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Lycoming valve lash adjustment

 
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akholland
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PostPosted: Thu May 22, 2014 1:14 pm    Post subject: Lycoming valve lash adjustment Reply with quote

So I went to check valve lash on my 540 and the intake is within limits but all the exhaust valves are over. 080. Their about. 0.100 to 0.120 is this extreme wear for a 540 with 1400ttsn? Or is this typical. Any recommendations for good prices on some new push rods?
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gbarrier
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PostPosted: Thu May 22, 2014 3:16 pm    Post subject: Reply with quote

I've never seen anyone check them after they were set up at overhaul unless there was a problem. Engine running OK?
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akholland
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PostPosted: Thu May 22, 2014 4:25 pm    Post subject: Reply with quote

Ive actually only ran this engine once at a idle while I bought it. I tore the plane down right after. It idled smooth and clean with no ticks. One of the cylinders had low compression so I replaced it with a serviceable used one. I put the original push rods in the replacement cylinder and that's why I was checking them. It was too much on the exhaust side so that prompted me to check the rest which were also too much clearance.
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aero101
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PostPosted: Fri May 23, 2014 2:04 pm    Post subject: Reply with quote

Usually never checked, except by more reputable engine shops at overhaul or after a valve job. Also this lash is not critical except if tight (no lash) will burn valves, if too loose will have tappet noise and excessive wear at tappit body, push rod ends, etc... And there is quite a large gap in there where tappit functions just fine due to hydraulic actions built into it. Also if adjusting properly, tappits and follower bore must be completely dry and free of oil when adjusting to limits in overhaul manual...
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pilot
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PostPosted: Fri May 23, 2014 3:46 pm    Post subject: Reply with quote

I think valve lash is an indicator of valvetrain health and should be checked. Usually the wear on cam/lifters is matched by the valve getting deeper in the seat so nothing really changes as far as clearance. Plus like Jim said the hydraulic lifters absorb the difference. If something goes wrong, like a cam lobe, lash will be way high. I would set everything within spec and check them after many hours of operation just to see if anything crazy is going on. If all exhaust valves are about the same I wouldn't worry, but I would run a sample at the next oil change.
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akholland
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PostPosted: Mon May 26, 2014 9:03 am    Post subject: Reply with quote

Yea your probably right, didn't think of that. I'll do that. Thx
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akholland
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PostPosted: Tue May 27, 2014 6:58 am    Post subject: CAM wear ...excessive valve lash Reply with quote

I changed out #1 cylinder due to excessive wear in the bore, I thought it was way out of spec at first but after I looking at it again I realized the exhaust valve stem cap had fell of the replacement cylinder.!.. oops.

#4 is my worst cylinder at .127. Mfg. serviceable limits Spec dry tappet clearance is .028 to .080 Likely indicating cam wear...? I wonder how much this would effect power if the lobe height was down 40 thousandths. I'll be keeping an eye out for a good yellow tagged cam and doing frequent oil changes/analysis.. I have a few extra sets of push rods out of a 0-320 parts motor. Maybe i'll see if these tighten tolerances up a little on the outliers, hopefully their longer. I wonder how much gap that little hydraulic plunger can soak up Smile

#2 intake .085
#2 exhaust .077

#4 intake .090
#4 exhaust .127

#6 intake .086
#6 exhaust .106

#1 intake .086
#1 exhaust .078

#3 intake .080
#3 exhaust .100

#5 intake .080
#5 exhaust .100
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pilot
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PostPosted: Tue May 27, 2014 8:24 am    Post subject: Reply with quote

You can figure out how much valve lift you are losing if you calculate it with the rocker arm ratio (I'm thinking it is 1.6 to 1 but that is a number out of my mind, which is likely way off). Also keep in mind you are measuring lash, which is wear on the base circle of the cam, so the lobe may be more worn if that is the case. To know exactly what's up you will have to measure actual lift at the valve.

It looks like you have even wear patterns, so unless you are finding lots of iron in the oil I would just keep an eye on it. Then again I know very little.
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aero101
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PostPosted: Tue May 27, 2014 2:10 pm    Post subject: Reply with quote

First off you're measuring heel of cam, which tells you nothing about lobe wear unless lobe is totally destroyed... Also the .127" means nothing unless you have a good reference point of where you started which may not have been within spec to begin with... If you consider where you set valve lash, it tells you absolutely nothing of camshaft condition until wear into heal and by then you'll be seeing plenty of metal in screen, filter... It will tell you if valves are seating further into seat maybe under some conditions which is entirely normal. You are losing no cam lift due to vlv lash on a hydraulic lifter because the lifter basically removes all lash when operating correctly.
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gbarrier
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PostPosted: Tue May 27, 2014 3:43 pm    Post subject: Reply with quote

Well said.

If it's not a clicking.....
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akholland
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PostPosted: Wed May 28, 2014 12:21 pm    Post subject: Reply with quote

Ok ill just listen for a potential Tick and call it good as long as putting it off won't cause damage. Sounds like the lifter can soak up the excessive lash and not come apart or bend a rod before I notice or hear the engine making lifter noise .
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akholland
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PostPosted: Wed May 16, 2018 4:58 pm    Post subject: Reply with quote

Yep I have a Ticker.... . Apparently 0.127 on a few is over enough to make a little noise at idle
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UP-M5
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PostPosted: Fri May 18, 2018 10:42 am    Post subject: Reply with quote

this is a very important measurement to have correct.
usually on the higher HP TIO540's we see intake valve damage that "tulips" the valve, and/or sinks it deeper into it's valve seat in the cylinder head which causes intake valve lash to get tighter and tighter. if not caught it will end up at zero and then the valve will soon burn.
also, any time you have a cylinder repaired or OH'ed where they grind the valves, you usually need a different size pushrod.
for your 540 the intake and exh use the same pushrods.
get a copy of lycoming service instruction 1060K. it shows the 4 different sized pushrods for your engine.
-34
-35
-36
-37

from shortest to longest.
they are labeled on the rod. there are also old style "thin wall" pushrods that you might have
73434
73435
73436
73437
again, from shortest to longest

o-320 pushrods are not interchangeable with a 540!
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akholland
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PostPosted: Fri May 18, 2018 10:45 am    Post subject: Reply with quote

Thank you! I have the number off the rod and I was just trying to make sense of them to source longer ones. Awesome!
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