pushrod installment Q

Top End (cylinders pushrods etc.)
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doc308
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pushrod installment Q

#1

Post by doc308 »

Here's a very basic Q. I'm ready to install a set of solid aluminum pushrods into my '48 pan and I'm not sure which end is up! Does the larger end of the rod mate to the rocker arm or to the lifter cup?
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Re: pushrod installment Q

#2

Post by FlatHeadSix »

doc
Big end goes up and fits into the socket in the rocker arm. If you are replacing the original set of hydraulic pushrods the answer should be in the parts you took out, the "oil can" in the original pushrod goes up and has the larger ball.

make sure you read all the stuff that has been posted about the cold adjustment on the aluminum shaft pushrods, "tight is right"! I've been running a set in my '49 for years, the quickest, cheapest, biggest single improvement you can make on an early pan motor.

mike
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Re: pushrod installment Q

#3

Post by doc308 »

Thank you, Mike!
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Re: pushrod installment Q

#4

Post by doc308 »

I have a Q about the "tight is right" statement. I've read a few previous posts on adjusting solid lifters with solid aluminum pushrods and I'd like some final recommmendations before I do this job. It seems that there is a difference of opinion re: how tight is tight. So, having never done this job before, how should I set the tappets--spinning very freely with no up/down movement OR spinning on the hard side requiring 2-3 fingers' effort?
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Re: pushrod installment Q

#5

Post by FlatHeadSix »

Doc
Since there is no reproduceable scientific method of measuring this, it will be different for each person that does it. The "tightness" is purely subjective and a matter of feel.

Lean toward the harder, 2-finger, you can still turn it, but with some effort setting. Aluminum has a different coefficient of expansion than steel so the initial setting must be on the tight side if you want the valve lash to be correct when all the components in the system reach equilibrium at operating temperature. If you really wanted to prove that it is correct after it all warms up I guess you could ride the bike hard and warm everything up, stop the bike and then instantly drop the push rod tubes and check the lash with everything hot.

tight is right for aluminum push rods and solid lifters.

mike
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Re: pushrod installment Q

#6

Post by NightShift »

Dear Doc,

Just not so tight you can't turn them.

Push the kicker through a couple a times and your fingers will feel if you really got the loose spot or not.
If it WAS loose, and then got too tight, your cam is sloppy.

Arthritis will make you set them a tad loose, but it wont blow up for a few summers.
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Re: pushrod installment Q

#7

Post by Hauula Pan »

I think people are making way too much of this push rod adjustment issue. Yes there is some difference in the way steel vs aluminum heat up and expand and contract etc. But these old motors are pretty forgiving where issues of wear and some adjustments are concerned. Weather you set them one finger tight or two fingers tight is really going to be a bit different with each person and their feel of what is snug vs what is tight vs what is loose. As long as you set them tight enough that they will stay in place and loose enough that they allow the valve to fully close your motor should run without damaging it. You'll know if you need to fine tune your adjustment by listening to it both cold and hot. Just remember, too loose & they'll clatter but too tight and you can damage a valve. A bit on the tight side is good but make sure you're not so tight that you hang a valve open.
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Re: pushrod installment Q

#8

Post by Cotten »

Don't look now folks, but if a valve stays open, the cylinder won't fire when you kick it.
No fire, no burnt valve.

So, let us hypothetically say its just leaky, and you still have enough compression to start.
As soon as combustion heat hits the head and cylinder, the pushrod gets looser, and the valve again contacts the seat fully.

But our critical concern is not the adjustment for start-up, it is the clearance at running temperature.
The problem we face with aluminum pushrods is that they get loose as a goose unless you start out as long as possible. That means a great deal of drag when rotated.
[But you still must be able to turn them.[/b]

I do not endorse aluminum pushrods.
If this subjective adjustment thing seems to be more trouble than it is worth, your right.

....Cotten
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Re: pushrod installment Q

#9

Post by Panacea »

Do we have a favorite steel pushrod?...Mike
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