There are a lot of helpful posts on Valve train geometry on this forum and I thank everyone for that. I was surprised to see how much there is to this subject. I made the mistake of letting a vendor substitute one of their "Jeg's Check'r" brand pushrod length checker instead of a useful tool such as comp-cams tool. This tool came with no instructions. I had asked their tech support for some written instructions - Here they are:

"They are a very basic tool that allows you to get a measurement. Simply install in the engine and adjust to the length needed, remove them, and measure them. I’m not sure what instructions you are speaking of needing. "

Well, lots of questions here:
1) There are 3 different measurements that pushrod manufacturer are using according to Comp Cams.. Theoretical, Actual and "Gauge Length". Comp ams says they use Gauge Length.

2) Comp Cams' version has numbers stampted in them. each turn is an additional .050. This version has no such functionality. Do they think I have a set of 8-11 inch calipers.. (I don't)

3) There are different points to set to and I need to understand what the goal is here.. According to Comp Cams, Base Circle, Mid Lift and Max lift.. I assume we are talking about base circle, but were is that to be set exactly on the valve tip?

Since then from the forum, I see that people are using marker on the stem and rotating the engine to see what gets wiped off. Then they are adjusting until the strip is centered.

My final question is on question number 1, using comp cams pushrods, do I order by gauge length? If so how do I calculate that from the total length that this "JEG's Check'r" would give?

BTW, the vendor closed the request for written documentation on their product with the comment that they only expect to sell this product to those who know what they are doing already and don't need doc. Needless to say, I was already doubting doing any business with this vendor. Now it is pretty set that I will bypass this particular vendor.

 

You measure and order by overall length, aka gauge length. You need to measure your test pushrod with 10-inch calipers. If you don't have a set, take the pushrod down to a machine shop and have them measure it once the length is determined. You don't need to know how much longer it gets with each turn or how long it is to start - measure the end result. Install test springs on the valves for the test setup.

 

Lars, thanks,
I am still not clear though, is'nt guage length the total length minus the the oil passage opening? The tool I have is not guage drilled, it is instead rounded. Is there an amount I should be subtracting?

 

the easy way is with a manley checker..here are the results....

 

You measure the length of your tool and find the closest pushrod length to that measurement. It's no more complicated than that.
Lars

 

How wide are your witness marks?

 

dunno how wide...i didn't measure the marks...they are comp roller rockers and after using the manley tool i had to go .010 longer and this was the result.....good luck

valve stems are 3/8"...the marks you see are after a 20 minute warm up and tune....just thought i would re check....

correction .100

 

I don't even mark the top of the valve I turn it over and look at the tip travel across the top of the valve. You are getting a little on the **** side here ( no offense intended ). Even when you get it exactly where you want it the pushrod you order could be out .025" either way anyway as they only come in .050" increments, unless you want to pay for a custom setup.

When I see the witness marks on the tips of the valves using a adjustable checker I just wonder where its going to be when the pushrods are ordered in the .050" increments.

I try and get the roller tip to go equally on each side of he tip centerline in one complete revolution as well as centered on the valve which is just as important and taken care of with shaft rockers, you might only be able to get it close as you can

 

Have you ever measured the lift at the valve while using an adjustable pushrod?

 

Can one use a hyudralic lifter and not replace valve springs when checking pushrod length with the Comp Cams tool (7703-1)?

...or will I just compress the lifter and shave the threads of the tool? :O

 

Anyone!?

...or will I get a good enough reading without rotating the engine?

 

You should really put a lighter checking spring on when using this tool. The threads on mine are course and not all that tight.
The idea is to have the contact pattern centred on the valve, with it starting slightly off centre towards the rocker arm, moving to the other side of the centre of the valve at mid lift, and finally moving back towards the centre of the valve (when spring pressure is greatest) at full lift.