Mike Busch Not a Fan of Top Overhauls?

How many here believe that due to dynamic compression being what it is, old cylinders that have low static compression, and new cylinders with high static compression will develop the same BMEP?
 
Checkout_my_Six said:
But, maintenance induced failures are a real thing....and something to think about.
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You bet it is real, but it is a very very small portion of maintenance related problems.
 
I just talked to Mike by email.
As suspected, he does not remove the engine just to replace a cylinder.
More later.

/internet rumors
 
Let'sgoflying! said:
omg. Were we...brothers? Or neighbors? I did that exact thing. To many other devices as well. Still doing it but in a more controlled fashion!
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My mother came to expect that of me, after I dismantled her vacuum cleaner when I was a kid so I could figure out how it worked. Now I carry the lifelong stigma of being an engineer...
 
kyleb said:
Maybe in some areas, but I agree with his philosophy on cylinders. A TOH implies pulling all of the cylinders and rebuilding or replacing them at one time. Mike believes in replacing or repairing cylinders on condition, and I agree with that. Each cylinder is a unique assembly and if one has a problem, that isn't an indictment against the others.
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Depends on the engine and what down time is worth.
 
Tom-D said:
So, You are down a week this month, then again next month for another cylinder, then again the next month, and so on.
It doesn't require that much more time to change them all.
But maybe you can only afford one cylinder a month (?) been there too.
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I'm not arguing for or against Busch's philosophy. You makes your choices, and you takes your chances.

But he got more than 3000 hours each out of a pair of turbocharged Continental engines, and at the 3000 hour mark I remember him writing about it. At that point, iirc, more of the cylinders were still original than had been replaced.

I highly doubt the airplane was down "this month, last month, and the month before". Let's remember Tom, you made money from aviation. Most of the rest of here just get to spend it. ;) :D
 
Let'sgoflying! said:
I just talked to Mike by email.
As suspected, he does not remove the engine just to replace a cylinder.
More later.

/internet rumors
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Look forward then to hearing the clarification of this excerpt from his article, link posted by OP on this thread:

4. Wrench access is limited. Both Continental and Lycoming call for a two phase tightening procedure where all the cylinder hold-down nuts are first torqued to 50 percent of their final torque in a specified tightening sequence, and then they are torqued to 100 percent of their final torque following the same sequence. An important reason for doing it this way is that consistent results can only be obtained if the final tightening sequence is performed using a single continuous motion of the torque wrench. If the movement of the wrench is interrupted, the “click” from the wrench that signifies that the specified torque has been achieved occurs too early because breakaway torque is significantly higher than running torque. While it’s usually easy to do this properly when the engine is out of the airplane and sitting on an engine stand with unobstructed access, it’s almost impossible to do when the engine is mounted in the airplane and various components restrict wrench movement. Frequently, two or three “bites” of the wrench are needed before final torque is achieved, and each adds uncertainty to the final result. “This is particularly true when wrench rotation must be stopped as the nut is approaching the desired ‘click’ of the wrench—but not there yet,” Fuchs says. “Time after time when the wrench is removed before it clicked, the wrench will do so upon attempting to tighten the nut further with no additional rotation of the nut.” This deceives the mechanic into believing that proper preload has been achieved when it almost certainly hasn’t.​
 
GRG55 said:
I'm not arguing for or against Busch's philosophy. You makes your choices, and you takes your chances.

But he got more than 3000 hours each out of a pair of turbocharged Continental engines, and at the 3000 hour mark I remember him writing about it. At that point, iirc, more of the cylinders were still original than had been replaced.

I highly doubt the airplane was down "this month, last month, and the month before". Let's remember Tom, you made money from aviation. Most of the rest of here just get to spend it. ;) :D
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I'd rather take less of your money to make you safe. Let's do the whole job the first time.

If all your cylinder are high time and one needs to be changed, What makes you believe the other aren't worn out too.
 
I'd like to repeat, It's the owner's choice, not the A&P's
 
Tom-D said:
How many here believe that due to dynamic compression being what it is, old cylinders that have low static compression, and new cylinders with high static compression will develop the same BMEP?
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Read an interesting article by lycoming or continental where they continually widened the ring gap until tests were somewhere around 40 per cylinder. The engine still produced damn near 100% rated power.
 
On Jul 7, 2019, at 8:30 PM, Mike Busch <mike.busch@xxxxxxx.xx> wrote:
That’s totally absurd. I’ve never recommended engine removal for cylinder work, even for replacement of all cylinders, much less one cylinder. What I have consistently recommended is:
1. Not removing cylinders unless absolutely necessary. (At least 50% of cylinder removals are unwarranted.)
2. Never allowing more than one pair of through bolts to be torque-relieved at any time.
3. Never rotating the crankshaft when any through bolts are torque relieved.
I did a top overhaul on the left engine if my Cessna 310 a few years ago following the above rules. I used torque plates to allow all through bolts to be torqued up while the cylinders were off.
It would have been crazy to remove the engine for this. —Mike

On Jul 7, 2019, at 6:43 PM, Dave Taylor <xxxxxxxxxx@sbcglobal.net> wrote:
Title "Engine removal for cylinder replacement"
Mike-
Some of the guys are saying you recommend this even for 1 cylinder; true or false?
If true...do you not feel this introduces significant opportunity for maintenance-induced failures with all the connections that are being broken and re-made?
Maybe in your 310 this is necessary because you don't have good access to all cylinders?
Thanks for any input,
Dave
--
Dave Taylor
Fort Davis Tx 79734
xxxxxxxxx@sbcglobal.net
432-386-xxxx cell
 
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Let'sgoflying! said:
1. Not removing cylinders unless absolutely necessary. (At least 50% of cylinder removals are unwarranted.)
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I wonder if he has actual data to back that up or is just pulling that number out of his ass.

Let'sgoflying! said:
Some of the guys are saying you recommend this even for 1 cylinder; true or false?
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Translation: Hey Mike, heads-up, since it's a public forum, you need to come over to PoA, check out what folks are saying about you, and then send them nasty PMs threatening libel lawsuits to get them to shut up.
 
1RTK1 said:
He was probably referring to ambient moisture
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Well...that's the point. Ambient moisture has nothing to do with how water gets into your oil. And he was asserting at the time that it does.

Gasoline and oxygen create water as a product of combustion: C8H18 + O2 -> CO2 + H20

(C8H18 = octane)
 
Lotta variables to consider. Bottom line, I don't want to be paying a mechanic to R&R the cowl, exhaust, intake manifolds, etc over and over, or have to break in one or more cylinders multiple times in a row. Depending on what you fly, you may be switching oils back an forth too (ashless dispersant to mineral to ashless dispersant) etc. What a PITA

Not all engines are the same or installed the same, some you have to take the entire exhaust off and others you can do one bank of cylinders at a time.


Also, if you know you needs some top end work, its a hellofa lot easier to bite the bullet before it lets you down and trashes something else IMHO. In theory you may even get to choose when to do it. Cooler weather would be my choice to help manage CHTs during initial break-in flights.
 
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Tom-D said:
because you must disassemble a lot of the engine to put a wrench on the cylinder hold down studs.
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Sorry Tom, I meant when you just finished up the final assembly of a replacement cylinder, then walk away for a bit then torque it again one last time. I agree, in-service torque checks on piston engines isn't practical.
 
bnt83 said:
[QUO


Sorry Tom, I meant when you just finished up the final assembly of a replacement cylinder, then walk away for a bit then torque it again one last time. I agree, in-service torque checks on piston engines isn't practical.
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Never hurts to re-check.
 
bnt83 said:
[QUO


Sorry Tom, I meant when you just finished up the final assembly of a replacement cylinder, then walk away for a bit then torque it again one last time. I agree, in-service torque checks on piston engines isn't practical.
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I don't know about the "walking away" bit, but on race engines (with always clean, properly lubricated, and typically new fasteners) we'd always warm the up good, let them cool, then retorqued them. That's not likely possible in most aircraft engines, unless you have a test stand. But the factory does it once, and that can be sufficient for 2,000 hours if nothing goes wrong.
 
GRG55 said:
An important reason for doing it this way is that consistent results can only be obtained if the final tightening sequence is performed using a single continuous motion of the torque wrench. If the movement of the wrench is interrupted, the “click” from the wrench that signifies that the specified torque has been achieved occurs too early because breakaway torque is significantly higher than running torque.
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He is correct in that there is a significant difference between static (breakaway) and sliding friction. For steel on steel coefficient of friction numbers are on the order of: static dry 0.7 static lubricated 0.12- 0.16, sliding dry 0.4 lubricated 0.03-0.12. I don't know about having to do the whole 50%-100% step in exactly one motion, but you don't want to stop just short of the final torque. Particularly if you have a click type torque wrench and you stop short, the wrench may click on the higher static torque before the bolt starts to turn - in which case you be skrewt. With a dial or beam or digital readout wrench you may be able push through the breakaway and still get a good measurement of the torque.

But, in general, the objective is to tighten the bolt / stud to a specific tensile load - torque is one way to do it, but the correlation between torque and tension is greatly effected by the condition of the threads and environment and isn't the best, but sometimes that is about all you have. Other methods, for example, would be to tighten to a torque then turn a specified number of degrees to stretch the bolts - common for cylinder head bolts in the automotive world. Another method is to directly measure the stretch. For something like a rod bolt where you can get to both ends a direct measurement is pretty easy with a large micrometer or a fixture to hold a dial indicator. Also for something like a blind stud - you can put a dial indicator on the end of the stud and measure the stretch as you tighten, but that requires some room to work.
 
GRG55 said:
My mother came to expect that of me, after I dismantled her vacuum cleaner when I was a kid so I could figure out how it worked. Now I carry the lifelong stigma of being an engineer...
Click to expand...

Have you seen the young Dilbert video of "The Knack"? Take a look at
.

My parents didn't understand Dilbert, but they understood that video. "That was you!" BTW, I am an engineer. :D
 
I believe that when replacing cylinders brake away torque has nothing to do with any procedure.

The torque is listed in the Overhaul manual. clean oiled threads. click, you're done.
 
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