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Oversize Cylinder

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Richard Stacey11/04/2010 17:20:49
16 forum posts
A newcomer to model engineering, I am in the process of building the Stuart S50 Steam Engine and due to a bad error in measurement I have bored the cylinder
31 thou oversize.  Will it be OK to machine the piston to fit or do I have to buy a new cylinder casting and start again?
 
Many thanks
 
Richard  
JasonB11/04/2010 18:04:12
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25215 forum posts
3105 photos
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Can't see why you should not be able to use an oversize piston.
 
Just make sure the larger bore has not affected the cast in steam ways and remember to machine the spigot on the cylinder covers to fit the bore as well. You may want to drill the cylinder cover bolts and a slightly larger PCD if they come close to the bore.
 
Jason
Richard Stacey11/04/2010 18:18:52
16 forum posts
Many thanks for that Jason, as far as I can see there is no problem with the steam ways. Having managed to make the cutter bit for the boring bar and machine the bore parallel, I would have been disappointed if I had to start again. Thanks also for the tips about the cylinder covers and PCD for the bolts - I hadn't thought of that!!
 
Richard 
chris stephens11/04/2010 20:33:41
1049 forum posts
1 photos
Hi Richard,
Don't look on your "mistake" as a negative, just think of it as a larger, more powerful version of the engine. 
chriStephens 
Circlip12/04/2010 12:14:38
1723 forum posts
You have highlighted one of the traps that most who "Mod" a design fall into Richard. Yours was one of neccessity due to an error of machining, but the same thing applies to two other forum golden oldies, Merticating designs from imperial and the "Why are the drawings not corrected" whingers.
 
  Pity they don't engage brain before trying to melt the keyboard.
 
  You may be able to re-centralise the PCD between the edge of the bore and the flange O/D.
 
  Regards  Ian.
Richard Stacey12/04/2010 15:34:58
16 forum posts
Thanks Chris,
 
I'm all in favour of positive thinking - all encouraging comments gratefully received.
 
Richard 
Richard Stacey12/04/2010 15:37:48
16 forum posts
Hi Ian,
 
I have checked the cylinder flange and there is no problem in centralising the retaining bolts with just a small increase in the PCD.
 
Regards
 
Richard 
mgj12/04/2010 18:28:16
1017 forum posts
14 photos
How did you make the error in the first place - just as a matter of interest.
 
As I recall the first hole I ever bored was a trifle ! oversize too
chris stephens12/04/2010 19:46:27
1049 forum posts
1 photos
If you think about it, a hole can either be right or oversize, if it were "under-size" it would simply be 'work in progress' or if you like, unfinished. There's one for you lot to ponder on.
chriStephens 

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