Stock valves and valve spring seat pressure

[46flattie]

The background:

401 rebuild
Summit K8600 cam
Crane 99839 springs recommended by Summit for the K8600 - Seat pressure at installed ht is around 118 -120 psi.

Is this too much seat pressure for stock valves? My machine shop has concerns. Crane tech will not comment. Summit tech says it's OK.

I have run these in the past on another 401 w/stock valves and had no issues, but maybe I was just lucky. Would like to here what your experiences are before I drop a valve in my new motor.

Thanks,
Scott

[tufcj]

Seems a little high to me. I think factory seated pressure is around 90 PSI. But if those are the springs that Summit suggests, and the installed height is correct, then I'd run with it. The stock valves will be fine.

On my old 304 I had Isky dual valve springs that were 135 PSI, with stock valves. After the cam went bad, I replaced it with a Crane with similar specs. It rounded a lobe in the Crane within a few hundred miles. (To Crane's credit, they did replace the cam/lifters for just the cost of shipping). That was my first lesson in seated pressures on valve springs.

Bob
tufcj

[46flattie]

Thanks for the reply tufcj.......
Also for clarification, the Crane tech was OK w/the spring pressure regarding the cam, but he would not comment on use of stock valves.........

Therefore, my concern is whether the stock valves can handle the seat pressure or do I need to upgrade to SS valves or lighter spring pressure.

Thanks,
Scott

[tufcj]

I ran the stock valves on the 304 HARD. Spun the engine to 6500 + regularly, never had a valve failure. What finally did the engine in was detonation. I ran a little too much advance with poor fuel (10.5:1 compression - forged pistons), broke the piston above the top ring and scored the cylinder wall. I built a 360 after that. I just sold the heads a couple of years ago, and as far as I know, they're still running in a guys Gremlin.

Bob
tufcj

[bulletbuilder]

Flattie
Seems like to much seat pressure. I've set those cams up with 105-110 # on new springs. Springs will lose about 10 percent in the first few miles. Please use some sort of zinc anti-wear additive to break the cam in. (like GM's EOS for instance). There has been talk on this forum or the other amcforum, on how these cams are not holding up for several of the members. I will personally not use Summit cams anymore either.
Larry

[46flattie]

Flattie
Seems like to much seat pressure. I've set those cams up with 105-110 # on new springs. Springs will lose about 10 percent in the first few miles. Please use some sort of zinc anti-wear additive to break the cam in. (like GM's EOS for instance). There has been talk on this forum or the other amcforum, on how these cams are not holding up for several of the members. I will personally not use Summit cams anymore either.
Larry

Yep, I've read the threads regarding the Summit cams and inspected my cam over thoroughly.

What springs did you use to get the 105-110 seat pressure?

Scott

[bulletbuilder]

Flattie
I think the springs I used were PBM #3175. Their spec sheet says Single with damper, 1.44" dia., 110# @ 1.68" installed hgt., 280# @ 1.18" lift. Coil bind @ 1.125".
PBM's site www.pbmperformance.com.
Hope this helps.
Larry

[AMX69PHATTY]

For AMC, stock installed spring height is 1.813" right ?

Stock valve spring diameter is 1.38" right ?

[bulletbuilder]

For AMC, stock installed spring height is 1.813" right ?

Stock valve spring diameter is 1.38" right ?


You are right. But the head is OE cut to handle slightly larger diameters with no issues. As I recall, the PBM #3100 I originally ordered were stronger than the spec sheet said. In fear of potential cam failure, went with 'plan B'. I used a set off my parts shelf. Just had to shim it up about .100". Those I think, were the #3175's. Working just fine. Changed the customers rockers to Scorpions the other day. Saw no problems with the shorter spring after almost 10,000 miles. Check the PBM site out for futher spring info. Larry

[AMX69PHATTY]

Ok.
When they cut my heads for larger springs it increased installed height by a lttle bit, and the location of the keeper groove in the valve stem can effect installed height also, as well as springs retainer "style", like Crane has retaners with +.100 or -.100 installed height. I always found it kinda strange that on stock AMC heads the tip of the valve is just flush or barely above the top surface of the retainer instaed of stick up above the retainer maybe .13 or so like other motors. My heads have Chebbie style Stn Stl 11/32 stem "tuliped" ? valves and used Crane +.100 Retainers to achieve a 1.880 installed height and the valve stem tip about .13 above the retainer.

[46flattie]

Flattie
I think the springs I used were PBM #3175. Their spec sheet says Single with damper, 1.44" dia., 110# @ 1.68" installed hgt., 280# @ 1.18" lift. Coil bind @ 1.125".
PBM's site www.pbmperformance.com.
Hope this helps.
Larry

Thanks for all the info guys.

Scott