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Rope trick or Air?

riobison

Well Known Member
While I'm changing out my cracked cylinder I'm going to check the other 3 to see if there are any sticking valves.

The question is, why not use air to hold the valves in place when removing the retainers?

Most everything I've read on the procedure talks about stuffing 3/8 rope into the cylinder.

Am I missing anything in attempting this with Air?

Thanks

Tim
 
I would use air. This is a pretty standard practice when pulling valve springs from non-overhead cam auto engines. No real sense sticking a rope in there, except for prop safety. you do need to be cautious of the prop spinning. I would use 80-100 PSI and that can swing the prop pretty forcefully if someone bumps into the prop.

Larry
 
I would use air. This is a pretty standard practice when pulling valve springs from non-overhead cam auto engines. No real sense sticking a rope in there, except for prop safety. you do need to be cautious of the prop spinning. I would use 80-100 PSI and that can swing the prop pretty forcefully if someone bumps into the prop.

Larry

Or, you could try doing it at BDC. Prop aint gonna move.
 
Yes, BDC would be the choice. I modified my valve spring compressor from my old Dodge 440 that I haven't used in 40 yrs. cost me $15 in parts and worked on my practice jug.
 
BDC

What Mike said. I've done it several times. Works great, easier than rope.
 
Nope. Rope trick. Always. Aircooled engines have very large piston ring gaps when cold compared to watercooled motors. With waters you can do the air because there is much less blow by, so youre not pressurizing the crankcrank case as much if at all really and for sure and not driving oil out of the cylinder walls, rings, oil scrapper etc. Not to mention that your watering your walls with compressed air blowing thru....unless I suppose, you might have N2 or scuba air to use instead....

Of course you can do what you want and yes pressure works on any motor even ones without rings, but you'll be dry scrubbing the rings & cylinder when the time comes to start it.

Theres a reason Lycoming recommends the rope trick. Dont over think this. The rope trick is easy. Do the easy thing.

BTW dont do any of this at BDC, no matter what method you choose. Drop the valve into the cylinder and youve just turned a minor mx issue into a major. As far as turning the prop, well.....theres no risk with the rope. Anything else, youre just trying to mitigate risks.

It bears saying, its one thing to know how to do something; its quite another to know why.
 
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Nope. Rope trick. Always. Aircooled engines have very large piston ring gaps when cold compared to watercooled motors.

This is not correct. As was discussed in another thread, a straight bore Lyc has a ring gap of .020 - .030 and a choke bore has a gap fo 045-055 (gap goes smaller than 020 at TDC). A typical big bore auto engine (such as a small block chevy), normally aspirated, will be 020-030. Any type of boost and they will be in the upper 30's. The minimum allowable gap on a lycoming is actually smaller than a small block Chevy.
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I will avoid addressing the remaining issues you list in your first paragraph, such as wetting the walls with air and blowing all of the oil out.

With compressed air, there is no risk of the valve falling falling in as the air is holding it. Once you remove the compressed air, you can move the piston up somewhat to act as a limiter for valve travel. However, it does need to come out completely at some point in order to ream the guide. If you don't know enough to hold the valve when you turn the air off, I question whether you should be performing the task without professional assistance.

Larry
 
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This is not correct. As was discussed in another thread, a straight bore Lyc has a ring gap of .020 - .030 and a choke bore has a gap fo 045-055 (gap goes smaller than 020 at TDC). A typical big bore auto engine (such as a small block chevy), normally aspirated, will be 028-032. Any type of boost and they will be in the upper 30's. The minimum allowable gap on a lycoming is actually smaller than a small block Chevy.
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Larry

Please...go build some motors before you talk. As for turbo and supercharged motors, anyone who knows how to build uses gapless rings for those applications.
 
I think both methods (rope or air) probably work fine. Personally I have only used the rope method and it has always been simple and effective. You don't need access to a compression tester (to apply the air pressure) or a compressor to use the rope method. You also don't need to have the noise of the compressor or even access to electricity. I do tie a knot on the far end of the rope that will not pass through the spark plug hole. Easy, cheap, and effective, doesn't get much better than that!

Just my thoughts
 
Please...go build some motors before you talk. As for turbo and supercharged motors, anyone who knows how to build uses gapless rings for those applications.

I have built more than 10 engines in the last several years. Yes, my memory failed me and the SBC is closer to 016 - 028 in gap, based upon a minimum .004" of gap per inch of piston diameter. However, that general rule of thumb translates to about .021 on our larger bore lycomings, which is what they spec. In fact, they spec only a minimu gap of .007 when measured in the full TDC position of a choke barrel. I fail to see how you conclude that these engines have WAY bigger gaps then auto engines unless you consider a couple of thou to be significant in ring gap and create a tornado of air in a leak down test. I would happily debate that one.

Larry
 
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For me the air is simpler. The valves are laying horizontal so not likely to fall in. They need to come out anyway (in a controlled manor of course) to ream the guides.

I've got the cracked jug out and on the bench so it will make a good piece to practice on as far as the reaming, fishing the valves back in and messing around installing the keepers without losing them.:rolleyes:

Tim
 
For me the air is simpler. The valves are laying horizontal so not likely to fall in. They need to come out anyway (in a controlled manor of course) to ream the guides.

I've got the cracked jug out and on the bench so it will make a good piece to practice on as far as the reaming, fishing the valves back in and messing around installing the keepers without losing them.:rolleyes:

Tim

Be sure to search this site. Someone did a really good right up with a few good pointers, if I remember correctly. I think he used a 3 jaw grabber through the exhaust port to hold and manuever the vavle while reaming. Seemed like a good idea when I ready it, though I haven't had to do this (knock wood) on my Lycoming yet.

Larry
 
Be sure to search this site. Someone did a really good right up with a few good pointers, if I remember correctly. I think he used a 3 jaw grabber through the exhaust port to hold and manuever the vavle while reaming. Seemed like a good idea when I ready it, though I haven't had to do this (knock wood) on my Lycoming yet.

Larry

Special incantations are useful. The 3 jaw grabbers need a shot of LPS-1 or 2 to help them operate smoothly, and a good headlight (the kind you strap to your noggin, not the ones on your car) helps. Throw a little salt over your left shoulder somewhere in the process. Open a bottle of your favorite IPA to celebrate after you get everything back together.
 
I did the guide reaming thing a few years ago. There is a really good post on this site with step by step pictures I followed. Also, get a copy of Lycoming service bulletin 1425A, which is the official instructions. Overall, it's not too hard to do, but here are a few lessons learned that might save time.

1. Air pressure worked great for removing the valve keys. Hard to imagine messing with rope.

2. I made the valve key tool from Home depot pry bars, but it barely worked. If I had to do it again I would buy or borrow a real one.

3. When the spring is off, check wobble, and check if the valve slides in and out and rotates easily by hand. If all checks good, put it back together and go on to the next cylinder. No point in risking going further.

4. Get a good gripper. It's stressful trying to regain control of the valve if you drop it in the cylinder.

5. When putting the rocker back on, I used the wood dowel trick to compress the lifter. A short piece of 1/2 inch wood dowel can be can be slid in with having to compress the spring. Once it's in, turn the engine over a few times to compress the lifter. Then remove the dowel and slide in the pin.
 
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