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Rebuild a Tired Old Engine or Buy a New One?
Is there a limit on the number of hours or the number of factory overhauls that an engine is capable of before it becomes prudent to buy a new one? I was told that when you send an engine to Lycoming, they pick usable parts out of bins to rebuild your engine. This overhauled engine may or may not have anything out of your old engine.
I have a Lyc O235-L2C with a total time of 10,000 hours on the serial number and original engine plate and with 1700 hours since the second Lycoming overhaul. The engine is leaking oil out of the thru engine cylinder studs and has some ring problems. So, is it wise to overhaul again or throw in the towel and buy a new or a low hour engine? |
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You can rebuild the O-235 but from the sounds of it, you will basically be moving your data plate to a new case with all new parts. In other words, there is no limit to how many hours or overhauls an engine has but at some point the only original part is the data plate. |
Is this correct?
It would be great to hear from some of the professional engine guys on this. I thought I heard John or Mahlon say at the Mattituck engine seminar a few years ago that engine overhauls usually require milling the case to ensure a tight sealwhen the halves are rejoined, and this can only be done so many times before the front bearing no longer fits.
I may have misheard though. Quote:
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CASE OVERHAUL
The issue is usually "deck height". The distance from the case split surface to the cylinder mounting pads. There is a minimum distance for this for certified cases. For experimental a case that is a couple thousands out of limit on deck height can be found for 1/3 to 1/2 of cost of overhauled certified case.
When the case is overhauled the crank and cam bearing bores are rebored so bearing fit is not an issue. |
overhaul vs exchange
it does depend on how many times the cases have been repaired and how much has been removed from the mating surface. The biggest issue is fitting the accessory case and sump to the 'thin' crankcase. Threaded holes in the accessory case as well as the 2 alignment pins have to be moved which means helicoils. There are also holes in the bottom of the accessory case that will have to be moved so the sump can be mounted at that location. The holes in the bottom of the cases where the sump bolts protrude will have to be reamed or drilled a tad oversize.
Another problem with high time engines is gear teeth wear. There are wear limits here as well and new gears ain't cheap! Problem is you just don't know whatcha got til you open er' up! Allen |
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Rebuild or Replace
Here is our decision to either replace or rebuild a tired old Lyc O-235-L2C engine. We got quotes from some of the major rebuilders in N Cal and Canada. They were all in the range of $17-18K, and they all depended on the crank, cases, and gears were in a reusable condition. Also, we needed to pack up the old engine and pay for shipment to the rebuilder. A one time new engine purchase thru Vans costs about $25K. Since there were so many uncertainties around rebuilding a tired old engine and it's effect on the planes reliability and future value, we decided to purchase a new O-235-L2C engine. If the old crank or cases did not meet spec, we could have easily spent about the same amount to rebuild as to purchase a brand new engine.
The new engine will add more value, probably will be more reliable, and much easier to sell than with a high time rebuilt engine. We were a little naive when we first purchased a newly completed 9a with a 10,000 hour TT engine, with 3 or 4 rebuilds, and with 900 hours since the last major overhaul. We sure won't make that mistake again. This engine lasted another 800 hours before it needed new rings and developed some severe oil leaks. |
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