Can some one help me solving the puzzle.....Is it true that every 0.027" push rod length increase will result in 1.28 x 0.027" = 0.035" dry tappet clearance decrease.
My finding was way beyond what I could comprehend. when I increased the push rod length by 0.027", I got over 0.100" decrease with dry tappet clearance. I did this to another valve and the result was the same. Those were ECI push rods I used, before I blame on the push rod, I went ahead and ordered the Lycoming push rod, the result was the same. I am really confused. The ratio is more like 1:3 instead of 1:1.28 to me.
Then I physically measured the rocker pivot joint to Push Rod and to valve stem length, the ratio is very close to 1:1.28, but why I'm getting such a big decrease with dry tappet clearance?
My dry tappet clearance was way too big, some were larger than 0.150" that's why I was playing with the new Rod. I know the proper way is pulling the Cylinder to look at the Cam lobe, but the engine was just overhauled 150 hours ago by the previous owner/builder/A&P. I have no idea if he checked the dry tappet clearance or not. The Engine is Lycoming O-320 B3B.
Can some one shine some lights on me?
Are you sure you have all oil removed from the tappet body? Even a drop will effect the result. Also after the tappet body is free of oil use a pin at the bottom of the tappet to collapse the tappet body. Before installing get the crankshaft in the proper point in revolution; the point at which the valve is fully closed. Now you can install the tappet body, the push rod and rocker arms and check the clearance.
Bill
Remove hydraulic lifter plunger like on this video.
Collapse the lifter plunger like on this video.
There can be some minor differences in push rod lenghts with the same part number. Just because clearance is out of spec with one push rod of the same dash part number does not mean that one you have with the same dash part number will have the same clearance.
Can some one help me solving the puzzle.....Is it true that every 0.027" push rod length increase will result in 1.28 x 0.027" = 0.035" dry tappet clearance decrease.
My finding was way beyond what I could comprehend. when I increased the push rod length by 0.027", I got over 0.100" decrease with dry tappet clearance. I did this to another valve and the result was the same. Those were ECI push rods I used, before I blame on the push rod, I went ahead and ordered the Lycoming push rod, the result was the same. I am really confused. The ratio is more like 1:3 instead of 1:1.28 to me.
Then I physically measured the rocker pivot joint to Push Rod and to valve stem length, the ratio is very close to 1:1.28, but why I'm getting such a big decrease with dry tappet clearance?
My dry tappet clearance was way too big, some were larger than 0.150" that's why I was playing with the new Rod. I know the proper way is pulling the Cylinder to look at the Cam lobe, but the engine was just overhauled 150 hours ago by the previous owner/builder/A&P. I have no idea if he checked the dry tappet clearance or not. The Engine is Lycoming O-320 B3B.
Can some one shine some lights on me?
to add one more variable to this:
I was going through the same process, trying to get the dry tappet clearances right on my engine. I did the same process, and ended up needing a slightly longer pushrod. Lycoming wasn't stocking the one I needed (I have a red-headed stepchild of an engine that had been decked in the '80s to increase compression, so it requires abnormally short pushrods). So, I ordered the Superior part number that was listed as the the required length. When I got it I could not even measure the tappet clearance because the rocker arm was contacting the head and the tappet clearance was something like 1/8"-3/16". I swapped cylinders, changed parts around, and finally measured the pushrods and found that the Superior part was shorter than the "same" Lycoming part by a significant amount. I talked to Superior about it, and after a few rounds of parts and discussing we determined that, sure enough, the Superior part and the "same" Lycoming part differ by a rather significant amount. I forget the exact value, but it was something like 0.050" or more.
So, when swapping pushrods and ordering new ones, be sure to buy the pushrods form the same vendor.
Thank you so much for all your inputs, I thought I did everything right,
1. set the cylinder to top dead center.
2. removed rocker, pulled plunger, soaked/washed with fuel.
s.
I avoided all these problems. after moving parts all around, I had three pushrods that were too short to meet spec. For each one I determined how much longer I needed it to be, using a formula similar to the OP's. (found the factor on a post here). I sent the 3 pushrods to Manton pushrods (I don't have calipars or mic's that large). They measured my existing rods and added/deleted the dimension I provided for each and they shipped me 3 new custom pushrods. I paid $10.50 per pushrod and the quality far exceeds the Lycoming. Pushrods are quite a bit beefier, but the weight penalty is insignificant in my opinion. They cater to the racing business where everyone needs thick-wallled pushrods, so they don't carry the thin-wall material.
Larry
Thank you so much for all your inputs, I thought I did everything right,
1. set the cylinder to top dead center..
2. removed rocker, pulled plunger, soaked/washed with fuel.
.
...put the old rod back (11.907") and measured DTC ... = 0.190" ... Then ... installed the new rod (11.945") which is 0.038" longer and measured DTC = 0.083"
The cylinder was on the top dead center and compression stoke, the plunger was disassembled and soaked/washed in the solvent. Then I put the plunger back together, twisted the cylinder clockwise until I head a click which engaged the spring. Before I put the plunger back in, I shook and heard the ball rattle freely inside of the plunger.
By swapping between the old/new push rod, I got big reduction with Dry Tappet Clearance, the ratio was close to 1:3 instead of 1:1.28.
At one point, I even thought about the curvature of the push rod end, that's why I went a little further and ordered a genuine Lycoming push rod, but the result remains no change.
any way, I'll try it again this weekend, and be sure to follow all your recommendation. Thanks a lot.
Hi Dan,
Sadly to say, the dry tappet clearance is 190/1000"=0.190", terrible isn't it. another one is 0.180", one is 0.150", two are around 0.120", the rest of them are within the spec which are between 0.028 - 0.080".
Hi Larry,
This Engine is 1960 Lycoming O-320 Engine, model B3B, the guy who overhauled it installed a new Cam but didn't replace the tappet/plunger, that's a terrible mistake.
I measured #4 cylinder cam lobe travel today, the exhaust cam traveled 0.359", the intake cam traveled 0.351", so they both are in the 0.350" region. I'll measure other cam lobe travel when checking their dry tappet clearance.
I replaced another push rod with 0.151" dry tappet clearance, the new clearance = 0.032". New rod is only 0.020" longer, but it cut the gap down to 0.032", with over all reduction -- 0.119". the ratio is near 1:6.
My theory is, the new rod needs to break-in with the rocker and plunger sockets, I'll re-check the dry tappet clearance again after running the Engine for 10 more hours.
I think measuring the cam lobe travel is the best way to determine the condition of the cam lobe and tappet without removing the Cylinders.
I avoided all these problems. after moving parts all around, I had three pushrods that were too short to meet spec. For each one I determined how much longer I needed it to be, using a formula similar to the OP's. (found the factor on a post here). I sent the 3 pushrods to Manton pushrods (I don't have calipars or mic's that large). They measured my existing rods and added/deleted the dimension I provided for each and they shipped me 3 new custom pushrods. I paid $10.50 per pushrod and the quality far exceeds the Lycoming. Pushrods are quite a bit beefier, but the weight penalty is insignificant in my opinion. They cater to the racing business where everyone needs thick-wallled pushrods, so they don't carry the thin-wall material.
Larry
Manton and Smith Brothers are the premier pushrods builders in the country. I found Lycoming pushrod length random at best. I use Smith Brothers for all my requirements. Stock ratio is 1.28 to one.
Thanks
Steve
Finally I checked all the Cam travel in my O-320 B3B engine....
Exhaust cam travel, Cyliner 1/2/3/4 = 0.352"/0.333"/0.348"/0.359"
Intake cam travel, Cylinder 1/2/3/4 = 0.349"/0.346"/0.348"/0.351"
Only cylinder #2 exhaust cam travel is a little bit weak = 0.333", all others are right around 0.350". Good to know that the cam/tappet doesn't have abnormal wear. Thanks for the advise. It's a great learning experience.
My next task is to bring Dry tappet clearance back to spec (0.028" -- 0.080").
Any one has the experience with adjustable push rod? if so, where did you get it?
Interesting that #2 & #3 exhaust have such different lifts when they both operate off of the same cam lobe. What and I missing?