Im checking my pushrod length and there is a difference of about .025" between the intake and exhaust on cylinder 1. Havent checked the others yet. How common is this?

 

can't speak to how normal it is across the board, but that's about what I saw in my measurements too to offer another data point. differences ranged between .020-0.030" across all 8 pairs of valves.

All the tolerances add up - base circle radius of intake vs. exhaust on your cam, valve length, how deep the valve seats were cut, minor differences in lifter cup height lifter to lifter, etc. I'd imagine it'd be more pronounced in hand worked heads.

 

Thanks for the quick response. Are you gonna run different length pushrods or just let the lifters soak up more/less preload?

 

Well my hand is kind of forced since I'm running the johnson short travels.... need to hit a .025-.030" preload window with only around .052" total travel available IIRC so I need different length pushrods. If your lifters have more travel you could probably just use the same length and let it eat.

 

Im just using Ls7 lifters ad trying to get around .080" preload. I will check all of them and order them for my shortest pushrod at .080" preload and that should give my lifters that need longer ones .060" so that should be a decent range.

 

Ok so I got them all checked and I got 8.25 turn on exhaust and approximately 8.65 turns on the intake. This was done without a head gasket, I will be running a .046" head gasket. I decided to use the 8.25 length.

8.25 x .050 = .4125

.4125 + 6.800 = 7.2125

7.2125 + .046 ( head gasket thickness ) = 7.2585

7.258 + .080 ( preload I want to run ) = 7.3385

I will round this to 7.350". The heads are milled .020" and cam is a custom grind 233/236 .618/.578 111+3, does this seem right? Every post I read seems people have to run longer pushrods for larger cams or stock size to compensate for milled heads, thinner head gaskets, but mine are .050" shorter than stock. Just want to make sure this is right thanks.

 

if you run a short travel lifter, you should run an adjustable rocker....
then you can order a standard set of pushrods and you can guarantee you get the right amount of preload on every single one.

 

Anybody know if this looks right?

 

Bump.

 

you measured and addeded your desired preload...correct?

then the numbers are right...

the only thing you can do is go back and double check by doing several intakes and several exhausts to see if its correct

you should error on the low side of 80 if you are going to pick a direction to go on pushrods..meaning pick the next size shorter if its a number that is close instead of going longer...
a little less preload is better than more preload when it comes to lifters..

get a 7.30 pushrod if you can.

I highly recommend Manton for pushrods..they will make any length you need

 

6 of one, half dozen of the other.

 

unfortunately...not with a short travel lifter...
when you have a liter that only has .050 of total travel, you need to get it right or stuff breaks.....
and you have to figure in thermal expansion as well.... its not a lot, but every bit counts when its already close

 

Or just measure each one and order Manton pushrods which are available to the thousandth of an inch.

That's what I did.

 

LOL @ Jake.......


or just do that...LOL

I always forget that is an option... I order close to an even number because I have adjustable rockers and can set the preload on each one individually anyways

the hardest part about ordering individual lengths, is you need to know which one is which and what hole it goes in....which can easily get confused...
with everything the same length, it all just drops in anywhere.

 

And Manton doesn't mark them. So you have to get your caliper out and measure each one then tape the length to it. And then write down which cylinder needs what.

But I ordered them all the same. 15 of the valves were within .005" of each other. And one was weird. Luckily, Manton gave me a pushrod not like the others and I used it there. So all were within like .007" of each other in the end. Pretty good...

 

exactly what most people dont want to do.....
Jeez....

Thank goodnes they have such an awesome product

 

Yeah. Exactly.

 

more than aware of that big guy

measured for each valve and am getting custom length rods cut as jake annotated. from there fine tune with rocker shim to make up for slight differences.