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Engine marathon: Case crack, bad cam, high CHT, stumbling

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saylor.dave(at)gmail.com
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Posted: Fri Sep 12, 2014 5:59 pm Post subject: Engine marathon: Case crack, bad cam, high CHT, stumbling

Tim, thanks for your notes.  Can you tell us what kind of oil you were

using?  Any additives?



--Dave



On Fri, Sep 12, 2014 at 5:59 PM, Tim Lewis <TimRVator(at)comcast.net> wrote:



[quote] 



 Case crack: During my RV-10 2014 Condition Inspection I found a small

 crack in the crank case under the #2 cylinder on my RV-10's IO-540. I had

 rebuilt the engine 500 hours earlier. I knew it was a high time case (6500

 hours) with overhauled but high time cylinders, so I had paid extra

 attention to looking for cracks. Unfortunately, I found one (confirmed by

 dye penetrant). So, of course, the engine had to come of the airplane and

 be completely disassembled for crank case replacement.



 Ruined cam: Upon splitting the case, I found significant pitting on

 several of the tappet bodies. The cam shaft had to be replaced, as did

 several tappet bodies. I got a lot of engine assembly assistance from a

 well regarded local repair station (Tom Schweitz at Aero Engines in

 Winchester, VA â€“ he's a super guy to work with). Tom told me that the cam &

 tappet damage was caused by rust forming on the cam shaft wear surface. I

 fly the RV-10 about 120 hours per year, which was apparently not adequate

 to prevent rust on the cam shaft wear surface. Following Tom's

 recommendation, I now use a Tempest engine dehumidifier to try to prevent a

 recurrence.



 CHTs too high (defective electronic ignition): Aero Engines provided me a

 very good price on a low time (1500 TTSN) narrow deck crank case. Since I

 had the engine torn down anyway, I elected to replace my existing cylinders

 (high time, but servicable) with new Lycoming cylinders. So I was expecting

 higher than normal CHTs on my first flights. I found, however, that CHTs

 remained high even after oil consumption had stabilized (beyond 10 hours)

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Kelly McMullen

Joined: 16 Apr 2008
Posts: 1188
Location: Sun Lakes AZ

Posted: Sat Sep 13, 2014 1:00 pm Post subject: Engine marathon: Case crack, bad cam, high CHT, stumbling

The Lycoming is particularly vulnerable because the cam is in the top of the crankcase, and isn't operated daily. The cam normally is nitrided which makes it more vulnerable to corrosion. (OTOH it makes the wear surface very hard to withstand the high loads of the cam lobes.) Auto engines run lower temps, get more oil, usually with positive lube of the cam, where Lycomings generally are splash lubricated.



Reground cams are a mixed bag, depending on the quality of the regrind and whether the lifters are new, how well the cam is nitrided after grinding, etc.



I had to overhaul a 200 hp Lycoming at 1300 hours, 11 yrs after it had been overhauled, due to cam and lifters badly spalled. So frequency of use didn't help it much either.

On Sat, Sep 13, 2014 at 9:34 AM, Mike Whisky <rv-10(at)wellenzohn.net (rv-10(at)wellenzohn.net)> wrote:

[quote]--> RV10-List message posted by: "Mike Whisky" <rv-10(at)wellenzohn.net (rv-10(at)wellenzohn.net)>

 

 Does any engineer or metallurgist now why parts like cam shafts are not made of an none corrosive steel alloy? Just reviewing to understand why not the root cause has been tackled in the past by the engine manufacturers. I guess that problems like this won't appear  in automotive engines.

 

 Just my 20cc

 Mike

 

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Mike Whisky

Joined: 05 Jun 2006
Posts: 336
Location: Switzerland

Posted: Sun Sep 14, 2014 10:20 am Post subject: Re: Engine marathon: Case crack, bad cam, high CHT, stumblin

Thanks Kelly for the explanation



mike

Do not archive

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