Field Overhaul

[getonit]

On a Lycoming IO-235, I have several exhaust valves/guides (basically the top end) on 3 of the cylinders that is worn and needs fixin. MX wants to put new jugs on at about 1000 apiece. The other part of this puzzle is that my camshaft is showing signs of corrosion/spalling, engine was still running good and making power. Another mx friend of mine suggested doing a field overhaul and getting everything taken care of now, because the engine is mostly taken apart and could save time and money. The prices I have seen for overhauls at engine shops look really expensive. Looking for some education on this.
Thanks.

 

[erj-145mech]

How much time on the lower end?

It's going to get just that more expensive when you crack the case, if you are worried about the price of the cylinders.

 

[getonit]

this is going to be a gradual process of me gearing up to spend the money to do it right and part of that is me learning what all of these things and what the options are.

I am accepting that I need to replace the cylinders. My mechanic friend (who is not doing the work) says because I have the worn camshaft, now might be time to break it the rest of the way down, replace the camshaft, "mic the crank, replace the bearings, etc" his words because it is going to need to be done sometime anyway. Is what he telling me valid? I am meeting with guys doing the work next week and I just want to go in there informed. Time on engine since last OH around 1400.

 

[avbug]

If you're going to have to replace the crank, split the case, and redo or replace most of the cylinders, now is as good a time as any to pursue the overhaul.

Lycoming has always had issues with crankshaft spalling and excess wear. Mic it as you will, but you're probably going to be replacing it.

Cylinders may not need to be replaced, but for what you'll spend redoing guides and regrinding valve faces, etc, you may as well replace the cylinders with overhauled or new. To say nothing of the downtime, and the availability of facilities wherever you may be. If you are going to have your own redone, I suggest you find someone who can do a five angle regrind. That's not easy to do , but it will be the end of your valve wear.

Remember that TBO doesn't mean the time you can expect; it means a recommended overhaul time, and doesn't apply after the first run, owing to the quality and variety of overhauls. Remember too that an overhaul doesn't mean a rebuild; it means an inspection to determine if the parts are within tolerance. An engine may be overhauled with no replaced parts, if the parts are found to be in tolerance. With that in mind, I'd suggest you do it right and bring everything up to new tolerances, rather than keeping what's legal to keep. That may mean a number of new parts and more expense, but so be it.

Even though the engine has been producing power, it may very well need a full overhaul, and it may be the most cost effective thing for you to do if the case needs to be split and most of the cylinders replaced anyway.

I had to open up an engine a few years ago in which a quarter of a million dollars worth of hot section work had been done. The previous director of maintenance had decided not to go to the minimal extra expense of doing a hot section inspection on the engines while they were apart. When the owner found out that he had spent that kind of money, and had the engine open where the inspection could have been performed, he went ballistic. It resulted in the shutdown of the flght department, sale of the airplane, and the loss of everyone's jobs. So much more cost effective to do it right at the time when you're already spending the money anyway, piston or turbine.

 

[skydivinguy]

Bug, he said the cam was spalled etc.

BTW, what kind of engine needs $250,000 for an HSI?!?

 

[avbug]

It was a JT12D, and a lot of engines take that kind of money, especially if anything of significance needs replacing. In that case, they'd done significant thermal damage, requireing replacement of a number of turbine inlet guide vanes, etc.

Both engines on a Sabreliner 60 had required that kind of work, and while they were open and the work was done, a hot section inspection could have been done for very little extra expense. As it turned out, the person overseeing the maintenance tried to cut corners and didn't get the HSI for either engine...even though they were nearing mid times anyway.

I got the airplane shortly thereafter (after the individual who failed to get the HSI done had left), about the same time an assessor came by as part of a refinance by the company with the flight department. Turns out the cost of the engines was worth more than the airplane, especially lacking a fresh hot section inspection, and the company elected to sell the airplane and shut down the flight department.

Bug, he said the cam was spalled etc.

I know...which is the reason I made the comments I did.

 

[erj-145mech]

Bug, I just had a JT-12D-8N go just over $425k for a HSI. It is on a T-39N (Sabre 40). The first stage turbine blades and disc were scrap. Four of the combustion liners were also BER. When it didn't pass test cell, went into the compressor section. Found the 6th, 7th, 8th and 9th stage compressor discs corroded where we couldn't read the part and serial numbers. The repair shop is in the St Louis area.

 

[avbug]

Sounds like work done by Avmats. Good shop. Helpful people.

Older turbojets tend to get quite expensive, especially for accessory items, or components as they become more scarce.

The cost of an overhaul or inspection can quickly exceed the value of the airplane itself. I've had a few people tell me how great a deal on a 20 series Lear sounds now....they don't think about what it actually costs to operate it. The purchase cost is the cheapest part.

 

[NW_Pilot]

Sounds like work done by Avmats. Good shop. Helpful people.

Older turbojets tend to get quite expensive, especially for accessory items, or components as they become more scarce.

The cost of an overhaul or inspection can quickly exceed the value of the airplane itself. I've had a few people tell me how great a deal on a 20 series Lear sounds now....they don't think about what it actually costs to operate it. The purchase cost is the cheapest part.

I know someone that purchased such an aircraft had a hard time finding anyone to fix it when he did he had to take some Nitro for his heart 1 engine repair quote exceeded what he paid. He still cannot sell it for what he's got in to it. It was a costly learning experience for him. I told him to stick it on ebay or turn it in to a mobile home.

 

[Frozen Ronin]

We've shifted from GA to turbine, but the same theory applies. If you don't have the money to maintain it, you don't have the money to own it. Those that do are operating in the land of gambling money against safety.

And~ lots of engines run just great until they stop making noise about 75 feet off the ground. At that point, the money for overhaul doesn't seem so expensive.

Ronin