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rob.sollart
Member
Username: robsollart
Post Number: 6
Registered: 03-2012
| | Posted on Tuesday, May 28, 2013 - 09:10 am: | 
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Hallo
I'm doing an overhaul on a Stuart P5m.
I've put in new cranckshaft ball bearings and new lip seals. Now I have the cranckcase with cranckshaft clamped on the corner of my working table, no gearbox, no cilinder, ignition etc. only the flywheel. It turns very light, there's only a very little bit of friction from the lip seals.
While guiding the piston end of the con-rod up and down I give the flywheel a good turn, it keeps turning for a while until it stops. I wonder if anyone else ever did this, I did this several times now, and it puzzles me.
I would expect it to stop with the con-rod in top, at top dead centre so to say, because the opposit side of the crankshaft is thicker and heavyer.
But it never does.
It always stops at about 45 degrees after TDC.
(or if it stops somewhere else, it wants to go to 45 degrees after TDC )
In the manual they write about "a perfectly balaced flywheel".
So what I would like to know is:
Should I bring my flywheel to where they can balance it, or did Stuart intend it to be this way? |
J.B. Castagnos
Senior Member
Username: jb_castagnos
Post Number: 802
Registered: 07-2002
| | Posted on Wednesday, May 29, 2013 - 01:35 pm: |
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Momentum will carry it past BDC, try spinning it the other way and see what happens. |
Roger DiRuscio
Senior Member
Username: solarrog
Post Number: 541
Registered: 03-2002
| | Posted on Wednesday, May 29, 2013 - 01:51 pm: |
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Please remember the rod and piston have weight also, if you are spinning it without those items
you will not be able to see the balanced state.
It will always spin past the heavy point. If there was no resistance it would back up after stopping. The friction stops this from happening |
J.B. Castagnos
Senior Member
Username: jb_castagnos
Post Number: 804
Registered: 07-2002
| | Posted on Wednesday, May 29, 2013 - 07:19 pm: |
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If there are no counterweights cast into the flywheel it should be balanced. If you can find a large ball bearing place the flywheel on it and see if it has a heavy side, it doesn't have to be perfect, just get it close. |
Miah Gregory
Member
Username: mace
Post Number: 18
Registered: 05-2008
| | Posted on Thursday, May 30, 2013 - 06:41 pm: |
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Vaguely related, Rob, do you have the bearing and seal dimensions to hand?
Bonus points if you can point me at an online supplier. 
Cheers. |
rob.sollart
Member
Username: robsollart
Post Number: 7
Registered: 03-2012
| | Posted on Friday, May 31, 2013 - 05:01 pm: |
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Thank you all for your answers, and sorry for the delay, I haven't been near a computer for three days.
I tried spinning the other way, if it for instance stops at TDC ( BDC? ) then it wants to go backwards to that same point about 45 degrees after TDC in normal turning direction.
Yes, the piston has weight also, the side of the crankshaft opposite to the con rod is heavyer to act as a counter weight for that, so because the piston is off, it schould want to stop with this counter weight down I think.
I'll try to find a big ball bearing tomorow morning to see if there is a heavy side.
I had a test run a few weeks ago, the engine runs, but there was a lot of trembling and shaking going on.
Miah :
The size of the bearings can be seen in the manual, there is a guy in america who was so kind to put the manual online: www.scottleslie.net/ostkust/StuartP5Manual.pdf
bearings MJ1 1/8
I bought them on ebay from: webtraders online PT and bearings.
Perhaps they have the lipseals too, but I bought them from David Shofield who also posts on this Forum
I think it's allright to give this information here? |
rob.sollart
Member
Username: robsollart
Post Number: 8
Registered: 03-2012
| | Posted on Saturday, June 01, 2013 - 08:49 am: |
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Hi, I did the experment as sggested by J.B. Castagnos, couldn't find a big enough ball bearing, but I did find a big marble. It goes in halfway.
I put a big bolt upside in the vice, hit a little centerhole in the head of the bolt to stop the marble from rolling by itself, and yes: it has a heavy side, right there where it explains what I saw.
So thanks to your suggestion I was able to confirm my observation.
It's not nothing: when I lay three bolts with nuts 10mm 6cm long on the opposit side it is balaced.
So now I can go do something about it. |
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