Doll 360/3 Annoying Knock

• Doll 360/3 Annoying Knock
  Posted by Nick on 20 Jun, 2020 20:08
• Any tips for curing this knocking? At first I thought the screws were going in too far and being hit by the pistons as the decorative caps were dented in a little... I was able to round them back out with a wooden dowel and hammer
  
  Runs quietly with the screws out, but any back pressure and the knock gets quite loud 
  
  https://youtu.be/Y9vD83Q_Ac0
  
  
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• #1 Reply
  Posted by yozhek on 21 Jun, 2020 02:50
• Hi Nick,
  
  That is quite violent at higher pressure
  Just a thought, can you retard the timing of the steam valve? As you know i know nothing about steam but looking at the rather insubstantial crank and bearings i hazzard a guess there is a fair amount of free movement there to create knocking if the timing is too advanced. Or maybe the crank has got bent in the centre where it is unsupported upsetting the timing?
  Apologies for sticking my nose in if you have already tried this
  Best wishes
  Ade
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• #2 Reply
  Posted by Nick on 21 Jun, 2020 21:53
• Quote from: yozhek on 21 Jun, 2020 02:50

  Hi Nick,
  
  That is quite violent at higher pressure
  Just a thought, can you retard the timing of the steam valve? As you know i know nothing about steam but looking at the rather insubstantial crank and bearings i hazzard a guess there is a fair amount of free movement there to create knocking if the timing is too advanced. Or maybe the crank has got bent in the centre where it is unsupported upsetting the timing?
  Apologies for sticking my nose in if you have already tried this
  Best wishes
  Ade
  

  
  Thank you for the help Ade, and yes it is a very violent knock. I have taken it apart enough to adjust the timing, unfortunately it's a toy and many of the parts are pressed on, so changing the timing is going to be a little more difficult than I had hoped...
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• #3 Reply
  Posted by parallelmotion on 22 Jun, 2020 06:56
• Nick,
  Maybe you could use slo mo video to figure out what's causing the knocking. Could be some wear/slop in the holes in the con rods that ride on the crankshaft--they tend to get oval-shaped over time. Another place to look is wear in the con rods where they join the piston rods. In either case the best fix would be to make new rods, although reaming and bushing them might also be possible. If there's this kind of wear you should be able to see and feel it.
  Brent
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• #4 Reply
  Posted by Dan-c on 02 Jul, 2020 15:20
• Sounds like big end knock are the ends worn oval ?
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• #5 Reply
  Posted by Tadfafty on 02 Jul, 2020 22:22
• Something worn being moved by the pressure?
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