Dd...

[Miss Lisa]

Why is it when a boat for sale that has DD engines the hours on the engine are always quoted
"SMOH". It might be 200 hours or 800 hours since major overhaul.

With CATS or Cummins or Volvos you don't see this designation(SMOH). Do these engines go longer than the DDs between overhauls? If so, why?

I saw a boat with 6V92s and the seller offered to show the invoice for overhauling the engines. The cost was around $115,000. The engines were removed from the boat and the engine room was cleaned and painted white. Engines were overhauled and painted and replaced. The asking price of the boat now is $128,000!

I have also read on this forum that $3,000 per cylinder is close to the cost to overhaul in place.

 

[Scott & Malina]

Why is it when a boat for sale that has DD engines the hours on the engine are always quoted
"SMOH". It might be 200 hours or 800 hours since major overhaul.

With CATS or Cummins or Volvos you don't see this designation(SMOH). Do these engines go longer than the DDs between overhauls? If so, why?

I saw a boat with 6V92s and the seller offered to show the invoice for overhauling the engines. The cost was around $115,000. The engines were removed from the boat and the engine room was cleaned and painted white. Engines were overhauled and painted and replaced. The asking price of the boat now is $128,000!

I have also read on this forum that $3,000 per cylinder is close to the cost to overhaul in place.

Miss Lisa,
To answer your question, it's because most, if not all of the older (30-40 years) Detroits have been rebuilt at least once, twice maybe even three of more times depending on the use. The issue with quoting actual since commissioned hours is more of a marketing strategy. If a consumer knew actual hours, no one would buy the damn things because it would scare the hell out of the common person. Beside that, a major overhaul (done properly) would yield practically a new engine, less the crankshaft, cams and block. So, that knowledge aside from scaring people is really a moot point, especially if one is trying to sell a boat.

Regarding "CATS or Cummins or Volvos you don't see this designation(SMOH)", they are out there, you do actually find SMOH hours on them too. They require overhauling too, just when, depends on how well the operators have taken care of them.

Scott & Malina

 

[seasalt]

I am looking at a couple of boats with 8-71TI's showing about 2400 hours...either SMOH or since new.

How many hours is typical before one needs a MOH?

 

[Bob Bradley]

I am looking at a couple of boats with 8-71's showing about 2400 hours...either SMOH or since new.

How many hours is typical before one needs a MOH?

The HP of the engines will make that vary. High HP will require an overhaul sooner; lower hp will last longer - much longer in the case of naturals. Dave Pascoe's rule of thumb is that engines with HP that is higher than 90% of the total cid of the engine will fail much sooner than those below the 90% mark.

For example, my 6v92's make 435hp. 6 x 92 = 552cid. 435/552 = 78.8%. I expect, and have experienced, decent longevity on those engines. They are 1979 engines, and now have around 3200 hours on them. They start right up, even cold, and exhibit very little smoke. The same engines tuned up to over 600HP would not be expected to last as long - perhaps failing after as little as 1000 hours. Low HP naturals (non turbo charged engines) could reasonably be expected to last 10,000 hours or more before needing an overhaul.

Obviously, how well they are maintained will affect longevity as well. And, a high hp engine where the owner didn't push them hard may also last.

 

[Miss Lisa]

Re: DD...

Bob,

Thanks for a great explanation!

So according to your example a CAT 3208 375 hp would be:

375/636 = 58.96% should last for a very long time!

 

[SKYCHENEY]

The other thing about DD's is that they are very intolerance of being overheated. If cared for and maintained, they will last as long as other diesels, but many neglect cleaning intervals for the heat exchangers and intercoolers/aftercoolers. The wet-liner 92's are especially susceptible to overheat damaging the o-rings around the cylinder liners.

That said, DD's will run when still very sick, so sick that other diesels would be DOA. They have their pluses and minuses but overall a great engine in a boat. Unfortunately, the ones that don't get used much end up many times to deteriorate faster. Salt air gets into the cylinders and rusts the liners. Think of the wear when you start up with surface rust in there. Its always better to run them frequently than to let them sit. This is why many are overhauled with low hours.

 

[Avenger]

It varies. Some designs like the 3208 are at their best at or below 1/2 HP/cu in. Others at 1 per cube. There are no hard rules.

More indicative of lifespan for a particular engine type is fuel burn. i.e. a 3208 has a lifespan of X gallons regardless of HP rating. So since a 375 burns fuel faster than a 260 you can expect less hours out of a 375.