RE: Low Compression ???
 

I took the measurement with the ring in the cylinder at several places but always measuring the ring end gap. I did this just to make sure I got the same reading and I did.</p>

RE: Low Compression ???
 

Kudos to all the contributors of this very informative thread [sm=thumbs_up.gif]

Karol

RE: Low Compression ???
 

Captn,

Bowman rings do not necessarily improve performance. Myself and others have tested the theory that his rings are better and it doesn't always hold water. There have been quite a few applications where they were not as good as OEM rings. They work, but they are not always better.

For the record, I have a DL 100 that has never had what I would call "good" compression. 6 gallons through it and, just as when new, does not have any compression until it is warm. Enough to start when cold, but no more. More than enough power but the lack of compression eliminated it from further consideration in other areas. To make it right I would need to replace both cylinder, piston, ring assemblies. Simply replacing the ring would only provide a new ring to continue grinding away at the cylinder in the hope that it might eventually round out the cylinder before the ring itself wore out.

.002" for the end gap is, imo, too little. It does not provide enough room for heat expansion. I'm with Jody on the .005 to .006 dimension for a starting point. No less than .004".

RE: Low Compression ???
 

If you only have .002" ring gap cold on a 2 year old engine you might have found the cause for the scratched cylinder walls. The ring expands when heated yet there's no room for it to expand. It warped and dug into the sides.
Two choices, run it as is till it won't run no more, or purchase the replacement parts. With the knowledge gained here you will be better able to determine if the replacment parts will perform better than the origional.

RE: Low Compression ???
 

hi   you left out the most important picture-  that of the cylinder walls do replace the ring  -it is a cheep fix and  can bring the engine back to life  ( ring tension may be gone from too much heat- low oil )-clean the piston with a stay  bright sponge-cross sand the cylinder walls with 320 emery and oil-  at a 45% angles reassemble and break in the new ring-while apart do check the rod for bushing were- (top and bottom ) if worn -consider replace it-do consider these costs -applied to the purchase of a new engine-

RE: Low Compression ???
 

And if the cylinder wasn't excessively worn before, it prolly will be after the 320.

I don't know too many people with hands calibrated well enough to sand something round and keep it that way. The plating is generally between .0025 and .004" deep so you don't have much room before you bare aluminum. Of course that's before the engine was run the first time, so an engine that started life with a slightly out of round cylinder would be seriously worn in several locations through the ring seating process. I do a lot of engines and only those that had carbon tracking down the cylinder walls need any kind of attention when replacing a ring. There are ways other than honing to perform the task that do not generate additional wear or a reduction in the plating depth.

RE: Low Compression ???
 

Very true TOM, "honing" with the suggested method cannot improve any defect in the cylinder and only serves to manualy induce unnecessary wear and forsome with the mostzelous efforts, can completely ruin a cylinder. Looking more at the pictures, this engine appears to me to not have that much time on it for being two years old.

Christian, can you give us an idea of how much time is on the engine, or gallons of fuel used. I also noticed the spark plug, very coked up and rich looking. Maybe a read of TOM's carb tuning article would help as well.

RE: Low Compression ???
 

Yes as far as the time/gallons go I would say aprox. 10 gallons of fuel. I fly several types of aircraft,helis,and even a gyrocopter. This is why I don't have a lot of time on one aircraft. I am seriously thinking of calling Valley View RC and getting the necessary parts.

RE: Low Compression ???
 

hi-  i am not suggesting honing-  -just a  very light sanding with 320 emory cloth and oil-  -that happens to be std proceedure for ring replacement-   will have no effect on the roundness of the cylinder walls-if any brass is showing on the clyinder walls -they are done

RE: Low Compression ???
 

as far as the ring gap, the ring is iron, the piston and cylinder are aluminum, the aluminum will expand a lot more and faster than the iron ring will, so a small gap shouldn't hurt anything.

RE: Low Compression ???
 

320 is for sanding BALSA. :eek:

You take 320 to a chrome plated aluminum cylinder and you'll have the chrome so gouged up after 10 passes, it'll be ruined. You might not go through it in 10 passes, but I guarantee it'll be trashed within 10 seconds of firing it up with a new ring. That chrome will eat through the ring, and flake off, and grind itself into the piston, and behind the rings, and................ it'll just be a total disaster..........

Our model engines are not "honed" after the plating process. You ever had a brand new chrome plated engine apart? There ain't no dang cross hatches in that cylinder. It's mirror smooth. And there's no reason to "hone" or "scuff" or "knock the glaze off" ANY used cylinder with 320 grit paper for ANY reason...... EVER. :eek:

That might be "standard" procedure for ring replacement on a car engine with an iron cylinder, but NOT on a 2-stroke model engine with a chromed aluminum cylinder.

I'm tempted to edit or delete your posts because I KNOW your advice is poor and I don't want others to follow it. But just because I disagree with you doesn't make it right to delete your posts. FYI...... your advice is WRONG. DEAD WRONG.

If we were talking about an old iron cylinder, I might be inclined to agree with you. But this is a chromed cylinder. Bad advice. Very bad advice.

RE: Low Compression ???
 

I hope the following pictures tell a little better story. You will see one that shows the shinny marks I talked about. You will see one that shows the ring end gap (I tried the ring in several locations in the cylinder and the end gap stays the same). This is a cheap camera and thats about as good as it gets.

RE: Low Compression ???
 

I understand what you are saying. But don't forget the ring doesn't always fill the entire ring groove. There is clearance behind the ring....... between the inside of the ring groove and the ring. The gap still needs to be large enough to prevent the ends of the ring from touching when the engine is at max operating temp.

Yes, the aluminum piston and cylinder will expand more than the iron ring. And you would think that would provide all the clearance needed to prevent the ring from binding up. But you have to consider the ring IS going to expand. Not as much as the aluminum, but it WILL expand. As the metal expands, the ends of the ring will get closer together. The ring gap will decrease with heat. Thats why we need more than .002" . It's not because the ring will expand out and hit the aluminum. It's because the ring will expand and the gap will close up. Once the gap closes up completely, the ring will start to get oval instead of round, as it continues to expand. [X(] Then it goes outward and hits the aluminum cylinder and creates more drag/friction in a few hot spots instead of even pressure on the cylinder walls all the way around the ring.

RE: Low Compression ???
 

Rcpilot,,, If the cylinder is coated in Nikasil or similar, the only thing that will cut it is a diamond hone.

RE: Low Compression ???
 

I have to ask...what brass??

Very, very few of our cylinders are nikasil plated. I can only name one manufacturer that uses real nikasil plating process. At $200.00 for less than 50cc cylinder we are not getting any of them;) Most are done through a process called "flame plating" It's the cheapest of the cheap ways to apply plating.

As for cylinder honing, there are many cylinders that are honed before the plating is applied. One of those companies immediately comes to mind, and I believe most of the Chinese cylinders are done the same way. A few cylinders are not honed at all, or polished out to remove any visible honing. Those are the mirror smooth cylinders. Nikasil plating appears somewhat dark gray inside a cylinder and I have not seen much of that in our engines. However, the Mahle engines made for Stihl have some of the best cylinders a hobbyist can get his hands on.

RE: Low Compression ???
 

I'm sure a determined enough person could cut it up quite a bit with 320 grit paper. Not that you'd want to do that.

It's pointless anyway. You don't hone a chrome cylinder. There's not enough material there to hone it. It's not meant to be honed. It's mirror finished form the factory and should stay that way for the usable life of the engine.

If it's glazed up polish it with a cotton cloth and toothpaste to cut the varnish. Notice I said "polish" ?

I just don't believe in honing a chromed cylinder. All thats gonna do is force you to get the checkbook out and buy some new parts once it's discovered that you ruined it.

RE: Low Compression ???
 

Looking at the photos posted, that ring gap looks quite a bit larger than .002". If the gap is as jagged as it looks in the photo(not sure what I'm seeing there), then maybe a .002" feeler blade fits, but the real gap is larger.

Ring gap only needs to be big enough for the hottest ring temperature and coolest cylinder temperature it will experience. The problem is unless you are shooting for a small gap and actually looking for signs of the gap being too small, it makes no sense to try to get an extra 50RPM this way.

Interesting thread.

RE: Low Compression ???
 

My 2 cents.... .002 thousandths is about right I think for that size of bore. The gap can be more on larger dia rings. I still say for the price of a Boman ring...it is worth a try. So far every engine I hand cranked with a new boman ring had real good compression even before runing. The last 2 was a ZDZ 50 and a Webra 1.2. The Webra fom new did not have much compression at all....dykes ring. It sure has compression now!!! on that using 320 grit. I would not do it. Some grit can embed cyl wall in some cases. Then what happens is fast wear. Now it seems like if you place the ring in bore and measure the same .002 in many places....the bore must be close to round and plenty usable. Get that Bowman ring...and find out for yourself. Not much to loose. Capt,n

RE: Low Compression ???
 

I agree 100% on that. I talked with Frank Bowman and he said he never had any problems with a .001 inch gap. If your engine has only one piston ring...it is important to not let compression escape with a ring end gap that is to big. The aluminum cyl is going to expand moe than the piston ring....increasing the gap. Capt,n

RE: Low Compression ???
 

Since there's no obvious damage other than a few scuff areas in the bore and the ring seams to fit fine down where heat doesnt get to, the probable cause for all the compression loss is the blackend area around the exhaust port. That area might have warped out from running hot. We don't know if DL runs their parts through a heat soak process before honing the bores. So it's very possible the cylinder warped out of shape at some time. Run another 10 or 20 gallons through it and maybe it will get better. Can't hurt.
PS. The Amsoil appears to have protected the parts quite nicely. Run some SeaFoam in your gas mix and maybe it will clear up the Carbon. Again can't hurt.

RE: Low Compression ???
 

.002" ring end gap is normal for the DL when new and will no way close up and force the ring out of shape. As Captn mentioned even a .001" end gap would work fine. The pictures of the cylinder look fine from what I can tell but the position of the ring for checking it's end gap on an engine with that much run time is all wrong. In the picture the ring ends are on the exhaust side of the cylinder, the ring endsshould be positioned in the same location and orientation as it is when running, on the intake side of the cylinder and with the antirotation pin relief towards the top of the cylinder. It can make a considerable difference in the measurement especially on an out of round cylinder.

RE: Low Compression ???
 

I thought I had it on the intake side my mistake. I wil check again tonight. What is a BOMAN ring ? On your experience (valley View RC) what would you do with this engine if you had it in the shop? I have no problem buying all the parts and I can rebuild it myself or will a new BOMAN ring do? I want to do the best thing and a little money may save a dead stick landing with a 27% plane.

RE: Low Compression ???
 

Frank Bowman is called the Ringmaster, who makes very excellent performing rings for our gas and glow engines. You can check with him at [email protected] or phone 505-327-0696.

Karol

RE: Low Compression ???
 

Not to detract from Frank, but if I wanted to do it right I would replace the entire top end. Unless Bowman has already made rings for any particular engine he likes to have the head sent to him. With some he's been fine with using specs provided by the owner.

There are several methods to make the engine run well. Depending on the severity of condition that could be all the way to replacing bearings in the bottom end. Not having the engine in my hands I could not make a definitive statement but I do not believe any more than a top overhaul would be needed to bring the engine back up to OEM specs. A simple ring replacement would help it run better but it's not the best way. The easy way but not the best. If you feel a need for a custom ring give Bowman a call, but it's not necessary.

RE: Low Compression ???
 

HI   RCPILOTI  use FRANK BOWMAN rings to replace my ringsabout two dozen to date- frank is the man when it comes to replacement ringshis instructions are to use 320 grit emory and oil lightly-as i  have stated -standard proceedure to replace a ring according  to frank -now what is your problem with tthat-no one said anything about honing but youby the way all my replacement rings brought the engines back to new compression-enough said !!