Pushrod length 4 vortec head swap

[mr_clean]

I have an 86 350 I'm rebuilding and was thinking I would get some of the L31 heads for it. I was also planning on throwing in an RV cam or some form of a mild performance cam. Do I need to get a pushrod length checker or can I just throw in stock ones and eyeball it to see if they are right or not?

Also how do you acurately measure pushrod length with hydraulic lifters? Don't the lifters have to pump up before you could get an accurate measurement?

Thanks,

Scott

 

[dyeager535]

Let's see if I get this right. Get engine to TDC #1. Put pushrod and rocker in place on that cylinder. If it were a roller tip rocker, you are looking for the roller to be slightly inboard or centered on the valve stem. I *assume* on a "stock" rocker, you would look for the same sort of contact. As long as you don't crank the rocker down, the lifter won't compress.

On my Vortecs I had to grind the heck out of the pushrod holes. It seems that there is a big variation in these heads as to whether or not things like this need to be done. In my case it was completely obvious I needed to grind what I did.

Another "if" is the lift the stock L31 setup will take. Mine was borderline at .452" lift, others apparently get more on the stock setup. Anything more and I would have had to cut the valve guides down. Of course, I had to change the springs too, (stock vortec springs are pretty weak, even though they were roller cam springs) so that was another expense.

 

[mr_clean]

Position 1 = no lift
Position 2 = mid lift
Position 3 = max lift

So if I install a stock length pushrod and adjust the valve properly, then find at TDC my contact point looks like position 1 in the above diagram I should be fine?

Assuming that picture is accurate for non-roller rockers (I was planning on using the stock self aligning rockers...)

 

[dyeager535]

To do what they are showing on that picture, you need a soft valve spring so you can move the rocker/valve as a unit. Have to make sure you aren't compressing the lifter as well of course. I made one for mine with a spring from the hardware store.

The tip of a stock rocker is much different than a roller, but I *suspect* that is still a generally correct method. We have pro engine builders here, I expect they will chime in.

 

[beater_k20]

if its just a flat tappet cam in an otherwise stock engines, use pushrods for your 86 350. the only difference in the roller cam/non-roller cam pushrods are accounted for by varying the height of the lifter.

 

[mr_clean]

the only difference in the roller cam/non-roller cam pushrods are accounted for by varying the height of the lifter

I'm not sure I understand. How can I vary the height of the lifter? Does this happen automatically because of the hydraulic action of the lifter or are there different sized lifters?

 

[4X4HIGH]

Roller lifters are taller than a standard hydraulic lifter which means the roller cammed engines use a shorter pushrod. If installing Vortec heads on your 86 blazer you will use your existing pushrods. Something that everyone is forgetting about is that (if i'm not mistaken) all Vortec heads have a round pushrod hole so you must use the GM self aligning rocker arms or some aftermarket self aligning rocker arms otherwise the rocker arm will move all over the tip of the valve. The earlier heads had rectangal pushrod slots in the head which centered the rocker over the valve tip.

 

[dyeager535]

Yes they do have the round pushrod hole.

He says in one post he'll beusing stock self aligning rockers, so no worries there.

 

[mr_clean]

Yes, I'll be using the self aligning rockers. The extra few hundred for roller rockers would put me over what I want to spend. Basically I'm just rying to get a good strong 350 without spending too much money . So I thought I'd throw the vortec's on there, RV cam, Performer vortec manifold and open up the exhaust a bit. I had been reading about how changing the valvetrain from stock would require measuring for pushrod length. I wasn't sure if I was actually changing from a stock valvetrain or just changing to a different stock valvetrain.

So it sounds like I should use the stock length pushrods for the 86 engine with the self aligning rockers and all should be well.

Thanks for all the help!!!