How to Check Crank Flange Runout

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wsimpso1

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OK, it has gotten to the point of actually examining an engine and I need a little help.

I am in the dark on how we anchor a dial indicator to the crankcase and then spin the crank to check crank runout and axial endplay. I can imagine and invent methods, but if there are standard ways of doing so, I would rather do it the standard way.

A magnetic mount won't grab the aluminum case. Perhaps a steel fixture is fabbed up and bolted to the existing bosses? And the engine without a prop on the flange seems to make turning the engine difficult. Engine in question is a Lycoming IO-360.

So, please explain the process and pieces for this newbie to engine measuring. Photos are great too

Billski
 

TFF

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I set the magnetic base to lock onto the #1 cylinder base. Baffles may have to come off. Straight out to the prop flange. There is a Lycoming service bulletin on how they measure the flange.
 

TFF

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Turning the crank is with something long. Take a set of plugs out to relieve compression. The last one I did was with a large wrench. Long screwdriver or such.

The last one I did was just within limits and probably was like that before from a previous incident. The surface of the flange can make the needle jump some. Don’t confuse that with out of round.
 
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trimtab

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Using a hand drill to turn the crank slowly makes this easy. The pulsing of a rtchet actuation can add a bit to the runout. Also, do it in the vertical orientation(engine stand, and make axial play measurements separately.


I've used a case fastener to mount something (anything really will work) for the mag base.
 
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Dana

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When I checked it on my Starduster, I clamped a steel plate to the top of the engine (there was a strap already attached to the top front crankcase bolts, not the lifting eye but similar) and used a mag base on that. Tried to attach a picture but for some reason I can't do it from the phone.
 

BBerson

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If the arm can reach the front face it gets a better reading inside the flange holes, I think. Try the magnet on the starter.
The outer flange is soft and may have been straightened by someone.
 

Deuelly

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If the arm can reach the front face it gets a better reading inside the flange holes, I think. Try the magnet on the starter.
The outer flange is soft and may have been straightened by someone.
But the tolerance is given as .005" TIR on the face off the flange just outside of the prop bolt holes.

Brandon
 

Dan Thomas

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If the crank or flange is bent it will show the most on the outside periphery of the flange.

And if there's a recorded propstrike with a metal prop, that engine should come apart. On a bench, not in flight:)
 

wsimpso1

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So, starter and cylinder bases work well for mag base anchors. Good to know - I can buy a Noga mag mount and indicator.

I am still unclear on what to put a wrench or screw driver on the turn the crank... Do you just put a long bar through between the hub and the prop bushings? What fastener would you put a wrench on? Remember, the prop and strarter gear are off the engine at the boneyards.

Billski
 

Victor Bravo

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I am imagining that you can use a leather/canvas "belt style" strap wrench (carefully) around the very outside edge of the prop flange to spin it slowly and deliberately. I have to think that the long bar through the bolt bushings is the wrong way to spin it, and will try to bend the flange in some way that affects the measurement.

You can probably take a two or three foot piece of square steel tube and ratchet-strap it or clamp it underneath the two cylinders on one side of the engine, such that one end of the tube extends forward of the prop flange. That way, it's a short, straight line between the magnetic mount and the flange, which would give you a more solid measurement.

ALL of this advice is theoretical, I am not an experienced engine rebuilder.
 

BBerson

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Here is a video for runout. Don't think video checks for bent flange. He should be checking the face.
 
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Dan Thomas

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I am still unclear on what to put a wrench or screw driver on the turn the crank... Do you just put a long bar through between the hub and the prop bushings?
Yup. That's what I do. With the plugs out there's little resistance. You can use a bigger open-end wrench for it, hooking the open end under a bushing with the wrench angle facing away from the hub. Don't overthink it.

Remember to push inward a little on the crank so it doesn't wander in and out and give alarming readings.
 

TFF

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I have put the box end of a large wrench on one of the prop bushings and pulled it through and I have used a large screwdriver or pry bar laced in the bushings to push or pull through. If you are having to fight to spin an engine, the cylinders are probably rusty. There it’ll be times at tdc Of any cylinder where it may be a little sticky because the rod is changing sides but other than that it should be smooth.

I check it a bunch of times. Like the bulletin, and I will do it on any flat surface like the rear and front of the prop flange too. I did my engine with no defections. And also checked it when I had it ground. The last one I did was probably iffy when the guy bought it. Unluckily he nosed over taxing before his first test flight to find it. Master cylinders had parking brake system that locked unexpectedly. New wood prop destroyed. So was the morale.

The real thing to note is a crank is just about perfect from the factory. Any more than a track of .001 has sustained a a bent flange. They are either perfect, within tolerance but bent, or out. They don’t leave the factory at a high tolerance.
 
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