340 xhead spring shimming, height and pocket question(s)

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4spdragtop

4spdragtop

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Ok, so got my spring heights measured on pass side head.
I measured(verniers and small machinists ruler) each valve in 3 different spots, and im averaging between 1.650" and 1.660".
That's with no shims and valves fully closed.
Springs are 942's
Specs 115lb/1.700" inst height
339lb/in spring rate
Coil bind 1.125"
See pic where I've hand written the rest of calculations, but end result I get is
Ex [email protected]"
Int [email protected]"
To note, when the valve job was done 30 years ago the OEM 340 springs were reinstalled with shims(see pic) 0.0585" thick.
Why would machinist(good mopar guy) shimmied them? To increase seat psi?
It couldnt have been to lower inst height as without shims I'm already around 1.65", 1.66"
Also of course shims I bought are too small ID :BangHead:, but in reality i dont think they need shimming?
Also the spring pocket is approx .125" deep. If I drop the prev shim in, then I'm reducing the pocket by the shims thickness(0.0585").
I placed a 942 in loose and I sure as heck wouldnt shim if i dont need to.
Input/advice?
I'm sure there will be more questions lol
Thanks
Steve

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What cam and rockers are you going to be running? Also, are the springs brand new O.O.T.B.?
 
Can’t know why someone would do that. I do know you are one anal MF if you are measuring spring shims down to 1/10000 of an inch. Lol :poke:
 
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Get the springs in the 120 pound on the seat range and go.
 
Only reason I can think of using shims(in this case) is to increase spring psi?
Without the shims and with my shitty measuring skills the inst height measurements are already tighter than the 1.700" spec.
Gotta measure to that many decimals with my lousy measuring lol.
I'll compare oem springs vs 942 side by side.
Thanks
Bodyperson said:
Can’t know why someone would do that. I do know you are one anal MF if you are measuring spring shims down to 1/10000 of an inch. Lol :poke:
Click to expand...
 
If you want more installed height, get some + 050 valve keepers. Still need to check afterwards, as some give less than 050.
 
Thanks Bewy, I'm trying to decipher the needs/wants, pros/cons of what I have so far.
Here is spring specs.
Bewy said:
If you want more installed height, get some + 050 valve keepers. Still need to check afterwards, as some give less than 050.
Click to expand...

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More math.....if my intake height is 1.6576" and my cams lobe lift is
0.329" call it 0.495" valve lift.
So if I take my inst height and subtract valve lift, I get 1.1626", coil bind is 1.125" pretty close, too close?
Open psi at 1.200"= 284 lbs, so obviously at 1.1626"(theoretical full open) the psi is 284 PLUS the extra 12.68, so 297 lb at full open.
Anyone see issues with this? Gonna chk cam/spring specs.
Thanks
 
4spdragtop said:
More math.....if my intake height is 1.6576" and my cams lobe lift is
0.329" call it 0.495" valve lift.
So if I take my inst height and subtract valve lift, I get 1.1626", coil bind is 1.125" pretty close, too close?
Open psi at 1.200"= 284 lbs, so obviously at 1.1626"(theoretical full open) the psi is 284 PLUS the extra 12.68, so 297 lb at full open.
Anyone see issues with this? Gonna chk cam/spring specs.
Thanks
Click to expand...
Subtract your valve lash from the lift.
 
Springs are good for 0.515" lift as per Summit, and I'm at approx 0.495".
Close? Too close? That 0.515" max lift, I'm assuming that my inst height has an effect on max lift?
 
4spdragtop said:
Only reason I can think of using shims(in this case) is to increase spring psi?
Without the shims and with my shitty measuring skills the inst height measurements are already tighter than the 1.700" spec.
Gotta measure to that many decimals with my lousy measuring lol.
I'll compare oem springs vs 942 side by side.
Thanks
Click to expand...
What was the usage before? What type of lifters? Maybe they were running or planning to run solids? That would be the only reason I could figure. The 942 is the sprAng I'm running on Vixen's engine right now with solids, of course. I set the head up myself and did use shims. I got the seat pressure right in the 130 range. You have to be careful though, because those springs don't have a big range and can't stand a lot of lift. That's why I had to have this cam ground with a low lift, but a FAT duration. It's only .465 lift, but 250 @ .050 duration. It's worked out very well, though, and has the reliability of a stock type camshaft with little stress on the valve train. What lift do you plan on running?
 
Heres specs on both cam(0.495" lift) and springs(max 0.515" lift). I have solid lifters on hand. I had heads redone by a good mopar machinist 30 years ago. They came back to me re-assembled with new valve job and new ex valves, then they sat up until 4 years ago. Shims were installed with orig springs by machinist. Heads are from 69 cuda, so they orig would have been hyd valve train. Only reason for shim is due to reusing orig(tired??) springs?
My inst height 1.6576" falls into specs from FSM, which is 1.625"-1.6875", BUT is slightly tighter than COMP spring spec of 1.700"?
 

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4spdragtop said:
Heres specs on both cam(0.495" lift) and springs(max 0.515" lift). I have solid lifters on hand. I had heads redone by a good mopar machinist 30 years ago. They came back to me re-assembled with new valve job and new ex valves, then they sat up until 4 years ago. Shims were installed with orig springs by machinist. Heads are from 69 cuda, so they orig would have been hyd valve train. Only reason for shim is due to reusing orig(tired??) springs?
My inst height 1.6576" falls into specs from FSM, which is 1.625"-1.6875", BUT is slightly tighter than COMP spring spec of 1.700"?
Click to expand...
I would be careful. You need to check the retainer to guide clearance very closely when you assemble. In fact, I'd mock it up first.
 
The original engine builder may have tightened up the installed height to gain a little pressure but also to close up the coil bind number. Springs work more efficiently in a range and should be shimmed to tighten it up to a point where the spring is effective at dampening spring surge. Ask your spring manufacturer where they want the coil bind clearance to be.
 
I installed viton oil seal as mockup. Oil seal height installed is 0.8335" up from bottom of spring pocket(see red straw).
Subtract (I think) that height from installed spring height. 1.6576"- 0.8335"= 0.8241" now I also subtracted the 2 lips/lands on 947 retainers(0.0960" and 0. 0237).
So 0.8241"- 0.1197"= .7044" of max avail valve travel??
Does this make sense so far?
RustyRatRod said:
I would be careful. You need to check the retainer to guide clearance very closely when you assemble. In fact, I'd mock it up first.
Click to expand...

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4spdragtop said:
I installed viton oil seal as mockup. Oil seal height installed is 0.8335" up from bottom of spring pocket(see red straw).
Subtract (I think) that height from installed spring height. 1.6576"- 0.8335"= 0.8241" now I also subtracted the 2 lips/lands on 947 retainers(0.0960" and 0. 0237).
So 0.8241"- 0.1197"= .7044" of max avail valve travel??
Does this make sense so far?


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No, but not becasue of how you did it, because my brain ain't that good at math. lol If that works out to you having adequate clearance between the bottom of the retainer and the top of the guide.....or seal, you're good.
 
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Thanks, my concern with the (tightened)installed height with new springs is the extra load on lobes.
Comp spec for CB is 1.125" I think I'm good there(feel free to scroll up and dbl chk my work??:))
Here is screen shot from Summit in regards to recommended seated and open psi for solid ft cams.
Currently 5th inline on tech line lol.
TT5.9mag said:
The original engine builder may have tightened up the installed height to gain a little pressure but also to close up the coil bind number. Springs work more efficiently in a range and should be shimmed to tighten it up to a point where the spring is effective at dampening spring surge. Ask your spring manufacturer where they want the coil bind clearance to be.
Click to expand...

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What did they say about coil bind clearance for your spring? You can use any spring you want as long as it’s gets you the seat and open load you’re after. Search around for a different manufacturers spring that fits your head and gets you the pressure you want/need. Might save you machining costs.
 
Thanks, I wanted to ask him about coil bind, but when he read the 942's werent recommended I was basically rushed off the phone lol. I even mentioned install height and was basically cut off.
I think my coil bind is good. I'll chk my calcs on it. Spec is 1.125".
TT5.9mag said:
What did they say about coil bind clearance for your spring? You can use any spring you want as long as it’s gets you the seat and open load you’re after. Search around for a different manufacturers spring that fits your head and gets you the pressure you want/need. Might save you machining costs.
Click to expand...
 
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