Push rod length,II

Greg Reimer 7376 · 07-01-2012, 07:35 PM

Some time ago, we got into a very interesting discussion about determining proper push rod lengths in a stock eliminator motor.I wrote of some of my experiences, then decided to go with a Dart legal accepted block instead of the OEM #660 casting.That changed a few things. I assembled the entire short block, used the same Bullet cam, replaced all the valves with Ferrea units, had Gregg Luneack massage them to get them to work, and arrived at a unit with very ample piston to valve clearances,some where around .095" on the intakes and.105" on the exhausts.Great shape here.
I checked the valve lift with a solid test lifter(the heads are final assembled, mounted, and torqued down), and used a 7.650"long push rod, then an OEM 7.800 long push rod for comparison. The results are as follows:
#1 Exhaust.399"--.408"
#1 Intake,--.388"--.398"
#3 Intake,--.384"--.390"
#3Exhaust-.398"--.406"
#5Exhaust-.397"--.405"
#5 Intake,--.381"--.389"
#7 Intake,--.380"--.389"
#7Exhaust-.399"--.405"
#2Exhaust-.398"--.405"
#2 Intake---.374"--.382"
#4 Intake---.387"--.397"
#4Exhaust-.401"--.404"
#6Exhaust-.398"--.407"
#6 Intake---.381"--.388"
#8 Intake---.380"--.387"
#8Exhaust-.390"--.405"

I used an Elgin R-1840 rocker arm on this comparison test, same rocker used in all 16 positions to insure consistant results
Next thing I checked was the rocker arms. I took the other 15 rockers, numbered them with a felt pen 2 thru 16, then selected the #1 intake valve for a sample, then tested the lift. All 16 rockers fell between .388" lift and .391" lift on one only. I'm used to OEM rockes varying by a much wider margin. These Elgin ones are for the 7/16" rocker arm stud , the latest thing before the accepted roller rockers came out.
Seems to me the engine could use an OEM exhaust pushrod, 7.800" in length and be close but safe on all eight valves, and the intakes could benefit by a 7.750" push rod. That would keep the lift safe by .005-.006" on all valves.
Hope all this was relevant and interesting.Oh,yes.The engine is a '68 327 250 horse unit, legal lift .390" intake, .410" exhaust.

tj310 · 07-02-2012, 09:05 AM

Yes thanks for sharing . ---Trevor

07-01-2012, 07:35 PM	#1
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,132 Likes: 172 Liked 698 Times in 216 Posts	Push rod length,II Some time ago, we got into a very interesting discussion about determining proper push rod lengths in a stock eliminator motor.I wrote of some of my experiences, then decided to go with a Dart legal accepted block instead of the OEM #660 casting.That changed a few things. I assembled the entire short block, used the same Bullet cam, replaced all the valves with Ferrea units, had Gregg Luneack massage them to get them to work, and arrived at a unit with very ample piston to valve clearances,some where around .095" on the intakes and.105" on the exhausts.Great shape here. I checked the valve lift with a solid test lifter(the heads are final assembled, mounted, and torqued down), and used a 7.650"long push rod, then an OEM 7.800 long push rod for comparison. The results are as follows: #1 Exhaust.399"--.408" #1 Intake,--.388"--.398" #3 Intake,--.384"--.390" #3Exhaust-.398"--.406" #5Exhaust-.397"--.405" #5 Intake,--.381"--.389" #7 Intake,--.380"--.389" #7Exhaust-.399"--.405" #2Exhaust-.398"--.405" #2 Intake---.374"--.382" #4 Intake---.387"--.397" #4Exhaust-.401"--.404" #6Exhaust-.398"--.407" #6 Intake---.381"--.388" #8 Intake---.380"--.387" #8Exhaust-.390"--.405" I used an Elgin R-1840 rocker arm on this comparison test, same rocker used in all 16 positions to insure consistant results Next thing I checked was the rocker arms. I took the other 15 rockers, numbered them with a felt pen 2 thru 16, then selected the #1 intake valve for a sample, then tested the lift. All 16 rockers fell between .388" lift and .391" lift on one only. I'm used to OEM rockes varying by a much wider margin. These Elgin ones are for the 7/16" rocker arm stud , the latest thing before the accepted roller rockers came out. Seems to me the engine could use an OEM exhaust pushrod, 7.800" in length and be close but safe on all eight valves, and the intakes could benefit by a 7.750" push rod. That would keep the lift safe by .005-.006" on all valves. Hope all this was relevant and interesting.Oh,yes.The engine is a '68 327 250 horse unit, legal lift .390" intake, .410" exhaust. Last edited by Greg Reimer 7376; 07-01-2012 at 07:40 PM.

07-02-2012, 09:05 AM	#2
tj310 Member Join Date: Sep 2009 Location: Dresden On. Canada Posts: 460 Likes: 0 Liked 0 Times in 0 Posts	Re: Push rod length,II Yes thanks for sharing . ---Trevor