The Raven

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?!"

Rudolph Hart

Rudolph Hart

Hi bruce you can be a dead set funny bugger sometimescheers mate

Hobbsy

My Feedback: (102)

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.

hsukaria

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.

blw

My Feedback: (3)

Sometimes it's only a few thousands.

Quikturn

My Feedback: (12)

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

FNQFLYER

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&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.

hsukaria

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).

FNQFLYER

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?

Quikturn

My Feedback: (12)

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.

rye

My Feedback: (10)

hey guys
going to use a satio 56 on my G-P goldberg ann cub kit what size prop size should i uses,thanks

FNQFLYER

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.

FNQFLYER

Spelling glitch again that should read 12 x 6 MAS prop

Rudolph Hart

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.

hsukaria

All this "dropping" engines makes me believe that there was some "sauce" involved, eh?

Quikturn

My Feedback: (12)

That's funny!

No, it was just a boneheaded move on my part. Just got to be more careful sometimes.

hsukaria

I have done some stupid things while carrying my planes.[&o]

flyingagin

blw

My Feedback: (3)

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.

FNQFLYER

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.

flyingagin

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

JohnB96041

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.

Quikturn

My Feedback: (12)

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.

Quikturn

My Feedback: (12)

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.