 110# seat pressure with my springs.
I wouldn't suggest seat pressures higher than 110# unless it is a race only application.

A stock spring will not provide enough pressure for a performance high lift cam without reaching coil bind.

My spintron testing with the pw3 was never complete. The quick change needle bearing in my spintron caused immediate failure of the cast iron cam's bearing journal. I got less than 1 minute of run time before failure. I will revisit that cam in the future. Jim
 
Hi Jim, I am really keen to see further spintron testing with the PW3 cam as I know of friends of mine who have fitted them to standard road bikes with no other real performance componenty changes and wondering why they arent getting the major increased performance they were expecting!!
With one case I have suggested perhaps a little more mechanical advance although he is reluctant to try.
It revs well to 6500 rpm but runs out of puff at about 85mph , given that NZ twisty road conditions dont need it to be doing 100mph + , it is good in the twisties. I have ridden it several times while changing carbs and exhausts , all to no advantage.
Regards Mike
 
The PW3 cam is quite a hot cam by my understanding. Am I right?

If so, I’ve often wondered about folk fitting them to otherwise stock motors, with 8:1CR.

The wild cam is gonna lose effective CR, how much I’ve no idea, but it certainly seems counter productive to any notion of increasing performance, to me at least.

But, I speak from a position of zero experience on the subject !
 
Brooking 850 said:
Hi Jim, I am really keen to see further spintron testing with the PW3 cam as I know of friends of mine who have fitted them to standard road bikes with no other real performance componenty changes and wondering why they arent getting the major increased performance they were expecting!!
With one case I have suggested perhaps a little more mechanical advance although he is reluctant to try.
It revs well to 6500 rpm but runs out of puff at about 85mph , given that NZ twisty road conditions dont need it to be doing 100mph + , it is good in the twisties. I have ridden it several times while changing carbs and exhausts , all to no advantage.
Regards Mike
Click to expand...

I would agree with your findings.

My experience says the same applies to any long duration cam unless it is installed as a part of a comprehensive engine building and tuning program. Then if all goes well you will maintain about the same amount of midrange power and get a boost at higher rpms.

To take advantage of long duration cam the intake and exhaust lengths, port flow and velocity and compression all need to be just right to keep the air moving in the right direction to help make and keep the pressure in the cylinder.

When looking at the area under the power curve I have never seen anything but a loss when just installing a big cam in an otherwise stock engine. Jim
 
Thanks Jim, Im not so sure one of my friends will take those findings too well as he is loath to make any changes.

I have stopped making suggestions!
Regards Mike
 
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