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Rebuild a Tired Old Engine or Buy a New One?

M

mfshook62

Well Known Member
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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mfshook62 said:
I have an Lyc O235 with total time of 10,000 hours 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.

Is it wise to overhaul again or throw in the towel and buy a new or a low hour engine?
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10K hours?! I would say throw in the towel- But I wouldn't keep the choices at just "towel or new". You may want to up the HP to an 0320 with a mid time engine...
 
mfshook62 said:
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 have an Lyc O235 with total time of 10,000 hours 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.

Is it wise to overhaul again or throw in the towel and buy a new or a low hour engine?
Click to expand...

There is the option of purchasing a core engine, having it overhauled , and using yours as a core. So you're basically trading cores in a sense. You come out with an overhauled low-time engine that's the same as, if not better, than your old engine.
 
AZtailwind said:
10K hours?! I would say throw in the towel- But I wouldn't keep the choices at just "towel or new". You may want to up the HP to an 0320 with a mid time engine...
Click to expand...

That would require him to replace the prop, engine mount, cowling, exhaust, baffles, carb, and a few other "minor" items. Been there, done that and it isn't easy or cheap.

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.


N941WR said:
That would require him to replace the prop, engine mount, cowling, exhaust, baffles, carb, and a few other "minor" items. Been there, done that and it isn't easy or cheap.

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.
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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
 
aparchment said:
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.
Click to expand...

Yes, there is a limit to how many times the case can be machined but once the case no longer meets the spec, you can replace it. Same goes for the crank, cam, cylinders, etc. The real question is, when is it simply not cost effective to overhaul it?
 
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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mfshook62 said:
Here is our decision to either replace or rebuild a tired old 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. A new engine thru Vans costs about $25K. Since there were so many uncertainties around rebuilding a tired old engine and it's effect on the planes future value, we decided to purchase a new engine. We could have easily spent about the same amount to rebuild as to purchase a brand new lycoming engine.

It will make the plane more valuable, probably more reliable, and much easier to sell with a new engine, rather than a high time rebuilt engine. We were a little naive when we first first purchased a new 9a with a 10,000 hour TT engine, with 2 or 3 rebuilds, and with 900 hours since the last 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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All of this is true, plus you can sell your O-235 and its accessories and make up a good portion of the difference between the overhaul cost and the cost of the new engine. You've made the right decision.
 
mfshook62 said:
We were a little naive when we first first purchased a new 9a with a 10,000 hour TT engine, with 2 or 3 rebuilds, and with 900 hours since the last 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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Yes but depending on how much you spent on this high time engine, getting 800 trouble free hours out of it before it started to leak was likely the most econimical engine deal one could ever hope for. Maybe as low as $10/hr. Most of us fly less 100 hrs/yr. That would be over 8 years in the example. Alllows lots of time to save up for an overhaul. Sometimes, the engines get "old" faster by non-use than over use. Why "waste" money on a new engine (by not flying it often like a commercial aircraft) when a proven mid/high time engine will serve your needs?

Bevan
 
New Vs rebuild

Start with a core say $4,600, send out the crank,cam,rods for overhaul,they all come back with a little work and yellow tags and a bill for $2,200.00 so now were at $6800 add new cylinder assemblies at $1100.00 ea and were at $11,200 send the rest of your parts out for overhaul say $800 were at $12K. Now you need gaskets,Bearings,new oil pump kit,hardware kit,fuel pump nail,tech drive add a another $1500 or $13,500, Fuel system(carb&pump $1000),(FI & pumps $3000) or 16,500.00,you still need two Pmags & those cute little gears say $3500 or $20K and now you got to put it all together measure and take it apart,put it back together and test run it in a cell.$25K to AeroSport,Eagle or Vans for a new engine is a bargain it saves time. I'm doing the roll your own and can say its a slug fest one piece at a time.
RHill
 
New Engine

We wanted a drop in replacement and did not want to change the mount, baffles, exhaust, cowling, etc. We are content with the 4.1 gph and 135 knph airspeed we get with the O-235.
 
mfshook62 said:
We wanted a drop in replacement and did not want to change the mount, baffles, exhaust, cowling, etc. We are content with the 4.1 gph and 135 knph airspeed we get with the O-235.
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Smart move Mike. (I only made the change because I was forced to. Loved the small engine in my -9 but I'm happy with the bigger engine.)
 
I had all the same discussions with myself before taking the plunge. A friend with a lifetime of lightplane experience said it best: "Write the check for new. You'll only cry once."
 
Sky Ranch

Mike,
If you need a little more reassurance, get your hands on a copy of the Sky Ranch Engineering Manual. Not expensive.

There is more info there on aircraft engines from the master than you will ever want to know.

Any metal will eventually fail even though it was never stressed to critical levels.

Dave A.
 
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