Cold Cylinder

[srf471]

This morning, on climb out, my engine (C85-12) sounded "rough" and wouldn't develop full RPM's. When I leveled off I was only getting 2100rpm full throttle. Of course I landed immediately. Cylinder number two was cold, both plugs. The other three were to hot to touch.
A friend suggested a stuck valve and something about a "rope trick" used to free the valve.

First question, any ideas as to what the problem might be.

Second question, if it is a stuck valve, what the heck is the "rope trick" to free it.

Nick
TF#695
N58075
N471F

[fearofpavement]

Re: Cold Cylinder

Well it would be easy enough to pull a plug and check to see if you have compression on that cylinder. If a valve is stuck open there wouldn't be any.

Pulling the rocker cover off would also make it clear if the valve was stuck as the spring wouldn't have retracted the valve and thus would still be partially compressed. (more than usual)

Regarding the rope trick, what that is, is to stuff the cylinder full of rope through a spark plug hole (cotton clothes line rope) with the piston on the bottom and then "gently" rotate the prop to squeeze the wad of rope against the face of the valves. If the valve is stuck open, this would close it but I would never consider that a "fix".

With the valve no longer in danger of falling into the cylinder, you can remove the valve keepers and springs, back off the piston a bit to loosen the rope so you have some working room and then move the valve around a bit in the guide to see if it is tight or not.

If it is, probably pulling the cylinder is going to be required unless someone has ideas for something that would loosen it up (magical mystery instant overhaul snake oil extract)

The main advantage of this rope trick is that if you have a leaking valve, it is possible to "lap" it in the cylinder. A bit of lapping compound can be dabbed on it and a piece of rubber hose put over the valve stem and then it can be rolled between the palms of your hands. Cleaning the valve grinding compound out when done is of course very important as it is very abrasive. Working through the spark plug holes is a pain but on an engine such as the TSIO-520 removing a cylinder is a major pain so a "let's give it a try" might be worthwhile.

Anyway, back to your stuck valve (if that is what it is) just pushing it back into position didn't solve the problem so it needs to be worked loose one way or the other.

When done playing, put the valve back together, back the piston down to the bottom and pull out the rope. Oh, be sure to leave some of the rope hanging out of the spark plug hole when you stuff the cylinder...

I do not believe the above procedure would fit into the owner maintenance category...

The simplest way to loosen the valve up would probably be to "stake" it. Make sure the piston is not on the top (don't want to bend something) and hit the stem of the valve in using a wooden or nylon dowel and a good sized hammer. This moves the valve in and the spring pulls it back out. If there is some crud on the stem it may solve the problem. This also busts up and removes chunks of carbon from the valve face if the valve is leaking due to it. I always try this before the "rope trick" thing. If you've never seen this done, maybe want to get a mechanic to do it. Improper staking could damage the guide. But hey, maybe it needed replacing anyway...

[Forrest Barber]

Re: Cold Cylinder

Bless u that was a complete and good answer...

[3Dreaming]

Re: Cold Cylinder

For sticking valves I've even taken the valve into the cylinder, and put the stem out the sparkplug hole to clean the stem. I've used the proper sized reamer to clean the guide. Then put it back together using mechanical fingers to start the valve back in the guide, and using the piston to push it back in place. After fixing the problem some Marvel Mystery Oil will help the sticking problem. Tom

[Dusty]

Re: Cold Cylinder

Speaking from very recent experience.....

Sounds like a stuck valve to me.

You can usually unstick (temporarily) by taking the covers off and (gently) whacking the valve stem. The rope is mainly for keeping everything tight when you're removing the spring.

Don't worry about being delicate or testing the fit (it's too tight - that's why you're here now!) - just pull the rope out and slide the valve back into the cylinder - yes, all the way, until it goes "plink!" - when you've got the spring off. I leave a little rope in there at this stage, you sometimes have to get a teeny bit violent to get the valve out and I don't want it bouncing around in the cylinder.

Now, fish the valve stem out of a spark plug hole and clean it up. The sticking guide probably has lots-o-carbon built up, you need to get it off _without screwing anything else up_. I used several brass (NOT steel) brushes (gun-cleaning type) in a Makita, along with a lot of MMO and WD-40 to eat all the crud off the guides.

Clean it up good, fish the valve back into the hole (a good magnet that will fit through the guide and a hunk of bent-up welding rod work for me), and repeat. My partner ended up doing #2 sticky valve 100 miles from town at -30F with a pair of pliers, a leatherman, and some trapping wire - if one's sticking, others will soon follow.

My mechanic's initial reaction was "pull the jug!" - don't fall for that. I found another mechanic who'd done it before to get us started. It sounds a lot more intimidating than it is - the last one will take you less than a half-hour.

[flybikefarm]

Re: Cold Cylinder

One of the best things I've found to remove the carbon from the guide and stem is hoppes no. 9 gun cleaner. This is also great for fuel injector nozzles. George

[mulwyk]

Re: Cold Cylinder

Great tip George!

That's the same stuff I use to clean my shotgun. Right?

How do you use it? Swab it on? Use the little brush?

Bob Gustafson

[flybikefarm]

Re: Cold Cylinder

Just use a brush on the valva, and use a soft bristle brush in the guide like you would use to clean a pistol. leave soak a while then brush again. George

[Forrest Barber]

Re: Cold Cylinder

I have been using GI bore cleaner for about 40 yrs... nothing beats a clean valva...

[Vasey fan]

Re: Cold Cylinder

I used to use Kroil and a piece of red Scotchbrite cut & rolled around a long drill bit. (the flutes of the drill hold the scotchbrite if you roll it on in the right direction).

Never thought of trying Hoppes or the GI stuff.

[Karl Rigdon]

Re: Cold Cylinder

On droping the valve inside the cyl I have seen where they tie a string (mono filiment) in the keeper grove and push the valve into the cyl. Then you go through the spark plug hole with a hook and pull the string out. After the guide and/or the valve are cleaned the string is fished through the guide with the hook. The valve is worked through the guide and held in place with air pressure for spring assy.

[Armstrong]

Re: Cold Cylinder

Rope trick works great,its much easier than pulling a cylinder, Ive only used it on larger engines though. I use an adjustable reamer for the guides. I once did all four cylinders on the county pot patrol 172, and it saved alot of money over pulling them all. Rob

[Bob Waldron]

Re: Cold Cylinder

Be certain that you have a stuck valve. If you are certain that you have a stuck valve, then I support the reply from Tom (3Dreaming). It sounds scarry, and the first time you do it, is the hardest, but they become very easy to do. I would work very hard at cleaning the valve stem and the inside of the guide. If you use a reamer on the guide, an adjustable reamer works best. Whichever reamer you do use (AFTER you have thourghly cleaned the guide) cover it with grease to catch any material that you cut away.

I generally tie a three foot piece of dental floss to the valve stem, to assist in re-installing the valve, but you don't need it. Don't be surprised if you find that the valve cannot be lifted with a magnet. Many valves are not all steel.