New prop

According to the specifications, the Atomic 4 should have a cruising RPM of 1900 and a wide open RPM of 2400. Apparently most people have too large a propeller and too low of an RPM. My problem was the opposite.

My cruising RPM was 3200 at 5 knots and if I wanted to get to 5.5kn I would be pushing 3500 RPM. While this RPM is still within the tolerances for the engine, it created a lot of unnecessary noise and vibration.

My old prop was a two blade 12x6 and it was undersized. I'm sure this helped a bit in my club racing since it had lower drag, and it was tolerable for cruising under power but it was an issue fighting heavy currents large waves. A sketchy trip through Letete Passage last year (yes, at the wrong tide...) confirmed my need for more available speed.

After a recommendation from Bill on Lady Hamilton I picked up a prop from Indigo Electronics. Indigo was very easy to deal with and were quick sending out the prop. The prop is a three blade 10x7.4 and seems to be of high quality.

After finally launching this weekend I was happy to test out the prop and see the results. My cruising RPM is now at 2600, at 5kn. This is still a little higher than desired, but much better.

Atomic 4 Rebuild - Introduction

Recently I came into possession of an Atomic 4 engine. A local sailor upgraded to a new boat and had a spare engine from his old boat that he had intended on rebuilding. I am taking over the rebuild project.

Goals

I have a few goals for this project:

1. Increase knowledge: Increase my knowledge of Atomic 4 engines so that I am more capable of troubleshooting and repairing my boat when needed. I am not mechanically inclined but need to be more self sufficient given my desire to cruise further in this boat.
2. Spare: Given that my current A4 is 42 years old, a spare is important to avoid lengthy losses in precious summer boat time.
3. Upgrade: Assuming that I am successful in this build, my plan is to eventually swap this new engine with my old one to provide more reliability and performance.  Not that my engine has been particularly problematic, it has been reliable for the most part.

Mechanical ineptitude 

Ineptitude may be a little strongly stated, however, I have very little mechanical experience. Over the last few years I have tried to increase my knowledge of engines and marine systems and I have successfully done some maintenance and repair jobs on my A4 (thermostat and exhaust manifold were the big ones).

All of this is to say that this engine rebuild will be completely new ground for me. While this is a great experience for me, it does mean that you should take my techniques, suggestions and recommendations with a BIG grain of salt. Talk to a mechanic if you want real advice!



My primary resources, initially, for this project will be:
THE COMPLETE OWNERS & SERVICE MANUAL FOR THE 
UNIVERSAL ATOMIC 4 GAS ENGINE

Engine Builder's Handbook

I will chronicle this rebuild as detailed as possible so that others might find something useful out of it. All of the posts will be available under the label Atomic 4 Rebuild.

Atomic 4 Thermostat cleaning

While investigating cooling issues in my Atomic 4 I came across an FAQ at the Moyer Marine site that described cleaning the thermostat every season. "It really is better to use a thermostat in the Atomic 4, and to keep it clean by soaking it in vinegar every season." 

While I have had my thermostat out annually for winterizing, I have never cleaned it. So I decided to give it a try.

Half way clean, after 2 days soaking in vinegar

I had no idea how dirty the thermostat was! In fact, I though that the thermostat had been rusty but, now that it is clean, I realize that the rust was just gunk. 40 years of gunk took 3 days of soaking to clean (and 3 changes of vinegar).

I also wasn't sure what temperature rating my thermostat was rated for so I tested it by boiling it.

The thermostat started opening around 125 degrees Fahrenheit and was fully open around 160 degrees.It was approximately 1/4" open at it's fullest. I'm not sure if either of these are measurements are within spec because I can't find a good reference online. If anyone knows, please comment below.

I'm not sure if my dirty thermostat was the cause of my cooling issues but it couldn't be helping.