Push Length Valve Witness Marks- thoughts
 

Guys, I am in the process of getting some engines together. Ian measuring for the pushrod lengths and I’m struggling to get a good contact area on my intake valve.

I have a 454 mark iv block that was stroked and I have promaxx heads (290) installed. The cams have a 0.592 lift with my crowler 1.8 ratio rockers.
I have Johnson hydraulic roller lifters.

I at first started doing this pushrod length check merely doing the dye on the end of the valve stem and look for most center and narrow mark. But I found as I was most centered on the valve, the mark was wide. I then used the mid-lift approach. This ended up having me lengthen the push rod such that it put the mark on the end of the valve closer toward the exhaust port, BUT the mark was very narrow.

The exhaust push rod witness mark looked good, first photo.

https://cimg8.ibsrv.net/gimg/www.off...bd665ea89.jpeg
Exhaust valve marking

The intake valve is another story. To get a narrow mark I have to have that rod fairly long, such that it puts the mark near the edge of the valve. On top of that, I most likely need a longer stud for here. 2nd photo, close to the mid lift process. The 3rd photo is of a shorter rod and as you can see the witness mark is centered but very wide.
https://cimg7.ibsrv.net/gimg/www.off...dda1fc652.jpeg
Intake mid lift approach.

https://cimg4.ibsrv.net/gimg/www.off...2c3d7dbba.jpeg
Intake valve shorter pushrod centered mark but wide.


So, the question is, what can I do to get the intake looking like the exhaust?

Did you buy the heads assembled or bare ? What valves did you use ? I wonder if a shorter exhaust valve would help if it doesn't mess up your installed hgt too much. I have never used a Promax head so I dont know how the geometry normally works out.

Crower makes rocker arms that have the stud hole backset. I think they come in .050&.090.

I ran into this issue building a 383 stroker years ago. Someone suggested swapping the rockers around. Didn't make any sense at all but out of desperation I tried it. Somehow it worked. Still scratching my head over that one.

The only rockers I have are 1.8 ratio and I’ve tried a couple, they all yield the same result. I’d say you may have had different ratio rockers on exhaust vs intake.

I just did another test with as best as I can to mid-lift approach. I had to shorten the rod to get a more legible mark on the valve stem vs being off further.

below are the results of that test and then with a micrometer. I measured center of mark to back toward center of valve. The largest offset crower has is 0.090 so I’m thinking that’s what I need.

do you agree?

https://cimg8.ibsrv.net/gimg/www.off...60e128649.jpeg
Micrometer reading.
https://cimg6.ibsrv.net/gimg/www.off...a42198285.jpeg
Best I can get mid-lift approach while keeping a mark on the valve.

Forgive me I run solids.
But, how are your lifters not collapsing with the springs in and no oil pressure? Wouldn't this throw off the contact pattern? I believe I used test springs on my last HR builds.
​​​​​​​

Yes, you would be correct, but I do have test springs on #1 cylinder intake and exhaust, can push them very easily.

All right…. Update guys, need to hear your blessings on if these are ok.

Below is the repeat of the exhaust valve, which I think looks good. Estimated contact pattern width is 0.042”.
https://cimg7.ibsrv.net/gimg/www.off...8289786e7.jpeg
Exhaust

As suggested, thank you, I picked up an 0.090” offset rocker and below is the intake pattern, estimated at 0.056” width.

https://cimg7.ibsrv.net/gimg/www.off...6fbe17ee2.jpeg
Intake

Am I good to go and move on to the next stage of this build?

The original exhaust pic looked not bad. Was narrow and relatively centred,

The exh you just posted is not like thatÿ at all.

I wouldn't run the exh the way it is. Too far off the center, despite being narrow.

The intake looks far better now. Would the 0.050" have place the contact patch in the center vs where the 0.090" pulled it past center tonthe other side?

Thanks for the feedback. I wondered what the 0.050” would do as well….. so I just ordered one of those. First time doing this work. Learning the hard way. Will test that out when it comes in.

Don't get all caught up with the witness mark needing to be perfectly centered on the valve. It is more important that the witness mark be as narrow as possible so that you get maximum valve lift. There are people that will tell you that being off center will wear the valve guide, but they are wrong. It is physically impossible to push a valve stem sideways with a roller rocker.

Good point, any 'sweep' over the stem is rocker movement that does not translate to valve lift.

Getting a narrow sweep is priority, but getting it close to center should be pri 2. Running too far off center increases rocker to stem pressure with less contact.

Thanks guys. That all makes sense. Will post up pics when I test with the 0.050 and whatever works the best. Maybe next week.

Update: So these promaxx heads needs some more work, ie longer rocker studs.

So I got a couple lengths of those, and then also got the 0.090” and the 0.050” backset rockers.

In conclusion, on my exhaust valve a longer stud and a 0.050” backset on gave a great, repeatable pattern that is fairly close to center. Estimated witness mark width is 5/128”. On my intake, the 0.090” backset gave a great repeatable again fairly close to center pattern. Estimated width is 7/128”.
https://cimg8.ibsrv.net/gimg/www.off...b4ef5b83c.jpeg
Exhaust
https://cimg6.ibsrv.net/gimg/www.off...90931fc96.jpeg
Intake


Thank you to everyone for their input to get this near perfect!

That is as good as it will ever get.

Great work. Thank you for getting a good detailed solution and photos.

Thanks guys! First time playing with engine stuff this much inside the engine. I learned a lot going through the motions here. Sure took a lot longer than planned. Now getting ready for number 2 engine. Should go much faster knowing I need longer rocker studs out of the gate and then knowing the offset rockers.