Minimum steam space between the piston and cylinder head

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10 Wheeler Rob
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Minimum steam space between the piston and cylinder head

Post by 10 Wheeler Rob » Sun Oct 15, 2017 9:36 am

I picked up an locomotive project to finish. Upon inspection I find there is only about .075" clearance between the pistons and the heads of the cylinder. This engine is using 2" dia. Allen Model Cylinders. Is this clearance adequate steam space for proper operation?

Rob

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NP317
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Re: Minimum steam space between the piston and cylinder head

Post by NP317 » Sun Oct 15, 2017 9:49 am

As long as functioning cylinder cocks are in place, minimum space is better for operation.
~RN

10 Wheeler Rob
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Re: Minimum steam space between the piston and cylinder head

Post by 10 Wheeler Rob » Sun Oct 15, 2017 8:54 pm

I looked up what is on the Allen Model prints. They have 0.093 nominal clearance when you do the math. I found the heads are machined a little thicker where they pilot into the cylinders than the print dimensions show. So I will correct them to the print dimensions.

These cylinders do not have the ports machined in for the drains either, so another task to add to the to do list.

Rob

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Bill Shields
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Re: Minimum steam space between the piston and cylinder head

Post by Bill Shields » Mon Oct 16, 2017 7:33 am

as close as you can get without banging is just about right.

why waste space expanding steam unnecessarily?

Kimball McGinley
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Re: Minimum steam space between the piston and cylinder head

Post by Kimball McGinley » Mon Oct 16, 2017 2:45 pm

Another thing to consider is the holes running between the ports and the cylinder end, you don't want the boss on the cylinder head to choke them off. A small flat or cut-out on the boss can help with that, and it will not ruin the centering function of the boss.

darjeeling
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Re: Minimum steam space between the piston and cylinder head

Post by darjeeling » Mon Oct 16, 2017 3:21 pm

One must be aware of wear that can occur on connecting rod and crosshead bushes. Too much, and the gap will close to the extent the piston may hit the cylinder cover ( I have seen this happen and destroy the cylinder casting). Yes small gap is good between piston head and cylinder cap, but take into account bush wear over time.

John Heald , New Zealand.

rkcarguy
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Re: Minimum steam space between the piston and cylinder head

Post by rkcarguy » Mon Oct 16, 2017 4:47 pm

I agree with Bills opinion, not like you have to worry about rod stretch/deflection or too high of a compression ratio with steam.
All my 200cc engine builds for my racing kart I shoot for .030" to allow for rod stretch, heat growth, and crank deflection.

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LVRR2095
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Re: Minimum steam space between the piston and cylinder head

Post by LVRR2095 » Mon Oct 16, 2017 5:16 pm

So Robin....what’s the locomotive?

Keith

10 Wheeler Rob
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Re: Minimum steam space between the piston and cylinder head

Post by 10 Wheeler Rob » Thu Oct 19, 2017 11:40 pm

The locomotive is a 7 1/4 or 7/ 1/2 inch gauge 2-4-2 called Mini. It is around 2" scale. Balloon stack, old american 4-4-0 head light and pilot. Stevenson valve gear. 9" dia. drivers.

The valve gear linkage needs to be corrected, it assembled with set screws instead of silver soldered or pinned joints of rocker arms to shafts.

It was set up for 7 1/4 gauge. I am regauging it to 7 1/2 to run during the winter season in Florida.

I am doing a down to the frame disassembly to see if there is any thing else that needs correcting.

So far I machined the drain ports in the cylinders, honed the bores and added brass cylinder jackets. I also had the boiler steam dome corrected and dry pipe added to the boiler at welding shop.

steamingdon
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Re: Minimum steam space between the piston and cylinder head

Post by steamingdon » Sun Nov 12, 2017 12:32 pm

any photos of progress?
steamer

steamingdon
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Re: Minimum steam space between the piston and cylinder head

Post by steamingdon » Sun Nov 12, 2017 12:36 pm

never mind, found in "Build Log"
steamer

10 Wheeler Rob
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Re: Minimum steam space between the piston and cylinder head

Post by 10 Wheeler Rob » Mon Nov 13, 2017 5:59 pm

Yes I started thread in Build Log for the regauaging and completion of the locomotive.

Rob

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