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PostPosted: Mon May 02, 2005 1:28 pm
by mmkarp
Anyone know where I can get some new piston rings for both 185's on my lazair. I am down to about 0 compression although they both run ok. I would just like to replace them and get it done. Any help would be greatly appreciated.

Marc <_<

PostPosted: Mon May 02, 2005 1:46 pm
by Guest
Any Rotax dealer will have them. I got all of my rebuild stuff from Rotec Research in B.C. They are the same piston that is used in the Rotax 277 so there's lots of rings and pistons readily available. The older piston had square cross section rings and the newer style has an upper ring that is L shaped. You'll have to inform them of which one your after. If your compression is that bad, it might not be a bad idea to get some specs on the 1st oversize piston. I had to install one in one of my engines, had the local automotive machine shop bore out the cylinder. Pretty quick and only cost a few bucks.

Brian D.

PostPosted: Mon May 02, 2005 9:10 pm
by flyalaz
Hi Marc,

Wildfire has them. Check for price.


PostPosted: Mon May 02, 2005 10:39 pm
by Guest
they may just be stuck...2 of 4 engines i've done so far had at least one stuck ring...

PostPosted: Sun May 08, 2005 4:15 am
by lazflyn
Marc's engines are pretty bad, as far as compression goes. I was at his hanger last weekend and turned his engines over by hand. I could hardly tell when the compression stroke occured. Apparently George C. knew that they were that way FIVE years ago! Can't believe they run.

Mine aren't that bad, but I get some compression loss at BTDC. I pulled the head off and presto: A stuck ring! Well, at least I think it is. The top ring is loose and in the right spot. The lower ring is the one that is stuck/gummy. I say gummy because it does move, but it doesn't move as easily as the top. There is absolutely no blowby past the lower ring though. The piston looks brand new (below the lower ring). So hopefully a new set of rings will cure the lack of compression.

I also checked the cylinder walls. I can still see the honing marks, so I guess that means they are ok, maybe they're not. I'm a complete newbee here so hopefully some experienced guys will chime in and help us read our engines.


PostPosted: Mon May 09, 2005 10:43 pm
by Shannon
Amazing isn't it. I've had first hand experience with a set of engines with a combination of problems.....i.e. completely blown seals, bad rings, and bad crank bearings. The engines still turned up 5,400 despite these problems. Of course they had no torque whatsoever. Maybe this is why the previous owner couldn't seem to get airborne while taking off downwind and rolled it up into a ball. He blamed it on the engines.

George tells me Reg rebuilt 686's engines at some point. I'd imagine they haven't seen a wrench since then. I'd be real suspect that these engines have been run with the wrong ratio at some point if compression is this low. A simple ring job may or may not be the solution.

Mark, sticky rings are almost always a function of rich ratio. More than likely a new set of rings and quick decarbon will get the engines back in shape.


PostPosted: Tue May 10, 2005 3:51 am
by lazflyn

When you say rich ratio, what exactly does that mean? Are you talking about the fuel mixture (ie. setting the low and high needles), or are you talking about fuel to oil ratio?

I was talking to a guy today about re-ringing. He said that you always want to re-hone the cylinders when you install new rings. Seemed to make sense to me. Is that a good idea?



PostPosted: Wed May 11, 2005 5:28 am
by lazflyn

I can't remember what Marc was running, but I read from here and a few other forums that I should run 32:1. So that is what I've done almost from the start. The "insides" of the engine were almost completely free of carbon after 200 hours. The exhaust port had a little buildup after 100 hours. You'd probably laugh if you saw my engines because I am probably doing everything right and they are in great shape, yet I still worry about it.

The first few tanks I did run a 50:1 and straight synthetic. Then I started reading about how straight syntheic is probably best suited for racing applications. You're right on when you say there are a lot of opinions out there. I guess it might come from everybody doing different things with different engines. I try to glean from those that have the closest type of engines and use that I have and will experience.

Not to drag this out forever, but what oil do you use? I have been using a basic 2-stroke outboard mineral oil with a TC-W3 rating. I read what Shorty posted from some engine "experts" on the Kitfox side of this website. Very informative. Thanks Shorty!! Seems I might be better off with another oil that is more tailored for air cooled engines. Mine did run great though for the 200+ hours I put on them last summer. The piston looks brand new (the machining marks are still on it) and the cylinder still has some honing marks. The only real problems I had were: Air pockets in the fuel line at altitudes above 7000 feet. And towards the end of the season, one engine wouldn't "clean out" (go to full power) until it had been running for about 20-30 minutes. I attributed it to a weak ignition, as I rebuilt the carb twice with no luck. I will be ordering ignition parts this week to totally re-do the whole ignition.

Thanks again for you help.


PostPosted: Wed May 11, 2005 7:45 am
by xgary
Mark and all.

My experience has shown that 32 to 1 has been excellent for 185's .

Personally I like Bombardier mineral oil for all UL 2 stokes XPS
It is made to API TC specs by castrol for Bombardier.

TCW3 outboard i have used occasionally but I don't think it is as good as API tc rated.

50 to 1 is too lean for 185s. Rotax 503 or 582 pre mis 50 to 1 is fine.

Synthetic does seem to lubricate ok but it does not store well. If you engine are used at least weekly synthetic will prolly do ok. But longer than that you can get poor coating of bearings that the synthetic oil does not seem to protect from moisture as well. -- try spinning a bearing at 6000 rpm with some galling on it and see how long it lasts.

I would reccomend your crank bearings to be inspected and or replaced if you feel any roughness in them.


PostPosted: Wed May 11, 2005 10:50 am
by Shannon
Hi Mark,

See that's the thing. Who knows how Marc's engines have been run. From what I understand 686 was flown and then stored for a number of years before Marc puchased it. I probably wouldn't feel comfortable with these engines until I could break them open and check things. No big deal really.

It sounds as if what you are doing works fine. 200 hours of good service with little wear and normal carbon build-up (exhaust side) is what you want. You are right on the time interval for ring change too.

I use Pennzoil "Air-Cooled" brand oil and have had excellent results. Other than a bit of normal carbon build-up up no problems. I'm sure other quality mineral oils are just as suitable. I personally will not be using synthetic however.

I can't say for sure why your engine wouldn't reach full power. Could have been a glitch in the carb, maybe the sticky ring was hanging up a bit, or as you mentioned an ignition problem. If I had to guess I'd say it wasn't an ignition problem as the ignitions either seem to work perfect or not at all. Not a bad idea to change the points for fresh set however.

No idea about the "air pockets" above 7 though some vaporized fuel bubbles in the lines seem to be entirely normal.