question for engine mechanics

MrNomad · #1 10-15-2006, 08:20 AM

One of the cylinders in our Continental O-200 cracked at the exhaust valve. While this is not an RV, I'm asking for some opinions from the experienced mechanics to help guide the solution.

The O-200 engine has 800 hours since TBO. Until recently, it ran great and is used frequently. Three cylinders consistently read 72-74 lbs during leakdown tests. We identified the leaking valve when cylinder #4 read only 60 lbs during the leakdown performed at annual.

Question: Putting cost aside, is it ok to replace only one jug, piston & rings or do we replace all 4 jugs? One side says there will be a possible lack of balance & compression between #4 and 1, 2, & 3 but others say that given the low speed of airplane engines (2700 rpm) versus car engines, not to worry.

If we simply replace #4 with new a Millenium, other than "feel" additional vibration, is there another way to determine if this decision was wise?

Comments please.

osxuser · #2 10-15-2006, 10:30 AM

Usually not a problem,especially in the nice smooth Continentals. One thing an TRUE engine shop might tell you is to replace both opposing cylinders (IE 1 AND 2 or 3 AND 4), but replacing just one is fairly common practice.

Brian Denk · #3 10-15-2006, 10:56 AM

I had the cracked jug issue on my Lyc. O-360 a few years ago. I replaced it with an overhauled unit. The next year, the opposing jug failed. (An A&P/IA friend of mine jokingly said, "yeah, you'll fix that one then the opposite side will fail shortly thereafter". He said so in a way where I wasn't sure if he was kidding or not, but I think there was a deeper meaning in there somewhere.

Then, it just continued; the third jug cracked..you guessed it....a year later. So, being the astute learner that I am, I says to myself, "self, let's just get this overwith". So, I bought two cylinders, installed them and all four jugs are doing well two years running.

I have no experience with Continentals, so this may be relevant, or not. That first cracked jug may be telling you it's time to yank them all. You can do it now, or do it later. Exactly when "later" is, well...?

Rick6a · #4 10-15-2006, 11:55 AM

Quote:

Originally Posted by MrNomad

One of the cylinders in our Continental O-200 cracked at the exhaust valve. While this is not an RV, I'm asking for some opinions from the experienced mechanics to help guide the solution.

The O-200 engine has 800 hours since TBO. Until recently, it ran great and is used frequently. Three cylinders consistently read 72-74 lbs during leakdown tests. We identified the leaking valve when cylinder #4 read only 60 lbs during the leakdown performed at annual.

Question: Putting cost aside, is it ok to replace only one jug, piston & rings or do we replace all 4 jugs? One side says there will be a possible lack of balance & compression between #4 and 1, 2, & 3 but others say that given the low speed of airplane engines (2700 rpm) versus car engines, not to worry.

If we simply replace #4 with new a Millenium, other than "feel" additional vibration, is there another way to determine if this decision was wise?

Comments please.

I am not an experienced engine mechanic and do not pretend to be but practical experience must count for something. In my experience it has been perfectly acceptable to replace just one cylinder in my O-200 and I have done just that on two separate occasions over the years to no ill-effect. Saying that, and having (under the supervision and signoff of a highly seasoned IA) recently majored my O-200, which by the way ran just fine even though it was 200 hours over TBO, I came to this economic conclusion. #1. I could have sent out and had the existing cylinders refurbished and yellow tagged for a cost of up to $580 per cylinder OR #2. I could buy all new ECI Titan cylinder assemblies with rotocoil technology for $717 each with 2 new spark plugs per cylinder assembly included as part of the deal. I chose the latter option. In any case, new cylinder assembilies typically include pistons, rings and gaskets, but likely do not include the rocker arms.

Stephen Lindberg · #5 10-15-2006, 08:06 PM

Keep in mind that any "overhauled, servicable" cylinder you buy has an unknown number of hours on it (could be 10,000, you don't know) and could crack from fatigue failure as soon after you install it. It is a total crapshoot. I buy new, it is cheaper in the long run. I would not hesitate to replace just one cylinder on an 0-200. You need to break-in that cylinder the same as if you had replaced them all. Usually that means straight mineral oil and high power settings, whatever the cylinder maker says to do. In my opinion, that business about balancing the engine by replacing opposing cylinders has more to do with balancing someone's checking account than balancing the engine.