School me on the effects of too much pre-load...

[Mike86Stang]

I've talked this over with some mechanics & some friends & even the guys at CompCams & no two people have the same answer.

What happend is I was racing & over reved the car. After I stopped & started
it again it developed a nasty tap (drivers side). It sounds like some one is taping on the block with a screw driver. It's deffinatly valvetrain but beyond that I can seem to narrow it down. I "think" I have a bent pushrod....

Anyway so far what I've been told so far is....
It will cause the valves to hang open
It will cause the valves not to open all the way
Over reving with too much preload will do nothing to the pushrods
Over reving with too much preload will cause the pushrods to bend...
I got about ten more

Just for some details when it's cold out side it get's this twangy sound to it..after it warms up the "twang" is gone. You can hear it below 2500 rpm but not above it. Light or heavy oils make no diffrence in the sound. I tried adjusting the pre-load & it made no diffrence. I tried the old roll the pushrod on a flat surface & they all "seemed" to be flat.

Who's got the straight scoop for me so I can figure this out.

TIA
Mike

 

[jrichker]

Think about what happens when a solid lifter cam is set with 0 lash or less than 0 lash. That's the answer. The valves don't close like they are supposed to, so they blow back compression into the intake & exhaust manifolds. The valves can have unpleasant intimate contact with other engine parts like the piston heads in extreme cases.

 

[Mike86Stang]

Wouldn't something like that show up with a compression test?
I did a compression test & although the cranking presuure went down
by about 25psi with the heads & cam, the cyls seem to hold pressure
unless the compression test just records the peak pressure..I dunno.
I would say things seem a little soggy performance wise but I assumed
it was due to the larger valves & large intake ect having poor velocity in the
lower RPM.

BTW compression test revealed 135psi across the board + or minus about 5psi.

 

[4dStang]

I would probably start by removing the valve covers and the rockers. Pull the pushrods and eliminate them as a problem or replace them. I think you have a bent push rod. Youata go with some hardened pushrods since you like to over rev! ha ha.

 

[Mike86Stang]

Not that I LIKE to over rev it just happens...wheel spin sucks sometimes