Pushrods, Rockers and Dry Tappet Clearance

So during my investigation into why may engine suddenly starting occasionally popping thru the exhaust, I discovered that the engine builder that put my engine together had improperly installed the rocker arms in the wrong places as determined by Lycoming SI 1454A. (Fairly certain that this had nothing to do with my original problem, just kinda lucky to find this error now)

He had some with the rockers switched and one with two of the same rocker arm on both valves.

With that situation I now must start over with setting the dry tappet clearance since I will be moving the rockers to the proper location.

Only 3 of the 8 pushrods in my engine have part numbers. 2 are 73435 and 1 is 73434. A couple of the rods look to have been ran in some kind of engine that can rub on them about 3-4 inches from the end as these rods have some material rubbed off of them in that area (nothing in my engine could possibly do this best I can tell). A couple more have some evidence of old corrosion from the past. The bottom line is that I plan to replace all of them for safety.

That being said, I plan to order new custom rods from Smith Bros. Pushrods. I understand that their quality is superior to OEM.

So first I plan to order an adjustable one in order to use it as a gauge to determine what length rod to order for each valve. In order to do that, I need to know what length adjustable rod to order. I have looked at the Lycoming SI 1060M and see that the range of rods for my engine is from 12.483 to 12.564. The 1060M does not state how this length is determined. I plan to purchase one with a middle length of 12.5235" which is dead center of the range of rods called out by the SI 1060M. This would be the overall length minus whatever is lost by the oil holes in the ball ends.

For the engine guru's out there....Any issues with this plan above?

Next question....
Do I set the clearance up to be on the tight (.028), wide (.080) or middle (.054) of the range allowed by Lycoming SSP-1776-3?

I am getting an education with this thing that is for sure!

Clearance will be reduced as valves "seat" so I would stay away from the "tight" end. On the other hand the spec is so wide that it should not be a concern.

IF you are lucky, the rods will have the Lycoming part number on them. Can swap push rods around to get the 0.028-0.080" clearance. I think I have one extra of every length (5) for O-320. By swapping around, you can figure out what part number you need to order.

I had an intake valve get burnt from a push rod that was in spec when it was put together but after 100 hours, it did not close all the way. When cylinder was repaired, I was able to use a push rod with same part number but it made the clearance in spec but the old one was out of spec. I agree with Mel about not being on the tight side.

The change in length of the pushrods in the manual for different part numbers does not equal the clearance you will measure.

This video show how to remove the hydraulic lifter.

This video shows how to collapse the lifter.

Why make life hard with adjustable rods?
Get the correct rocker arms in there, then measure dry clearance. Pull the rods, measure them, look at the clearance numbers, and then you'll know what to order to get the clearance right in the middle of the allowed range. (This won't work of course if one or more have zero clearance.) Make sure you allow for rocker geometry, it may not be 1:1.

Mel said:

Clearance will be reduced as valves "seat" so I would stay away from the "tight" end. On the other hand the spec is so wide that it should not be a concern.

Click to expand...

Thanks Mel. Exactly the kind of advice I was looking for. Nothing beats experience!

RV6_flyer said:

IF you are lucky, the rods will have the Lycoming part number on them. Can swap push rods around to get the 0.028-0.080" clearance. I think I have one extra of every length (5) for O-320. By swapping around, you can figure out what part number you need to order.

Unfortunately, only 3 of the 8 have numbers. The ones with no numbers don't even have the dots or grooves that others talk about.

I had an intake valve get burnt from a push rod that was in spec when it was put together but after 100 hours, it did not close all the way. When cylinder was repaired, I was able to use a push rod with same part number but it made the clearance in spec but the old one was out of spec. I agree with Mel about not being on the tight side.

Thanks for the advice. Hearing it from multiple people is helpful! Since I am gonna have 8 custom rods, I think I will aim for 60%
of the spec...

The change in length of the pushrods in the manual for different part numbers does not equal the clearance you will measure.

Got it due to the rocker ratio which I understand is 1.28:1 ?

This video show how to remove the hydraulic lifter.

This video shows how to collapse the lifter.

Click to expand...

I found those video's the other day! Thanks for posting them!

BobTurner said:

Why make life hard with adjustable rods?
Get the correct rocker arms in there, then measure dry clearance. Pull the rods, measure them, look at the clearance numbers, and then you'll know what to order to get the clearance right in the middle of the allowed range. (This won't work of course if one or more have zero clearance.) Make sure you allow for rocker geometry, it may not be 1:1.

Click to expand...

Bob,

I suppose your way works fine but I like tools (believe it or not a custom adjustable rod is amazingly inexpensive) and the adjustable one will allow me to order custom rods exactly the length I want them (about 5/32 the cost of a Lycoming). The custom rods are way less expensive and reports are much better quality than Lycoming rods. It is my understanding that the Lycoming O-360 rockers are 1.28:1 ratio.

FWIW, My Factory overhauled Lycoming was assembled the same way, rockers were not indexed to the proper valve. Didn't seem to hurt anything but it's not right and that's the place you would figure would get it right.
The new rocker P/N IS interchangeable, 8 rockers, 1 P/N.
I agree with Mel, stay away from the tight end of the spec.
And finally, I'm pretty sure the lash is suppose to be checked and adjusted after 200-300 hrs. Don't recall where I read that now.
Tim Andres

I used my existing rods for measurement when I ordered custom rods. Install each current rod and measure the lash. Then tape a note to that rod with the + or - in .000"'s you want and mail them off. Smith Bros will measure each rod and make the indicated adjustment for the new one. No sense going through the hassle of ordering an adjustable rod along with a 12" micrometer or whatever size you need (not cheap). you can't get an accurate measure without a mic or caliper. They also have the tools for a proper measurement, using the radius of the cap which is more accurate.

I am sure you already know this, but be sure to diassemble and clean each plunger assembly then very lightly coat the surfaces with oil. You want to keep oil away from the small ball at the bottom of the assembly. Thick oil in that area will allow the ball to seat easily making it much harder to insure you have fully compressed the plunger assembly when checking lash.

Larry

Interestingly the cylinders for my Tiger TOH and the O-360 box of parts engine in my RV-6A all came with rockers that the overhauler had written "IN" or "EX" with a sharpie on all of the rocker arms.

lr172 said:

....

I am sure you already know this, but be sure to diassemble and clean each plunger assembly then very lightly coat the surfaces with oil. You want to keep oil away from the small ball at the bottom of the assembly. Thick oil in that area will allow the ball to seat easily making it much harder to insure you have fully compressed the plunger assembly when checking lash.

Larry

Click to expand...

This SI from Lycoming tells you how to handle the lifters -

https://www.lycoming.com/content/service-instruction-no-1011l

Mel as always.

Mel has it here. We set them up at dead center of range or one size down so they can wear and all the parts can settle over time and yes the range is so wide if you get close to the middle you will have more than enough to allow for heating and cooling of the case, cylinders, heads, valves and so on.
Just what we do close to the book. If you like the adjustable ones, just check the every 3-500 hours so you will feel good about them too.
Yours, R.E.A. III #80888

Robert Anglin said:

If you like the adjustable ones, just check the every 3-500 hours so you will feel good about them too.
Yours, R.E.A. III #80888

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To clarify, I am not putting in adjustable ones permanent. The adjustable one is just for measuring and getting solid ones made.