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How to install rocker arms

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Doug Rohrer

Well Known Member
I had to replace a leaking pushrod tube seal on my O-320. No problem getting everything off. However, the tappets seem to be holding the pushrods out enough to prevent sliding the rocker shaft back in through the bushings in the cylinder and the rocker arms. What is the trick to depress the pushrods and rocker arm enough to slide in the shaft? I am standing by at the hangar. Thanks.
 
Taking a chance here...

turn the prop (with safety in mind) till both valves on that cylinder are closed.... :)
 
Use a wooden "tooth pick" to depress the little check valve ball in the hydraulic tappet. Once you remove the push rod socket you can then see the hydraulic lifter where the check valve ball is located. One must do this before you put the push rod shroud on.

It is a LOT easier to do that than it is to type up how to do.
 
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Did you take the tappet all the way out and collapse it in your hand Doug? Gary is right it isn't hard to do, but it is a bear to try and describe! If it came apart, it will go back together, and the only trick I know is making sure the tappet is truly collapsed all the way. I had to be shown the trick to understand it (years ago).
 
You could make a little hook from safety wire and gently work the plunger and body out of the tappet. Oil tension may or may not tend to hold them in - it could even feel as if there is a spring or some resistance holding the parts in - there isn't. So be careful on the way out to avoid dropping them (if so, throw away - these parts are paired / don't mix). Plunger and body can be separated with a twist and cleaned / dried. Put together dry and check that the dry clearance is between .028 and .080" - avoid turning the prop when you put this back together or oil may reenter and you get to do it again.

PS - don't use a magnet to remove these parts

Dan
 
Thanks Gary, Paul and Dan. I got the whole exhaust tappet all the way out and got it to collapse real good. I can only get the upper part of the intake tappet to come clear out of the bore. The lower part is trapped in by the sheetmetal stamping pressed into the cast case. It appears I will have to pry this part out to get the lower part of the tappet to come out, and hope I don't deform it and cause another leak. Then I should be able to get this thing back together. I was hoping there was a way to do this without taking the tappets clear out and risk dropping/damage.
 
Clever VAFsters!

I'm glad Dan, Paul, & Gary posted elegant solutions while I was typing up my no-kidding lumber solution.

powerleveling.jpg
 
A little late now, but my old time A&P IA, PE, etc. buddy warned me to never mix up these components (lifter & cup). They are matched.
 
Doug Rohrer said:
I can only get the upper part of the intake tappet to come clear out of the bore. The lower part is trapped in by the sheetmetal stamping pressed into the cast case. It appears I will have to pry this part out to get the lower part of the tappet to come out, and hope I don't deform it and cause another leak. Then I should be able to get this thing back together. I was hoping there was a way to do this without taking the tappets clear out and risk dropping/damage.
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In my experience this means the cam lobe is slightly lifting the body. Make sure you are TDC and not 25 before.
 
The trick is to bleed down the lifters as the first step. The easy way is to just turn the prop so that the intake valve is full open, then leave it there for 15 minutes or so. Then do the same for the exhaust valve. Then everything can be disassembled and reassambled by hand.

Otherwise you have to have a valve spring compressor, unless you pull the lifters and bleed them down manually. Normally I shoot brake cleaner into them and blow them out when doing that.
 
Low Pass said:
A little late now, but my old time A&P IA, PE, etc. buddy warned me to never mix up these components (lifter & cup). They are matched.
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I don't believe this is true. The lifter assembly has three total parts. The main body, which is installed from inside the case and rides on the cam. Inside the body is the plunger assy. This is made up of two parts. These are honed as a matched set and cannot be interchanged. When the previous poster was explaining how to separate the components with a twist and a pull, he was referring to the plunger assembly parts and not the main body.

To my knowledge, new plungers are routinely installed in old lifter bodies. This is even recommended in the service manual. In fact, I don't believe Lycoming has a part number that includes both the tappet body and the plunger assy.

Larry
 
Doug Rohrer said:
Thanks Gary, Paul and Dan. I got the whole exhaust tappet all the way out and got it to collapse real good. I can only get the upper part of the intake tappet to come clear out of the bore. The lower part is trapped in by the sheetmetal stamping pressed into the cast case. It appears I will have to pry this part out to get the lower part of the tappet to come out, and hope I don't deform it and cause another leak. Then I should be able to get this thing back together. I was hoping there was a way to do this without taking the tappets clear out and risk dropping/damage.
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Doug,

Please see my previous post. The members here are recommending that you remove the plunger assy from the main lifter body. Once that plunger assy is out, you can bleed it down as recommended. You DO NOT remove the main lifter body. It is retained and CANNOT be removed from the outside. It has a lip and is removed from the inside. You don't need to remove it. It is the plunger assy that uses oil to take up the gap and needs to be dry for installing the rockers.

Larry
 
Use a magnet to get the inner section out, it's a little finicky but it will come out. Just did all 8 this afternoon in a 320, 15 minute job. The lycoming manual states not to mix these parts up as they are matched. Just saying.
In a Continental, you can bleed them from the front.
 
C-FAH Q said:
Use a magnet to get the inner section out, it's a little finicky but it will come out. Just did all 8 this afternoon in a 320, 15 minute job. The lycoming manual states not to mix these parts up as they are matched. Just saying.
In a Continental, you can bleed them from the front.
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The manual also states that using a magnet is not recommended but it seems to be a very common practice.
 
You don't want to magnetize the lifters. If the lifter becomes magnetized fine iron particles will be attracted and cause scoring in the bore of the tappet body.
 
Success!

Lots of good info here. I got the job done tonight by using the Mahon trick of prying the valve spring down slightly with a pry bar stuck into the adjoining spring. With the valve depressed a little, the rocker shaft slid right in. I just had to find the right shaped pry bar to get the job done. Kyle Boatright sent this trick by PM. Thanks Kyle. Now I know a lot more about how the lifters work on these engines. Thanks for all the posted solutions.
 
The easiest way to do this is set the piston at TDC and use two small spring clamps (like a welding clamp) and compress the pushrod by clamping it inward using the cylinder casting. Takes about 10-15 minutes for the lifter to bleed down.
 
For the plunger bleed down, I made up some small .125" thick aluminum shims and placed them between valve stem and rocker on all cylinders to speed up the process bleed time while working on other valve adjustments in order.
 
G3i Ignition said:
For the plunger bleed down, I made up some small .125" thick aluminum shims and placed them between valve stem and rocker on all cylinders to speed up the process bleed time while working on other valve adjustments in order.
Click to expand...

Here is a video showing how it is done using a toothpick.
 
Or just use the other straight end of the safety wire hook you made to remove the plunger with.
Good Luck,
Mahlon
 
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