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Stihl MS660 big bore conversion.

Old 11-26-2015, 05:11 PM
  #76  
ZAGNUT
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would be nice if the 10mm spigot was bored and taped for a small clamping screw to hold the prop.

having the 10mm spigot integral to the jig is a much better idea than tapping the jig for an M10 screw.
Old 11-27-2015, 12:00 AM
  #77  
Jim.Thompson
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Originally Posted by ZAGNUT View Post
would be nice if the 10mm spigot was bored and taped for a small clamping screw to hold the prop.
That's a neat solution!
having the 10mm spigot integral to the jig is a much better idea than tapping the jig for an M10 screw.
For sure.
I've started it. Just need to machine the large spigot and then set out the centre punch points for the six retaining screws before boring the holes.
Old 11-28-2015, 05:24 PM
  #78  
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I had to abandon my first attempt at this as I have machined the 10 mm spigot too small. Also, the piece of stock I started with was not long enough for me to machine the larger spigot on the hub end. So I will get some more stock next I'm in town.
The 10mm spigot also only needs to be short, perhaps 6 or 8 mm. I will make up a washer with 10mm spigot through which the 5 mm retaining screw will go through, to centre it in the prop centre hole while drilling the six retaining screw holes.
Old 12-04-2015, 03:17 AM
  #79  
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Whats a Spigot? Are you talking about the prop adapter?
Larry
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Old 12-04-2015, 11:03 AM
  #80  
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Originally Posted by Larry882 View Post
Whats a Spigot? .................
From the Free Dictionary:
". (General Engineering) a short cylindrical projection on one component designed to fit into a hole on another, esp the male part of a joint"
In this case, the 10mm projection on the prop hub that fits into the propellor when using it to drill the holes in the prop. Similarly, the larger 25 mm that fits into the propellor hub when drilling it for the tapped holes to receive the machine screws.

I'll post a screenshot of the drawing of it later when the site is working better. Sometimes with my poor line speed, it just does not work.
Old 12-23-2015, 10:00 AM
  #81  
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I need a prop adapter for a stihl 65cc 4-mix engine Anyone have one or want to make one to sell? Thanks Kevin
Old 12-23-2015, 10:41 AM
  #82  
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Whats a 4 MIX engine? Does it have a 5/16" 24TPI thread? Post a picture of what your looking for. I can make you one.
Larry Kopecky
Conyers, Georgia
Old 12-23-2015, 10:53 AM
  #83  
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Larry, It's out of a stihl br600 back pack blower. It's a 4 stroke engine that runs on mixed gas. I have not measured the crank thread yet, But I think its 11mm (odd ball). email me at this address. [email protected] and I can send you some pics. (I can't see how to add them here) Thanks Kevin
Old 12-23-2015, 10:58 AM
  #84  
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Lets see if this worked (the first photo is where the flywheel goes)
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Old 12-24-2015, 04:25 PM
  #85  
Jim.Thompson
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Hi Kevin. Do you realise what is meant by a thread highjack? I think your posts above constitute one. Try opening your own thread with a descriptive title and you will received more responses and I will have my thread back on the subject of this engine build. No offense implied.

Meanwhile I have made some progress with the machining of the engine parts. The pictures speak for themselves, so to say. The only one that has me a bit intimidated is fitting the centering spigot/plug to the prop drive. It fits very nicely for part of its length, but won't go in further without some force; I am reluctant to push it, as it might pick up the soft aluminium and create more of a problem. I did try spinning it in the lathe with a piece of 100 grit sandpaper on my finger, but did not seem to take out sufficient to alloy the plug to go all the way in. I am very reluctant to chuck it up again and machine more out of it, but cannot see an alternative at this stage. So far, all the machined parts I've made have been serviceable on my first attempt. I've surprised myself with the good results!
Any ideas for this?


It seems like my internet link is not working well enought to accept pictures; I will post them later, maybe in the morning.
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Last edited by Jim.Thompson; 12-25-2015 at 01:16 AM.
Old 12-27-2015, 11:06 AM
  #86  
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maybe removing the hub from the mandrel put a scratch inside? air not escaping due to oil on the parts? that would feel spongy and not a hard stop though.

is the plug steel or aluminium?

and what wall thickness do you have on the rear end of the hub where it was turned down?
Old 12-27-2015, 12:57 PM
  #87  
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The plug is aluminium. The same grade as the prop hub.
The wall thickness of the hub is 3.5 mm.
Old 12-30-2015, 03:23 PM
  #88  
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The crankcase has been assembled with the new bearing and seal. The engine mounting standoffs (ex Hobbyking!) seem to be good and are now fitted on the crankcase studs. Locktight on all threads.
I have to machine up a mounting disc on which to mount the CDI hall sensor. Also, I have to machine up a prop retaining plate to go on the front of the prop through which the retaining screws will pass.
Getting close to completion now. Might be ready for a bench start up in a week or two!

Question:
Is cheap vinyl tubing suitable for the line from the crankcase to the carburettor?
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Old 01-01-2016, 01:12 PM
  #89  
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fine as long as the tubing doesn't harden and leak at the barbed fittings with exposure to the fuel. small spring clamps would be good insurance.

i really would have left the hub full diameter for its full length. the stress riser mentioned in post 70 does come into play now. this isn't the type of part that you can periodically check for cracks, only failure mode here is catastrophic.....and if it does fail it can do some very serious damage. proceed with caution and maybe get someone with engineering credentials to look it over.
Old 01-01-2016, 03:10 PM
  #90  
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Originally Posted by ZAGNUT View Post
fine as long as the tubing doesn't harden and leak at the barbed fittings with exposure to the fuel. small spring clamps would be good insurance.
I'll do that. Also, it could be replaced once a year or so when it hardens etc.
i really would have left the hub full diameter for its full length. the stress riser mentioned in post 70 does come into play now. this isn't the type of part that you can periodically check for cracks, only failure mode here is catastrophic.....and if it does fail it can do some very serious damage. proceed with caution and maybe get someone with engineering credentials to look it over.
I have had my mechanic/engineer friend to look at it as a matter of fact. He is the most informed and experienced person I know in this field. I thought it was too thin too, however, he is of the opinion it is plenty strong enough. I know where I can get a second opinion at some later date when I meet up with another flying friend.
You have got me thinking further about it though. I could machine up another one I suppose.
Old 01-01-2016, 05:26 PM
  #91  
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I will try to post a screenshot of the revised drawing. I'm not sure it will work, as I have a file permission problem currently in my operating system.
But here goes:
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Old 01-02-2016, 06:08 AM
  #92  
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there have been quite a few hub failures with the cheap RCGF engines where the wall thickness was around 2mm. these are smaller engines from around 20cc to 45cc and no idea what alloy was used.

it's not all about the power being transferred but HOW it's being transferred....a sharp hammering pulse every revolution.....constantly accelerating and decelerating. if the carb is out of tune that hammering can get much worse. and then on the other end a big stick that will never be perfectly balanced statically or dynamically and constantly fighting gyroscopic forces as well. a good comparison is how the sockets designed for use with impact wrenches have a much thicker wall even though the final torque being applied might be much less than with a regular ratchet handle.
Old 01-02-2016, 08:50 PM
  #93  
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You have convinced me Zagnut. I will machine another one.
However, the only thing I would question is your comment @ post #89 regarding leaving the hub at full diameter for its length. That seems a bit excessive to me, but I welcome further clarification and comment. I might get access to the lathe again tomorrow and if I have enough stock left, I could machine another one then.
Old 01-04-2016, 11:30 AM
  #94  
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if you neck it down to 40mm then you're only saving ~40g....and then you have to worry about where the holes for your prop screws are going to end up.

with the rear of the hub at 32mm like it is now you would not want to drill past your 18mm thick flange and that means messing with blind holes.


easy way to avoid the mess of tapping blind holes for the prop screws is to go all the way through (front to back) with the 5mm hole and then from the back of the hub counterbore with a 6.5mm bit leaving about 15mm of 5mm hole at the front for tapping for your M6 screws. to do this with a 35mm bolt circle you would need the hub to be no less than 44mm......may as well leave it at 48mm for the whole length.
Old 01-04-2016, 12:46 PM
  #95  
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I now realise that the hub can be shorter than my first one - possibly 32 mm. I will draw it up later.
Old 01-05-2016, 12:52 AM
  #96  
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shorter is always better but be sure to leave enough depth for the prop centering plug to stay nice and square with the clearance it has....i'm sure there are charts out there for that kind of thing but i would just guess that 15mm would be a safe minimum and then go with 20mm just for peace of mind. and don't forget to account for the thickness of the washer and the length the threaded nose on the crank.
Old 01-05-2016, 01:15 AM
  #97  
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I was thinking of making it 20mm plus nut and washer, as a matter of fact. I have no washer yet. If the size available is too large OD, I may have to machine a rounded edge on it to fit the rounded interior of the counterbore. I'll see what I have in stock.
Shorter better due to less cantilever on the crank etc.

The drawing attached is from one of my engineering/model builder/flying buddies for the hub.
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Old 01-05-2016, 05:06 AM
  #98  
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that looks more than adequate but will still have the mess of tapping blind holes for the prop screws. with the 18mm thick flange at front you will be lucky to get 14mm deep threads and you will want a spiral fluted tap to do it with. really just a personal preference of mine....i HATE tapping blind holes.

good flat and hardened washers can be found under automotive head bolts/studs. the ones at the hardware store next to the carriage bolts are useless....
Old 04-12-2016, 04:31 PM
  #99  
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I was able to get back to the lathe and machine up a good hub following the drawing above. Half way though machining the taper, I realised why I was having such difficulty with the taper changing each time I did a very slight cut. The transverse slide on the tool carriage was wobbling! It has a good .5 mm slop from side to side which made the angle I was setting (and constantly changing), variable and somewhat arbitrary. I became aware of this just in time to save this hub (attempt #3) and to machine the taper with a clamp on the cross carriage to hold it in the same place each cut. In hindsight, this is why attempt #2 was a failure.
I am assuming there might be some kind of backlash adjustment on the slide for this sloppy carriage. If not, we will have to investigate some repair or other.

I have been working on a mock up of the pickup hall sensor mount. Alternatives are to make it out of welding grade aluminium and get a proffessional to weld it for me, or to make it in steel and weld it myself. I need extra weight up front anyway.

This is purely an academic question: Could the propellor hub be made out of steel? This model will need more weight anyway, so if it would be suitable, and I was doing it again, I would do it in steel.

I'll post a picture later; the site is not cooperating at the moment.
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Old 04-21-2016, 04:47 PM
  #100  
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I quickly found the dovetail slide adjustment for the lathe. I adjusted it up and it now has zero slop.
I am in the process of tapping out the 5 mm holes in the prop hub. Not experiencing any difficulty, however, I am withdrawing the tap at about half way and blowing out the swarf with compressed air. Finish with a plug tap at 18 mm depth minimum.
My flying buddy John Garland of Garland engineering, Singleton, NSW Australia machined me up two excellent drilling guides on his CNC lathe. That was a task I was not looking forward to doing myself. Two sets of holes, one set at the 4.2 mm tap drill size and one set at the 5 mm clearance size.
Many thanks to John!
I have made a little bracket to mount the hall sensor. All I need to do is to machine up a prop centreing spigot, assemble everything and devise a strong safe bench mount before giving it a start. Oh, and there is the timing and fitting of the magnet in the prop hub to do also. The only magnets I have are very small, perhaps 3mm. Will they be big enough?


I'll post the pictures later when the site responds better.

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