New a little DD education

[The Revenge]

Thanks in advance. I'm just trying to be a little more educated while searching through some of the boats on the market.
Mainly looking at 53 MY.

Some have the 8V71TI and some have 8V92TI (seems newer boats). I'm pretty sure the 8 denotes 8 cylinder. The TI turbo charged. Not sure what the 71 vs 92 means.

I've also been browsing around on dieselpro.com (just stumbled across it) browsing parts to get an idea of parts costs. Are there certain engine parts that are problem areas or you need to plan on changing more frequently? Are there key parts I should question in terms of when they were last replaced?

Are they only equipped with the Allison trans?

I've also read Pascoe's piece on marine diesels. He points out, although not recommended bumping up HP on these engines is nearly as simple as changing the injectors? Has anyone done that?

When these motors are overhauled do the blocks stay in place in the boat?

Thanks again. I've only owned stern drive boats.

[nor'easter]

Welcome,
The first number is # of cylinders, and if followed by a V is well, you guessed it a V. The 71, 92, 53 denotes the CI per hole.

So a 671 is an inline 6 with 426cid, and an 8V92 is a V8 with736 cid.

Much easier to make sense out of than the designation numbers for CAT engines.

[Passages]

Another little tidbit to keep in mind is the HP rating should not exceed CID for reasonable engine life. The lower the ratio the better. Pascoe explains it better than I can.

[Boatsb]

Jim there is a point of diminishing returns with the low HP. Yes my naturally aspirated 8V53 is a 424 CI engine at 280 HP. Do the math I am a bit over 1/2 HP per CI and will get 10,000 hours of service if I run them conservatively which make sense since it will take that long to get anywhere.

[REBrueckner]

"Are there certain engine parts that are problem areas or you need to plan on changing more frequently?"

If you want to run fast, use most of your HP, you'll be rebuilding faster, that's for sure. There are no particular problem parts I've heard about, but in general the cooling systems on the higher HP engines need to be kept especially clean for proper temperature control in tropical waters. The 71's rarely fail to get you home, unlike computer controlled modern high HP engines, unless it's a lack of fuel (say dirty) problem.

[I've not owned the larger displacement 92 series engines which are similar.)

On my 1972 435HP 8V71TI's, for example, the cooling system was disassembled and cleaned after I bought the boat....I wanted to be "sure" all was well as I cruised full time for six mos a year. It's now almost 14 years later, maybe 1600 hours, and the current owner ofover 2 years has had no problems. All in the NY to Maine NE area of the US.

If an engine runs too hot, a typical problem becomes scored cylinder liners...that means in general replacing rings and liners at a minimum, maybe pistons too depending on hours of usage.

"Are there key parts I should question in terms of when they were last replaced?"

None I know. Getting verification of any claimed "rebuild" or other work is required; otherwise disregard the claim. Good to know if the cooling system has ever been cleaned...but if the engines run at proper temp, around 180 or 185 degrees for a half hour at WOT in warm water, likely the cooling system is ok for at least few more years.

Are they only equipped with the Allison trans?

Seems most of the 71 series engines used them...On occasion an owner might specify a custom, like a HURTH...but the Allison M20's and MH20's are generally trouble free judging by posts here over the years. You can search here for trouble shooting and repair discussions....as with engines, proper operating temperature (via temp gauges) clean filters and proper, clean oil helps a LOT.

"I've also read Pascoe's piece on marine diesels. He points out, although not recommended bumping up HP on these engines is nearly as simple as changing the injectors? Has anyone done that?"

I know of a 46 '72 Bertram SF that had the same 8V71TI's as mine...a few slips away....he had bigger injectors and some other (not major) modifications and got another 2 knots cruise....but my former mechanic who did the work did NOT recommend it for my boat as higher HP means shorter engine lifespan. The mechanic did make some modification for additional cooling...don't recall any longer exactly what.

"When these motors are overhauled do the blocks stay in place in the boat?"

Can be done that way, but purists here claim removing them is better. It also depends on the engine room access and definition of "overhaul".

In a typical overhaul of maybe pistons,liners,etc but maybe not a crankshaft, seems unnecessary to haul the engines out...I had all that done in place....but maybe if transmissions AND engines need complete rebuild/overhaul, makes more sense to remove them for shop work.

If you are going to cruise at moderate speed most of the time,say 8 or 10 knots, be sure to consider 8V71 naturals....

Good luck searching for your Hatt!

[The Revenge]

Thank you.

[rsmith]

"If you want to run fast, use most of your HP, you'll be rebuilding faster, that's for sure."

No its not for sure. If your talking about one of the pumped up engines thats pushed beyond its rated hp maybe but DD recomends normal ops 200 rpm under WOT. I have run my engines and a bunch others at WOT for hours and hours without a problem. When I was in my teens I mated on a lot of different boats and everyone ran their engines "on the pins" back when fuel was cheap. I have seen NO documented evidence that a extra 200 rpm is going to make any signifigant difference in engine life. The real damage is done by lack of use and inital startup. And running bad injectors. The rest is just "old wives tales".

[The Revenge]

This is all great info. I'm up to page 132 of reading on this forum.
So far I've also gotten:
Don't idle the engines up to temp's. Fire them up and go.
Don't cruise around at hull speed all the time. Run at WOT at least once every time out.
Make sure to get them up to temp to help eliminate any water in the engine.
I think I also read the 8V71's don't have water jacketed exhausts.
Standard stuff: keep oils clean, cooling system clean, they are going "sweat" oil.
Some have installed "air seps".
Folks have installed water flow sensors to ensure adequate flow. Kind of questioning the whole mufflers made of fiberglass and can catch fire if too hot deal.
I also read the 8V71's are loud. Can you have a conversation in the salon underway? Or do they mean loud out of the pipes.
I also saw a pic of someone that put what looked like big pvc pipe extensions on their exhaust ports. Not sure what that does.

All in all these engines sound user friendly mechanically and way more durable than the gas motors I'm used to. They sound like there easy to work on.

"DD recomends normal ops 200 rpm under WOT"
What is typical WOT?

[yachtsmanbill]

Standard stuff: keep oils clean, cooling system clean, they are going "sweat" oil.

Ya dont hafta worry unless you turn them upside down and shake vigorously! It is whatcha make of it... ws

[The Revenge]

Was that a fire?