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Old 04-16-2018, 10:23 AM
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DanH DanH is offline
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Default Measuring Lycoming Pushrod Length

Consider the "Approximate Length" listed in SI-1060S.

Is the given dimension based on the theoretical tip of the hemisphere (top), or is it measured from flat to flat (bottom)? Or is it something else entirely?

Dan Horton
Barrett IO-390

Last edited by DanH : 04-16-2018 at 02:20 PM.
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Old 04-16-2018, 10:27 AM
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Brantel Brantel is offline
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I found inconsistent answers to this question last year, looking forward to learning the real truth...
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Old 04-16-2018, 11:25 AM
mahlon_r mahlon_r is offline
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I believe it is measured from the portion of the rounded end of the push rod to where it will intersect with the bowl in the rocker arm. So no way to easily measure the rod length. If you measure from flat to flat on the pushrod, the dimension you get will be longer and nothing near to the dimension listed for that particular pushrod. Also, if you measure several pushrods of the same P/N the length will differ between each one using the flat to flat method.
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Old 04-16-2018, 11:55 AM
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rocketbob rocketbob is offline
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I made up an adjustable pushrod I used to measure the length. I use that measurement, and a correction factor I determined using a radius gage and some wire feelers. I can't remember the dimension now but when you order custom pushrods from someone like Manton they don't flatten the ends and I've never seen it done on any other pushrod engines, so you have to give them exact lengths based on a full radius. Fraction of the price of Lycomings BTW. Never had any problem with oiling with the non-flattend end pushrods.

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Old 04-16-2018, 01:25 PM
Bicyclops Bicyclops is offline
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What's really fun is trying to use the length via part number....when the part number stamped on the pushrod is incorrect. I went around and around trying to adjust my valves until I figured that one out. I kept ordering the next one longer and it came in way too long. I finally figured it out by measuring them with a caliper and comparing them to the part number/length chart.

Ed Holyoke
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Old 04-16-2018, 01:31 PM
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Default Pushrods

T.L.A.R.- "that looks about right"

"Trial and error"

What could possibly go wrong?
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Old 04-16-2018, 02:49 PM
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DanH DanH is offline
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Originally Posted by mahlon_r View Post
If you measure from flat to flat on the pushrod, the dimension you get will be longer and nothing near to the dimension listed for that particular pushrod.
The two 73555 pushrods on hand measure less flat to flat (about 13.000") than the "Approximate Length" listed in 1060K (13.034").

Thinking out loud...

The flats seem to measure 0.1875" diameter. If so, the length removed works out to be 0.021" for each tip, or 0.042" total.

The nominal 13.034 less 0.042 is 12.992, real close to the 13.000 figure. Given I was measuring 13.000 with a good steel rule, it seems likely.
Dan Horton
Barrett IO-390
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Old 04-16-2018, 05:07 PM
BillL BillL is offline
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It is typical to measure such things with gauges. Likely, a conical gage in this case, based on the spherical diameter of the ball end. From there, it is what the designer says it is, i.e. on the print. Both dimensions and gauging specifications are always specified on a proper print. The gauging may be an in-house or industry specification, though, necessitating further digging.

I realize that this maybe perfectly correct, and perfectly useless to the OP's specific question.

So what is the diameter of the spherical contact anyway?

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Old 04-16-2018, 05:45 PM
krwalsh krwalsh is offline
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Default Lycoming vs Superior

In my experience the same -# part number from Lycoming and Superior are NOT the same length. I ended up ordering and swapping quite a few pushrods to get them right because there was a decided difference between the two. I ended up talking to a tech at Lycoming and he confirmed that just because the two have the same part dash number does NOT mean they are the same length. I forget which was which in terms of longer or shorter.
Kevin R. Walsh
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Old 04-16-2018, 07:16 PM
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Oh, the horror, "with a good steel rule". Tell me it ain't so!

I'm starting to deliver reverse engineered dimensions to 5 decimal places these days with the appropriate $$$$ attached. THEN the customer can finally decide on their TOLERANCE and PRECISION.

I love this thread. It drives me bananas.
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