I was sent a set of Comp Cams Magnum Pro lifters with my Scott Brown Cam. Right now I'm trying to measure for the correct pushrod length however according to this document these lifters only need 0.002" to 0.004" or preload . . . this seems very small to me. I've always heard .030" is correct for a hydraulic lifter. Am I wrong? https://static.summitracing.com/global/images/instructions/cca-865-16.pdf
Looks like these particular lifters need very little pre load. They say 0 and 1/8 of a turn. http://www.compcams.com/pub/media/productattach/c/o/comp4-115_4_.pdf Never heard that before, but those are the instructions.
Most likely a short stroke lifter. Their used with higher RPM cams so the lifter doesn’t pump up and hold the valves open.
Got it, thanks guys! I will report back once I've measured for all the pushrods. 12" vernier calipers should be arriving today!
Actually now that I'm thinking, it's going to be near impossible to get that little preload with one sized pushrod on all 16 lifters . . . should I go adjustables?
I would use one adjustable to determine the correct length and order them unless your valve heights are all over the place. IMO with adjustable pushrods and adjustable roller rockers you have 32 things to loosen up. I've had it happen on roller rockers.....
Yeah, but his valve stem heights only have to vary by .002-.004 to make the fixed length push rod plan, not a good idea.
That was my plan and I started measuring with the single adjustable yesterday but realized that since there it so little room in the preload spec that averaging the measurements would lead to lots of inconsistencies. Can you recommend a good brand of adjuatables? Smith Bros and Crower seem to both make some. TA has some for $200 . . . Also, is there a difference between "Pushrod Length Checkers" and actual "Adjustable Pushrods"?
I have roller rockers now, but on my first motor, I had adjustables installed by the PO. I do not know who made them, but they were big, 3/8", and I never had any problem with any of them, nor did I need to readjust them, ever. The checkers I just looked at frequently don't seem to have a way to lock the adjustment, that's one difference, and the other difference is the price, the checkers are about 23.00 or more each. Wanna buy 16 of em? at 368.00 a set?
I used to run 3/8" Poston adjustables. Worked well, depending on lift, etc., you could have slight rubbing on head pushrod holes. Might need slight enlarging. 5/16" adjustables would be ultra safe for clearance, but not as stiff.
Isn't it challenging understanding the nuances of making a correct measurement? Seems like the length is theoretical as it's from one point in space to another due to the spherical end and hole.
Haha yes it is! It's these minute details that seem to drive one insane. Ahh got it, yeah I am looking at options! Will give Crower and Smith Bros a ring tomorrow. Hopefully they're not too expensive! Interesting, my cam's max valve lift is only .485" (.313" lobe) Intake and .477" (.308" lobe) Exhaust so I'll run 3/8" rods with 5/16" balls if I can clear! The extra rigidity seems worth it.
3/8" pushrods WILL rub, the hole in the head isn't big enough Run 5/16" chromoly or whatever they're called, there way stronger than the stock 5/16" pushrods, PLUS you wont have a set of expensive 3/8" pushrods sitting on your bench like I did from years ago Many guys run 5/16" with huge spring pressures with no issues.
Both 3/8" & 5/16" adjustables have the same 1/4-28 fine thread tips, PLUS an oil hole weakening it further. The tips can and do sometimes break.
