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New Life For An Atomic 4

Replace or Make Whole?



After serving well for 35 years and an incident that rather scared me I decided it was time to take a close look at the Atomic 4 again and see if indeed it could continue on as a safe, reliable source of propulsion.  Don’t get me wrong; the A4 has delivered a remarkable level of performance and reliability, and it still runs well.  But sooner or later the marine environment has to take its toll and I wondered if that time was coming soon.

So, what happened?  On two occasions, each lasting less than a minute, the number 4 (aft-most) cylinder cut out, only to reactivate by itself just as I finished determining which cylinder was not contributing.  Hmmm, strange, but not alarming.  Thinking that it might be an electrical problem I started to remove the number 4 spark plug, only to find that it took considerable effort to unscrew the plug – not just getting it started but turning it all the way out.  I replaced the plug with a used spare and the motor ran just fine, so forgot about it from then on.  Without realizing it I had just glossed over a severe problem.

Some weeks later and four days before we were to head for Maine and join other Tartans at a rendezvous the scary thing happened.  Having just finished sailing with some guests on board we were motoring back to the mooring with about five minutes to go.  Joyce was driving and I was just relaxing when I noticed the oil pressure gauge suddenly quiver and drop to zero.  Aagh!   But the engine was purring along smoothly and not clattering in death throws, as one would expect with no oil flowing, so I didn’t dive for the ignition key to shut it down.  Not wanting to cause alarm I calmly went below and lifted the engine cover, saw that the A4 still seemed OK, and reached my arm in past the port side of the engine with the intent to wiggle the oil pressure sending unit wire.  I never got that far.  Hot exhaust blasted against my arm from somewhere near the forward end of the engine.  Now suddenly holding my breath I returned to the cockpit and ordered everyone to stay out of the cabin.  There was no exhaust smell that I could detect, but I attributed that to having all the portlights open.  By then we were just arriving at the mooring.

About six weeks before this I had replaced the hot section of the exhaust and the flange that attaches the exhaust pipe to the exhaust manifold.  I simply thought I must have screwed up the job somehow.  So, the following morning, armed with another gasket I went to reset the flange and started the engine.  Still, there was the blast of exhaust.  With a mirror I looked for the source and discovered a rather large hole in the exhaust manifold – right over the carburetor intake.


While poking around the exhaust manifold I noticed that the flame arrester on the carburetor intake was piled high with pieces of rust, no doubt from the disintegrating manifold.  I cleared away the debris and removed the carb to clean it, reasoning that some rust must have gotten inside.  One glance inside revealed a very rusty choke plate and a considerable build-up of salt cake all over the inside.  One thing was certain: this problem had been festering for quite some time.  Judging from the size of the hole in the exhaust, the amount of salt build-up in the carb, and how rusty the choke was, this could have been coming on since sometime the previous year! 

But it ran so nicely!  Why?  Why hadn’t we succumbed to carbon monoxide poisoning?  Remember the difficult-to-remove number 4 plug?  All four of them were like that.  Apparently the motor was ingesting most, if not all the exhaust from the hole in the manifold, which might explain where the CO went.  But the salt?  The only thing I can fathom is that with some of the exhaust exiting early through the hole, the reduced exhaust pressure at the waterlift muffler must have allowed some of the seawater meant to cool the exhaust to back up to the manifold hole, where it sprayed down on the carburetor.  That would explain the corrosion of the adjacent oil pressure transducer that caused the OP gauge to quit working.  And yes, I do check the exhaust for water pumping - regularly.  It always appeared OK. But a little saltwater and exhaust had been passing through the engine all the time.  The cylinders were all very dry and thinly rusted, as if pressure-washed and blow-dried.  Not good.  I poured Marvel Mystery Oil into each cylinder to soak until I could replace the manifold.  Had I destroyed this engine?

Chancing that I hadn’t, but suddenly worrying that we might not make the trip to Maine I placed a rush order for a new manifold from Moyer Marine and had it sent overnight at great expense.  It came the next day but I could not get the old manifold off because the middle of three studs was corroded fast to the manifold.  I worked all day, trying and failing to remove the stud or manifold.  On the day we were to leave I resorted to manually hacksawing through the manifold in two places so that I could rotate the mid-section and unscrew the stud from the block.  The new manifold was in place by 6 PM.  True to form, the A4 started up instantly and ran as fine as ever.  We left for Maine the following morning and cranked the A4 hard to make up for lost time.  It purred on like nothing had ever happened - truly an amazing engine!

The only thing that wasn’t quite right with the A4 during the Maine trip was that the oil pressure ran about ten pounds less than what it typically had.  This could have been from the water/exhaust mix wearing the cylinder walls and rings.  But it never missed a beat!  After the trip I changed the oil, which had always remained clean and full.  (Adding oil filtration to this engine back in ’02 was a smart move.)  Between the time of the oil change and the end of the season the oil pressure gradually regained its ten pounds – hopefully because the rings smoothed out and reseated themselves. 

I made up my mind to pull the A4 out of the boat in the fall for two reasons.  One, I wanted to give it a thorough going over during the winter and examine it for wear, corrosion and any elements needing replacement or adjusting.  Besides, it could use a new paint job.  Two, something that had been under my skin for years, I wanted to put in some proper motor mounts in the engine bay.  The engine was bolted hard to the rails and resonated the whole hull at cruise speed.  I checked the compression and found all cylinders to be in the 100-105 lb range, so apparently the rings and valves were OK.  (This engine was rebuilt nine years, or about 500 hours ago.)