Atomic Bomb:

The Universal Atomic Four Engine:

The venerable, but discontinued, Universal Atomic Four gasoline engines is often affectionately called the "Atomic Bomb". The original engine installed in my boat, Mystic, in 1975 is still going strong, with no major repairs. The Universal Motor Company started business as a marine engine manufacturer and the A-4 was designed from the ground up as a marine engine. It even utilized special corrosion resistant metal alloy's. Of the 40,000 A-4's originally installed between 1947 and 1985, in boats from 25' to 41', around 20,000 of these reliable little engines are still in use. At thier peak Universal had 85% of the sailboat market. For more interesting facts on the history and design of the engine, visit the Atomic Four Engine Service web site by Robert Hess .


Over the years owner's manuals often get lost. Below you can view and download a digital copy of the one that came with my boat. This Universal Motors manual is not copyrighted. Each image (1-2 pages) can be viewed seperatly so you can read or copy only those that you need. Small diagrams have been enlarged so you should be able to read just about all of the text in the diagrams.
TOCA4.TXT 9k A text version of this Table of Contents
A4Cvr.GIF 32kFront cover only
A4Pa.GIF 68kEngine Operation & Important Note
A4Pb&P01.GIF 90kWarranty & Page 1
P02&3.GIF 95kPage 2 & 3 Engine Specifications
P04DD.jpg 68kPage 4 installation dimensions, Direct Drive
P04RD-AP.jpg 90kPage 4 installation dimensions, Reduction Drive & Aqua Pack
P05Stbd.GIF 90kPage 5 Photo Starboard (right) side engine
P06Port.GIF 90kPage 6 Photo port (left) side engine
P07.jpg72kPage 7 Gen. suggestions & exhaust diagrams
P07F1-2-3.GIF 63kPage Enlarged exhaust diagrams
P08&9.GIF 122kPage 8 Suggestions before starting, Page 9 Zenith 61 series Carberators
P10&11carb.GIF 108kPage 10 & 11 Zenith 68 series carberators
A4carbA.GIF 77k Page 10 Enlarged Carburetor Diagram A
A4carbB.GIF 68k Page 10 Enlarged Carburetor Diagram B
A4carbC.GIF 63k Page 10 Enlarged Carburetor Diagram C
P12&13.GIF 113kPage 12 & 13 Electrical Diagrams
P14&15.GIF 131kPage 14 Electrical, Page 15 Cooling system
P16&17.jpg 126kPage 16 Oil circulation, Page 17 Valves, ignition, safety
P18&19.GIF 126k Page 18 Transmission adjustment Page 19 Water pumps, generator, V-drive
P20&21.GIF 104k Page 20 & 21 preparing for spring service and winter storage
P22&23.GIF 113kPage 22 & 23 Trouble shooting
P24&25.GIF 104kPage 24 & 25 Trouble shooting
P26.GIF 36kPage 26 A Final Word


The following are not part of the Owner's Manual
A4BrochF.GIF 197kAtomic Four Brochure Front Page
A4BrochB.GIF 167kAtomic Four Brochure Back Page
A4Parts.txt 26k This text document lists parts, suppliers and maintenance information. I suggest you print it out and keep a copy aboard as a reference.
A4Tips.html 128k: NEW IMPROVED: collection of maintenance/repair tips for the Atomic Four Engine
Port Side:Original A4 engine (Serial #s 170507 & older).
Starboard Side: Original A4 engine (Serial #s 170507 & older).
FUELPUMP.GIF Mechanical fuel pump rebuild diagram provided by Terry Kuhn - Engines by TK
FUELPUMP.TXTMechanical fuel pump rebuild instructions provided by Terry Kuhn - Engines by TK
Dirty Carberator If you have never overhauled your carberator, the photographs on this page make it clear why you should consider doing so.
A4Mechanics.txtList of Atomic Four Mechanics, USA & Canada
A4 muffler Photograph of A4 muffler installation.
Oil Pump OutI installed a tee and valve on the oil pressure take off port so that I can use the engines oil pump to remove the oil. Read more about it here.
What is this? strange device inserted in alternator wire by previous owner (PO), it is in the alternator wire that connects to the positive terminal of the coil. The pencil notes on the diagram are from the PO
Step 1 Step 2 Step 3 Step 4 Step 5 These photo's illustrate the steps to remove a rusted Galvanized Iron pipe from the exhaust manifold fitting. These fittings are expensive so worth a little effort ot salvage them.
NewExhaustA: Comparison A new and old exhaust pipes.
NewExhaustB: Comparison B new and old exhaust pipes.
A4 wiring diagram: I've combined the information shown on several different A4 wiring diagrams, you may find this useful
reserved: Photo of burnt out Petronix Electronic Ignition. This component will burn out if the ignition key is let on when the engine is not running. This also burns out coils. Neither of these problems were documented by the A4 Owner's manual or the Petronix installation instructions at the time when I bought this ignition. Subsequently I learned that electronic ignitions are very hard to diagnose when they malfunction. I've gone back to the much more reliable and easy to diagnose breaker point system.
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...The amount of oil that an Atomic Four engine can hold varies with the angle or slope at which it is installed. Most Pearson hull sections that I have seen indicate that the engines are installed at around 14-15 degrees from horizontal, which is the maximum recommended by Universal. The Owner's Manual says the engine should hold 4-5 quarts of oil, this always puzzled me because I have never been able to remove/add more than 2.75 quarts. Don Moyer advised that the engine traps about 1.5 quarts of oil inside its various passageways. At this extreme slope, the remaining amount of oil that you can remove from or add to the crankcase is only 2.25 to 3.5 quarts. Since you cannot remove all of the dirty oil from the engine it is very important to check and change it after every 50 hours of use, OR no less than once every fall before lay-up, which ever comes first. You may also want to change the oil, let the engine run awhile to flush it out and then change it again to remove more of the contaminated oil.


Featherman Enterprises: John Featherman is back in business sellin the most common A4 maintenance parts

"Featherman Enterprises"
John Featherman
To Order Call: 717-432-9203

Atomic Four Links:


NEED HELP? For lots of FREE advice on troubleshooting or repairing your A4 engine, join the Atomic Four Mailing list at by sending an email to

Indigo Electronics

Cruising Design Prop for A4

Care and Feeding of Atomic Four, George Dinwiddie's Alberg 30 website

Engine repowering by Oldport

Torresen Marine: Universal Atomic Four parts, used and rebuilt engines.

Marine Parts

Foley Industrial Engines (A4 Carberators/Fuel Pumps)

Pearson Ariel (26) Association:

This site has interesting information on what the boat and Atomic Four (engine options) cost in 1962 +/-
Pearson Ariel
With outboard motor well $6,500
With Atomic 4, lights, wiring generatory & battery $7,950

Atomic Four Engine Service - Canada

Rebuilt engines, parts and more. This site, by Robert Hess has an EXCELLENT history of Universal Motor Co. & Atomic 4.

Atomic Four in a Pearson 30

Chris Wilson's ( Pearson 30 web site. Includes photos of the water pump. This installation looks identical to that in my 1975 Pearson 28, including that funky galvanized muffler pipe, except engine access is worse in the P-30.

Atomic Four Chat Room

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Captain Ron