Primer hole on U heads.

[Robert Luland]

Good morning Gentlemen, time for another mind chartering question! On early U, UL, ULH heads I noticed there was a plugged primer port. Were primers ever used on these engines or was it just a carryover from VL and does anyone know when they stopped drilling and tapping this hole. Thanks, Bob L

[Steve Slocombe]

Dear Bob, the front UL heads are not identical to the 1936 VL ones, even though they have the same part number, as the UL ones have a dogleg in one fin to clear the new 1602-37 spark plug cable guide. The 1930-40 parts book shows the primers used 1915-37. I've guessed they were blanked off for another year or so, then the castings were smooth after around 1939/40. Like you, I'm interested in info from original bikes to show what really happened.

[Robert Luland]

Thanks for posting Steve; I personally don’t feel that the holes were ever used. Just an engineering carry over. In the engineer’s head was the seed that if ya got a flat head, you put a primer port in it. It’s not like you had a syringe in the tank as in earlier days. They would have been pretty hard to have gotten to and I can’t see the motor cycling enthusiast of the day running around with a metal turkey baster in his back pocket. Bob L

[Steve Slocombe]

Dear Bob, the priming gun 3517-25 was a standard feature on the bikes through 1934 and, when the larger tank caps were used 1935/6, the Riders Handbook says it 'can be obtained from your dealer'. The bikes were used every day, year round, in those times and older guys have told me that when the temperature dropped below zero Fahrenheit you not only had to use the primers to cut the oil on the cylinder walls, but also pour a pan full of boiling water over the gearbox to thin the oil enough for the kickstart to work. At the moment I believe the parts book that says the primers were still fitted to the first year ULs but, as always, original bikes will tell the story better than book studies.

[ronald]

1938 was the last year for primer holes. I believe the primer valves were available through that year. If the valves were not ordered, the holes were plugged at the factory with a square headed plugs.
Ron

[Kozy]

I've seen the primer cups on '38 U's. I had a set of heads with primer holes plugged with a slotted plug.

[Robert Luland]

I've never seen anything but the slotted plug. A pipe plug was against Harley's religion. Even the set screws on my 1917-23 side car connecting balls are slotted. I would like to see a factory picture with a pipe plug. Do the cast iron heads differ them selves over the years? I mean was there a differance in fin height or a differant casting or are they all the same thing? Bob L

[Steve Slocombe]

Dear All, I've only seen the slotted plug in early UL heads. With the new quarter turn tank caps you couldn't mount the older threaded primer gun, and I haven't seen any evidence of a primer for the new style tank fittings, so it must have made little sense to continue with the primer cups. I've mentioned the 1936 VL front head is different from the UL ones. There are some who say there are also differences in the finished height of the spark plug holes in the early heads.

[oldsouthmcy]

The primer gun for 1936 61" & 1937-1938 twins is #3517-36. It is not listed on the order blanks nor is it in any of the rider handbooks but it is listed in the parts catalogs through 1940, the 1936 Accessory Book & the 1940 Accessory Book. Don't have a 1937 Accessory book but I cannot find it in the 1938, 1939, or 1941 Accessory books.

The 1940 part book states it is for the twins up to 1938 but the 1940 Accessory book is making a pitch for owners up through 1940 to buy it.

Attached is a photograph of an original that John Nowak gave to me back in the 1980s. It came off of Bill Harley's 1936 EL that John bought from him in 1937. John did not find much use in the primer so he pulled it off and stored it.

IMG_9187.jpg

A close-up of the cap. I don't know if you can tell from the photo but the knurling is not even in height around the cap. It almost appears as though the cap was hand-knurled. Perhaps an Eaton proto-cap.

test.jpg

[Steve Slocombe]

Great picture, I've never seen one before, and yes I've just found it in my 1940 parts book saying it was used on 1936 knucks and in 1937/8. Many thanks, it's always fun to learn new stuff about old bikes. Does that mean 1936-38 knuck cylinder heads also has holes for the primer cups?