Detroit Myths debunked

[madhatter1]

Myths are just that. I was waiting for 5 full years of ownership to post something like this. Getting close to 6.

Detroit’s are cheap by other standards to rebuild. Yes parts sourcing can be a not so fun game. Potentially equal value replacements as I has to deal with on turbo’s.

They don’t bleed oil all over the engine room. Maybe unless poorly rebuilt. Possibly this is more of a 71 deal than on the 92’s. I’ll claim ignorance on this one.

This one is true. They run better hurt than most do healthy. Cannot stop them . This is based on my 46 Bertram that had worn 8-71’s. What a smoke show firing up in the Florida winter. First 1 cylinder would fire. Then more would join in. No mosquitoes for miles!

Reliability! We PM’ed ours to a great deal and they have been work horses. Nuff said.

Fuel burn. This is a big one based on 5-6 years of paying attention to comments on threads. Here and THT. Any boat my size will burn the same (although negligible amounts less for modern common rail engines) fuel per mile as my old Detroit’s.

At the end of the day it is better to deal with old Detroit’s for anyone without megabucks rather than repower to save fuel (yeah, right) or avoid catastrophic Detroit failure and bankruptcy by spending $400K to repower right now before it’s too late!

Really only downside is finding a good seasoned 2 stroke DD mechanic. I get that. When you find one make sure you become a “good customer”.

 

[madhatter1]

And in no way is this a rub on anyone’s choice to repower, past or future.

 

[jap201]

Really only downside is finding a good seasoned 2 stroke DD mechanic. I get that. When you find one make sure you become a “good customer”.

That's the only downside to a dd that i can see. The good 2 stroke dd mech's are all aging out, and the kids don't know what to do unless a laptop is hooked up. But if you find one, you're right. Be a good customer. Or learn to wrench on them yourself, like some of the guys here.

 

[Captain Ralph]

After 20 years with our 56' Bertram MY, our 46 year old 12V71TIs run just great.

Just have to find a good DD guy still with a strong back. None left around here.

 

[madhatter1]

After 20 years with our 56' Bertram MY, our 46 year old 12V71TIs run just great.

So they didn’t explode as soon as you started them? Not the norm according to the myths. Bet they burn 200 gallons an hour apiece.

 

[Captain Ralph]

So they didn’t explode as soon as you started them? Not the norm according to the myths. Bet they burn 200 gallons an hour apiece. 

2 stroke, 4 stroke or anything else, it takes the same amount of fuel to make the same horsepower.

The newer lighter engines, the newer paper shell boats, less horse power required.

New paper shell boats are ugly and expensive. And don't ride or sleep like an ole Bert or Hatt.

So we keep running what we have with smiles.

 

[Play'N Hooky Too]

I wouldn't say "bleed" oil...it's more like sweat.

 

[madhatter1]

I wouldn't say "bleed" oil...it's more like sweat.

Mine do “sweat” some oil. But certainly not leaks. Seems we are all on the same page.

 

[madhatter1]

The one thing I will stand strongly on is the don’t burn any more measurable amount of fuel per hour pushing the same boat. Most are installed on old school heavy glass boats. Crazy thing is I’ve noticed over the years is that any 45-46 boat burns what I burn. Oceans maybe slightly less• any other lighter boat same length same thing. But never enough to matter. $9k fuel bill for Bahamas would be what? $8500??

 

[Pascal]

There is no fuel Burn difference between DDs and 4 strokes. When my 8V71Ns bit the dust, the choice was to rebuild them or repower. An Inframe would have been cheaper but left me with many untouched parts incl the gear. By the time you add everything else incl the gear, all the ancillaries, etc the cost grows to close to what the Cummins factory reman with NEW ZF gears was. No brainer in the long run.

 

[CGHOST4]

I was in the same situation as Pascal, rebuild or repower. I chose repower, one unexpected difference was the reduction of weight. Those old 871 DD with the gears are very heavy. I went with Yanmar 6LY3, 485hp at the prop with ZF gear. The reduction of weight and the increase in HP resulted in a very economic 9 knot cruise, or a not too bad 17 knot cruise. As of today, 3864 hrs with just normal maintenance. For me the repower was the right choice, and the engine room sure has a lot more space.


Caesars Ghost
1980 58YF # 472

 

[madhatter1]

When they go pop decisions need to be made on best way to move forward. What I am getting at is the bad rap on perfectly good (which honestly probably are still in need of some PM) Detroit’s in an older boat. We did the repower thing on the34 converting to diesel. Quite an undertaking and this was on the small side of the scale.

But it was well worth it. Those who repowered here on this site did so to keep the boat. So of course happy with the outcome.

 

[jim rosenthal]

If Detroits hadn't been good in their day, Hatteras, Bertram, and all those other yacht builders wouldn't have installed them from new. The engine market wasn't nearly as big as now, but there were some alternatives.

 

[ageless]

2 months ago, while my 12/71 was being rebuilt the prices DD wanted for kits and a head were astronomical, mechanics concerned their phasing out the 2-stroke. FP kits are the way to go. Super excited to get the ole girl to the grounds, it's been waaaay too long.

 

[SKYCHENEY]

2 stroke, 4 stroke or anything else, it takes the same amount of fuel to make the same horsepower.

The newer lighter engines, the newer paper shell boats, less horse power required.

New paper shell boats are ugly and expensive. And don't ride or sleep like an ole Bert or Hatt.

So we keep running what we have with smiles.

Wrong. The new engines are more efficient. They burn the fuel with less emissions(unburnt fuel). My Tier III Cats burn 15% less fuel than my Detroits at every speed setting.

 

[SKYCHENEY]

If Detroits hadn't been good in their day, Hatteras, Bertram, and all those other yacht builders wouldn't have installed them from new. The engine market wasn't nearly as big as now, but there were some alternatives.

Cummins were a factory option on many of the models in the 70's but few buyers chose them.

 

[Boatsb]

They were an upgrade for many. More power but more cost. Most went in sportfish boats.

Not that detroits don't do the job but if I could trade up I would.

 

[CanadianBoater]

So are you saying the 12V92's are a better engine than the 12V71TI's?
Just curious.
I ran 871N's for 25 years and agree - they were bullet proof and very economical on fuel. Yes, smoked a little on start up and relatively clean...

Myths are just that. I was waiting for 5 full years of ownership to post something like this. Getting close to 6.

Detroit’s are cheap by other standards to rebuild. Yes parts sourcing can be a not so fun game. Potentially equal value replacements as I has to deal with on turbo’s.

They don’t bleed oil all over the engine room. Maybe unless poorly rebuilt. Possibly this is more of a 71 deal than on the 92’s. I’ll claim ignorance on this one.

This one is true. They run better hurt than most do healthy. Cannot stop them . This is based on my 46 Bertram that had worn 8-71’s. What a smoke show firing up in the Florida winter. First 1 cylinder would fire. Then more would join in. No mosquitoes for miles!

Reliability! We PM’ed ours to a great deal and they have been work horses. Nuff said.

Fuel burn. This is a big one based on 5-6 years of paying attention to comments on threads. Here and THT. Any boat my size will burn the same (although negligible amounts less for modern common rail engines) fuel per mile as my old Detroit’s.

At the end of the day it is better to deal with old Detroit’s for anyone without megabucks rather than repower to save fuel (yeah, right) or avoid catastrophic Detroit failure and bankruptcy by spending $400K to repower right now before it’s too late!

Really only downside is finding a good seasoned 2 stroke DD mechanic. I get that. When you find one make sure you become a “good customer”.

浪藍樂️浪

 

[madhatter1]

So are you saying the 12V92's are a better engine than the 12V71TI's?
Just curious.
I ran 871N's for 25 years and agree - they were bullet proof and very economical on fuel. Yes, smoked a little on start up and relatively clean...

No. In fact everything I have learned over the years is that the 92 series is vulnerable to the o ring failure. In theory the 71 series is a more sound design. At least that’s the way I understand all that I have read over time. Not really sure but doing well with my 92’s.

 

[SKYCHENEY]

No. In fact everything I have learned over the years is that the 92 series is vulnerable to the o ring failure. In theory the 71 series is a more sound design. At least that’s the way I understand all that I have read over time. Not really sure but doing well with my 92’s.

92's are easier to rebuild for the same reason (wet liner). Honing of the block to get the new sleeves to fit right on 71's takes more time and if not done correctly can cause a hot spot on the liner that will cause it to fail.