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Measuring Lycoming Pushrod Length

DanH

Legacy Member
Mentor
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?

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Following.....

I found inconsistent answers to this question last year, looking forward to learning the real truth...
 
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.
Good Luck,
Mahlon
 
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.
 
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
 
Pushrods

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

"Trial and error"

What could possibly go wrong?
 
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.
 
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?
 
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.
 
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.
 
Oh, the horror, "with a good steel rule". Tell me it ain't so!

Oh ye of little faith...

When jigged in a fixture this AM, and measured with the trusty digital caliper, my "about 13.000" was 13.005". Both 73555's were the same length.

The flats on both ends of one sample were about 0.160 dia, while the other pushrod was more like 0.140 on one end and 0.175 on the other. Those measurements are necessarily by visual comparison to a micrometer, with magnification. Nominal ball diameter is assumed to be the same as the tube, 7/16".

Given 0.160 flats, length of material removed would be 0.0152 per end, or 0.0304 total. Add it to 13.005 and we have 13.0354", very close to the 13.034" listed as "Approximate Length".
 
It seems like "theoretical length" (the length if the flats weren't there) would be a better phrase. But there's really no way to actually measure that, is there?
 
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.

5 places!?! What are you in to? I can't imagine what that would cost to manufacture.
 
It seems like "theoretical length" (the length if the flats weren't there) would be a better phrase. But there's really no way to actually measure that, is there?

Looks reasonable to measure the pushrod flat-to-flat and add 0.030" to match the listed length. Ya'll measure some and let's see.
 
Dry tapper clearance

My engine builder had a go-no go gauge that he uses to determine pushrod lengt, just double ended feeler gage really . Did not seem very scientific as the clearance range is rather large and I think there were only 4 or 5 pushrod lengths to choose from. Basically he looked at it and said order this for this one and that for that one. Had em next day shipped and everything was installed and clearances were within spec. Seemed to me these engines were built like a ak47 with quite large tolerance in the valvetrain. Just another data point not a sermon.
 
no answer here, but an idea. When I had pushrods made for the IO-320, I used an old one for a reference and sent them to the company with a desired increase or decrease measurement for each and got exactly what I wanted. They use a special tool for measuring them and I don't know what the measure point is.

Whenever I needed pushrods for auto engines, I made an adjustable pushrod and took measurements from that. I would always send the adjustable unit with a description of how I took the measurement so they could compensate for that or simply explained the type of ends that my adjustable unit had.

Larry
 
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