8V71TI and M 20 weakpoints?

[REBrueckner]

Passcoe at http://www.yachtsurvey.com/boatreviews/Hatteras53.htm
says:
"...The primary weak point is the 8V71TI engines which have a poor turbocharger/intercooler system. The two part AirResearch turbos are held together with acorn clamps that frequently crack and leak. And the intercoolers are notorious for getting clogged up with sludge and causing high engine temperatures. Plus the venerable 8V71 was never intended to put out this much power, so its being run on the edge of her power range. The Allison M20 gearboxes were another weak point. They had trouble with getting adequate lube oil to the upper shaft bearings, which was a design defect. Many of these got a fixit kit installed after the boxes went bang.

Most of these boats through the early 80's had upsweep, water jacketed risers. Which means that if the riser leaks, as it eventually will, the water runs into the engine. Many of these systems were revised, others were not. Best to look for one that has insulated risers..."

I'd like to get inputs on those points.

I don't believe the half of them I have heard about. I'm aware that the turbo intercoolers may get clogged, but at 25 years only one of mine (of four total) was partially clogged. What's this about waterjacketed risers..on turbos?? what's that? Not that I have seen.

M20's "weak"..Since When? Anybody know when the alleged "upper shaft bearing lube problem" occurred in M20 transmissions..or the "fixit kit" identification??? I thought these were quality heavy duty trannys ...elsewhere he says under 1 HP per cube is fine....so 435HP on 8 x 71 cubes is 0.77HP/cube, way under his target...What's going on here??? Older 8V71TI's are conservatly powered relative to newer 575HP 6V71TI's which ARE shorted lived....

Comments appreciated??

[AquaNav77]

Hello fellow Hatterascals:

This is one thread that I can personally address first hand. Just a little history here first. Back in October 1971, DD announced an upgraded version of the 8V71TI rated at 400 BHP using the N80 injectors, to a new rating of 435 BHP with the then brand new N90 injectors. But first, this package was going to be field tested in three pleasure boats - 58' Hatteras Yacht Fisherman, 55' Chris Craft Commander, and a 48' Pacemaker Sport Fisherman.
My family was fortunate to be the owners of one of these boats. (It wasnt the Hat). The test period lasted for about a year with the DD engineers coming aboard every three months in order to do inspections and lots of movies were taken of the exhausts, on cold starts, idling and cruising speeds. This upgrade was finally brought to full time production in late 1972.

I can comment on what Mr. Pascoe is stating. It is true that the clamps were initially held by acorn nuts and did loosen. The engineers that conducted the tests on our boat did note that and a factory mod kit was sent and replacement done. This apparently did not make the production line until way later. As far as to the intercoolers clogging, we never had this problem and nor have I heard of this. However, that is not to say, that the boats that he has been on may have been grounded and injested all kinds of crud since the intercoolers were/are seawater cooled. Also there were 2 very distinctly different 8V71TI engines, depending on the height availability of the engine room. They were simply differentiated by naming them either "High Profile" or "Low Profile". On the basis of a ratio, I would have to say that I have seen the HP about 10:1 over the LP. Most in the group here should have the HP model. How do you tell them apart?? Very simple.
On the HP model, the Intercoolers sit on top of the engines above the blowers. On the LP models, the intercooler sit behind the blowers, between and slightly below the turbos but above the water pump. Horsepower ratings were identical. Height difference was about 4 inches. However, maintenance items on the LP was more difficult. As far as to power output,
the turbo engine had additional beefing in the basic block, cross-head pistons were used and at the time the crankshaft and connecting rods were upgraded. The Allison gears were certainly a weak link surviving initially about 1000 hrs and then bang! I believe there were 3 succeeding retrofit kits available until this problem was finally solved in the 1979/80 time frame. Many Allisons went bang behind these engines with the port transmission being the most frequent.

As to the risers, I can only say yes that is true too. A friend of mine bought a 1976 53 MY with them and had water intrusion because of the wet exhaust.
He had to replace a turbo and riser. Others have been converted to dry with the water injected AFTER the hump to prevent this from happening. Forgive me for saying this, but I do not consider the Allison gears in the same light. After having owned a pair of Allisons on our 8V71TI engines, my personal preference is Twin Disc and ZF. The Allisons lost public favor very quickly because of their failures and for that reason Allison is no longer in the marine field.

I agree with you concerning the 1hp/ cube issue. However, the early iterations of the both the 8V71TI and the 12V71TI engines were indeed short life engines but were gradually upgraded through the 70's until they were uprated in Horsepower in late 1978. The 8V71TI's highest rating was 462 BHP attained in 1978 and was left there until its production run ceased. The 12V71TI which was rated at 675BHP for many years with the N90's, were uprated many times starting in 1979 and went from 750 to 800 to 900 and they were banging all the way up to the top. Many blocks were changed.

Even though DD made the mods in order to increase the power, the 8V71N will always have more hours of longevity than its TI sibling. Same with the V12. Some have said that the 71 series was never intended to be a turbo
engine, that it was only a stopgap in order to get the '92 series up and going while still maintaining their market share superiority over Cummins and CAT during those years. However, the public seemingly slow at first, eventually migrated to those other makes during the '80s and eventually the DD's all disappeared. Subtle hint. Today everything is stamped with three letters, MTU, with engines that dont even fit in a great majority of our group's boats.

Regards,
AquaNav77

[REBrueckner]

So if my 1972 exhausts have (dry) cast iron risers wrapped in heat blankets , with water injection after the hump via the "showerhead" arrangement, it's been modified?? I never knew that....thought they were all dry....The few 8V71TI's I have seen have all had blanket wrapped dry risers...fascinating!!!! Great post..thanks for the history....

[Nonchalant1]

I certainly had crud in all 4 of my intercoolers on 8V71TIs, but it was mostly from about 40 different pieces of old water pump impeller vanes from prior owners. The two impellers I changed out were still 100% there when I threw them away. I also have two tubes in one intercooler that expanded from flat oval tubes to almost round, but they don't leak when pressure tested. I'm sure it was from either the blocked tubes and water pump pressure or from a moron radiator shop guy that blasted them with 100 psi when those two tubes were blocked.

I don't understand the stuff about the wet "risers". Is that where the exhaust exits the first hot manifold to go into the shower head? How do you know which kind you'vs got?

Doug Shuman

[Genesis]

A number of these boats used riser pipes that were wet jacketed. Those bite for the reason that Pascoe indicated - they WILL eventually leak, and when they do, its bye-bye engine.

You want the dry ones with blankets on them. If you don't have those its easy to swap them and not even very expensive - the dry hotpipes are under $200 each, plus another boat-buck for the blanket.

[Genesis]

Boat Buck

Is that like 100 of the other kind?

You bet....

[Passages]

Boat Buck

Is that like 100 of the other kind?

[AquaNav77]

Hey Guys:

I just remembered to add something here to the what I replied to before and it is applicable to all diesel operators.

In order to lessen the chances of a hydrolock as Detroit Diesel put it, when starting an engine hold the engine stop button or switch or whatever you have in the shutdown position while cranking to start. Count 1-2-3 while cranking with the stop activated, let go stop and engine will then start.
This was in a letter from Detroit Diesel given to us on our startup inspection and the purpose was to eliminate any water and moisture by the piston action before any starting occured in order to avoid a bent rod or worse.
The engine would start much easier and of course more safely.

Regards,
AquaNav77

[captddis]

unfortunately if you have liquid in the cylinders, as soon as you crank the engine you will bend a rod. The wet risers that are referred to were used on the natural engines. They were seawater jacketed and went from the exhaust manifold outlet up to a football like collector, then dumped into a single ex hose. These did leak and bend rods or worse.

[AquaNav77]

Then why were my friend's risers of the wet type with water backing up into the turbos on his 53MY. Or was this a refit from the original dry?

AquaNav77