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[gondolier88]

I suspect the purpose of not using rings on the tug engine was reliability.   No ring issues...period.

If your hauling railroad car barges or petroleum in New York Harbor.....failure is not an option.

All the bearings where water cooled....including the crossheads.

She's about 750 BHP @ about 120 rpm.  That puts the average piston speed at 600 feet/minute.

30/12 feet x 2/rev x 120 rpm= 600 feet /minute.

With a Stuart D10... your piston speed at 2000 rpm  is 250 feet/minute.

.75/12 feet x 2/rev x 2000 rpm = 250 feet/minute

So the Tug piston is traveling on average more than twice as fast.......funny how math works .

Dave

Can't argue with that- always forget the piston speed consideration!

Would change of direction per RPM change your consideration of whether they should be fitted or not?

Too, my pistons are brass on cast iron cylinders- they will wear, rather have cast on cast to get even mating of the piston/cylinder wall, does that make sense to you?

Greg

[Steamer]

".....Too, my pistons are brass on cast iron cylinders- they will wear, rather have cast on cast to get even mating of the piston/cylinder wall, does that make sense to you?..."



YUP!

Brass's Coefficient of Thermal Expansion (CTE) is higher than iron.

You will need some clearance to avoid the pistons expanding and seizing in the bore......
Some Data to review
Red Brass.....half hard
http://www.matweb.com/search/DataSheet.aspx?MatGUID=8d2bad4a1e69429fb69b6e47cc16f521&ckck=1

Durabar continuous cast iron bar stock...
http://www.matweb.com/search/DataSheet.aspx?MatGUID=383ea2d3274d40f2b2e7f36c94252cf1


You can see that brass is something like 10.4/1000000 and iron is 6.4/1000000 or Red Brass expands  10.4 /6.4 = 1.624 times more for a given change in temperature.   On a 3/4 " bore that would be calculated via  Delta L = Lo * CTE * (T2 -T1)

Lets say you build your engine at 68 F  and run it at 250F    T2 -T1 = 250 - 68 = 182 F

Furthermore assume you build the piston with no clearance with bore at room temperature.

If we use the difference as the CTE  we get Delta L = (.75 ) x (10.4 - 6.4) x (10-6) x  (182F)

The end result would be a .0005" press fit.  This press fit would go away when it cooled off.

Needless to say you would never get to full steam and the run would be short.

So we run piston rings to avoid this problem as it allows the piston to have some clearance in the bore.

 
Dave


Oh and yes the tugs HP piston and piston valve are cast iron on a cast iron cylinder.

[gondolier88]

Thanks Dave, exactly what I thought.

...You will need some clearance to avoid the pistons expanding and seizing in the bore......

So we run piston rings to avoid this problem as it allows the piston to have some clearance in the bore...

Youv'e seen my machining tolerances then

Greg

[Steamer]

Hey Rosyth....any word on our model maker?


Curious....


Dave

[ROSYTH]

Nothing as of yet, I guess he is just to busy or isn't replying to mail anymore...................

R