Valve spring: installed height too low • The Dodge Challenger Message Board

by **CHTA** » 07 Mar 2009 21:27

Rebuilding 340 T/A heads
New valve job has been performed, new Mopar Performance standard lenght single lock valves and new MP springs (P5249847).

Installed height on MP spring chart is 1.670 to 1.680.

With spring micrometer, I was surprised to measure 5 installed height between 1.640 and 1.650.

The spring is designed to work with .480/.535" lift range. The new cam will have .491 valve lift.

Should I have valve seats machined or springs can be installed with a lower height (-.030) in my application ?

by **dave-r** » 07 Mar 2009 22:25

Yes. If the installed height is too small your seat pressure will be too high and you run the risk of coil bind at max lift.

by **CHTA** » 08 Mar 2009 7:03

Max spring recommended lift is .535 with 1.670 installed height.

My cam will have .491 lift.

If my installed height is 1.640, I shoul still have .014" before theoretical coil bind risk.
Am I wrong?

by **dave-r** » 08 Mar 2009 10:02

14 thousanths of an inch is not a lot of headroom.

Overall you will have too much seat pressure too.

You also run a risk of wiping a cam lobe or breaking a spring.

Another option for you would be to cut the valve seats deeper.

by **Eddie** » 08 Mar 2009 16:32

You need at least .060 clearance between the spring coils to prevent bind. At .014 the coils will bind. Options are a longer valve,(you might be able to grind a bit off the valve tip on the longer valve and still keep the tip in proper relationship with the rocker arm., different retainer,(have you tried 'mixing&matching parts to get the desired clearance,,,retainers& locks?), keep the valves with their respective seats they were lapped with. And the last option but a risky move is to grind a slight amount off the valve spring seat floor. There is water directly under the valve spring pocket. I would probably use a different retainer, ones that have deeper offset and allow more room under the retainer for the spring being used. Sinking the valves into the head hurts flow but at the small amount of clearance you need, it wont be a 'deal breaker'. Good luck :thumbsup:

by **CHTA** » 08 Mar 2009 18:18

Thank you.

I'm still wondering why I have short spring height with "Mopar standard" equipment (standard lenght valves, original style Mopar locks and retrainers). After the valve seat job, I even expected higher than normal height.

Actually, I think that .014 is not clearance before coil bind. Tell me if I'm wrong.
In the MP chart, there is no information about coil bind height (solid height). They only give the lift range. For P5249847 springs, lift range advised is .480 to .535 .
My cam will have .491 lift. Considering 5 on 16 spring installed height will be .030 shorter than normal, I guess open load on these springs has to be considered as if lift was .521 ( .491 + .030), which is still in range of the spring ( max .535).

I agree that closed and open load will be different than on the other 11 correct installed height springs. Is this very important ? (street use, never race)

I will call MP tech line to ask for solid height values.

Thanks again

by **CHTA** » 08 Mar 2009 18:28

Eddie,

I forgot to mention that as you suggested, I tried to "mix&match locks and retainers (without mixing valves !).

This was successful, but I still have five .020 shorter installed height values.

by **dave-r** » 08 Mar 2009 18:55

On second thoughts just leave them alone. I think we were both getting lost in the numbers there. I am sure if a few valves springs are only 20 thou short you will be OK.