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Pushrod length formula
https://www.slantsix.org/forum/viewtopic.php?t=44144		 Page 1 of 1
Author:  Dizzydean [ Mon Mar 21, 2011 7:08 pm ]
Post subject:  Pushrod length formula
Is there a formula for foguring out how much shorter a pushrod is needed, I mocked up the head and rocker assembly to see how far off Id be with the new cam and make necessary adjustments but none are needed when all of the intake or exhaust,I can't remember now, ones bent like ripe metal bananas. As far as the spec sheet goes and the shaving of head and block I am .230 in the minus. .080 head, .080 block, .070 higher cam lift. AAgghhhhhh :evil:
Author:  66aCUDA [ Tue Mar 22, 2011 6:23 am ]
Post subject: 
Dean
Best way is to measure. I have made a Push rod gauge by cutting 1 inch out of a standard push rod and threading the insides to 1/4 20. then take a piece of all thread (1/4-20) and adjusting it to ?? then measure that and order.
Hope this helps,
Frank
Author:  Charrlie_S [ Tue Mar 22, 2011 7:21 am ]
Post subject:  Re: Pushrod length formula
Quote:
As far as the spec sheet goes and the shaving of head and block I am .230 in the minus. .080 head, .080 block, .070 higher cam lift. AAgghhhhhh :evil:
Actually the cam is approx .070 shorter, not longer. A higher lift cam is made by making the base circle of the cam smaller, and the nose stays the same hight. Therefore the lifter sits lower. In your situation, .080 head+.080 block-.046 cam(cam lift, not valve lift, (rocker ratio)) = .114
Author:  Doc [ Tue Mar 22, 2011 8:06 am ]
Post subject: 
If pushrods are bending during a mock-up then the valve spring retainer is hitting the top of the valve guide or the valve spring itself is going into coil bind.
Correct the interferance problem before selecting a pushrod length.
DD
Author:  Dizzydean [ Tue Mar 22, 2011 5:26 pm ]
Post subject: 
You guys are beyond awsome. Im going to put the head back on tomorrow and see whats going on. Thanks for all the help and advice
Author:  Charrlie_S [ Tue Mar 22, 2011 5:39 pm ]
Post subject: 
Quote:
If pushrods are bending during a mock-up then the valve spring retainer is hitting the top of the valve guide or the valve spring itself is going into coil bind.
Correct the interferance problem before selecting a pushrod length.
DD
I totally agree. One other thing to check, it is unlikely, but possible. If the cam is large enough, and not degreed in properly, the valves might be hitting the pistons. That situation would be a problem on just the intakes, or just the exhaust, depending on whether the cam was too far advanced, or too far retarded.
Author:  Dizzydean [ Wed Mar 23, 2011 8:30 pm ]
Post subject: 
I can agree with the degree part since I lined up the marks on the timing set and checked the tdc with a dial indicator and came up with a 4-5 degree difference from zero. The cam is 4 advanced. So I put the head on and snugged it down then started with #1 and installed the rods then did a hand spin- all good. I did the same with the rest and I have no clue what happened but everything went great. I snugged the rocker stud about 1/2 inch on top for each one and did each cylinder indiv and watched for binding or tight coils or valve trouble...nothing at all. So I put them all together that way loose and started hand cranking. All I heard were the valves singing in the chambers. no funny noises no bent pushrods no knocked on pistons. Im not going to complain or question but so far I have a happy chapter. On to the next item.
Author:  Doc [ Thu Mar 24, 2011 9:01 am ]
Post subject: 
While into the checks... put some clay or "play-doo" on the top of a piston and run the rotations again, at valve lash, to see how much clearance is between the valve and piston. (cut and measure the impression in the clay)
You need .060 min... .080 is better if you plan to rev the engine high.
DD
Author:  Dizzydean [ Thu Mar 24, 2011 5:35 pm ]
Post subject: 
I will do that. Thanks Doc
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