Swapping Out Engines

[JCG]

I believe garyd may be right. I am planning on swapping out engines for completely remanufactured engines from Diesel Specialist. These will include new blowers, manifolds and etc, I sure hate to start taking all that stuff off to get them through the door.

Was height a problem?, with a crane/jib, chain and engine, all of that adds up to something. I am afraid I may run out of head room before I can clear the floor boards.

I am located in Alexander City Alabama, so is the boat.

[JCG]

Concerning the engines themselves, I was thinking that just rebuilding the existing 8V71TIs would be the simplest approach. However, now I am asking myself if I should consider other options such as the 6V92s. I believe the current 8V71TIs are around 460 hp, newer 92s are more powerful and probably take up less space in the engine hold.

The current engines are coupled to allison gears. I don't know what would be involved if a larger Detroit engine was used. I would be interested in information related to gears, mounts, props, shafts and etc, if different engines mean changing all this the 8V71TIs will have to do.

Comments?

[mike]

The M20 allison gears will bolt up to the 92 motors, however unless you have the HD series M20 gears I wouldn't use them. I have just completed replacing all of the bearings in both of my M20 gears (3k hrs) behind 8v71N's. The failure was do mostly to poor alignment, destroyed both sets of output shaft bearings and drive gear bearings + 1 of the shafts had to be replaced. Having personnely worked on these I can tell you that usless you have the upgraded HD series with the roller bearings (std are ball bearings) your will be in for real problems with the higher HP and torque of the 92 motors. mike

[saltshaker]

Allison M gears will go behind a 6V92 only if the bell housing is set for allison gears. If not you will spend a small fortune to convert the engines. If you buy 6v92's or 8v92's with allison gears, they should be MH gears. If you buy bobtailed engines, it is unlikely they will be set up for Allisons.

I went from 350HP 8V71N's with Allison M20 gears to 550HP 6V92TA's with Twin Disc 5091 down angle gears. No change to the running gear, a lot more overhead room and a bit more forward of the engines. Unless you keep the 8V71's you will have to modify the engine beds and use new mounts. Most likely the mounts on the old 8v71's are shot anyway.

What power are you looking at and what are you performance needs/desires? You can fit a lot in that engine room, 6v92's, 8v92's, Series 60 Detroits 10cyl MANNS, Cummins QSM11's, C12 or 3196 Cats, 3406 Cats (very tight).

Jack Sardina

[garyd]

WE had about 3" to spare total. We were able to see the top of the engine and the opening. It was really easy.

thanks garyd.

[JCG]

It sounds like I need to stay with the 8v71TIs.

What performance do I want? This may sound funny but I really don't know how the boat performs with the current engines. I was told cruise would be around 18 knots, which makes sense with saltshakers 16.5 knots with 8v71Ns at 350 hp, then with 6v92s 21 knots @550 hp. When I test ran the boat, there were no electronics. This boat had been beat up on by IVAN and was in fairly poor condition and the owner wanted to get rid of a headache, but he had stripped all the electronics. I would like more speed and thought that since I was considering engine relacemnet it may not be that expensive to move up on horsepower. But based on the concerns of gears and etc I probably need to stay with what I have.

There was no information on the engines, just the promise that they were rebuilt several years ago. Based on this and the amount of oil in the bildge I felt that I should go ahead and be sure that the engines were in good shape. The main thing I am looking for is dependability. Since I have no real history on the engines and since the boat in my backyard(out of the water) it seems to me that making sure the engines are in good shape is the thing to do.

Does this logic sound good to those experienced with diesel boats? This is my first. While I am in the restoration mode what other sytems should be addressed?

[djudja]

The yard setup an A frame over the engine, lifted it, and then removed it using a large fork lift with a boom attached to it.

I had 8v71N's so I only cruised at 16-16.5kts and 19-19.5kts WOT. The new engines are 550HP 6v92TA's. I am a bit underproped but I still cruise 20-21kts @1950, 23kts @2100 and 26kts WOT. This is with full fuel, water, gear etc. My boat is also on the heavy side for a 46C. Previous owner added another layer of 5/8" plywood to the salon sole, all new wood covering the old walls, moved the galley up with new cabinets and island etc. This added a lot of weight.

If I had the right props I think I would pick up another 1-1.5 kts. I am happy with the speed and prefer to keep the load on the engines lower. I run 2400rpm fully loaded or light on fuel and water.

Is it possible to get your props specs,as well as the the specs that you would consider ideal.

Thanx

Djudja

[Liquid Asset]

JCG,

Since the boat is in your back yard, concider rebuilding those 8-71's and do it right by pulling them out and making them right. It appears since your boat is on the hard that you have some time. While they are out of the boat, you can do whatever it is that you want in the engine room since there will be tons of rooms in there to move around.

I think the 871's are good engines, and if you dont need a lot more performance you can be happy with them. But it what you want is speed, I would look at 8v92s.

[Fanfare]

I don't know about a 46 Hatteras, but when I wrote Jack Hargrave around 1992 about replacing or rebuilding the 8V-71Ns (350 hp) in my 50MY he recommended using 6V-92 TAs. He specifically said not to try using 8V-92s because they would not fit. The heat exchanger is much larger and takes up more room than the two missing cylinders. I used the 550 hp units with the Twin Disc 5091 down angle transmissions, 1.71 to 1 gears, and 28 x 28 Nibral 4 blade props. The Hatteras 50 has 2 in. shafts and I did not want to have to install larger diameter ones because the shaft tubes and struts would be a pain to replace (the tubes are really long). I went to Aquamet 22 shafting, which has a 70,000 pound yield strength in torsion. Also went from 6 in exhaust to 10 in exhaust with mufflers, which has worked out fine, but I now suspect was a bit of overkill. I couldn't figure out how to make my engine room vents larger without ruining the looks, so I put this off. I get a little vacuum pressure inside if the boat is all shut up and rigged for rough seas. It just puts a little more load on the air conditioning.

I now cruise at 16 to 18 kts (speed goes up as fuel burns off) at 1950 rpm, top around 22 kts, burning about 60 gph. I have had almost no trouble after 12 years.

[boogiewoogie]

Jim

Do you know what your boat weighs ?

Thanks,

Bob