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Dry tappet clearance problem

Bicyclops

Well Known Member
Got a problem setting dry tappet clearance. Superior roller lifter bottom end with Lycoming cylinders on a home assembled parallel valve IO-360 with all new parts. I've got 6 valves that I can't get in range. It's supposed to fall between .028 and .080. If I use a Superior -30 pushrod, the clearance is out of range big and if I use a -31, it's out of range small. I'm getting a delta of about .080 when I change pushrod length which is neatly bracketing the .052 allowable range. I have confirmed that the hydraulic units are fully collapsed and that isn't contributing to the problem. Has anybody else had this problem?

Table 3 of:
http://www.lycoming.com/sites/default/files/SI1060L Push Rod Identification.pdf
shows a difference in nominal pushrod length of .023. At 1.28:1 rocker ratio, .023 should move the clearance about .030. I measured the difference in length between 2 of mine at .061 which makes sense with my approximate .080 delta.

I think I have a choice between buying Lyc pushrods and starting the process of finding the right length all over or getting custom rods made. Do you guys think there would be a substantial performance or wear penalty from using adjustable pushrods?

Ed
 
Pushrod

Depending on the way the pushrod is constructed you MAY be able to remove the end of the longer pushrod and machine some off the end in a lathe and reinstall the ball end. I know people who have done this successfully but the extra pushrod I tried I could not get the end off.
 
With the longer pushrod, what is the compressible lash measurement ? as long as there is enough to not come near holding the valve off the seat for cooling, with too short a pushrod the lifter plunger retainer ring can disassemble itself.
 
When working with the 540 engines I have found slight differences in the same part number pushrods and by jockeying them around in the engine I was able to get all of them within tolerance.
 
Tried that

I tried moving the pushrods around, but there just isn't enough difference in length among them to do any good. I've got 6 of them between .105 and .115 with the -30s and they all fall around .015 or thereabouts with the -31s. They are consistently too much different from the next dash size to bring the clearance into spec.

Ed

When working with the 540 engines I have found slight differences in the same part number pushrods and by jockeying them around in the engine I was able to get all of them within tolerance.
 
Superior vs Lycoming

Are the -30 and -31 both from Superior? Much to my surprise when I was doing mine the Lycoming and Superior parts with similar part numbers were not, in fact, the same length. If memory serves, there was a 0.075" difference.
 
I tried moving the pushrods around, but there just isn't enough difference in length among them to do any good. I've got 6 of them between .105 and .115 with the -30s and they all fall around .015 or thereabouts with the -31s. They are consistently too much different from the next dash size to bring the clearance into spec.

Ed

Ed, appears you need to order some Lycoming pushrods. I recall for my 320 Lycoming made 4 lengths and I had to change a few when I purchased new cylinders. Per your Lycoming reference, looks like Lycoming makes 8 lengths for roller cams. ;)

As the top end systems wear, the clearance gap will reduce. So with this knowledge you do not want to be near the tight end of the range.

I do not have any experience with adjustable rods.

Regards, Greg
 
SL parts

Yup Kevin, they are SL part numbers and the difference in length tween -31 and -30 rods is .067. I measured them today.
Greg, the -31s appear to be almost exactly the length that Lycoming calls. The -30s are 44 thou longer than they are supposed to be which is causing my problem. I might end up with some genuine Lyc rods, or maybe I'll have some custom ones made. Some calls to make.

Ed

Are the -30 and -31 both from Superior? Much to my surprise when I was doing mine the Lycoming and Superior parts with similar part numbers were not, in fact, the same length. If memory serves, there was a 0.075" difference.
 
The -30s are 44 thou longer than they are supposed to be which is causing my problem.

Y'know, from a quality control standpoint, that is awful and in my view inexcusable. Would a piston fit if it was .044 too big? We talk about valve guide diameters in tenths of a thou for goodness sake. It amazes me that parts this bad (meaning out of specification for length or mismarked depending on point of view) actually make it out of the factory and into the field.
 
Push rod length is NOT the overall measured length of the push rod! When manufactured the length of the push rod is determined by where the ball on the end of the rod will interface with the socket in the rocker arm and tappet body. So when measuring them end to end you are getting worthless data as the ends do not encounter the sockets on the tappets and rockers on the extreme ends of the balls. That is why the listed length of the rod is different than the measurement of the rod end to end.
Good Luck,
Mahlon
 
Push rod length is NOT the overall measured length of the push rod! When manufactured the length of the push rod is determined by where the ball on the end of the rod will interface with the socket in the rocker arm and tappet body. So when measuring them end to end you are getting worthless data as the ends do not encounter the sockets on the tappets and rockers on the extreme ends of the balls. That is why the listed length of the rod is different than the measurement of the rod end to end.
Good Luck,
Mahlon

But that wouldn't affect the delta in length between two part numbers, would it?
 
Pushrod length and PMA

Howdy Mahlon,

I measured the pushrods with a dial caliper from end to end, as you say, then I took a radius gage and spark plug gap gage to it. So, with the radius gage over the end of the ball end of the rod and a wire gage between it and the machined flat, I can get a pretty good picture of nominal length. .015 was a little sloppy and .018 won't go through, so I'm calling it .016-.017. When I add .032 to the measured length of a dash 31 rod, I get almost exactly the nominal length in Si 1060. When I do that with my 6 dash 30 pushrods, I get, within a few thousandths, the nominal length of a dash 28. I downloaded the PMA, dated 4/13/2011, and it references Lycoming service instruction SI 1060 and states that it is an approved replacement for part # 15F19957-30. I have mismarked parts. This could be a serious problem for Superior. I have tried twice to get a call back from them. So far, crickets.

Ed

Push rod length is NOT the overall measured length of the push rod! When manufactured the length of the push rod is determined by where the ball on the end of the rod will interface with the socket in the rocker arm and tappet body. So when measuring them end to end you are getting worthless data as the ends do not encounter the sockets on the tappets and rockers on the extreme ends of the balls. That is why the listed length of the rod is different than the measurement of the rod end to end.
Good Luck,
Mahlon
 
Try swapping the rockers around, or if they are all new find a serviceable used one that has been resurfaced.
Like you I have seen them different lengths under the same p/n.
Good luck
Tim Andres
 
You can also buy a custom pushrods for about $20. I had 3 rods that I could not get in spec through swapping. I determined how many thousands I wanted each one to be larger or smaller. I wrote those numbers on masking tape on each pushrod and mailed them to the custom pushrod company. 7 days and $50 later I had perfectly fit rods.

Larry
 
Pushrods on the way

Darrell from Superior called this morning. He acknowledged that they had a pushrod length problem a few years ago. I've been a while building and just got around to doing the tappet setting so these rods were from that era for sure. He's shipping new ones. He offered to overnight them and I said save a couple of bucks. I should have them by the weekend. So that means that I don't need to get custom rods made which was my backup plan. Thanks for all the suggestions.

Ed
 
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