Author Topic: 25 cc Horizontal Engine  (Read 83836 times)

Offline Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: 25 cc Horizontal Engine
« Reply #285 on: June 25, 2016, 08:27:54 PM »
I filed some teeth on the broach with a triangular Swiss file and then trimmed the gear to length and made a recess for the fixing nut with an 8mm end mill. The broach went through fairly easily with frequent withdrawals to clear the swarf. It all seems to fit together so I now have to file up a 2mm stainless steel key, probably from a piece of rod.

I then mounted the piston in the lathe and polished off the pickup marks, removing a couple of hundredths of a mm.
Best regards

Roger

Offline Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: 25 cc Horizontal Engine
« Reply #286 on: June 25, 2016, 08:35:52 PM »
Next I needed to make some more piston rings. I had 2 unbroken blanks from the first batch and enough of the CI rod left to make another 2. Luckily the piece went back in the 3 jaw chuck sufficiently on centre to use.

The blanks were broken with a pair of side cutters and fixed in the heat treatment jig. I heated them to a dull read for around 5 mins. Once again they grew a little. I wasn't so lucky in getting the skimming jig to centre and had to mount it in the 4 jaw independent chuck. The first two rings fitted without breaking  :whoohoo: so I now have two spares.

I reassembled the piston and rod and there seems to be adequate compression  :)
Best regards

Roger

Offline Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: 25 cc Horizontal Engine
« Reply #287 on: June 26, 2016, 05:20:24 PM »
I filed a 2mm key from a piece of 3mm stainless steel rod, put the water pump back together and refitted it ready for the next trials (or disasters  ::)  )
Best regards

Roger

Offline Admiral_dk

  • Full Member
  • *****
  • Posts: 3752
  • Søften - Denmark
Re: 25 cc Horizontal Engine
« Reply #288 on: June 27, 2016, 10:47:37 PM »
Looking good so far  :ThumbsUp:

Offline zeeprogrammer

  • Full Member
  • *****
  • Posts: 6811
  • West Chester, PA, USA
Re: 25 cc Horizontal Engine
« Reply #289 on: June 27, 2016, 11:56:40 PM »
Looking good so far  :ThumbsUp:

Yep. I'm following along too.  :popcorn:
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Offline Art K

  • Full Member
  • ****
  • Posts: 1761
  • Madison, Wisconsin USA
Re: 25 cc Horizontal Engine
« Reply #290 on: June 28, 2016, 04:43:11 AM »
Rodger,
I am starting to suspect that the plastic gears have a larger expansion rate when they heat up.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King

Offline michaelr

  • Full Member
  • ****
  • Posts: 163
Re: 25 cc Horizontal Engine
« Reply #291 on: June 28, 2016, 09:26:40 AM »
I have just made a gear water pump for my Centaur Gas engine, I used Hostaform gears (Delrin) the pump works good until the water flow gets warm and the belt drive starts slipping I put this down to a problem with the belt itself.

But reading Art's suggestion that it could be a expansion problem with the gear material when warm, I looked up Hostaform Gears and found they have a Maximum  operating temp of 90 degrees Centigrade, now I don't know if my engine gets to this temp but I think Art may well be on the right track.

I think I will try a change of gears to either Brass or Stainless.

Mike.

Offline Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: 25 cc Horizontal Engine
« Reply #292 on: June 28, 2016, 12:40:08 PM »
Thank you for your interest and thoughts  :ThumbsUp:  :ThumbsUp:

I looked up the coefficients of expansion for Hoastaflon, ~1 E-4 /K, and aluminium, ~2.3 E-5 /K. Taking a temperature rise of 100K for the gear and 80K for the body (assuming it will lose some heat to the surroundings) the clearance for the gear diameter will be reduced by around 0.1mm and for the width by around 0.07mm. The bores in the body are ~0.05mm over nominal so if the gears are a little under nominal it should be ok. I need to check the axial clearance as that is where there may be a problem. I have ample water flow so increasing the clearances a little should not be a problem. They will also close up when everything is hot and the cooling is most needed.

The data sheet I have states that the gears are usable under light loads up to 140°C.
Best regards

Roger

Offline Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6133
  • Switzerland
Re: 25 cc Horizontal Engine
« Reply #293 on: October 20, 2016, 08:56:12 PM »
The axial clearance on the water pump gears was close to zero so I increased it to ~0.1mm. This survived the fuel injection trial but I will have to see how it copes with a full load run  ::) As winter comes the possible running time reduces  :(
Best regards

Roger

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal