I am trying to find the correct pushrod length on an engine I am freshening up.
It has a Crower hydraulic flat tappet camshaft of unknown duration lift etc.
CHI 2v heads on a stoke stroke 351c.
3 coils for valve springs. Proform 1.73 ratio roller rocker arms, Manley valve guides.
The pushrod are 3/8" 8.4 length and when rotating them, some are slightly bent.
They are not centered on the valve, some maybe 30% contact, I will cut / modify the guides so they will.
Watching the roller tip and viewing the wear marks on the valves, they seem too short, just rubbing on the intake side.
I have a CompCam pushrod length checker and a length of 8.7 will bring the tip rubbing the intake side and into the centre.
The question I have is, that the hydraulic lifters have 'collapsed' so I will not be getting a true lift at the valve.
This will change when the lifters have filled with oil, at max lift the contact point I am trying to measure.
I do not want to remove the heads or remove the existing valve springs to fit lighter ones.
Is it okay to measure the amount the hydraulic lifter is collapsing and extend the pushrod length checker that amount?
I understand I need to be careful about valve contact.
Other suggestions?

Does 8.7" length seem a lot?
If I use this length of pushrod the polylock is only gripping about 4 turns on the stud, is this enough?

At least one of the rocker studs is bent also so I want to replace them. I do not know the manufacturer.
Is there a longer rocker stud available so I do not need to shim them up to get more threads in the polylock?
I have stock factory screw in studs that I compared these to and they are about the same length.

I would check this way...using the intake valve as an example.

Set the intake valve preload when the exhaust valve on that cylinder is just starting to open. This will insure the lifter is on the heel of the cam lobe. (You set the exhaust valve when the intake valve is starting to close.) When you get there, use your pushrod length checker, rocker arm, and polylock, and set the preload on the lifter. You will want to go to zero lash, plus about a 1/2 turn.

When you check for zero lash, a lot of people will tell you to twist the pushrod back and forth to gauge the drag. I've never liked that method and prefer to move the pushrod up and down axially until there is no play left. You can feel the instant when everything tightens up, but before it starts to compress the plunger.

Now...

You are correct in that the plunger will compress and bottom out so that you won't be able to get a mid/full lift reading. If the intake is on and you don't want to change over to checking springs, then you really don't have much of a choice. However, if you mark the top of the valve stem with a marker, you will be able to get a witness mark of where the rocker roller started before movement, then what kind of progression it made as it at least moved a little bit.

If it were mine, I'd take 10 minutes and pop the first two valve springs off and put some checking springs on.



Brent Lykins
B2 Motorsports, LLC

just a good used lifter set at .030 to .060 preload, with the cup tack welded, you could also take one apart and put shims in it for the same effect. Your rocker studs seem to short, what is the measurement?

I was thinking he had the intake on for some reason, but if he doesn't, it would be easy to take a lifter apart and shim it up and use it like that.

When I'm assembling a new engine, I'll use checking springs, but the method that Roo described works on an engine that's fully assembled and intact.

Brent Lykins
B2 Motorsports, LLC

I used an overhead valve spring compressor but I was unable to compress the inner spring of the 3 springs.
Not using air I was able to spin the valve but when I used compressed air it would not move and the collar would not move down.

Plan B. I remembered I had some hydraulic lifters from an old engine.
I took the lifter apart and used 2 nuts inside to make it solid.
I compared the base height of the original lifter and my "solid" lifter and they seem the same.
With my pushrod length adjuster at 8.7" and marker on the valve tip, the resulting scrub mark was very close to the middle if not on the middle.
I am happy with that and will now check more.

I saw an old post on here with somebody who went to 8.7" and he got some long length Trick-Flow rockers studs, I think I will go that route.

The effective height of the rocker studs installed is 1.75".

Thanks everyone.

You don't have to pull the heads to change the springs. If you don't have a air compressor, you can take some nylon rope and feed it through the spark plug hole. Then bring the piston to the top. This will keep the valves from dropping down and you can change the springs. If you have a air compressor they make an adapter that screws into the spark plug hole.