Before you order just a ring. Put a light film of some white grease or grease or crayon all around in the cylinder. Then align the ring as it fits in the bore. Then push the ring in to it's normal stop position and see if there's places the ring isn't touching. If it wipes all the film or crayon clean then put it all back together and run it cause there's nothing wrong with it. Just up the oil content till you have compression.
If there's places with material left on the cylinder sides you need a new cylinder.

...another good one, you canmeasure your ring end gap with it installed in the cylinder, at different positions throughout the 'stroke' to see if the bore has worn abnormally (different gap as it proceeds through the stroke) I like the white lithium grease idea!

<p class="MsoNormal" style="margin: 0in 0in 10pt"><span style="font-size: 9pt; line-height: 115%; font-family: "Arial","sans-serif"">An engine that new should have a reasonable amount of compression.First avisual inspection, which you noted a few bands of wear and the rest of the cylinderseemed to have the usual somewhat crude looking hone marks. Either the ring or thepiston should have a corresponding wear pattern. Then I would measure the ring end gap with the ring in the cylinder in the same position as it would be if it were running and note the gap. Then measure the bore at several locations up and down the cylinder and also around the cylinder. New cylinders whether DL50 or 55 are always within .001" in taper and concentricity, not to say that a mistake or the lack of a QCstep can't let something out of spec go through but of the ones I've measured (quite a few) that is the norm. On a new or used cylinder, anything approaching .002" taper or out of round I would suggestreplacing. I would also measure the piston and ring, ring thickness should be .0335" and width about .085" (new). Piston to cylinder clearance should be around .0015" at the skirt and .0025" just below the ring perpendicular to the wrist pin.

The ring width is the only one of the measurements that has a tolerance of more than .001"-.0015" but as the ring width shrinks the end gap increases, once you lose .008"-.010" of ring width it's time for some new parts.My guess would be that this cylinder or ring may have been out of spec since new and with the normal wear from break in is just getting worse.</span></p>

This is a good quick test to see if you have a very poor ring seal and fit, hard to see a .0005" thick film of grease though.

I'm leaning towards things originally out of spec as well, which is my reasoning behind replacing the entire top end.

Which reminds me, I've got a 100 in similar straits but I've been too preoccupied to do anything about it. It's one of those that I'm certain will never finish "breaking in".

Well, at least until it wears out.

Hey now Pat don't be replacing that engine. I get a kick out of spinning it and hearing the blowby.... In your engines case I think they forgot the ring.

One or both? We were laughing about the lack of compression and blow by in the engine room yesterday. I was offered a set of DA tops to fix it

I have read somewhere some types or (brands)of emory is not good too use. I would get a quality USA brand if you do the emory cloth trick. Make sure you do it with the exact way Frank says. Probablywith light oil...with light pressure! Capt,n

The original poster already did as you suggest. He put the ring in the cylinder and measured ring gap at several different places through the length of the cylinder.

The grease is a good idea. Never heard that one before, but will definitely use it in the future. [sm=thumbs_up.gif]

Well i felt that i should put up a post because i have the exact same problem. this engine is 1 1/2 years old with about 4 gallons or so thru it. it is version 2 of the DL50 and has NEVER had the compression that my version one did (never should have sold that one:&lt;( anyways.
i have taken the top end apart and it is in great shape remeasured everything and all seems good. this engine would run good rpm but was just hard to start because of NO/LOW compression. Compression is so low that i was having problems with my idle last year and when i dead sticked it the prop would windmill like it had no compression.
Anyways. i installed a new ring and it starts better but no where near like version one. i talked to the supplier and he said that there was a problem with the fit between the pistion ring land and the ring itself. i have not had a chance to look into my problem further but i will keep you posted in the next couple weeks.

as for everybody's RINGENDGAP concern. the rule of thumb is .003-.004 for every inch of BORE. i usually use the .004 as a mechanic we play on the safe side.

P.S i am a OPET by trade and have been for 13 years. In my experience this value holds true all the way from 250hp outboard 2stroke engines snowmobile engines dirt bikes etc etc all the way down to sthil and echo weed wackers,chainsaws etc etc etc. as long as it is a 2 stroke this holds water

cheers

I spoke with Jody at Valley ViewRC andsince this is were the engine was purchased I will ship itback to him for repair.I plan to ship it today during my lunch hour. I hopewith his trained eyehe can tell what may have happened. Hopefully we can keep this post going long enough to get to the bottom of the low compression issue.

I recieved an E-mail from Jody about my engine tonight 06-24-09. I will give a brief overview of what that e-mail stated.

1) The ring was worn. Less than .075" in some places ( .085" new ).

2) The cylinder was worn more that expected and a small area between the boost ports has poor machining and a little chrome chipped off.

3) The engine appeared to have been worked on before in the bottom end, both bearings are spinning in the crankcase and some parts are not OEM.

I called and spoke with Jody personally and assured him this engine has never been worked on until the low compression issue came about. He said this was one of the first shipments of DL's they got. We both were puzzled about this, but it dosen't have anything to do with low compression. I asked that he fix the engine since he already has it and has the expertise to do it correctly. We agreed on a price ( some was covered by warranty issues) and I was very happy with the out come. I want to say thanks again to Jody at valley view rc for his help.

This goes to show how important it is to buy your new engine from someone who will stand behind your purchase and that has the ability to correct any problems

What i think was admirable was that, Jody offered to help BEFORE he knew the motor was purchased from him originally. I dont know Jody myself, or ever done buisness with him, but thats a good way to get future buisness......Gene

The DL50 I got certainly has less compression than other similar engines, it will slowly windmill on dead stick. It has had abot 15gal of 32:1 mineral through it. That said it is the hardest pulling 50 around here.

Your engine sounds a lot like mine (Eagleburger). I have it on a 27% Cap232G and the week before I started this post it was clocked at over 70 mph. It's so strange that an engine that had no compression would run this good and never a dead stick landing.[sm=cool.gif]

Compression is a funny thing. There's a lot of engines out there that don't have a lot of compression that run better than many that do.

My engine is on the way and should be here Thursday (07-16-09 ). Jody said it's got good compression and running like a top. It was ready last week but my wife deleted the message (she said "I thought you heard the message") I was smart [8D]and didn't get into an argument with her.[>:]I will try to get it flying this weekend and keep everyone up to date. One more thing I have 32:1 pennzoil mixed and ready to go.

Another awesome oil to use is Belray H1R synthetic. I run it at 32:1. It leaves no hard carbon.

Good thread - good attitude guys.

Cheers,

Andrew.

Very good and civil thread, gentlemen, it has taught me a couple of new things.[sm=thumbs_up.gif]

Low compression is more evident to low rpm’s and open throttle, when it is easier for gasses to escape thru cylinder-ring-piston.
Gasses’ inertia and friction help increasing compression of a worn out engine at high rpm’s.

Excess and increased viscosity of the oil has a similar effect at low rpm’s, which makes an easy verification of low compression without disassembling the engine.

Once the original ring-cylinder seal is damaged or worn out, there is no much to do in this type of engines, other than what has been done in this case: send it to a qualified mechanic.
A new ring by itself may or may not help.

I have a new quart of this oil on the shelf (Belray) given to me by a belray rep. I am not sure what I will do after break-in. My thoughts now are to stay with Pennzoil for the life of the engine. I just fly around do some mild aerobatics and no 3D. I guess using 32:1 Pennzoil the life of the engine will be fine, May have to clean the plane a little more, but thats ok with me. In response to lnewqban and diviatix about this thread being civil , it is a good thing when several people can have several opinions and the end results are still the same. I gave each person's remarks the same value to contribute to the repair of my engine.

Great thread. Real knowledge and experience. I have learned a lot, over one cup of tea!!
Thanks!!

Ok, I got my engine back and it's installed and ready to go. I hope to fly it Friday (07-17-09). I will keep everyone informed as to how it runs. Here is a picture thrown in for good measure.