The 340HP springs are a short-wire higher spring rate spring that only puts about 70# on the seat, shimming them is crucial to make sure it is at least that, if the old cam was well within' it's lift wheelhouse it was an "insurance" move.
340 xhead spring shimming, height and pocket question(s)
- Thread starter 4spdragtop
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If the 942 doesn't coil bind and if the retainer to guide clearance is good, run the 942. The 995 is a dual spring and you're just opening up an unnecessary can of worms there, IMO.
The heads were done without any specific cam in mind. Back to stock specs.
Do not rely on 'specs' on the box or elsewhere for the coil bind dimension of a valve spring; measure it. Put a spring in a vice & compress until solid, & measure. I just measured some PAC springs last week for CB, was NOT what was on the box.
I never stack a spring solid, & it's not required, min. installed ht. - max poss. lift. Where the gaps are depends on spring type(traditional/progressive/beehive/conical), but the spring should have a min. of .025-.035" space left. A beehive/conical, it may all be on the top coil, traditional .005-.010 between each, straight progressive somewhere between the two.
Agree for sure, check all dimensions, & loads at the relevent dimensions. Take NOTHING for granted, especially these days..
And that's a great thing to point out, if You don't TELL a shop current & possible future plans, that's what You will get....stock spec with a little "cover their ***" thrown in...which could screw You if You put a cam that should "just work" within the stock specs.
Yeah, these heads were done 30 years ago lol and at that time I was fine with "stock". I didnt realize this cam was that much above stock?
Thanks for your input.
Thanks for your input.
I always try to install springs at the manufacturers recommended height, and the rule of thumb that I have always used is to have at least .060 clearance for coil bind. If you are installing these springs at 1.650 with a .495 cam it seems that you have about .030 of coil bind clearance, to me that is too little. Now, others may disagree, but I would do as a previous poster said and get some .050 taller retainers or locks and shim the springs to the suggested 1.700 installed height.
Thanks for chiming, I understand the coil bind, but confused with how shimming increases installed height? Shims lower it correct? Or are you talking the combination of taller retainers and shims?
The 340HP spring is good for .500", but it has to be at the stock installed ht., which is 1.685" iirc. When You sink the valves during the valve job, it will increase the height, so shims will restore that. Those HP springs are short & high-rate, which means(just like suspensions) as fast as the load rises on compression, it disappears on extension. So it's critical to get that right & maintain that 70# on the seat. With a stock, or stock lift cam, the max was .475". Adding .025" of shim plus the amount the valves sank will ensure seat load, and not bind the coils, but throw another .020" lift on it & now You're on the razor's edge.
Aggressive profiles require more seat load, so total lift isn't the only consideration. For instance, My plan to use LS beehives from Comp(all roller cams & 1.7 or 1.8 rockers) with a .904" Mopar specific aggressive lobe was torpedoed, because neither the PAC 26915(1st level LS upgrade) nor the 26918 were up to the task. The reality is that an aggressive FT will out-accelerate a roller, the roller can maintain it's lift velo longer tho', I couldn't even use a Ford .875" ramp lobe. So I settled for a very nice pair of Extreme Energy solid lobes, Comp had just come out with the even higher load LS beehive, but I am not confident the stock-type valves can handle that much...so I compromised.
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He is stating to use offset or "raised" retainers, which will increase the ht., maybe more than needed. You would then shim the seats to the desired ht.
If i remember correctly inst height for factory spec is 1 5/8-1 11/16. Which mine falls between, BUT doesnt meet Comp specs. If the tech line had pointed out from the get go the proper springs lol. I even researched and compared PAC and a few others...I dont really want to machine the spring pocket as it would kinda leave the heads matched to those springs.
Tech mentioned beehives but not sure of their price.
Thanks again.
Tech mentioned beehives but not sure of their price.
Thanks again.
The LS units install @1.80", I'm using longer valves on this project, but there are beehives in the range You need....new retainers a must anyway for those so...it's only $$$ Steve!!! Lol..
I think the beehives may be cheaper than machining? Approx $250 for hives, plus retainers...
Ironracer
Gearhead
Man, I feel for Ya! When I did the Drag Bike, my cam measured .565 at the lifter! Springs for that were not available... hope You can get this sorted out soon Brother!
It's a mechanical cam. Don't forget to add valve lash. Also if coil bind is going to be close I like to measure actual coil bind of the springs. Then the actual lift of the valves with a dial indicator. All this mocked up with the valve springs you are using and on the engine it's going on. I find that actual lift can be less than calculated lift due to deflection and geometry of pushrods and rockers. For me, if it's not close calculating is fine.
This is just my opinion. If both surfaces are final machined and you keep track and replace the gaskets in the same orientation as when mocked up then yes. You can torque them short of your final torque spec in mockup. I save old gaskets ( in good condition) for mocking things up.
If you end up with plenty of coil bind clearance with the springs you end up using you can skip it. Unless you want to do it for the experience which I completely understand.
If you end up with plenty of coil bind clearance with the springs you end up using you can skip it. Unless you want to do it for the experience which I completely understand.
duster 344
Well-Known Member
A while back I asked the question about single valve springs for a 510 lift, I got lots of suggestions. Including the 942, I did all the math it should work I figured. When I talked to comp they told me they weren’t going to. I called three times and finally got a guy to explain that the spring rate wasn’t good enough for the lift plus the duration. I had to get the 995s. As far as machining there’s not to much. Take the valve guides down a little, and cut them for different seals. Summit sold me the tool to do that along with the seals and the install tool.
duster 344
Well-Known Member
I have a set of 596 heads I’m building, and the 995s drop in just fine, and the will work at factory so stall height, but the factory seals don’t fit in the spring
I am talking about the combination of taller retainers or keepers and shims to get you to the correct 1.700 installed height. Being that you said the heights now varied from 1.650 to 1.660 a .050 taller keeper would put you over the 1.700 installed height and you will just need to shim it a bit.
Thanks guys, in my opinion my install height at 1.660" is good(fsm spec is 1.625-1.6875"), but correct me if I'm wrong? The shorter height gives me increased psi at closed and open.
When I spoke to tech he wanted nothing to discuss doing anything using the 942's. He said the cam was too aggressive for them. When I mentioned the increased psi he said "not enough". I intended to ask him what psi this SFT could take and he cut me off before I could ask.
Im not married to Comp, I dont mind using PAC or anyone else for that matter. I'm hoping I find something that has a 1" ID.
I'll have to wait until Monday to get a quote on machining. I dont have tools for cutter/machining.
Good point on reusing old head gaskets thanks!
Cam is degreed in, so I would like to continue with the measuring etc.
That's what led me to here, I enjoy doing this figgering lol. Heres the build thread.
Restart the rebuild
Looks like beehives are one option without having to machine the pockets?
Man I never thought with this cam it would need some machining.
Any other quality suppliers/mfg of springs out there?
Thanks all, much appreciated!
When I spoke to tech he wanted nothing to discuss doing anything using the 942's. He said the cam was too aggressive for them. When I mentioned the increased psi he said "not enough". I intended to ask him what psi this SFT could take and he cut me off before I could ask.
Im not married to Comp, I dont mind using PAC or anyone else for that matter. I'm hoping I find something that has a 1" ID.
I'll have to wait until Monday to get a quote on machining. I dont have tools for cutter/machining.
Good point on reusing old head gaskets thanks!
Cam is degreed in, so I would like to continue with the measuring etc.That's what led me to here, I enjoy doing this figgering lol. Heres the build thread.
Restart the rebuild
Looks like beehives are one option without having to machine the pockets?
Man I never thought with this cam it would need some machining.
Any other quality suppliers/mfg of springs out there?
Thanks all, much appreciated!
The 942 will work fine for your cam. I think you're running down an unnecessary rabbit hole, but have at it.
Heres a screen shot of Summits PSI recommendations for SFT cams.
Agree? Disagree?
Agree? Disagree?
Anyone know the best way to to see if you can mix n match different mfg springs with different retainers?
Putting Comp 747 on Eddy 5767 springs?
Putting Comp 747 on Eddy 5767 springs?
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