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Design Evolution of the 20hp Stanley Engine

Posted by douglas kephart 
Design Evolution of the 20hp Stanley Engine
January 19, 2015 07:44PM
A Stanley owner once opined that the design of the engine changed about every fifth one built! An examination of engines undergoing overhaul revealed many, many changes and a curiosity emerged to catalog them. The following timeline focuses solely on the 20hp engine, which had the longest run and greatest number of surviving examples to make observations on. Charlie Johnson, Mike May, Howard Johnson, and the Friends of the Auburn Heights Preserve contributed additional details, and their help is gratefully acknowledged. A few details and most of the help on the model numbers using the 20hp engine came from the Kit Foster book. It must be recognized that a number of Stanley engine parts are interchangeable across the years, making present-day observations of survivors fraught with peril. In years past less concern was given towards authenticity, verses getting and Stanley engine going, keeping it running, and perhaps improving the original. Original, undisturbed examples are rare and prized. For brevity, the terms “presumed” and “probably” have been omitted but should be assumed before any definitive statement that follows! An earlier version of this article was published in the 2013 summer edition of the Auburn Heights Herald. Since then a few more details have come to light that have rounded out the picture, but it is hoped this post will spark some discussion and fill in the missing gaps, or correct any errors that I have made. When finished (if ever?) it will serve as a resource for those that are restoring a 20hp and are sorting through a pile of parts trying to figure out which bits date to which year. See attachments with each post for examples of the various features discussed. I have divided this post up to spread out the number of attachments. If you have a picture that can throw some light on missing details, by all means add it with your reply. This only covers the 20hp engine, but if someone wants to tackle the 10hp and the 30hp, that would make a great companion topic and help preserve engine originality before all the pieces get swapped around during restorations. Or send me the information and I will compile it. So, in the beginning…

1905 The 20hp engine is introduced with the Model F. Bore and stroke is Ø3-5/8" x 5". The cylinder mounting ears are not flared in to cylinder trunk, and are particularly prone to fracture. Steam enters through the front end of the valve chest via the hollow front mounting stud. The exhaust manifold exits to the left. The main frame is of Ø3/4” rods, spaced 5" wide by 5" high (on centers). This is a “dry” engine, which, while enclosed in a sheet metal wrapper to keep out dust, is not designed to keep oil in or facilitate lubrication. The piston rod is Ø5/8", and the crosshead is poised between a pair of 5/8" bearing balls that oscillate back and forth along the crosshead guides. The connecting rods are 11-1/2" long (on centers) and use crowded 1/2” diameter balls loaded through a radial port. The port is sealed with a plug transfixed by a pinch bolt; despite appearances this does not allow adjustment for wear. The fork (wishbone) of the connecting rod has to be bent to install over the crosshead. The main crankshaft bearings are 3/4” diameter crowded ball, running in split outer housings separated by shims to effect adjustment. Adjustment is only fore and aft, but this is the direction of the most wear anyway. The crankshaft itself is Ø1-1/4”. In late 1905 or early 1906 counterweights were added to the cranks. The reversing actuation lever is directly over the Stephenson links, on the centerline of the engine. It has an adjustable stop for setting cut-off in the forward direction, but no hook-up. The pump drive is indirect from the right crosshead, via a short link, a rocker arm, and then the pump reach rod. Models using the 20hp engine: F.

1906–1907 The Model H, with its successors the H-4 and H-5, utilize the Model F engine with higher gearing. Models using the 20hp engine. 1906: F, FX, H(some were 15hp), H1, H2, H3.1907: F, H, H3, H4, H5, J.
1908 The reversing actuation lever moved to the right side of the engine and incorporated, for the first time, a latch to “hook-up” the valve linkage into a shorter valve stroke for the purpose of more economic use of steam when the engine was not working hard. The pump drive is taken directly from right crosshead, via a curved pump reach rod with no links or rocker. Early in 1908 the cylinder mounting ears for the frame rods are reinforced by a small gusset. An example has not been seen, so the accompanying illustration is based on the same type of reinforcement seen on a 10hp cylinder block. Late in the year they are fully flared into cylinder casting, much like subsequent Ø4 x 5 engines. Externally the valve chest on the top of the engine extends the full width, such that recesses are required for the mounting nuts. Presently I do not know if this was done when the small reinforcing ribs were added early in the year, or when the fully flared mounting lugs were introduced late in the year. Also a boss was added for steam admission to top of valve chest but seemingly not used. Models using the 20hp engine: F, H, H4 (none sold), H5.
1909 About June/July, the Model R and U (with higher gearing) were introduced to supersede the venerable Model F. The bore and stroke becomes Ø4 x 5 inches, and in general many of the engine components increased in size to suit. This bore and stroke remained throughout the life of all remaining 20 hp models. The cylinder casting is appreciably larger overall, with “C/1501” in raised, cast characters on the upper valve chest surface. Steam enters via a boss on the upper face of the steam chest; however, the front of chest is still tapped for a pipe thread to take a solid mounting stud. Main frame is now Ø7/8" rod, spaced 5-3/4" wide by 5-3/4" high (on centers). The piston rods increase to Ø11/16”. The new design is splash-lubricated; from the piston rod packing glands to the crankshaft is encased as one compartment. Introduction of the “wet” engine was a major improvement eliminating the need to oil all the moving parts in the crankcase by hand as was required in the “dry” engines of the earlier models. The drive gear increases from 7/8” wide to 1” wide. The crankshaft increases to Ø1-5/8”. The Model F hung on for part of the year using the ‘old’ 1908 engine. Models using the 20hp engine: F, H, J, R, U.

1910–1911 A cast aluminum baffle (diaphragm) separates the crankcase motion compartment from the cylinder’s piston and valve stuffing glands so that leaking glands are less likely to contaminate lubrication. This adds length to the main frame, necessitating approximately 1” longer piston rods (not sure of exact length) and a connecting rod of 12-5/8”. A larger crosshead bearing ball of 3/4” appears about this time. The connecting rod now has a solid eye; no pinch bolt. The inner bearing race was of two halves allowing for assembly and adjustment. The outboard half was threaded onto the crankpin and screwed up against the inboard with shims betwixt to take up clearance. The crankpin nut locked (jammed) the inner race. Models using the 20hp engine. 1910: 70, 71. 1911: 70, 71, 72.

1912 An example of a 20hp connecting rod with crowded ball bearing big end but a detachable wishbone leg has been reported. A Stanley illustration of an engine attributed to 1911 shows the solid wishbone still in use, so this connecting rod design would seem to date to circa 1912. Models using the 20hp engine: 73, 74, 75.

Re: Design Evolution of the 20hp Stanley Engine
January 19, 2015 07:47PM
1913 Addition of a feed water heater necessitates a deeper flue alongside the engine. Consequently, the exhaust manifold now exits to the left and forward. This is the first year for the roller bearing engine. Main bearings are Ø3/4" x 3/4" hollow rollers, mounted on pins, and riveted into side plates to form a caged assembly. Rollers run on a cylindrical inner race with a shallow lip toward the outboard end. The main bearing housings have a shallow groove (double lip). The connecting rod bearing design is caged like the mains, but of Ø5/8" x 5/8" rollers running in a shallow groove of a solid (not split) eye. No method of adjustment. Connecting rod has detachable fork leg to ease installation onto crosshead. Shims between the two cones set the wristpin clearance. Crosshead has recirculating Ø5/8" x 1/2" roller. Models using the 20hp engine: 76, 77, 78, 79.

1914 No information. Models using the 20hp engine: 710, 711, 712, 713. 714, 715.

1915 All 20hp models are now condensing cars; which started with the 714 & 715 models the previous year. Driving position moves to left-hand side of the car; so hook-up moves to the left side (of the engine) with the pedal(s). Therefore exhaust manifold exits to right. Pumps are now driven off the rear axle, so there is no slot in the bulkhead for the pump rod to pass forward through. Pinch bolt returns to the connecting rod eye, which, with shims in the gap, allows the eye to be contracted and so take up clearance on the rollers. The main bearings and connecting rods change from caged to crowded rollers. Likely the extra cost and complexity of the cages was not warranted, when a simpler manufacturing solution of running the rollers in a deep groove (mains) or between guiding sidewalls (connecting rods) would suffice. For the main bearings, the rollers (still the same size) run in a deep groove of an inner race. The main bearing housing has a single lip towards the outboard side. The shims for the wristpin are eliminated and the running clearance set by tightening the crosshead bolt (but not too tight!); a jam nut maintains the setting. Crosshead guides are steel with convex surface, fitting the curve of the earlier style piston rod crosshead; no ball (or roller). Lugs appear on cylinder block casting for diagonal truss rods between cylinder and rear axle. Models using the 20hp engine:720, 721, 722, 723.

1916 No information. Models using the 20hp engine: 725-5, 725-7, 726, 727, 728 (August).

1917 Crosshead guide remains steel, but is now concave. New piston rod crosshead with convex surface to match. Models using the 20hp engine: 728, 730, 731.

Re: Design Evolution of the 20hp Stanley Engine
January 19, 2015 07:50PM
1918 With the model 735, the eccentrics change from 37º to 35º. Previous eccentrics marked with a center punch dot to the outside to aid correct refitting. Later eccentric stamped (sometimes!) “35º” on the outside face. Piston rods locked to piston with a jam nut in a recess. Previously the piston rod was peened to lock it to the thread through the piston(s) with no jam nut. Crosshead guides are now bronze castings, concave in shape. After the 735 model, eccentric timing reverted to previous value. Some sources give this as 40º, not 37º. I did not check eccentric angles on earlier engines, so not sure. Seemingly undisturbed 740 and SV engines have been seen with the (marked) 35º eccentrics so after 1918 they may have not reverted to the earlier eccentric angle after all. There are likely many different slide valves with different length laps used over the years, so beware! Models using the 20hp engine: 735, 736, 735D (September).

1919–May 1922 Hardened slide valves, requiring a change in cylinder oil. A 1919 service bulletin states because of this the new oil is not compatible with earlier engines, and vice-versa. About this time the markings on the cylinder block change. The date cast appears (M D Y), and the foundry trademark of “MFCO” within a diamond, and a (part?) number 101. One cylinder block seen on a 740 engine with date 2 23 20, indicating (if it is original to the car) they were still using this batch of castings over two years later (the 740 came out in mid-1922). Models using the 20hp engine. 1919-20: 735A, 735B, 735C, 735D. 1921: ditto, plus 735E, 735F.

May 1922–1924 740 model introduced in May 1922 and probably superseding the 735 in production; that is negligible model overlap. Tie rods between the upper and lower engine frame cross members are double-nutted to rigidly fix distance. Previously tie rods only stopped the upper and lower frame rods from spreading in the area of the crosshead guides. Engine number now (additionally?) stamped on a frame rod rather than the upper rear cross member casting. Models using the 20hp engine. 1922: 740A, 740B, 740D, 740E, 740F 1923: ditto, plus 470G. 1924: 740A, 740B, 740D, 740E, 740G, 750A, 750B, 750D, 750G.

Re: Design Evolution of the 20hp Stanley Engine
January 19, 2015 07:52PM
1925–1926 Introduction of the “SV” engine. Engine has cast aluminum sides to motion chamber (engine crankcase) with pressed steel upper and lower panels for a boxlike construction. No trace of casting number on cylinder. Forward mounting lug on the cylinder reinforced with large boss and gussets. Diagonal tie rod lugs still present on the sides of the cylinder block, but not drilled and tapped for tie rods. Semi-elliptic springs at the rear were introduced in 1924, negating need for perch poles and possibly the need for a braced engine. Or it may be that the box construction and larger diameter frame rods (between cylinder and main bearings) sufficed for rigidity. Or perhaps the larger engine case of the SV simply got in the way of installing the tie rods. Exhaust manifold exits to the left. Main bearings are commercial ball bearing units; main bearing housings are consequently not split. Helical final drive gear (many replaced with earlier crank assemblies using the spur gear). Cylindrical trunk guides integral with cast aluminum baffle. The engine number is stamped on the baffle where the upper left frame rod passes through. The engine rods are about Ø1-1/8”(?) from the cylinder to the main bearings, with an even larger diameter sleeve between the bulkhead and the cylinder block. The frame rods revert to the old Ø7/8 through the main bearings and out through the rear axle. Connecting rods have a solid eye and crowded rollers; a regression to no means of adjustment. Small end eye fitted with a bronze bush for a conventional gudgeon pin in a cast iron crosshead “piston”. Models using the 20hp engine. 1925: SV-252-A, SV252-G. 1926: SV262-A, SV-262-G.

Douglas Kephart, Jan 2015, Glen Mills, PA, USA

(fix typo in dates. DK, 22jan15)

Edited 1 time(s). Last edit at 01/22/2015 01:11PM by douglas kephart.

Re: Design Evolution of the 20hp Stanley Engine
January 20, 2015 04:04AM
Douglas - thankyou for that - an excellent explanation of the history. Good to have it on record.

Re: Design Evolution of the 20hp Stanley Engine
January 20, 2015 08:47AM
Bravo! This is the kind of thing that people like Mike and Charlie and Howard can rattle off the top of their heads, but I can never build the whole picture for myself. Great research, great writing, and an invaluable service.


P.S. For this record, the helical gear in the SV was unsatisfactory because it created thrust on one side, and the crank bearing design was not altered to manage the thrust. It's a mystery to me how they could have missed this simple mechanical issue. If they had to leave the spur gear, a herringbone would surely have been better, although no doubt more expensive.
Re: Design Evolution of the 20hp Stanley Engine
January 20, 2015 11:12AM

1918 Piston rods projects 1/4" through the piston (so piston rod is probably longer) and locked with a jam nut. I am not sure when this started, (after 1913) but it was in place by the 735 models. There is a recess in the cylinder head to accommodate the nut, so the head now has a large central boss to accommodate this recess. This would be visible externally. Previously the end of the piston rod was flush with the piston and peened to lock it to the thread, and the head had just the cross rib that you hammered on (!) to tighten/loosen the head. (see attached)


I too have heard that the SV was unsatisfactory due to the helical gear. But I wonder if this is an old chestnut perpetuated down through the years? Technically it is true that they did not specifically provide a mechanism to take the thrust load. Practically, the radial ball bearings used can handle some thrust load, though not as much as angular contact ball bearings could have done. They are of a generous size and likely adequate for the trust load. From an engineering perspective I would be more concerned about the frame rods twisting between the main bearing housings and the rear differential housing. This would miss-align the teeth as the two meshing helixes would try to repulse away from each other. With the angle slightly out of skew, that would throw a lot of load on the outer ends of the teeth and shorten the life of the gear; giving them a bad reputation. With the previous spur gear the frame rods would bend, but there would be no twist (at least not introduced from the gear). The line of contact between the gears would remain relatively unchanged and impact on the wear would be negligible.

Of the two SV engine bottom ends that I have seen in detail, one had been previously converted to a 735 crankshaft. I do not know if this was due to a failure with the gear, or the whole crankshaft unit was swapped out because it was in overall better shape. The other with original helical gear and bearings looked fine, but who could say how little mileage it might have done. The only way to be sure would be for a large response from folk that have seen distressed helical gears in their collection of Stanley bits. That would confirm that the SV Co. erred in their design.

P.S. I would be interested in copies of engine spares lists (if such exist), as changes in part numbers might be a way to determine when the components changed.


Edited 1 time(s). Last edit at 01/20/2015 11:20AM by douglas kephart.

Re: Design Evolution of the 20hp Stanley Engine
January 21, 2015 06:02AM
Beautiful! first engine design almanac i seen yet, efforts like these can come only from highly experienced and passionate folks.
had a few learner questions,

1. Twin cylinders look the same. Were they neither HP/LP reheat cycle engines, nor unaflow?
2. How long did the Stanley take to start below freezing conditions, with the feed water heater? was there a operating temperature limit at the lower end?
3. Please elaborate on the convex, concave crosshead design detail.
4. Please elaborate on the eccentrics. It sounded like there are two things, angle and timing. Angle I could figure is maybe the maximum angular displacement of the connecting rod to the piston rod.
5. Are any folks working on a Stanley like with 21st century materials and other ideas, even as a serious hobby? those CAD drawings made me curious.

Thanks a Ton!
Re: Design Evolution of the 20hp Stanley Engine
January 21, 2015 07:11AM
I can probably answer most of these:

1. All Stanley's were were 2 cylinder double acting slide valve (D Valve) simple engines. Not uniflow and no reheat or anything fancy.
2. Stanley advertising running the cars in freezing conditions. You likely had to keep the pilot going to keep things warm and actual times surely varied a lot. If left too long without driving, obviously some pipes/pumps/etc may freeze (and do).
3. The first cross heads were concave on the piston rods and shoes with a ball bearing roller. The evolution then had some cross heads with concave piston rod portions and convex shoes and the later engines all seemingly had convex piston rods and concave shoes up to the piston like crossheads in the SV's.
4. The angle in discussion is the timing. This is the keyed angle of the eccentric rotated relative to the crank pin. I don't believe anything has to do with angular displacement of any rods.
5. That I do not know. There are various modern or modernized Stanley type conversions and other complete home builds. There are also various CAD guru's (myself included) with a lot of parts modeled for restoration of recreation purposes...

Hope I have helped some and provided accurate answers. Thanks!

Jared Schoenly
Re: Design Evolution of the 20hp Stanley Engine
January 21, 2015 10:54PM
rchou Wrote:

> 5. Are any folks working on a Stanley like with
> 21st century materials and other ideas, even as a
> serious hobby? those CAD drawings made me
> curious.
> Thanks a Ton!
> Rahul

Yes, most all Stanley engine re-builders use modern metals, bearings and in some cases, have even added piston valves in the place the of D slide valves. David Nergaard has a 1922 Stanley driving test bed. It would take an hour to list all of the changes that David has made to his Stanley's engine and rear axle. Most all of David's changes are towards improved performance and reliability. Howard Johnson sells Stanley 10 HP engine kits that replaces 90 % of the moving parts of the type 6 engine. The parts are all modern metals and are of better designs for strength and reliability. I too have used improved technology on the Stanley engines i.e. hard chromed piston rods, modern bearings, improved wrist pins, and more. I have been running Stanleys for over 30 years and I have learned from mine and others mistakes. Broken wrist pins were the most expensive lesson I had to learn. It took me many rebuilds before I finally got the 10 hp wrist pins bullet proofed.
Re: Design Evolution of the 20hp Stanley Engine
January 21, 2015 11:39PM
Douglas Kephart & all the folks here, Thank you very much! Will study further ahead, practically grasping a golden reference of a steam engine has been on my mind for a while now, as a first step. all the more important, as mech is cross disciplinary for me. And so are magnets and power electronics.........
Re: Design Evolution of the 20hp Stanley Engine
January 24, 2015 02:02PM
Walter Winship thought the side ware was excessive on his SV engine and he cut a new straight tooth gear from 4140. I located a supplier that had short round cutoff to cut a slice from.
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1905-cylinder.jpg 23.9 KB open | download douglas kephart 01/19/2015 Read message
1907 conecting rod.jpg 61.4 KB open | download douglas kephart 01/19/2015 Read message
1907 crankshaft.jpg 48.4 KB open | download douglas kephart 01/19/2015 Read message
1908 crosshead.jpg 41 KB open | download douglas kephart 01/19/2015 Read message
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1913 connecting rod.jpg 54.3 KB open | download douglas kephart 01/19/2015 Read message
1913 crankshaft.jpg 63.2 KB open | download douglas kephart 01/19/2015 Read message
1913 cylinder.jpg 72.7 KB open | download douglas kephart 01/19/2015 Read message
1913 main bearing.jpg 69.4 KB open | download douglas kephart 01/19/2015 Read message
1913 roller crosshead with bronze guide conversion.jpg 39.9 KB open | download douglas kephart 01/19/2015 Read message
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1924 connecting rod.jpg 67.6 KB open | download douglas kephart 01/19/2015 Read message
1924 crankshaft.jpg 70.9 KB open | download douglas kephart 01/19/2015 Read message
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