Author Topic: Am I expecting too much from a ringed engine? (Read 2066 times)

frank mccune · « **on:** June 14, 2013, 03:32:03 PM »

Hello:

I have been attempting to get an older O.S. .40S to "break in." I have run a quart of fuel through it and had the ring replaced twice but I still have very little compression. Yes, the cylinder was honed both times.

I can take my finger and rotate the prop with about the same resistance and feel as when I remove the plug. There is no pop or the prop moving off of my finger when the prop is flipped. The prop stays on my finger at all time.

Is this how a ringed engine feels under compression? There must be some type of compression when the engine is flipped but I can not detect any. Get ready! The engine is easy to start by hand flipping even without any compression!

Is this typical for ringed engines? I have spent my time flipping lapped engines most of my life so I do not have any prior experience with ringed engines.

Stay well,

Frank

Brett Buck · « **Reply #1 on:** June 14, 2013, 03:49:02 PM »

Quote from: frank mccune on June 14, 2013, 03:32:03 PM

Hello:

I have been attempting to get an older O.S. .40S to "break in." I have run a quart of fuel through it and had the ring replaced twice but I still have very little compression. Yes, the cylinder was honed both times.

I can take my finger and rotate the prop with about the same resistance and feel as when I remove the plug. There is no pop or the prop moving off of my finger when the prop is flipped. The prop stays on my finger at all time.

Is this how a ringed engine feels under compression? There must be some type of compression when the engine is flipped but I can not detect any. Get ready! The engine is easy to start by hand flipping even without any compression!

Depends. Most conventional ring engines have plenty of compression when just flipping. If this is a Dykes ring, then there is little tension on it under normal circumstances and it can sometimes feel like it has little compression when hand-flipping. It counts on the combustion pressure pushing it against the bore, so it works fine when the engine is running normally.

Brett

RandySmith · « **Reply #2 on:** June 14, 2013, 04:05:59 PM »

Quote from: frank mccune on June 14, 2013, 03:32:03 PM

Hello:

I have been attempting to get an older O.S. .40S to "break in." I have run a quart of fuel through it and had the ring replaced twice but I still have very little compression. Yes, the cylinder was honed both times.

I can take my finger and rotate the prop with about the same resistance and feel as when I remove the plug. There is no pop or the prop moving off of my finger when the prop is flipped. The prop stays on my finger at all time.

Is this how a ringed engine feels under compression? There must be some type of compression when the engine is flipped but I can not detect any. Get ready! The engine is easy to start by hand flipping even without any compression!

Is this typical for ringed engines? I have spent my time flipping lapped engines most of my life so I do not have any prior experience with ringed engines.

Stay well,

Frank

HI Frank

Exactly what S OS is this? what type ring? what was the end gap set at when you checked it and installed in the motor?
Is the sleeve belled out?..wear at the top?
need more info

regards
Randy

frank mccune · « **Reply #3 on:** June 14, 2013, 04:38:54 PM »

Hi Randy et al:

Like I stated, the engine is an O.S .40S from the 70's. This was supposed to be an engine built for Stunt Flying. It has one conventional ring and a baffled piston.

The chap who made the ring also honed the cylinder and fit the ring. This is the second ring that he has fitted to this engine. The first ring had a tremendous amount of blow by around the ring and I could not start it by hand flipping. He is supposed to be the expert when it comes to making rings and fitting them.

To give one an idea as to how little compression that I have with this engine, I can turn the engine over via using my thumb and forefinger on the drive washer. Like I stated above, there is not much difference between turning the engine over with or without the plug in place.

This does not appear to be a proper ring to cylinder fit! Am I correct about that?

Stay well my friend,

Frank

Jim Kraft · « **Reply #4 on:** June 14, 2013, 05:33:44 PM »

Frank, I have had rings from Frank Bowman that I thought would never seat as they are very hard. Well, after running for hours they finally seated and I had compression when cranking over. I would make sure you do not have a head gasket leak, or a glo plug leak, and since it will start I would continue to run it. Try putting a couple of drops of motor oil in the exhaust port and see if it has compression then. If the ring, rings are not seated it should have some pop over with oil in it. Flip it both ways as sometimes depending on where the ring gap is it will have compression one way but not the other. It could also be the the sleeve is out of round or being distorted by the head, or as Randy says it could be worn at the top. It is really hard to tell without actually feeling the motor. You really don't have anything to loose by running it, and if you have a plane to fly it in that would be best. Flying seems to seat rings better than bench running at least for me.

EddyR · « **Reply #5 on:** June 14, 2013, 07:04:14 PM »

Frank I have re ringed a lot of ST motors over the years and some of them did not have a lot of compression when first assembled, no pop at all. I ran them a few times in the test stand and then flew them and they all got better with a few runs on them. They started hard the first time but were normal after one or two runs. I am sure a OS would be the same. Run it and let us know what happens.
Ed

Brett Buck · « **Reply #6 on:** June 14, 2013, 07:53:25 PM »

Quote from: frank mccune on June 14, 2013, 04:38:54 PM

To give one an idea as to how little compression that I have with this engine, I can turn the engine over via using my thumb and forefinger on the drive washer. Like I stated above, there is not much difference between turning the engine over with or without the plug in place.

This does not appear to be a proper ring to cylinder fit! Am I correct about that?

Hard to say. Most of my good ones on the ST46 were great from the start.

One thing to note - you don't need to run them real slow in a blubbering 4-stroke. Put a 9-4 on it and let it run in a medium 2 for a while, and make sure you have at least some synthetic oil.

Brett

Balsa Butcher · « **Reply #7 on:** June 14, 2013, 09:23:14 PM »

Is it just plain worn out? New ring or not, it happens. 40 plus year old engine...it happens. If it was a stunt engine it may have lots of flights on it but not show its age because its previous owner knew how to take care of it...and when to get rid of it. I have had two engines in the past few years that fit that description. I would run fly it, see what happens and try to find a new P&L. May be hard to locate for that vintage and type OS.

Chris Brainard · « **Reply #8 on:** June 15, 2013, 06:30:06 AM »

I had a similar experience with my O.S. .40H (i.e. - replacement ring installed/cylinder honed). Lot's of bench running, but the compression remained poor, making it difficult to even start. Finally, in desperation, I mounted it to a model and tried flying it. On about the fourth flight, it seated and the compression has been great ever since. I was running Powermaster 10/22.

frank mccune · « **Reply #9 on:** June 15, 2013, 11:40:22 AM »

Hello:

Thanks for all of the advice.

I am going to install this engine in an older Nobler and go fly!

I did put some ATF in the engine and it seems to have great compression and seal when I do that. It has great pop and does not leak compression around the ring.

The great thing with this "new" ring is that it is easy to hand start! I will allow the ring to "seat' itself as I fly.

Why well this engine start very easily with low compression when I can ot get a lapped engine to start with low compression? Lol

Stay well my friends,

Frank

Brett Buck · « **Reply #10 on:** June 15, 2013, 01:28:33 PM »

Quote from: frank mccune on June 15, 2013, 11:40:22 AM

Why well this engine start very easily with low compression when I can ot get a lapped engine to start with low compression? Lol

Because the pressure from the firing pushes the ring against the piston groove, which seals it up better than when you are just flipping it.

Brett

Bill Little · « **Reply #11 on:** June 15, 2013, 01:37:41 PM »

I am having a tough time trying to seat the ring in a HP .40 Gold Cup. The engine is of the last runs and has a hard chrome plated liner. The engine came from the factory brand new but no ring installed. It's running but hasn't seated.......... any opinions?

Thanks
Bill

frank mccune · « **Reply #12 on:** June 15, 2013, 02:13:02 PM »

Hi Brett:

You are correct about the ring expanding when the engine fires! Of course a lapped piston will not do this!

In my younger days, I was taught that the piston rings contract after the cylinder pressure drops from the power stroke. This was due to the spring in the ring. It was claimed that this would ensure that the ring would not be in contact with the cylinder and would have a long life. Only the piston made contact with the cylinder walls during the other cycles.

Have you ever heard of this before?

I was also taught that the rings turned on the piston to maintain an even wear on the rings and cylinder. How was this done you may ask? Easy, if one looks at the metal that is between the rings ,one can see that it is wavy. The oil striking the waves in this spacer is what caused the ring to turn in the cylinder. Basic automotives 101!

Stay well,

Frank

Rick_Huff · « **Reply #13 on:** June 15, 2013, 02:54:13 PM »

I also have a 70's vintage OS Max H .40S that has little compression when "flipped" by hand. However, it starts easily and flies a beautiful 4-2-4 break. It does not have a dykes ring, and I'm not sure why it has so little compression when "flipped". Since it flies so well, I haven't put more thought into it. I hope your's flies well too.
Rick

Author Topic: Am I expecting too much from a ringed engine? (Read 2066 times)

frank mccune

Am I expecting too much from a ringed engine?

Brett Buck

Re: Am I expecting too much from a ringed engine?

RandySmith

Re: Am I expecting too much from a ringed engine?

frank mccune

Re: Am I expecting too much from a ringed engine?

Jim Kraft

Re: Am I expecting too much from a ringed engine?

EddyR

Re: Am I expecting too much from a ringed engine?

Brett Buck

Re: Am I expecting too much from a ringed engine?

Balsa Butcher

Re: Am I expecting too much from a ringed engine?

Chris Brainard

Re: Am I expecting too much from a ringed engine?

frank mccune

Re: Am I expecting too much from a ringed engine?

Brett Buck

Re: Am I expecting too much from a ringed engine?

Bill Little

Re: Am I expecting too much from a ringed engine?

frank mccune

Re: Am I expecting too much from a ringed engine?

Rick_Huff

Re: Am I expecting too much from a ringed engine?