T/A Racer

alright so here i am thinking that im going to be free and clear with assembling my engine this weekend because the machine work is supposed to be done and i have all my parts but i just got to thinking about something. if my block is zero decked and my heads have been surfaced wouldnt this change the geometry and distance of the pushrods? how much adjustment is there between a pushrod. i think stock length is 7.2in? i have hardened rods now but im wondering if these are going to be too long? or will i still be able to adjust the rocker with the lifter to compensate for the few extra thousandths? thanks for the help.

Guest47904

Follow this page using the ones you have now. http://www.compcams.com/Technical/Cu...ML/306-307.asp
If you determine they are the wrong length then order the correct measurement rod that is adjustable to the correct length and obtain the correct measurement from that and then order them.

rskrause

PR length has to be checked with any rebuild where the block or heads have been resurfaced or if any valve train components have been changed.

Rich

96speed

IOW, always check it anyway. It might not be setup correctly from the previous build! A length checker is a cheap investment.


Ryan

T/A Racer

i understand the stock pushrods are 7.2" now, lets take some assumptions here
.025 decking (zero decked from stock)
.015 head surfacing
.004 (.043stock gasket-.039felpro) head gasket
all this adds up to 44 thousandths difference (these are run with 1.6 crane rr)
now what all sizes do they make pushrods( i mean that are in stock not custom) anyways if i went with a 7.15 PR this has got to be close. granted people dont build engines with close specs but im wondering what the chances are that if i went ahead and bought these that when i checked them in my setup i will be fine with them. dont worry im not going to throw them into the motor and just start her up and hope for the best, they will be checked very carefully im just in a time crunch and would like to just assemble the engine, not get it mostly assembled then send out for rods. please dont hate me

T/A Racer

the pushrod checker im looking at measures in 50 thousandths so im not sure how i could get closer than that anyways even with using a checker? okay im an idiot for not adding the extra variable of my camshaft, for some reason that didnt click right away. now im starting to see the reason for the checker. maybe this is going out on a limb but does anyone know or know how i would calc the difference in length for a pushrod for a cc305. im sure its directly related to the lift #'s its just a question of equations im guessing.

3gc

If you have until the weekend order the checker from summit now. You'll get it in a few days. Then use it this weekend. get everything assembled aside from putting the valve covers on. Check the length. Order the correct length pushrods. Drop the motor in the car and wait until the right ones come. I'd rather have my project pushed back a few days and have some peace of mind then to throw money at pushrods on a complete guess at the length.

Guest47904

The reason you put a rod in and check the geometry is bacause it is near impossible to calculate. Remember the base circle has much to do with final geometry. The reason you use the originals is because you don't know if it will require shorter or longer rods. I have read numerous articles of rebuilds that ended up being stock length. I have a 383 with a custom Crane grind, AFR heads and Comp 1.6:1 RR. It ended up using the stock length. So start by checking the geometry according to the page I listed with the stockers and then go from there. Stop trying to calculate and just check it.

T/A Racer

Must be some of the mechanical engineer coming out in me. i stare at formulas all day and have actually come to appreciate them for what they are worth. although i do realize the time when it comes down to just plain and simple measurement. ill order the checker, o and my engine is 200 miles away at home so that means itll be atleast a week longer (only vehicle borrowing one right now) but i suppose its worth it.

OBE1 95Z28

Some other things to think about are:

• will your intake line up correctly?
• will your accessory bracket line up correctly?

T/A Racer

dang i hope my intake lines up alright, i guess atleast i have a surfacer where im putting it together so we could always adjust the intake if need be. do many people have problems with the intake fitting after zero decking a block?

cehan

When you check your pushrod length, be sure you use one of the lifters that is the same kind as you will use in your final assembly, and disassemble it, put in washers or some other kind of spacer to make it like a solid lifter. You should use checking springs instead of the regular valve springs, because there is a chance that the regular springs can crush the threads on the pushrod checking tool.

Chris

T/A Racer

damn so i cant use the lifters and springs like they are in the engine normally?

1racerdude

If the check PR's have a jam nut ya will be OK with hyd roller springs. The lifters will have to be made solid. Take one apart and get some small washers from the hardware store an put enough in so that the top just fits to get the lock ring back in. Use the one in each hole I/E.Get some persian blueing (paint dye) to check with it doesn't dry and leaves a good mark.The mark on the valve stem should be as close to center and as narrow as possible. When ya get it right have your machine shop measure the length of the adjustable PR's and round up to the next highest/even number and search fo PR's as close to the number as ya can get. There are some in .025 lengths,ie. .700-.725-.750 or get a custom set made.
Make sure the lifter parts are CLEAN when ya put it back together.

cehan

Yeah, the pushrod checker I was referring to is the Comp Cam Hi Tech, which does not have a jam nut. Every complete turn = 0.050", so it makes it easy to figure out how long your pushrods should be. But those threads probably are not strong enough to handle the regular springs.

Chris