alright - think I have the pushrod mystery solved.

First...is appears the problem the whole time was...wait for it...pushrods too long. The new V10 lifters went in just fine, but when I installed the valvetrain I noticed something very not awesome - the pushrods were 'contacting' the snap rings at the top of the lifters - the preload was so deep that the angle of the pushrods into the lifters was so far in that they contact the snap rings - even bent in a couple of the tabs (with the snap rings facing up - a pure coincidence - I'd never have noticed it if the horse shoe hadn't just happened to be facing up).


Well that's not awesome, so I contacted Dave at Top Line (and sent a couple pics of the 'contact'), and he and his tech folks indicated that there was way way too much preload. So, I put a fresh battery in my dial calipers and did my best to measure it, and if I measured correctly or even close to correctly...my lifter preload is .167 ...and my research indicates it's supposed to be in the .030 range, so it's about .137 too much preload - that over 1/8" too long.

As I understand, lifter preload is the distance the push rod socket depresses into the internal lifter bore before the rocker arm gets tight (pic below).


This is how I measured that distance: I started the rocker arm bolt, threaded it in until there was no slack between the pushrod and the lifter socket, and then measured how far the pushrod/socket 'travelled' before the rocker bolt got tight - it went .167 , which as I'm seeing is a whole lot.



My current pushrods measured out at 6.941 (which are the new rods that are .036 longer than stock (6.905 I think is the OE length)), which with the new Comp cam (and presumed lower base circle) I installed because we thought the rods would be too short. Apparently that was not the case, and was apparently an overcorrection. The original rods were 6.905, but, with .167 preload and a target of .030, I need to get rods that are .137 shorter, or 6.804.

I hoped my calculated eyeball math indicated a 6.800" pushrod would do the trick...and I think I was right. Got a pushrod checker (Speedmaster 401.1001 - https://www.summitracing.com/parts/SDM-PCE401-1001), and at zero lash on a couple different holes the checker measured out between 6.759-6.763 , which with an additional .037-.041 will equal 6.800, and I am near certain that is within the preload spec for these magnum lifters (they said .030, and that was essentially an 'average'), and is also well below .075 preload which is how far the preload has to be for the pushrods to contact the snap ring clips. Soon as I get the e-mail back from the Top Line tech folks to confirm my math I'll be ordering a nice simple set of off-the-shelf-in-stock Comp Cams #7632-16 6.800 pushrods (https://www.summitracing.com/parts/cca-7632-1), which should make my valvetrain a lot happier...and hopefully a lot quieter too.

Bottom Line - get a pushrod checker and don't guess like I did - know.

Happy Motoring!

- Sam