And Now for the Twin

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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Lopez Mike
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Re: And Now for the Twin

Post by Lopez Mike » Mon Feb 26, 2018 11:43 pm

Over the years I have done quite a few small engines like the Stuart #5 and #1. Enough of them that I have templates. They look just like a cylinder head. They have a shoulder that drops into the bore with a central hoel for a through bolt that goes through the cylinder casting to a cross bar. Once that long bolt is snug, I can do the rest on a drill press if needed. These are models where I am using many, many small studs to make it look like a full sized engine. Like 24 on a #5.

This all is predicated on using far too close a tolerance for the stud locations. If you stick with easy numbers like 6 or 8 studs, just lay them out with blue dye and a scriber and then make the holes in the head oversize. It subtracts nothing from the strength and makes disassembly worlds easier.
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Re: And Now for the Twin

Post by fredrosse » Tue Feb 27, 2018 1:47 am

If the cylinder heads are to be full circle they can each only be 3.3 inches diameter. Often the cylinder heads on twins have a section cut flat where the heads meet between the two cylinder bores,to get more flange area all around. I assume you are going to have that arrangement, so what is the turned diameter of your heads?

The attached sketch may be close?
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2CYLc.jpg
SIX BOLT HEADS
2CYLc.jpg (34.86 KiB) Viewed 911 times
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Re: And Now for the Twin

Post by Mike Rometer » Tue Feb 27, 2018 8:54 am

Fred, that's exactly it, the heads intersect, and why my wondering if one shared bolt at the join would work better or just as well as the arrangement you draw. An East/West axis, rather than your North/South. I'm thinking the two pairs between the cylinders will be very close together and may 'spanner' foul. I need to get the heads finished (today, maybe) and fitting together.

The heads are currently 3.85" -ish O.D. so don't quite reach the edge of the adjacent bore.
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Re: And Now for the Twin

Post by fredrosse » Tue Feb 27, 2018 10:43 am

If you put two bolts on the line where the two heads meet, then an 8 hole pattern could work well, and allow cylinder drain cocks at 90 degrees from the cylinders axis. That would reduce the distance between bolts on the valve port end, and you want to avoid restricting the steam port with bolting that pierces the port passage, although that is not necessarily a show stopper.

The sketch attached shows this arrangement, along with 22-1/2 degree red lines that would represent even spacing for 8 place bolt circle. Some deviation from the true bolt circle, as well as the angular position of bolt holes is compromised somewhat, but still acceptable geometry.
Attachments
2CYLd.jpg
8 bolt circle layout
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Last edited by fredrosse on Tue Feb 27, 2018 11:10 am, edited 1 time in total.
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Re: And Now for the Twin

Post by dampfspieler » Tue Feb 27, 2018 10:53 am

Hi Mike,

what do you think about a 5- or 7-bolt design like this. It is from my STUART Launch Twin-Steam engine. So you can also set the drain cocks into the standard /original position.

Image

Cheers Dietrich
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Re: And Now for the Twin

Post by fredrosse » Tue Feb 27, 2018 1:04 pm

As far as bolts vs studs, I would recommend studs, threaded into the iron with hi-temp loctite. The steel studs wear better for many disassemble cycles, with little chance of stripping threads in a relatively weak cast iron cylinder piece. Studs and nuts are also more authentic for the period I think.
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Re: And Now for the Twin

Post by Mike Rometer » Tue Feb 27, 2018 1:14 pm

dampfspieler wrote:Hi Mike,

what do you think about a 5- or 7-bolt design like this. It is from my STUART Launch Twin-Steam engine. So you can also set the drain cocks into the standard /original position.

Image

Cheers Dietrich
Hi Dietrich, the DRO doesn't care how many you want, just enter the number, it works out to co-ords. :lol: :lol: :lol:

The only minor concern with the East/West positions would be that one stud(?) is directly over the port, but I've checked the casting thickness there and it will manage fine without breaking through. The drain cocks are then completely clear (11 stud).

Also the stud on the joint line will still be on the PCD (slightly adjusted).

Both covers are now ready for their flats.
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Re: And Now for the Twin

Post by fredrosse » Tue Feb 27, 2018 3:39 pm

Second post of mine on 27Feb, 14 studs on two heads.
Stud stress is 3700 PSI at 150 PSIG Cylinder pressure, well within limits for 1/4 inch studs.
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Re: And Now for the Twin

Post by Mike Rometer » Tue Feb 27, 2018 7:34 pm

fredrosse wrote:Second post of mine on 27Feb, 14 studs on two heads.
Stud stress is 3700 PSI at 150 PSIG Cylinder pressure, well within limits for 1/4 inch studs.
Yes, that takes those two off the P.C.D, though not really a problem, just a case of resetting the DRO, or drilling them independantly.

I was thinking of using all Metric threads, Imperial stuff here is still available, but Metric is so much less hassle, even available over the counter very locally. M6 is where I was, M8 being a bit heavy looking.

Edit :- Covers now completed to drilling stage.
Cyl Cover (8) (600 x 450).jpg
Cyl Cover (8) (600 x 450).jpg (68.32 KiB) Viewed 887 times
I laid the nuts M6 and M8 on for size impressions, I'm now not sure that M8 is too big, it certainly fills the land well.
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Re: And Now for the Twin

Post by fredrosse » Wed Feb 28, 2018 12:36 am

With the low stress value for M6, that would be fine. Steam engine nuts, I usually get "Heavy Hex Nuts", somewhat more meat in them. USA availability, is there a similar option in Metric?
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