Author Topic: Crank Shaft (Read 3399 times)

john e. holliday · « **on:** April 13, 2011, 05:18:47 PM »

I need help, but not that kind of help. Looking thru the Tower site, they only list a crakshaft for the LA/FP OS 35-40. I need a shaft for the LA .46 that used to be in my P-39. The shaft is just barely noticable, but I can see it is not true when clamped to the bench and slowly rotated. Thanks ,

Randy Powell · « **Reply #1 on:** April 13, 2011, 05:31:08 PM »

Doc,

Might try this: http://www.osengines.com/parts/discontinued.html

jim ivey · « **Reply #2 on:** April 13, 2011, 06:09:35 PM »

well doc ya know us old guys don't bs eachother others maybe but never us. if you have access to a lathe with a 5-c collet attachment. a mag base with dial indicator and a nylon or rubber mallet, a light one. stick the threaded end in the collet and close it adjust it so its tight rnough to hold it rotate it by the adjustment collar in nuetral. bump the high side with that mallet till it looks pretty true. DON"T HIT IT! they bend easy. once it looks pretty good open and reclose it in the collet then put the indicator as close as you can get to the crank throw on the shaft journal.turn it by hand and check run out bump it lighly on the high side untill it runs true. its only the threaded part thats bent. If you know someone who has a mach shop. and he knows what to do cool. if he dont' show him this. he'll say "oh ok I get it". ( Its an an easy fix, 1/2 hour or less) jim

Russell Shaffer · « **Reply #3 on:** April 13, 2011, 06:14:21 PM »

Jim has the plan. I did an Enya 29 the other day, but I just used the three jaw chuck. The cranks are soft and bend really easy. He's really right about not hitting it.

Jim Kraft · « **Reply #4 on:** April 13, 2011, 06:25:19 PM »

I have straightened a few with the mallet. A couple of thousands of runout won't make much difference. I bent a McCoy 40 Red Head shaft so bad I could not straighten it. My son is a machinest, and he drilled out the shaft and tapped it for a stainless stud. Works great, and if I ever bend it again, I can just replace the stud.

Marvin Denny · « **Reply #5 on:** April 13, 2011, 06:49:40 PM »

It is good to hear this information--- I got an OS LA 46 shaft that looks like the figure L on the threades end. It will probably break before it gets straight.

Bigiron

Air Ministry . · « **Reply #6 on:** April 13, 2011, 07:07:42 PM »

Then use oxyacetalyne on it !

. Doc, sounds like youd put the prop end in a chuck & spin the other .

Shades of a pressed together motorcycle crank . A (large) mallet is used to align the Flywheels , with
the shafts sitting on ' centres '. Kwakersikis apparently suffered n the H2Rs or whatever from haste there.

Then theres the frame straightening with a rubber Sledge Hammer . ~^Dont volenteer to hold the frame.

Greg L Bahrman · « **Reply #7 on:** April 13, 2011, 07:28:38 PM »

Well Matt you made me laugh....Back in the sixties my Bultaco had a pressed together crank and we beat on them also for alignment after a rebuild.

John Tate · « **Reply #8 on:** April 13, 2011, 07:39:37 PM »

What I have seen lately is that the threads are not cut true to the diameter of the shaft (off center) on the last batch of LA 46s. The Tower 40 cranks were made better. I would replace the LA 46 shaft with a Tower 40 shaft (if you can find one).

John Tate
Norfolk Aeromodels

jim ivey · « **Reply #9 on:** April 13, 2011, 07:44:04 PM »

heck ive done them in a #3 jacobs drill chuck,but very carefully. I never saw one I couldnt straighten, but maybe. Hi loved it when I'd straighten a bent shaft on a repair. he could charge for a new shaft they didnt even get, well i guess they did!

jim

Brett Buck · « **Reply #10 on:** April 13, 2011, 08:10:31 PM »

Quote from: Jim Kraft on April 13, 2011, 06:25:19 PM

I bent a McCoy 40 Red Head shaft so bad I could not straighten it. My son is a machinest, and he drilled out the shaft and tapped it for a stainless stud. Works great, and if I ever bend it again, I can just replace the stud.

The RO-Jett is like that, and I can attest to the fact that running it full speed into the pavement will only bend the stud.

Brett

Bill Heher · « **Reply #11 on:** April 13, 2011, 08:31:56 PM »

I've got a piece of 3/4 X 3/4 inh bar stock with a hole drilled in it to match the front journal dia f a Fox .35. It has a piece of 3/4 angle iron welded to it with a tapped hole for a 3/8" bolt that aligns vertically with the center of the crank hole in the square tubing.

You just slide the crank in, put the hih point under the 3/8" bolt and tighten it to press on the crank stud.

Cost was $0, and I'm sure you could drill another hole on the other side of the angle iron and have it for 2" crank dia.

If I was home I'd take a pic - but it is about as simple as it gets. Harder to describe than to make.

Dennis Moritz · « **Reply #12 on:** April 13, 2011, 11:27:41 PM »

Are the cranks the same dimensions or different on the FP40s, LA40 and LA46s? Or will a 40 crank in a 46 make the 46 a 40. I believe the FP35/40 crank has the same dimension as an LA40 crank. I think the FP cranks are machined forgings, while the LA cranks are cast. Perhaps it's possible to swap. I know the difference between an FP35 and an FP40 is piston/cylinder diameter. Is that also true for the LA40/46. Junker FP40/35s are around. I've bought them for $15, even less. Just bought a Tower 40, for that matter, for $4. The Tower after I unstuck it is a keeper. Any of these engines might be a possible source for a crank.

Come to think of it, the LA40/46 must use the same crank. Because it uses the same crankcase. (I THINK!)

Geoff Goodworth · « **Reply #13 on:** April 14, 2011, 02:58:46 AM »

Dennis wins the prize.

The cranks for the FP 35/40 and the LA 40/46 are the same. The LA crankcases have different part numbers but the external dimensions are the same.

I think the LA liners are different ODs.

dennis lipsett · « **Reply #14 on:** April 14, 2011, 03:54:44 AM »

Quote from: John Tate on April 13, 2011, 07:39:37 PM

What I have seen lately is that the threads are not cut true to the diameter of the shaft (off center) on the last batch of LA 46s. The Tower 40 cranks were made better. I would replace the LA 46 shaft with a Tower 40 shaft (if you can find one).

John Tate
Norfolk Aeromodels

The Tower 40 was superior to the OS40FP in every way including quality. Perhaps that explains why it is no longer available from the company, (Great Planes), that imports OS.
Dennis

Phil Coopy · « **Reply #15 on:** April 14, 2011, 06:55:11 AM »

The LA40 and LA46 cranks are the same. The 46 has more vibration because it uses the same crank (with the same counterweight) but the piston is quite a bit heavier causing an out of balance condition. I have experimented with pressing a tungston (heavy metal) slug into the counter balance and it helps some.

Phil

Dennis Moritz · « **Reply #16 on:** April 14, 2011, 07:43:20 AM »

I'm a fan of Tower 40s. The real chrome liner as opposed to the nickel simulation(?) is a harder longer wearing surface. At least it seems that way. Towers that I've used hard for years retain wicked compression. There are subtle differences as well. I think there's a bit more cooling fin area on the Tower 40 heads, also the combustion chamber looks shallower on the Tower. The head gasket on the T is .010 whereas as the OSs use an .015 shim. Machining appears nicer on the Tower. However, at least one, T I bought had flashing cast. Knocked it off, no problem. I've actually gotten Towers (3 head gaskets) to do a decent 4x2 break.

Cannot swap p/l between the LA and FP series.

Bill Little · « **Reply #17 on:** April 14, 2011, 10:07:38 AM »

Quote from: john e. holliday on April 13, 2011, 05:18:47 PM

I need help, but not that kind of help. Looking thru the Tower site, they only list a crakshaft for the LA/FP OS 35-40. I need a shaft for the LA .46 that used to be in my P-39. The shaft is just barely noticable, but I can see it is not true when clamped to the bench and slowly rotated. Thanks ,

Hi Doc,

Sounds like the guys have solved the problem. The LA/FP 40 crank is the same as the LA .46 crank, so you are good to go. I guess.............

Big Bear

FLOYD CARTER · « **Reply #18 on:** April 14, 2011, 10:44:54 AM »

I was horrified when my Elfin 2.5 went in and bent the crankshaft threads. So I sent the motor to Don Blackburn to have a new crank made or fitted. What do you know? It came back with a note saying that he replaced the threaded stud. He didn't have the proper thread in a hardened stud, so he used a hardware store bolt, cut off.

It didn't look like a replaceable stud. That one fooled me.

Floyd

Will Hinton · « **Reply #19 on:** April 14, 2011, 11:15:40 AM »

The RO-Jett is like that, and I can attest to the fact that running it full speed into the pavement will only bend the stud.

Brett

Brett, may we ask just how you became privy to that information?

Brett Buck · « **Reply #20 on:** April 14, 2011, 11:19:38 AM »

Quote from: Will Hinton on April 14, 2011, 11:15:40 AM

Brett, may we ask just how you became privy to that information?

Well, truth be told, it was a team effort. But that's also the engine that won the NATs 2 years later, after once again testing the theory on the dirt on the 600x600 pad.

Brett

Steve Fitton · « **Reply #21 on:** April 14, 2011, 12:26:20 PM »

Doc is you can't get it fixed send me a message, I probably have a few spare ones lying around not doing anything.

Will Hinton · « **Reply #22 on:** April 14, 2011, 04:40:14 PM »

"Well, truth be told, it was a team effort. But that's also the engine that won the NATs 2 years later, after once again testing the theory on the dirt on the 600x600 pad."

Brett

A good testament to the success of the design!

Garf · « **Reply #23 on:** April 14, 2011, 10:37:50 PM »

This is from the official Tower site.

Geoff Goodworth · « **Reply #24 on:** April 15, 2011, 02:08:48 AM »

Phil Coopy, what is the tungsten that you use? I note that several others do the same and grind a bit off forward of the crankpin.

john e. holliday · « **Reply #25 on:** April 15, 2011, 09:55:31 AM »

Thanks for all the info guys. Back in the day I would box up the old Fox and send it to them. Will try the small mallet on it.

Ward Van Duzer · « **Reply #26 on:** April 15, 2011, 10:37:06 AM »

Send your bent cranks to Randy Smith. He has a world class collection bent crank collection

W. !