To overbore or not to overbore…that is the question!

[Matt Stevens 1Participant @mattstevens1]

In a former post, i showed a problem with a cylinder for a Stuart Victoria that i bored out of true. I was able to correct this by over boring but the bore is now 1.1" instead of 1" and the remaining 'meat' on the cylinder walls is also about 100 thou which i think should be ok.

Now – i happened to purchase another Victoria single and will therefore make the two singles into a twin engine.

Question is – should i bore the second cylinder to drawing at 1" or should i deliberately overbore this also to 1.1" to match the other side? Does it matter if there is a difference from one side to the other on this size of engine?

Another option is i could try sleeving the first cylinder and then re-boring to the correct size. If i did this, what material should i use as a sleeve as i don't want different expansion rates cracking the cylinder.

Thanks

Matt

[Matt Stevens 1Participant @mattstevens1]

[HopperParticipant @hopper]

Up to you really. It will be a more balanced engine if both cylinders are the same size. On the other hand, triple expansion engines ran with massively different sized bores. It's a matter of personal preference but if it were me, I would put a cast iron sleeve in the oversized bore and take it back to original. I always find that once you start deviating from the drawings you end up working yourself into some unexpected corner down the road, or you forget and make the piston rings to the old size instead of the new etc.

[not done it yetParticipant @notdoneityet]

I would think that over 20% difference is a bit much, but no experience with steam. Certainly not a good idea in a higher revving engine. Difference in power between cylinders (and weight of what should be balancing components, particularly if running as a 180 degree crank).

I think I would follow Hopper’s advice…

Same material for liner – shrink fit and both liner and cylinder will expand at the same rate?

Edited By not done it yet on 14/05/2018 04:32:46

[JasonBModerator @jasonb]

Quite a few compounds can be run as double highs by use of the simpling valve so you should not have a problem particularly if it is going to be run as a display engine.

The Twin Victorial is (or should be) a slow running engine, with 90deg crank and has no balancing weights anyway.

I would aim for 1" and if need be the bore can be increased until you get a good finish. If you do decide to sleeve it down then a CI sleeve can be loctited into place which is a far more relaxed affair than shrink fitting. Loctite 648 if going to be run on steam.

[RedsetterParticipant @redsetter]

If the castings will accept 1.1", then overboring the second cylinder to match the first will give the best results for the least work, so do it that way. Unless of course you are one of these model engineers who likes to make everything as complicated as possible.

[Neil WyattModerator @neilwyatt]

Posted by Redsetter on 14/05/2018 11:15:28:

Unless of course you are one of these model engineers who likes to make everything as complicated as possible.

In which case discard the second cylinder casting and fabricate a new one with a smaller bore and make a twin compound. /16" or 5/8" ought to do it

[Matt Stevens 1Participant @mattstevens1]

Thanks for the responses….I think I had every possible answer/option there! I guess what it tells me is that it shouldn't really matter if one cylinder is different to the other. Given that, I will likely make the second cylinder according to drawing at 1"….continue the model and if needbe, I can always sleeve the first cylinder later.

Thanks

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