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Old 02-21-2013, 02:17 AM
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ORIGINAL: rebranger

Bent Cranks:
I wonder if metal has a ''memory'' ? Anybody know? Something scientific, data, tests, studies?
I think it does..sometime all is takes is one lick (hit) in the right spot & Wala! They're back straight..Go Figure??
Depends on a number of factors but it's not unusual to straighten engine parts.

Many moons ago (pre-internet) I worked at an automotive engine rebuilding company and we used to straighten bent cam shafts. These weren't 'modern' engines and the straightening wasn't very scientific. Still, it worked better than you'd believe.

V blocks, a dial indicator, and a special 'whacker'. The trick was to find where the bend was and know how much force to hit it with. This was on cast iron cams, which we never managed to break.

It definitely worked, as I occasionally had the job of fitting new cam bearings. If you have a bent cam, you'll know about it when you try to fit it into new bearings. Don't ask what the solution was to that, equally crude but very effective...

For me, the big question has always been "How do you bend a cam in the first place?!"
Old 02-21-2013, 04:46 AM
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ORIGINAL: flyingagin

Quikturn, that was Flyboy Dave<span style=''font-family: tahoma, verdana, arial; font-size: 11.333333015441895px; background-color: rgb(251, 252, 255);''> who was fixing bent cranks.
</span>
Here is the thread.
http://www.rcuniverse.com/forum/m_69...tm.htm#6948801

But on post 347 He states he is not fixing bent cranks anymore, the very last post in the thread. That was <span style=''font-family: tahoma, verdana, arial; font-size: 11.333333015441895px; background-color: rgb(247, 250, 255);''>3/24/2012

It maybe tedious, but does not sound that hard to do.
</span>
Ken
Well to do it well..it is



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Old 02-21-2013, 04:51 AM
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Hi bruce you can be a dead set funny bugger sometimescheers mate
Old 02-21-2013, 05:33 AM
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The secret to getting the crank as straight as original is to bend it beyond straight in the straightening direction and then let it spring back to straight. This takes much practice which is not going to happen often enough to get good at it. It is pure stroke of luck to get it just right.
Old 02-21-2013, 08:48 AM
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I can see where hammering a forges piece of metal like a crankshaft can help with bending. But I can't imagine how a cast iron camshaft that is bent can be straightened out without inducing some cracks. Cast iron is very brittle, unlike forged steel.
Old 02-21-2013, 09:21 AM
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Sometimes it's only a few thousands.
Old 02-21-2013, 12:28 PM
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ORIGINAL: flyingagin

Quikturn, that was Flyboy Dave<span style=''font-family: tahoma, verdana, arial; font-size: 11.333333015441895px; background-color: rgb(251, 252, 255);''> who was fixing bent cranks.
</span>
Here is the thread.
http://www.rcuniverse.com/forum/m_69...tm.htm#6948801

But on post 347 He states he is not fixing bent cranks anymore, the very last post in the thread. That was <span style=''font-family: tahoma, verdana, arial; font-size: 11.333333015441895px; background-color: rgb(247, 250, 255);''>3/24/2012

It maybe tedious, but does not sound that hard to do.
</span>
Ken




<br type=''_moz'' />
Ken,

That was it. Too bad he stopped doing them but it was very generous of him to offer his services in the first place.

The crankshaft I bent was on an OS Max 40H engine and finding a new part was next to impossible. I ended up straightening out myself and like you say, it was tedious but not very hard. The hardest part IMO is detecting the offset and figuring out where to hit it. If I remember correctly, I had the prop nut on the end to elevate it and for thread protection, and used a heavy hammer and a hardwood block against the crankshaft.

The crankshaft still had a very slight wobble to it but the engine ran just fine.

Joe
Old 02-21-2013, 02:35 PM
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Sorry old fart, Quickturn, re OS 40Hs they are a popular engine for one of the O/T events here in OZ.  I actually have a number of those crankshafts stored against bad days at the field (bought from "broke" hobby shops) and yes I have straightened various cran and cam shafts.  Bent cranks usually come about because of impact with something solid, cam shafts can bend due to poor metal, combined with not being supported at suitable points along its length.  I won't bore people with examples and fixes (even P&amp;W round engines had their moments) but in conclusion I ask given the cost of the bit combined with the problematical success of the effort put into straightening these cranks why bother??  I your object is to get the engine running again (and you have to consider damage / distortion to the crank case here) buy a new one if your object is to resurect a damage piece of goods go for it.  Isn't what this is about.
Old 02-21-2013, 02:56 PM
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Are these crankshafts heat treated also? Or just forged (cold worked)? It may be that you have to anneal the shaft, straighten it, and then heat treat it. Of course, that is all I remember from my school days regarding metallurgy (I didn't like that class anyway).
Old 02-21-2013, 04:02 PM
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Re the metalurgy of the various crankshafts, you really have to refer to the manufacturer, most are drop forgeed and the machined, though some are cold formed and hardened.  On that note I have discovered that Ford here in OZ cold form the crown wheel and pinion for the differentials on the current B series Falcon.  That is the reason why they only last around 100,000kms before needing replacement.
As I said previously why bother?
Old 02-21-2013, 04:50 PM
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Why bother?

Because I'm a cheap ***** and I like to fix things.

Actually, I had it on a test stand before installing in the airplane and I dropped it somewhere in that process. It wasn't too much work to get straightened out a bit.
Old 02-21-2013, 05:54 PM
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hey guys
going to use a satio 56 on my G-P goldberg ann cub kit what size prop size should i uses,thanks
Old 02-21-2013, 06:41 PM
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I used a 12 x6 MAS a few years ago. It was on a Saito 50 though. A couple of suggestions for te Cub. Cut the strip ailerons down with a ration of 1/3 lenght to use as Aileron 2/3 for flaps. I had a servo for each aileron and I used the original aileron horns joined together and used a single servo for the flaps..
Improved the handling no end the best bein a reduced tendency to tip stall.
Old 02-21-2013, 06:42 PM
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Spelling glitch again that should read 12 x 6 MAS prop
Old 02-22-2013, 05:02 AM
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ORIGINAL: Quikturn

Why bother?

Because I'm a cheap ***** and I like to fix things.

Actually, I had it on a test stand before installing in the airplane and I dropped it somewhere in that process. It wasn't too much work to get straightened out a bit.
Say what?? you 'dropped it'.Did that once myself.Had a 115 screwed to some soft pine board while running it in.During the first full throttle run the engine took an unauthorised short cut and departed the engine mount,really exciting.
Old 02-22-2013, 08:53 AM
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All this "dropping" engines makes me believe that there was some "sauce" involved, eh?
Old 02-22-2013, 09:11 AM
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That's funny!

No, it was just a boneheaded move on my part. Just got to be more careful sometimes.
Old 02-22-2013, 11:04 AM
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I have done some stupid things while carrying my planes.[&o]
Old 02-22-2013, 03:17 PM
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<div><span style="font-size: 9pt; line-height: 115%;">Oh boy is that story familiar. Happened when I was teen,. Still have the scars from it deciding to go free flight right into my hand, and I had my hand well back from the engine. Stinking bloody guided missile it was!

Ken<br type="_moz" /></span></div>
Old 02-22-2013, 03:25 PM
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I dropped a new 2 stroke at work on a linoleum floor. It broke off several cooling fins in the cylinder head, and the remote needle bracket. Also bent the needle.
Old 02-22-2013, 06:24 PM
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I gave up on Fox engines becase they didn't / coudn't survive the "drop test".  I was constantly replacing needle valves / spray bars that got bent.
Old 02-22-2013, 06:41 PM
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I have not damaged an engine by dropping it, but in a cross country move I ended up with a busted off cooling head fin (1 one the edge of head). Been afraid to run it since then.
It is an OS .61. It has less than an hour on it.

Ken<br type="_moz" />
Old 02-22-2013, 07:05 PM
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I have a lot of OS engines. I would not be afraid to run it. Just set it a little rich if it only has 1 hour run time. It takes more that 1 hour to really break in an OS engine. After several hours of flying it will be time fine tune it.
Old 02-22-2013, 07:10 PM
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One broken fin shouldn't affect performance. If you had several fins broken on one side I could see a danger of warpage or over heating.
Old 02-22-2013, 08:52 PM
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I'd like to thank everyone for their replies to my question regarding the stripped out Saito 91 rear cover. What I ended up doing is just working the 3.5mm tap into the stripped out thread on the lower left side. It worked just fine and you can't tell once the screws are installed.

Now to clean up the crankcase a bit more before I install the new bearing set. Out of curiousity, is it preferred to install the bearing with the cage (ball bearing holder) ring facing the crankshaft? My thought is to install it this way as to contain the ball bearings in case the cage fails.
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