Recovery of oversized sheaves

This topic has 6 replies, 4 voices, and was last updated 9 September 2020 at 16:03 by Tony Martyr.

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9 September 2020 at 10:00 #494821
Tony Martyr
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@tonymartyr14488
I have finally got round to stripping and rebuilding a model triple expansion engine that I built from Reeves casting some years ago. I am very impressed by some of the work (!?) except that all the excentric sheaves seem to be too loose – can't be wear from the few hours run so I must of not appreciated the clearances needed when I built the engine. The thought of machining a completely new set of 6 sheaves or excentrics fills me with dread so I wondered about 'remetaling' the sheave bores with silver solder and reboring. This is probably more difficult than making new excentrics but seems more interesting.

Has anyone done such remedial work succesfully?

Tony
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9 September 2020 at 10:00 #27625
Tony Martyr
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@tonymartyr14488
9 September 2020 at 10:29 #494826
Brian H
Participant
@brianh50089
Hello Tony, what materials are the sheaves and straps made from? If the straps are one of the brasses then a coating of white metal bearing material should do the trick at a much lower heat than silver solder which may lead to distortion.

Brian
9 September 2020 at 13:54 #494877
Tony Martyr
Participant
@tonymartyr14488
Hi Brian, Your reply has triggered a memory of my apprenticeship days and metalling of big gearbox bearings – this led me to the answer! I will mill a small amount of each of the halving joints, thus pinching the bore below size on the vertical axis and then machine out to the correct size, there is sufficient metal in the casting to allow this – I don't have to add metal!!

cheers – Tony
9 September 2020 at 14:38 #494888
Jim Nic
Participant
@jimnic
Surely what is proposed will indeed reduce the bore size in the vertical plane, but leave the opposing, horizontal plane the same dimension, ie still oversize. As I see it after machining the reduced vertical bore you will still have a sloppy side to side fit. Or am I missimg something?

Jim
9 September 2020 at 14:44 #494890
JasonB
Moderator
@jasonb
A lot will depend on how oversize the holes are, as soon as you start to take metal off the mating faces the cord will become less than the diameter which may just be enough. The smaller the sheave diameter the more the reduction for the same given amount removed from the mating faces.

Edited By JasonB on 09/09/2020 14:56:48
9 September 2020 at 16:03 #494911
Tony Martyr
Participant
@tonymartyr14488
Since the working loadlines in the top and bottom halves must be 50 odd degrees centred on the vertical centre-line I don't think the crescent shaped gap around the halving joint is going to be of concern, indeed it may aid lubrication. As Jason says it all depends on the amount the originals are oversized. I will do some careful measurement and report back.

Tony
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