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Atomic 4 replaced by Volvo MD6A diesel?

Apr 23, 2014
54
Irwin 28 Long Island
I've had some trouble with my Atomic 4 and have compression issues, potentially something really bad going on in the block. I have a hell of a deal being offered to me for a Volvo diesel MD6A that is beautifully rebuilt and ready to go.

My boats total displacement is 7800 pounds. So with a 10hp diesel I believe that is considered too weak for coastal cruising.

Would you swap the motors or stick with the A4?
 
Oct 26, 2008
5,011
Catalina 320 Barnegat, NJ
I went the expensive route and replaced with a new diesel that has almost twice the hp that the old 1GM had.

But it really depends on your budget and desires. I tend to spend money on what I want rather than make do with what I consider to be a poor compromise.

It also depends on whether or not your A4 is repairable for long-term. I don't consider short-term repair an option ... where is that going to leave you when you try to sell the boat or suffer the same circumstances at a later date?

I agree with your assessment that the 10 hp will leave you under-powered. Does the A4 provide suitable power?

So what are your compromises .... an underpowered, reliable diesel, or a marginally suitable A4 that may be totally unreliable. Neither may be the answer.

I've suffered some remorse for the money spent on the engine that is my first choice (naw, not really), but never when I'm cruising along under power. Obviously, I think enough about the boat to make the improvement (another important factor).
 
Feb 10, 2004
3,508
Hunter 40.5 Warwick, RI
Point of comparison: I had a Morgan 30 (10500#) with an A4- 30hp. I generally ran it at the point on the power curve that it produced about 17-19hp. I think the Volvo diesel would produce more torque than the A4, but at 10hp I would think that it would be too light for challenging conditions but OK for 95% of what you would encounter in LIS.
 
Apr 23, 2014
54
Irwin 28 Long Island
Thank you for your input Scott and Rich,

I think in the long term this A4 is just not a viable option. I will most likely encounter the same issues again. So that does make me want to go for the diesel, even if it is a bit under powered.

I'd rather be cruising with a reliable motor, even if it is a bit less powerful, then taking such a big risk of being out there with this A4 that will most likely fail me when I need it most.
 
Nov 7, 2012
678
1978 Catalina 30 Wilbur-by-the-Sea
You can buy a like new A4 block for about $2500 from Moyer Marine and just swap the outer parts. Heck. You can buy a brand new A4 from them and just hoist it in.
 
Feb 10, 2004
3,508
Hunter 40.5 Warwick, RI
Have you checked Beta Marine? I think (but not sure) they have a drop-in replacement for the A4.
 

Sumner

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Jan 31, 2009
5,254
Macgregor & Endeavour 26S and 37 Utah's Canyon Country
....But it really depends on your budget and desires. I tend to spend money on what I want rather than make do with what I consider to be a poor compromise......
Wise words :). Doesn't make any difference if it is the house, the boat or the car I'll do what makes me happy and forget if I ever get it back or not. It has worked well,

Sumner

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ebsail

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Nov 28, 2010
241
O day 25 Nyack. New York
You need at least 2 HP per 1000 lbs. 10 HP will move your boat just fine with NO current or NO headwind or sloppy conditions. When the chips are down,(getting dark, home is upwind and a 3' chop, and 25 knotwind in your face) you will have a speed of "not enough" Those conditions need horsepower. Not torque. I had a 35 Ericson 12,500 lbs. with a 24 HP diesel and with a headwind of 20K we made good 3 K over the ground. 2 HP per 1000 lbs is the minimum when the conditons deteriorate.
 
Jun 8, 2004
853
Pearson 26W Marblehead
engine replacement

my 2 c In the past I have dumped 2 gas inboards one a palmer 22hp The other, the ubiquitous Atomic 4 The Atomic 4 was obsolete over 30 years ago. Why look for trouble. Most certainly the beta made to replace the A4 would be a good choice. The Volvo would also do the job. I doubt if the Volvo would be underpowered except in the most extreme conditions.
 
Apr 23, 2014
54
Irwin 28 Long Island
You can buy a like new A4 block for about $2500 from Moyer Marine and just swap the outer parts. Heck. You can buy a brand new A4 from them and just hoist it in.
The block from Moyer is a bare block so the cost goes up a lot once you figure in all the internal components you need. But that was a thought of mine considering my starter, carb, fuel pump, fuel water separator, coil, and distributor are all brand new. I am having a mechanic look over the block to see if he can remedy the issue, so I am going to try and stick with the A4 as long as I can. I am contacting Beta Marine for pricing though. Thanks for the info everyone.
 
Jan 25, 2011
2,223
S2 11.0A Anacortes, WA
Kinda hard to answer this question since we don't know what the "hell of the deal" is.... At least that I could see.
 

Joe

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Jun 1, 2004
7,446
Catalina 27 Mission Bay, San Diego
Wise words :). Doesn't make any difference if it is the house, the boat or the car I'll do what makes me happy and forget if I ever get it back or not. It has worked well,

Sumner
Ditto that.... It's exactly what I was thinking during the "house paint" thread.... Just couldn't understand the point of trying to save a few bucks to achieve an unknown result.
 

BobM

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Jun 10, 2004
3,269
S2 9.2A Winthrop, MA
Keep in mind that parts availability for old Volvos can be poor. If something has to come from the motherland you could lose weeks of sailing.
 
Jan 13, 2013
214
Catalina 22 Lake Champlain
I suggest using HP as the basis of what is - or isn't powerful enough to do the job will result in a poor choice.

Compare the torque of the Volvo MD6A (or any other diesel) and the A4.

Regarding parts availability? The 50+ year old Volvo Penta series still has all parts available from someone...
 
Jan 22, 2008
53
Macgregor 21 MN
First of all this is a sailboat, right? I have a 7.5 hp (peak) 1GM Yanmar in my stock 6,000# Cal 27. While I don't have strong currents to deal with, It will maintain 5 knots in direct headwinds and waves under power alone. Under mainsail and power it is even better. You will need a bigger prop for the diesel conversion.
 
Jul 18, 2014
14
Hunter 34 Sydney
2 HP per 1,000 pounds?
I recently acquired a 1985 Hunter 34 with the 3-cyl. 22HP Yanmar (leaks oil from pan gasket). This boat is overweight with extras (lift scale says 15,000!!), it is over -propped with a 15x15 (should be 15x10?) so will only make 3,000 rpm with (smoke), but dialled back to 2,200 rpm (which is approx. 14 HP) this efficient hull will make 5.5 knots in slight chop, no headwind. Smooth water, 6 knots. The magic is 1.5 litres/hour at that setting which translates to 17 usmpg!

Before you say (I have heard this from several boaters) that you need to run these diesels at 80% of redline otherwise you'll have problems, I met an old German mechanic who specialized in Yanmars and he said this was nonsense. The lower rpm is no problem, in fact should extend engine life.

So.... lugging this engine with a over-pitch may be a beneficial solution.
 
Jan 15, 2013
4
Catalina 30 San Diego
Atomic 4 vs Volvo 10hp

We bought our Catalina 30 two years ago. The previous owner had converted from the Atomic 4 to the 10hp Vovo Penta engine. It was very underpowered. After backing out of the slip, we would have trouble getting the boat to move forward into a moderate wind. We decided to get a larger prop because we had more torque with the diesel but less horsepower. We found we couldn't increase prop size because the tip of the current prop is already within an inch or two of the hull. Our only solution was to get a prop with a larger pitch which cost a few hundred dollars as I recall. It did help the boat speed by about a knot, yet our max speed with this engine is still only around 4 knots. Not good on a windy or choppy day...
 
Dec 31, 2012
91
Catalina 28 mkll #649 Port Charlotte, fl
I want power…. I have been in some real rough seas that I really don’t want to be in….. With current, wind, rain, rough seas and other potential problems should I turn the key; I want to have the needed power to get through that cut or around that point without fighting for hours……. A good strong engine is a potential long term solution for one of the major problems boaters face…..
safe sailing
keys please, ( is what my boat whispers every time I hoist my main…)
 

Clark

.
Jun 30, 2004
880
Hunter 280 Lake Guntersville, AL
I've had some trouble with my Atomic 4 and have compression issues, potentially something really bad going on in the block. I have a hell of a deal being offered to me for a Volvo diesel MD6A that is beautifully rebuilt and ready to go.

My boats total displacement is 7800 pounds. So with a 10hp diesel I believe that is considered too weak for coastal cruising.

Would you swap the motors or stick with the A4?
Another point of reference. A friend has a Cherubini Hunter 27 (7000 lb) with a single cyl diesel. We are on an inland lake/river so conditions are generally pretty tame. His single is IMHO inadequate. If I were to go through the trouble of converting to diesel (remember, you'll have to drain and clean the tank, reconfigure engine mounts, replace prop and maybe shaft) and; going that far, I'd replace all the fuel lines and upgrade the primary filter), I'd opt for a 2 cyl in the 14 - 18 hp range. Would not be cheap but you would LOVE the performance and reliability.
 
Oct 26, 2008
5,011
Catalina 320 Barnegat, NJ
The block from Moyer is a bare block so the cost goes up a lot once you figure in all the internal components you need. But that was a thought of mine considering my starter, carb, fuel pump, fuel water separator, coil, and distributor are all brand new. I am having a mechanic look over the block to see if he can remedy the issue, so I am going to try and stick with the A4 as long as I can. I am contacting Beta Marine for pricing though. Thanks for the info everyone.
It makes it doubly hard to abandon your engine when you've already spent money on it. I had a re-built tranny and a new starter in my 1GM when I decided to cut bait!

Good luck with the repairs. It doesn't hurt to extend the service of this engine if that is what you want. I agree with you if you think the alternative isn't enough power. It doesn't make sense to purchase a replacement (with the substantial effort needed for conversion, as others mentioned) and still come up short in that regard.

The 2YM15 that I put in my 5,700 lb boat takes me up to 7 knots in smooth water. My prop was over-pitched and the 1GM, while making a little over 6 knots, topped out at 2400 rpm (with black smoke - 2200 was smoke-free). I disagree with the earlier opinion that this is ok. It definitely contributed to the need for re-build ... which I haven't done (she's in my basement waiting for some attention).

There are some nice advantages to the new engine as well ... it's freshwater cooled with heat exchanger to make hot water. It has an 80 amp alternator, rather than the smallish 35 amp alternator. It runs far cleaner, smother and quieter than the old chitty chitty bang bang! All things to consider ...

The footprint is just 2-inches longer (same width) and the compartment had no problem with the retrofit so it worked out very nicely for me. I was ready for a new tank and exhaust components so it was a good time to make the switch. Much as I like to sail, I couldn't live with anything that doesn't make hull speed when you need it or want it.