pushrod length help

General engine tech -- Drag Racing to Circle Track

Moderator: Team

77cruiser
Guru
Guru
Posts: 1084
Joined: Fri Dec 29, 2006 10:32 pm
Location: I Falls MN
Contact:

Re: pushrod length help

Post by 77cruiser » Sat May 12, 2018 11:06 am

I'm thinking Profilers have .1 long valves too & the pattern up nearly dead center, with Scorpion rockers.
Wonder if they put the rocker studs in the wrong place?
Jim

GOSFAST
Expert
Expert
Posts: 584
Joined: Tue Jan 08, 2008 7:09 am
Location: Long Island

Re: pushrod length help

Post by GOSFAST » Sat May 12, 2018 5:21 pm

Haven't seen the video mentioned but personally I don't put too much faith in any videos due to mfr's tolerances!

If you choose 10 different brands of rockers you'll end up with at least 6 different valve tip patterns, maybe even more, been there many times.

Don't have all the OP's specs but he should be somewhere between 7.000" and 7.300" on the pushrod lengths, assuming this is a conventional 23* retro-hyd roller SBC build? Largely depending also on the brand of lifters used! There's approximately .200" difference in the pushrod seat cup hgts between some brands of lifters!

Thanks, Gary in N.Y.

P.S. I can give you one "positive" over here, we will not build any more units using the Scorpion line, had many headaches over time with this particular brand! This is my own take on them, right or wrong.
Jan. 2016 - New York Street Ride 7.56 @ 190 @ 3800#
(https://www.google.com/url?sa=t&rct=...12064104,d.cWw)

smokie
New Member
New Member
Posts: 34
Joined: Fri Aug 26, 2016 7:18 pm

Re: pushrod length help

Post by smokie » Sat May 12, 2018 10:39 pm

GOSFAST wrote:
Sat May 12, 2018 5:21 pm
Haven't seen the video mentioned but personally I don't put too much faith in any videos due to mfr's tolerances!

If you choose 10 different brands of rockers you'll end up with at least 6 different valve tip patterns, maybe even more, been there many times.

Don't have all the OP's specs but he should be somewhere between 7.000" and 7.300" on the pushrod lengths, assuming this is a conventional 23* retro-hyd roller SBC build? Largely depending also on the brand of lifters used! There's approximately .200" difference in the pushrod seat cup hgts between some brands of lifters!

Thanks, Gary in N.Y.

P.S. I can give you one "positive" over here, we will not build any more units using the Scorpion line, had many headaches over time with this particular brand! This is my own take on them, right or wrong.
here is what i have, if you need more info just let me know.
the heads are assualt/proheader,nkb200 dart copies. +.100" longer valves. the rockers are scorpion 1.5 roller rockers for 7/16's studs. the block has been decked to 9.005". the cam is XR294HR-10. Duration @ 0.006": 294° / 300°, Duration @ 0.050": 242° / 248°. Max Lift w/ 1.5RR: .540" / .562". the lifters are lunati street retrofit hydraulic roller lifters.

using the mid lift method, it calls for a 7.65"pushrod. a 7.200" (factory vortec) centered the sweep, but it was about an 1/8th inch wide.

steve cowan
Expert
Expert
Posts: 540
Joined: Wed Jul 27, 2011 5:22 am
Location: brisbane AUSTRALIA

Re: pushrod length help

Post by steve cowan » Sun May 13, 2018 12:48 am

GOSFAST wrote:
Sat May 12, 2018 5:21 pm
Haven't seen the video mentioned but personally I don't put too much faith in any videos due to mfr's tolerances!

If you choose 10 different brands of rockers you'll end up with at least 6 different valve tip patterns, maybe even more, been there many times.

Don't have all the OP's specs but he should be somewhere between 7.000" and 7.300" on the pushrod lengths, assuming this is a conventional 23* retro-hyd roller SBC build? Largely depending also on the brand of lifters used! There's approximately .200" difference in the pushrod seat cup hgts between some brands of lifters!

Thanks, Gary in N.Y.

P.S. I can give you one "positive" over here, we will not build any more units using the Scorpion line, had many headaches over time with this particular brand! This is my own take on them, right or wrong.
Gary,
i have a set of 1.6-1.5 Scorpion rockers on a set of cast dart sportsman 2s
i had to machine a chamfer on the base of the posilocks as they were touching the inside of the rockers at TDC.also it looks like the case hardening is starting to wear off the roller tip,FT solid cam 327sbc hase not done a lot of work.
i don't want to bash the BRAND but i am curious with your findings,
thanks
steve c

steve cowan
Expert
Expert
Posts: 540
Joined: Wed Jul 27, 2011 5:22 am
Location: brisbane AUSTRALIA

Re: pushrod length help

Post by steve cowan » Sun May 13, 2018 1:25 am

smokie wrote:
Fri May 11, 2018 9:16 pm
the heads are assualt/proheader,nkb200 dart copies. the rockers are scorpion 1.5 roller rockers. the block has been decked to 9.005". the cam is XR294HR-10. Duration @ 0.006": 294° / 300°, Duration @ 0.050": 242° / 248°. Max Lift w/ 1.5RR: .540" / .562".

using the mid lift method, it calls for a 7.65"pushrod. a 7.200" (factory vortec) centered the sweep, but it was about an 1/8th inch wide.

how can i make sure the lifters are pumped up? i guess i need to use checker springs as well.

thanks everyone
smoke,
sometimes you cant always find a perfect sweep and centre of valve,i have had a few engines i have run off centre slightly to the exhaust side of the valve,my 383 sbc with 680''solid roller with 1.6 rockers 230-600 on the nose is an example of that,12 months of street driving and track twice a month to 7600 rpm,just had heads cleaned up and seats and valves done,guides are still good,
i think you might find as well that most pushrod companies offer pushrods in 0.050''
increments unless you go custom made,dont quote me on that one but when i look at a online listing for pushrods that is what they offer,comp,CV to name a couple,trend might be different as i have never delt with them.
i think you will find it difficult to try and use a hydraulic lifter without a soft checking spring as the lifter will collapse and give you a false reading.
steve c

tresi
Pro
Pro
Posts: 269
Joined: Sun Mar 24, 2013 10:10 pm

Re: pushrod length help

Post by tresi » Sun May 13, 2018 3:03 am

I have heard horror stories of some import heads that had valve guide and rocker arm stud angles all over the place. I have no experience with Assault heads. They may be fine heads but is this a possibility?

smokie
New Member
New Member
Posts: 34
Joined: Fri Aug 26, 2016 7:18 pm

Re: pushrod length help

Post by smokie » Sun May 13, 2018 2:00 pm

SPEIER RACING HEADS use them or at least used to. i don't think Q.C. was the reason for the change though.

User avatar
af2
Guru
Guru
Posts: 6241
Joined: Sun Jan 28, 2007 4:42 pm
Location: Grass Valley, CA :Northern Foothills

Re: pushrod length help

Post by af2 » Sun Jul 01, 2018 6:16 pm

mdla wrote:
Fri May 11, 2018 5:14 pm
I ran across this video the other day from Straub Technologies. It does a good job of explaining how to correct your problem, I think. I hope it helps!


https://www.youtube.com/watch?v=o5is9BsH5OU
As Chis said the geometry is far better and the only way to set it up. I have a BBC as we speak that with the correct geometry is close to center on the exhaust and outboard on the intake (not falling off but within .070"outside) I will take geometry over center any day. I could put lash caps on it to gain .050 valve side. I don't think it is big deal beaker.
GURU is only a name.
Adam

Walter R. Malik
Guru
Guru
Posts: 3865
Joined: Tue Jul 24, 2012 11:15 am
Location: Roseville, Michigan (just north of Detroit)
Contact:

Re: pushrod length help

Post by Walter R. Malik » Sun Jul 01, 2018 9:13 pm

Most rocker arms in the marketplace are NOT "mid-lift" geometry.
Among the others ... Jesel, (for instance), has what they refer to as "low pivot geometry" which has a pretty wide wipe pattern on the tip of the valve; INTENTIONALLY.
Starting toward the inside third of the valve tip and having most of the wiping pattern in the first half of the valve lift and as little width as possible wipe pattern during the second half of the valve lift. Which usually means that maximum rocker ratio is achieved somewhere between 67% and 75% of the total valve lift; NOT mid-lift.
There really is no right or wrong way as long as you do whatever that rocker arm is designed to do.

The differing rocker arms in the marketplace are usually some kind of compromise between the two geometries and depending upon how the geometry is on the pushrod side, will normally determine what compromise they have.
http://www.rmcompetition.com
Specialty engine building at its finest.

Post Reply