Jacobsen 2cycle info Needed

Andrew Mackey

Moderator
Re: Jacobsen 2cycle info needed.

The engine pictured is typical for those used on the 4 acre, estate and others built from the 1920s into the early 1940s. hard to date if you do not have the original data plate from what it was mounted on, as jacobsen did not tag the engine, only the equipment. If your engine has the drip oiler on the intake, the engine is probably pre 1930s, as jacobsen eliminated it around 1931 or so. That year, they went to a 16:1 fuel to oil ratio, using SAE 30 non-detergent oil. before that they used around a 32:1 mix and you set the drip oiler so the engine just smoked a bit. On all engines, you had to drain off a little crankcase oil, if the engine began spewing liquid oil out the exhaust or if the engine wet fouled the spark plug. These early jacobsens needed liquid oil in the sump, the con rod big end actually had a diper, like 4 stroke engines! The rod is solid phosphor bronze, as are the crankshaft main bearings. Early Jacobsens had gears between the end of the crank and the American Bosch mag. Earliest had fine teeth that caused breakage when grass clippings built up between the teeth. Later engines had coarser teeth and a little more slop in gear mesh, but no more broken mags! Around the mid 1930s, jaobsen went to a direct drive off the end of the crnk, using a lovejoy link, usinga WICO mags. As for parts - virtually non-existant unless you can find a donor parts machine.
 
Re: Jacobsen 2cycle info needed.

Can you give me a little more on starting it...looks like there is a spring check of sorts that screws on the end of the carb..
 

Andrew Mackey

Moderator
Re: Jacobsen 2cycle info needed.

On the carb inlet, on some of them, there is a snifter valve that acts as a partial choke. this is because the carb venturi is innefecient, and like some 4 cycle engines, the carb needs a little choke to work properly. On the carb, under the fuel tank, there should be a button on the float bowl top that will dunk the float. depress the button until gas coes out the overflow. this floods the carb, acting as a primer to get gas into the engine. on my 4 Acre, i had to open the fuel valve 1/2 turn to start the engine, and then turn in about a 1/4 turn to run. You do have to adjust the mixture screw for the throtle settings! each engine has its own particular wants and needs, trial and error settings if you will. Some pictures of your engine would be a grat help in getting you started.
 

Andrew Mackey

Moderator
Re: Jacobsen 2cycle info needed.

Yes any oiler should work. 3/8 pipe base. I do not see the flooder on that carb. so you will have to open the fuel nedle to about 3/4 turn out to start. If the engine does not start after 4 or 5 revolutions, close and crank a few tuens to clear out the carb, and re-try.
 
Re: Jacobsen 2cycle info needed.

ok another question i have m
never started this engine...so it looks like it used a crank of sorts. my question is which way does it start, cw or ccw....
 

Andrew Mackey

Moderator
Re: Jacobsen 2cycle info needed.

clockwise opposit the mag side (carb to the right, muffler to the left). On a stand alone power unit I had, a wrap a rope starter was used. I have a jacobsen 2 cylinder 2 stroke I made a wrap a rpoe starter for. i used a piece of 1/2" pipe and a wall plate, and bolted on a large B&S wrap a rope strrter from a 1960s aluminum block engine. The pipe ws drilled to accept a bolt that went thru the flywheel on the input side. It took a 5/16 bolt that went thru the flywheel hub.
 

Andrew Mackey

Moderator
Re: Jacobsen 2cycle info needed.

I didnt get a chance to ask, the computer shut down on me. Do you have the tin work for the engine cylinder? If not, it probably will overheat if run for long.

The hand crank I had for my 4 acre engine was made up out of pipe and fitings. If you can envision this: on one end, a 3/4" x4" nipple with the threads cut off on one end. A notch was cut in at a 45 degree angle, about 1/2" deep, from the left side of the end.. A second straight in cut was made to intercept the angled cut. That straight cut engages a pin on the shaft that was installed into the end of the flywheel. When the engine was cranked, the flat would drive against the pin, and when the engine started, the pin woulld drive against the 45 degree cut, forcing the crank out of engagement. The nipple was threaded into a 90 degree ell. A second 3/4" nipple, 5" long, was threded into the ell. On the other end of that second nipple, a 3/4 x 1/4 ell was mounted. A 1/4 x 5" nipple was installed into the ell. A 1/2 x 5 brass nipple had both threaded ends cut off and then was installe over the 1/4" pipe nipple, and then a 1/2" washer, then a 1/4 pipe cap installed on the end of the 1/4 nipple. This allowed the 1/2 pipe to rotate as you turned the 'crank'. All joints were tightenned until extremely tight, so all nipples were on the same plane. The cap on the 1/4 nipple was tightenned just enough to make for minimal clearance for the ends of the 1/2", so you would not get pinched when turning the crank.
 
Re: Jacobsen 2cycle info needed.

i do not have the tins,,, i may try to recreate that crank set up,,not sure on the plug type the white part of mine is busted...
 

Andrew Mackey

Moderator
Re: Jacobsen 2cycle info needed.

If I remember right - 18mm plug, Champion D-21 comes to mind, modern number. old number was 9 COM If a pipe thread base, Champion X works fine
 
Re: Jacobsen 2cycle info needed.

.................Yes............
How can I tell if the one iam buying, has a ck ball...if it doesn't...is there any way to ais there any way to add a ck valve, also on the 4 acre mower how big around was the drip feed.
 
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Doug Tallman

Subscriber
Re: Jacobsen 2cycle info needed.

I found this carb and tank in a swap somewhere years ago and bought it in case I ever decided to do something with my 4 acre mower. I'm fairly certain all the parts were original, including the oiler. I couldn't figure why you needed a check ball for this application. If you have blowby out the carb, you have more serious problems than an oiler without a check. The oiler measures about 2 1/2 inches across. The main body is a little over 2 1/2 tall too. The ball would be seen in the inside of the threads if it had one. This oiler doesn't have one.
 

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Andrew Mackey

Moderator
Re: Jacobsen 2cycle info needed.

The Jacobsen 2 stroke is a piston port induction engine. No reeds as the piston does all the work. You do not need a check in the oiler. You start the engine and adjust the oiler so the engine just smokes a little. use SAE 30 NON deterhent oil or oil rated TCW-3. NO pre mix, nor synthetic lubricants. They are not made for the plain bronze rod or bearings. To be safe, i would use the 16:1 mix to start with.
 
Re: Jacobsen 2cycle info needed.

what should the plug gap be set at? so open the fuel valve 3/4 of a turn and see what happens? then go from there? also when i set the mag up, i need the piston about 1/8 from tdc
and the points on the mag just starting to open? going to try and start it for the first time tomorrow...any sujestions?
 
Re: Jacobsen 2cycle info needed.

so i got this engine running runs well... but since it not mounted on a mower, just a metal stand it viberates to beat hell...can the flywheels be balanced, or is there any way to smooth it out? it came with another set of flywheels..
 
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