Stuck valves are my enemy!

Maintenance, parts and services related to Cessna 120/140's

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Stuck valves are my enemy!

Postby Lear31A » Sun Dec 02, 2012 4:44 pm

Bought the C120 1 month ago. I have flown it 15 hours and have had stuck valve 3 times! Twice was the same valve (exhaust). I used an additive that everyone recommended to no avail......the C85 was overhauled only 300 hours ago but it was done in 1988. My mechanic offered to do an owner assisted top overhaul! I am excited. I removed all the cylinders and I am beadblasting and repainting everything while I am at it. The valve guides were terrible on all cylinders! I have a few quesions;
What else should I do while its apart? I am replacing the rings, honing the cylinders, cleaning the galve guides, beadblasting all the pistons, repainting everything and cleaning the plugs.
What can I do in the future to prevent all the build up in the valve guides?

I am learning so much and I highly recommend that you get involved with the maintenance of your plane, if you dont already. Its not very complicated stuff...........
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Postby Lear31A » Sun Dec 02, 2012 4:45 pm

I have tons of before and after pics on my IPad but when I try to attach them, it says the file is too big........urg!
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Postby Lear31A » Sun Dec 02, 2012 4:51 pm

Some cleaned and painted parts
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Postby David Sbur » Sun Dec 02, 2012 5:03 pm

I'm sure your A&P will check valve guide clearance to determine whether the guides need replacing.

When I re-honed my cylinders I should have used the straight-edged hones rather than the balls, maybe that's just overkill on my part. Of course check ring gaps on installation.

Make sure to check valve lash afterwards (deflate the lifters), don't make the mistake I made and assume the lash would be the same after I cleaned things up (burned an exhaust valve in the process).

May as well remove/clean/check lifters while you can.

New connector hoses/gaskets for the intake tubes and pushrod tubes.

Check valve spring strength (I had a few lazy ones which decided the TOH for me in the first place).
Last edited by David Sbur on Sun Dec 02, 2012 5:19 pm, edited 1 time in total.
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Postby Lear31A » Sun Dec 02, 2012 5:15 pm

Valve lash, thanks I will have to ask the mechanic about that as I am not familiar.
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Postby Lear31A » Sun Dec 02, 2012 5:17 pm

We are also grinding all the valves with a valve grinder.
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Postby 5095 » Sun Dec 02, 2012 7:58 pm

I know it would cost more, but you would be better off replacing the cylinders with ECI's or other new ones. They handle avgas better and have stronger rocker bosses. BTW there is an AD that needs to be done on your old cylinders if you go that route. Sometimes it is pay now or pay again later.
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Postby David Sbur » Sun Dec 02, 2012 9:58 pm

Good point. Are these 'old style' cylinders or perhaps first-run 'new style' cylinders?
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Postby 7036 » Sun Dec 02, 2012 10:01 pm

What oil are you using? My experience with Robinson helicopters was Shell 15-50 equaled stuck exhaust valves after about 300 hours. We used straight grade Shell, W80 or W100 and no more problems with stuck exhaust valves. To fix a stuck valve I would push the valve into the cylinder, ream the valve guide and then fish the valve back in place. The cylinders are so easy to remove on a C85 I would ream the exhaust guide with the cylinder off as fishing the valve back into place with the cylinder installed on the engine can be a challenge.

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Postby Lear31A » Sun Dec 02, 2012 11:38 pm

I am not sure if these are old or new style cylinders. They are chrome however. What AD should I research on these cylinders while they are off?I have been using Aeroshell 100plus 50 wt.....that is what I was told they were running before I bought it. Thanks for the tips, this is my first plane to own and I value all of your opinions/expertise..................i will post more pics tomrw of the cylinders. BTW, all the cylinder comkpressions were in the mid 70's, thats why I was reluctant to pull them but I am sure I will be glad I did.
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Postby Randy Thompson » Sun Dec 02, 2012 11:52 pm

It is AD 94-05-05 R1.
Break in should be done using Mineral Oil.
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Postby David Sbur » Mon Dec 03, 2012 1:15 am

Easier way to tell from old style/new style.

Also, this old thread may be of interest...

http://www.cessna120-140.org/forum/view ... b80af25c7f
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Postby Randy Thompson » Mon Dec 03, 2012 1:53 am

That particular new style head has been found to be problematic. Locking the pin leads to rapid wear on the rocker pins and rocker bushings.
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cylinders

Postby 120 Driver » Mon Dec 03, 2012 12:02 pm

Don't really mean to steal this thread.
I'm trying to research my ships history. My log book says 4 new Superior cylinders. I have a rcpt from St,Louis Engine & Cylinder Service for 4 cylinders P/N 21477. I also have a receipt for 4 cylinders Item No. SA-10200A20P, described as "complete cylinder/0-200" same shop. Entries and rcpt dated 8/94 - 10/94.
How can I tell what's on my engine?
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Postby Randy Thompson » Mon Dec 03, 2012 1:27 pm

Up near the rocker cover the cylinders will have a number. If it starts with SA they are Superiors.
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Postby Robert Staib » Mon Dec 03, 2012 2:27 pm

Lear31A, I hope your valve problems will be fixed and don't follow to the Lear. 8)
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Postby Lear31A » Mon Dec 03, 2012 5:18 pm

Robert Staib wrote:Lear31A, I hope your valve problems will be fixed and don't follow to the Lear. 8)

Haha, thanks! I reamed the valve guides today and boy are they clean now!
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Postby David Sbur » Mon Dec 03, 2012 8:38 pm

That particular new style head has been found to be problematic. Locking the pin leads to rapid wear on the rocker pins and rocker bushings.


Randy, my new-style continentals/steel don't seem to have the lock/set screw for the rocker pin and other than one bushing you replaced awhile back I don't seem to be having problems.

Lear31A's cylinders look like the older style bosses? The orange bases are throwing me off...
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Postby Lear31A » Mon Dec 03, 2012 8:54 pm

The mechanic told me that the orange base indicated chrome cylinders.... :shock:
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Postby Randy Thompson » Mon Dec 03, 2012 9:00 pm

Quote: Randy, my new-style continentals/steel don't seem to have the lock/set screw for the rocker pin and other than one bushing you replaced awhile back I don't seem to be having problems.Lear31A's cylinders look like the older style bosses? The orange bases are throwing me off...[/quote]
Lear's cylinders are not Superior brand. They are the traditional early cylinders and the orange does identify them as chrome bores.
The lock/set screw on one version of the newer cylinders was a problem. It held the shaft in one position and the rocker bushings and one side of the pin took all the abuse. A floating pin like yours have is the way to go in these engines.
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Postby David Sbur » Tue Dec 04, 2012 12:21 am

Would removing the set screws on any of the 'new' style continental rocker pins help negate the problem? Will keep an eye out for them on any of the local birds.

All I need to worry about is the usual wear on the inside of the rocker covers from the pins, the dang things don't seem to want to stay center...

BTW, they are running great after your last go-thru.

Never honed chrome bores before, any tricks? I would think there would be some worn thru spots if it's the second time around.
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Postby David Sbur » Tue Dec 04, 2012 12:21 am

Would removing the set screws on any of the 'new' style continental rocker pins help negate the problem? Will keep an eye out for them on any of the local birds.

All I need to worry about is the usual wear on the inside of the rocker covers from the pins, the dang things don't seem to want to stay center...

BTW, they are running great after your last go-thru.

Never honed chrome bores before, any tricks? I would think there would be some worn thru spots if it's the second time around.
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Postby MC » Tue Dec 04, 2012 11:55 am

Lear31A wrote:The mechanic told me that the orange base indicated chrome cylinders.... :shock:


That's correct and I suspect that may be the reason your guides are getting coked up. The chromed cylinders tend to burn more oil than standard. It could be the burnt oil is fouling your guides.

What's your oil consumption like ?

Not sure you can hone chrome cylinders either.
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Postby Lear31A » Tue Dec 04, 2012 3:32 pm

Since I have owned it (15 hrs), it burns 1 qt every 4 hours! Hopefully this overhaul will help the oil burn..........
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Postby MC » Wed Dec 05, 2012 10:27 am

How do you plan to "overhaul" those chromed cylinders ?

Not sure you have many options except changing the rings and hoping to get a better seating with new.
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