Help - Determining Pushrod Length

Richard Le

Richard Le

New member
I don't have any expertise when it comes to valve train, so I read this link but I'm still at a lost: http://www.compcams.com/information/Products/Pushrods/

Today, we dropped two COMP Cams Pro Magnum Hydraulic Roller Lifters into the lifter holes for the #1 cylinder with the cylinder at TDC. Then we inserted two stock length pushrods and tried on two 1.5 ratio stainless roller rocker arms that I got from Hood:

rocker01.jpg


There were only two threads from the stud that the rocker arm nut was able to grab onto. So I need shorter pushrods, right (or do I need longer studs)? I'm going to get one of those Adjustable Pushrod Length Checking Tools. So the problem is how to use the tool. Please educate me.

This is for a set of RPM Vortec heads.
 
4C FED

4C FED

Absolutum Dominium
Re: Help - Determining Pushrod Length

Assuming you adjusted the valve lash correctly, longer studs. But that does not necessarily mean you won't need different length pushrods either.

And, are those self-aligning rockers?
 
Richard Le

Richard Le

New member
Re: Help - Determining Pushrod Length

Not sure if the valve lash has been adjusted or not. Another challenge I guess.
 
S

syclone0209

Member
Re: Help - Determining Pushrod Length

you should have told rpm you were using full bodied roller rockers. you needed to have them drill the head for the longer studs. some people have opted to use the hardened washers from comp and put them under the stud to give them the extra height to get a few more threads on the poly lock. the poly locks can be machined down to get another thread or two.
 
U

Upgrade

I suffer from boost envy
Re: Help - Determining Pushrod Length

Richard Le said:
I don't have any expertise when it comes to valve train, so I read this link but I'm still at a lost: http://www.compcams.com/information/Products/Pushrods/

Today, we dropped two COMP Cams Pro Magnum Hydraulic Roller Lifters into the lifter holes for the #1 cylinder with the cylinder at TDC. Then we inserted two stock length pushrods and tried on two 1.5 ratio stainless roller rocker arms that I got from Hood:

rocker01.jpg


There were only two threads from the stud that the rocker arm nut was able to grab onto. So I need shorter pushrods, right (or do I need longer studs)? I'm going to get one of those Adjustable Pushrod Length Checking Tools. So the problem is how to use the tool. Please educate me.

This is for a set of RPM Vortec heads.
Click to expand...

Are you sure your on the base circle of the cam??? Are you running push rods for an HR or a flat tappet? They are ~0.400 longer than a HR rod.
I don't recall the difference in length between the two studs, but you need to know if the heads were cut to run guide plates or not.
If yes, then you need to get head bolt washer to take the space normally used by the guide plates and run a self guided rocker. Or run regular unguided roller rockers and guide plates with hardened push rods. Don't go cheap on the push rods in a boosted motor.
Also, you should use a checking spring instead of the regular valve spring to ensure the lifter doesn't compress and throw the pattern off on the stem tip.
 
JSM

JSM

Active member
Re: Help - Determining Pushrod Length

My dad helped Richard since the motor is at his house. So I know my dad knows it was not trying to open the valve.

I suspect for sure custom push rod lengths, and as mentioned possible rocker studs being longer.

Get the adj. push rod richard, adjust it so the rocker arm travels across the valve and is centered on the valve. You don't want it to be off to one side.

Here is a good article.

http://sbftech.com/index.php?topic=317.0

camshaft_basics_rocker_sweep.jpg


Looking at your picture again it appears the roller of rocker at the tip of valve is way toward the exhaust side. Telling me pushrods are too long. Shorter pushrod should give you more thread engagement for sure, had to do this on my engine in my ty when I went to roller lifters.

Another good article and info they will need to order a set.

http://www.compcams.com/information/Products/Pushrods/
 
Richard Le

Richard Le

New member
Re: Help - Determining Pushrod Length

Upgrade said:
If yes, then you need to get head bolt washer to take the space normally used by the guide plates and run a self guided rocker.
Click to expand...

Pushrods are hardened for HR tappet. The heads came already installed. I was told to use self aligning rocker arms for 3/8" studs. Head bolt washers?
 
MRKING

MRKING

New Parts for Old Trucks
Re: Help - Determining Pushrod Length

I have a full extra set of 7808-16 comp cams pushrods for my rpm vortec heads . I can sell them cheap if you find they are the right size for your application as well .
 
Richard Le

Richard Le

New member
Re: Help - Determining Pushrod Length

4C FED said:
Can you measure from the length from the base of the stud to the top of the stud?
Click to expand...
We measured the stud from the base to the top, which turned out to be 1.58". I bet I have these studs: ARP 100-7201. So I will need to go with 1.895" long studs.
 
Last edited:
Richard Le

Richard Le

New member
Re: Help - Determining Pushrod Length

MRKING said:
I have a full extra set of 7808-16 comp cams pushrods for my rpm vortec heads . I can sell them cheap if you find they are the right size for your application as well .
Click to expand...
Thanks, but I also have a set of 7.192" long pushrods, which are the same length as those 7808-16.
 
U

Upgrade

I suffer from boost envy
Re: Help - Determining Pushrod Length

Richard Le said:
Pushrods are hardened for HR tappet.
Click to expand...

They come hardened or not. Nothing to do with the tappet. Tappet makes a difference in the length.


Richard Le said:
The heads came already installed. I was told to use self aligning rocker arms for 3/8" studs. Head bolt washers?
Click to expand...

Traditionally, when you tell a machinist to cut heads for screw in studs. They get cut to include the thickness of the guide plates. If you run guided rockers, you can't run guide plates. So you put 2 head bolt washers on instead to make up the space.
 
4C FED

4C FED

Absolutum Dominium
Re: Help - Determining Pushrod Length

Richard Le said:
Speaking of which, are the holes in the Vortec heads M8 x 1.25mm or M10 x 1.50mm?

These are longer studs with metric base threads for Vortec: http://www.summitracing.com/parts/ARP-134-7201/
Click to expand...
Richard, I pulled one out of my heads & the base thread is 7/16-14.

I suggest you get one of these. http://www.boltsizeit.com/
You can usually find them at hardware stores or Harbor Freight Tool stores.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=39240
 
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ghettosled

ghettosled

SYTY SUPERSTORE
Re: Help - Determining Pushrod Length

The V6 vortecs are m10x1.5. The washer trick may help, and you can usually machine down the poly locks so the threads are on the very edge of the nut.
 
Richard Le

Richard Le

New member
Re: Help - Determining Pushrod Length

Thanks. I might as well go with COMP cams Magnum roller tip rockers and be done with it even though I prefer full roller rockers.
 
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