BadDog

I have been having a miss starting at somewhere between 3200 and 4800. Pretty steady, just sounds like it is breaking up. Sounds like ignition but I have;
Replaced Cap and Rotor
Change Plugs
Ran + wire straight to coil
Swapped out alternator
Changed entire ignition system out (removed Crane box went stock)
Replaced pickup in dist
Swapped electric fuel pump (suspected RF or bad motor windings)

All to no avail. I am now looking at the valve train. Got the valve covers off and everything looks fine. Nothing obvious. Near as I can see the springs look fine. Hard to see the inner springs. If I had a bad spring what am I looking for?

Pulling my hair out on this one.

1BIGJIM

iTrader: (1)

When I bought a set of "rebuilt ready to run" heads off EBAY I found out when I started to have a backfire around 4,000RPM.
Everything looked fine when I assembled the engine. I ended up taking the heads back off, took them to a machine shop, where I had new guides and springs put on. Moral to the story is always check anything you buy. I would never buy any used parts like that off Ebay again.

Griff

You should be able to buy a tool that will measure the spring pressure.

BIG SLICK

hi,simply put a vacuum guage on a port on the intake or base of the carb and if the guage flucuates it probabaly has a bad spring.

rmbuilder

BadDog,

Valve springs are a “read” component, similar to a spark plug, in that they contain a great deal of information relating to the operating condition of your engine. Not only are they responsible for returning the valves to their seats, they need to keep them there; a difficult task compounded by aggressive ramping and (in some cases) forced induction. In the process they are required to dampen and stabilize the harmonics created by the valve train and dissipate the resulting thermal buildup. Spring life has so many variables it’s difficult to put a cycle value on them. Because they are affected by heat, RPM (one “zing” can kill a spring), wire quality/heat treat, and camshaft profile, the degradation curve is not linear and varies greatly from application to application. Heat is generated in the spring from multiple sources. First by cycling the spring through compression and extension. Secondly the friction between the coils generates heat. Third is heat absorption.
I would suggest that you check your springs for current values at seat load and open load, compare that to spec and see if you are within tolerance. These figures will give you baseline references for future fatigue evaluation and alert you to other potential valve train problems. Many cam/lifter failures originate with the springs inability to maintain dynamic stability. It may also create a fuss point that will cause instability at a certain RPM point (above where you take a static vacuum reading). Check springs for discoloration and/or cracks. If you do find a break that is jagged, that is due to harmonic resonance. A clean break is a sign of improper heat treat. Monitoring your springs for degradation is cheap insurance. Below are links to on head spring test tools of various prices.
http://www.power-t.com/spring/pt-700.html
http://www.buxtonengineering.com/vst_600.htm
http://www.intercomp-racing.com/detail.cfm?ItemID=121
http://www.powerhouseproducts.com/Ca...6pdfs/ph21.pdf
http://www.moroso.com/catalog/catego...?catcode=27105
http://www.lsmproducts.com/p3.htm
Bob

2112

RM, you are every bit the good read as McColliston once was (do I sense a challenge?). Seriously, thank you.

BadDog

Thanks for the links Bob, I started a new thread regarding valve spring testers.

Vacuum is steady at idle and gauge shows not flucutation right up to boost while running. I did manage to pull the valve covers and sling oil all over the place testing in the driveway up to 3000. I have the drive sumberged in a bucket fed by a hose to avoid sucking the water out of the hose.

Valve train looks stable and no noise so I am looking into getting a tester. Boat ran fine when it was all put together 100 hours ago. Problem started developing some time ago and only showed up at WFO. Seems to be getting worse with time so I suppose I could have a spring going south.

Thunderstruck

Bob, have you added rap lyricist to your resume? "One zing can kill a spring." (Insert appropriate sound effects here.)



You da man Bob,

Tom

cuda

When you pull a valve out of the piston, you can assume they need changed.