valve spring question

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moparfanatic56

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Ok motor gurus I have a pair of J heads that had been rebuilt when I bought them. I purchased a mutha thumper cam to put in my 340. I went to install the vale springs that came with the cam but the inside spring will not go over the valve seal. Now for the question, the springs that were on the heads (going by the diameter measurements that I took) are mopar performance springs part # P4120249 good for .430-.500 lift so will these be adequate and compatible with the cam mentioned.
Thanks for any and all recommendations.
 
There is far more to it. You have spring rates and installed height to get a certain open and closed load. Sometimes shims are needed, extra clearance of the guides are needed or cutting the pockets deeper. If you have a reliable engine or cylinder head shop they can set this up for you. Do this wrong and you can have bent push rods, flattened cam lobes, valve float, destroyed seals, and possible rocker to retainer interference.

I would also have the heads gone over. A shops idea of rebuilt can vary, greatly.
 
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dano said:
There is far more to it. You have spring rates and installed height to get a certain open and closed load. Sometimes shims are needed, extra clearance of the guides are needed or cutting the pockets deeper. If you have a reliable engine or cylinder head shop they can set this up for you. Do this wrong and you can have bent push rods, flattened cam lobes, valve float, destroyed seals, and possible rocker to retainer interference.

I would also have the heads gone over. A shops idea of rebuilt can vary, greatly.
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I did do some reading about all that you mentioned. So with that being said when I removed one of the current springs there were shims on the bottom which makes me assume (we all know what happens when you assume something) that all of the checks and balances had been done. I will for my own personal peace of mind take them to a shop I have to much invested to have a catastrophic failure.
 
Do the heads have umbrella seals or Viton seals? What are the specs of the cam? If they are umbrellas and you're taking them to the shop anyways, have the guides cut for Viton seals and use the springs the cam manufacturer recommended.
 
Here is a picture of the current valve seals not umbrella possibly viton. You can see the shims there are 2 of them. The cam is a comp cam k20-602-4 there was not a cam card with it (bought from another member still in the box) so not sure of the specs without looking it up.

100_0820.JPG
 
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moparfanatic56 said:
Here is a picture of the current valve seals not umbrella possibly viton. You can see the shims there are 2 of them. The cam is a comp cam k20-602-4 there was not a cam card with it (bought from another member still in the box) so not sure of the specs without looking it up.

View attachment 1715518300
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Then look them up. It's the only way you'll know if the MP (if that's what they are) springs on your heads will do the job. Call Comp and run your combo past them and see if they agree that will work. They made the cam, they know what it needs. And double check the springs you got with the cam, make sure they're the right ones- stranger things have happened.
 
And when you break the cam in make sure you remove the inner springs and then re-install after break in.
 
If your spring seats are OEM, you can't use double springs, without cutting new spring seats.
Have no fear, there's plenty of spring choices out there in a single that will probably work.
BUT, all this depends on what the cam needs and whether it will fit under the stock 1.700 installed height.
Umbrella seals, aren't really seals, they just 'umbrella' the oil from the stem. But not very well.
Positive seals are out there in just about any flavor you need. Just measure the top of the guide and buy accordingly.
Also too, the OEM guide height will limit how much lift you're going to be able to fit. Usually less than .520 even being careful with seal size.
I need more info Mike... I mean, moparfanatic56
 
I had to cut my valve guides to accept a positive seal to clear mine. Looks like yours has already been cut but at the wrong od. I cant remember what size mine was right off but I used the comp cutter and guide you may have to recut them or find a smaller seal that will fit.
 
check your used springs what are they now? check at thump lift
thumpers for mopars are mild mopar lobes not chevy lobe and not hard on springs
check but the mopar springs should work
Thanks Proff
There are mild Mopar grinds like the Mild Eggles, Mopar performnce, some Cranes and the Thumper and Purple Plus from Comp and some Crowers, Jones "Motorhome" cam
Lunati voodoo somewhere in the middle
then there are the Comp HL and Howards which have more lift but not really radical
then there are race only lobes
Still wonder why anyone would need that exhaust split even with stock heads and manifolds I'd watch my exhaust temps if any heavy use
 
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