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Field Notes

Thread Standards Concerns


Restorers of old engines and machinery inevitably run into problems involving thread or fastener standards, the most common being the 1/2-12 UNC standard that appears to have been used before World War I. I have not seen this standard on anything built after about 1918, when it changed to 1/2-13 UNC. In the British Whitworth threads, the 1/2-12 BSW continued until Whitworth was effectively abandoned in favor of metric in the early 1970s. Yet even standard sizes can vary slightly, which leads me to assume that many early manufacturers made their own taps and dies and didn’t always adhere to national standards. In addition to thread standards being “loose,” I have come across nuts or bolt heads with unusual hex sizes, sometimes made to the nearest 1/32 inch.

A frustrating thread-related problem recently occurred restoring a 4 hp Excelsior engine, where I found that all the tapered pipe threads used on the fuel tank, fuel pump, mixer and return circuit were oversized. The threads on a modern fitting bottomed out before they mated up. Clearly, Excelsior made their own taps and chose to make them about 1/32 inch oversized!

To overcome this, I purchased a taper turning attachment for my Hardinge lathe in order to custom make the oversized tapered pipe fittings. This attachment has since come in very handy for producing British Standard Pipe threads. Anyone owning or contemplating owning an English engine will find the common use of BSP threads. In every case the Whitworth thread angle is 55 degrees and in almost every case there is a different number of threads per inch. The basic pipe size and taper are the same, which means you cannot visually tell the difference between NPT and BSP. Don’t make the mistake of thinking a few extra turns of Teflon tape will fix the problem!

NPT and BSP are the only two tapered pipe thread standards in the world. Modern machinery uses one of the two, and you might be surprised to know that machinery (CNC lathes, milling machines, etc.) made in Taiwan or Japan is quite likely to have BSP threads used on the various hydraulic components.

I have experienced some real disasters that occurred at the port of entry where accessories are added before shipment to the end customer. Unfortunately, there is no color coding or distinguishable marks to alert technicians to the lack of interchangeability, and the inevitable happens. I never cease to be surprised at the number of “experienced” engineers and technicians who believe there is a metric pipe thread system or that BSP is metric: neither is true.

Perhaps the most shocking aspect of lack of standardization occurs in the metric thread system. While metric threads don’t show up often in engine restoration, they are out there. I came across two instances of standardization lapses recently. The first showed up when I tapped a metric M-10 x 1.0 hole in a model engine to accept an NGK CM-6 spark plug. The plug was so loose I dared not get it more than finger tight. When I measured the pitch diameter of the threads I discovered that they were 0.006-0.008 inch (0.2mm) undersized.

More recently, I made an adapter to install a modern NGK glow plug into an early Ruston & Hornsby open-crank diesel engine. The published size of the glow plug was M-10 x 1.25 and I ran into the almost identical problem after tapping with an ISO standard tap; the plug fit so loose I couldn’t risk using it. Again, the threads checked out at 0.008 inch (0.2mm) undersized. I sent an email to NGK outlining this problem, but have not received a response.

Having been an engineer and a journeyman machinist for over 60 years (I trained at Rolls Royce’s aircraft engine pision) I have certainly seen my share of peculiar thread problems. Many younger engineers are convinced the metric system is the ultimate in standardization, but as an “old timer” I know that the Whitworth thread standards (no longer used) and the American Unified screw thread systems are the two most standardized in the world, and this results in absolute interchangeability within their respective systems, something that does not happen with metric threads.

Please send your questions and comments for Flywheel Forum to Gas Engine Magazine, 1503 SW 42nd St., Topeka, KS 66609-1265 or email

More Tiny Tim Generator Information

Tiny Tim

J.D. Schmidt sent photos published in the October/November 2017 issue of a Tiny Tim 12-volt, 300-watt generator powered by a 1/2 hp 4-stroke engine, asking if readers knew more about the units. We noted that small generators like the Tiny Tim were inspired by efforts to supply like-type units for military use, prompting the following note from reader Ken Karrow, who writes: 

“I believe they were developed and sold to charge batteries for the home owner as opposed to a military application. I have one with a Montgomery Ward tag on it that says Wards Airline. It is a 6-volt unit with battery ignition. As an ex-Wards employee, I know that Airline was Ward’s trade name for their home entertainment items. This would include radios back in the day when REA had not reached lots of homes yet, so this would have been sold with a radio to a customer who did not have electricity yet. 

“Lots of radios in this time period were 6- or 12-volt, and the amp draw was too high to use dry cells. The expense of dry cells would be prohibitive, so wet cells were used and needed to be recharged. I have two more of these that I have not got to working with yet. Neither have tags so I don’t know the voltage. One is a Tiny Tim look-alike and the other is a Pincor. All three of mine are electric start, and I suspect the one in the photos is, as well. There is a button directly under the handle that looks like an old dimmer switch button. I suspect that will energize the generator as a starter and they switch to a generator when up to speed. I have tried the Wards unit on a run-down 6-volt battery and it will crank slowly and start. The pulley is an ordinary V-belt pulley with a notch in it so you can rope start, but on mine you still need a battery with at least a little charge to operate the ignition. You can also use the belt pulley to operate anything that uses only about 1/2 hp with the battery fully charged. If the battery is low, it won't have enough power to operate something else and charge the battery as well.

“I know this is getting long, but I will relate a story that my dad tells about my grandfather. When Dad was young they had a radio on a battery, but Grandpa was too cheap to buy a charger. He would park his Chevrolet on a hill in the yard and my dad had to remove the battery and hook it to the radio and when grandpa was ready to go to town, Dad had to take the battery back out and install it in the car. I believe that it was a 1918 Chevrolet. Then Grandpa would let the car roll down the hill, engage the clutch, start the car and go to town and do his business. When he got back the battery was charged up and he would repeat the process.”

Please send your questions and comments for Flywheel Forum to Gas Engine Magazine, 1503 SW 42nd St., Topeka, KS 66609-1265 or email

Sandwich Engine from the Archives


Thumbing through the GEM archives, we  found this photograph of engine enthusiast Elwin Cunningham tending to his 6 hp Sandwich engine at a June 1977 gathering at the Museum of Transportation in Owls Head, Maine.

The photograph was taken by Elwin’s friend, Charles Chiarchiaro, and includes the note, “Ran all day, never missing a beat.” It was subsequently published in the September/October 1978 issue of GEM, along with a short story by Charles about his friend. At age 19 Elwin, who was born in 1913, was working for the Diamond Match Co., first tending boilers and then operating two Ames Uniflow engines. He went on to work for the Central Maine Power Co.

One of the founders of the Maine Antique Power Assoc., Elwin had a collection of over 40 engines, including a 15 hp IHC Mogul sideshaft, a 15 hp IHC Famous, a 15 hp Fairbanks-Morse, and of course the 6 hp Sandwich. You can read Elwin’s story at

Please send your questions and comments for Flywheel Forum to Gas Engine Magazine, 1503 SW 42nd St., Topeka, KS 66609-1265 or email 

Leader Iron Works Engine and Pump Unit

Leader Iron Works.

Months ago, reader Eugene Cook sent in a photocopy picture of his Leader Iron Works 4 hp engine and pump unit, along with a brief note. We lost track of Eugene’s letter and are just now running it, with an enhanced version of his photocopy. Our apologies, Eugene! 

Eugene writes: “It has been in our family since the mid-1930s when my father used it to pump water for our dairy cows from a hand-dug water source in the pasture during summer drought periods. With the help of my mechanic friend ‘Scottie’ the unit was put back in operation several years ago and mounted on an antique display wagon that Scottie found. The water barrel has been replaced with a large antique cast iron kettle we used on the farm to heat water when butchering pigs before World War II.

Eugene Cook

Please send your questions and comments for Flywheel Forum toGas Engine Magazine, 1503 SW 42nd St., Topeka, KS 66609-1265 or email

Lauson Frost King Junior Down Under

Lauson Frost King

I would like to make contact with a Lauson expert. My engine is a Frost King Junior, serial number 14800, dated 1916. When the engine came into my position it was in a very poor state and needed a complete overhaul. The engine had in its working life been converted to high-tension ignition and with this setup runs very well. However, I have installed a modified Fairbanks-Morse igniter using a Sumter magneto with a homemade striker, but have not been able to get it to fire. From the information that I have, Lauson made its own igniter, but these are non-existent here in Australia. Lauson engines are rare in Australia and parts are scarce as the proverbial hen’s teeth. I belong to the Adelaide Hills Motor Restorers Club. We have about 200 members and we cater for vintage stationary engines, tractors, cars, motor bikes, farm machinery and women’s hobbies. I have 21 engines in my shed.

Warwick Ward

Please send your questions and comments for Flywheel Forum to Gas Engine Magazine, 1503 SW 42nd St., Topeka, KS 66609-1265 or email

Fairbanks-Morse Engine on the Job

Fairbanks Morse engine

Fairbanks Morse engine

Regular contributor David Babcock sends in two period photos from his collection, each showing a Fairbanks-Morse engine on the job. David says the horizontal engine is a Type N, and likely a 15 hp, judging by its size. The date and location are unknown. Type N engines were phased out beginning about 1914. The second image shows what looks to be a 6 hp Z. David thinks the photo was taken circa 1915, which would make this a very early 6 hp Z. The following was written with the photo: “I suppose you have your wood all cut. I have a six horse Fairbanks and Morse engine and a 30-inch saw with 126-pound flywheel which cuts wood very nicely. Have had some winter here the last month, 25 below. Next week will be time to get out the sap buckets.”

David Babcock
3491 E. Deckerville Road
Cass City, MI 48726

Please send your questions and comments for Flywheel Forum to Gas Engine Magazine, 1503 SW 42nd St., Topeka, KS 66609-1265 or email

More Vincent Engine Information

vincent engine

vincent engine

vincent engine

A few months back (Flywheel Forum, October/November 2015) I sent you some information about a Vincent “sailboat” engine (see photo, top). In addition, I had a few questions about a 2 hp Witte hit-and-miss. The Witte is now running and will soon be mounted on a cart. The Vincent turns out to be somewhat of an interesting story. It was made by Vincent, the British motorcycle manufacturer, but not for sail boats. It was an attempt to revive the company after it quit making motorcycles in 1955, and the engine was developed for lawn mowers and the first personal watercraft. My engine was used in the Amanda Water Scooter. It is a 100cc 2.1 hp Vincent 75. Neither the lawn mower nor the Scooter managed to save Vincent. The lawn mower had too much torque and the Scooter engine generated such high heat that it melted the fiberglass used in the Scooter and caused them to sink. Both are rumored to have caused the final demise of Vincent. There are numerous videos on the internet.

Robert Lundberg,

We had a suspicion your engine was related to the Vincent Amanda, a fact borne out by your research and further supported by photographs from the Barber Vintage Motorsports Museum in Birmingham, Alabama, which has in its collection both an Amanda Water Scooter (middle) and a Vincent lawn mower (bottom). Looking at other photos, we think your engine was originally installed in an Amanda Water Scooter owing to its fan-cooling cowling. The lawn mowers don't appear to have utilized this feature, only the Water Scooters. – GEM

Please send your questions and comments for Flywheel Forum to Gas Engine Magazine, 1503 SW 42nd St., Topeka, KS 66609-1265 or email