JT Detroit 6v92's for a 46' POST

Most people rebuild either when 1 engine fails, or when they show signs of a lot of wear, like smoking out the entire marina on startup. I haven't had a lot of issues with Allison's.....but not sure on how robust they are. I'd cruise the engines at 1900-1950rpms and don't believe you're doing them any favors at 1800rpms. Parts are readily available for the DD's. Make sure they turn up to proper WOT rpm's. A simple call to a DD allison dealer will give you the answers you're looking for on parts and longevity. I'd recommend giving J+T a call and asking the questions you have asked here.

The best possible way to determine the current health and estimate remaining engine life is to hire an experienced, professional and reputable engine surveyor. It will be money well spent.

Cold start and load/no load WOT and temp gauge are a good start.

I think the bore scope on a DD is a MUST for a pre-purchase.
Not just the liners but a clean(ish) airbox tells a lot too.

The 6-92 has wet liners, so I would pay special attention to the coolant to ensure that the proper coolant is being used and changed at the recommended intervals.

Brian,

Looks like you are in CT?

If the boat you are looking at is also in or aroud CT, Try Perfomance Diesel out of Branford or East Coast Diesel out of West Haven.

RT 46 is right spend the money and get the right guy to do compression on the cylinders. They will able to look at the cross hatching as well. 46 Posts with the 92s fly but thrusty.

I agree, get a good engine surveyor as well. But it says the OP is going to get an engine surveyor and just wants general knowledge.

The 6v92's are a lot more forgiving than their big brothers. I had an owner start and run one without oil till it shut down (cold start up). The oil drain hose had blown. It continued to run for the last 5 years after that and is still running.

But I agree coolant changes are critical and they are not forgiving to an overheat and such.

I've never heard of turbo's "blowing up" on any D.D.

Checkout Boatdiesel.com also, for only $ 25,- you can get a lot of info!

Regarding the Allison transmissions, they are a gear originally designed and manufactured for around the clock, commercial service and are as tough as nails. Their service history is literally unparalleled in terms of commercial and recreational service reliability and longevity. That said, any machine twenty-seven years old can have issues, but Allison gears are not intrinsically sensitive to them. Plenty of Allison gears are still in commercial and recreational service, plenty of service parts and support for them, if needed. In a recreational application they will never wear out from hours of service, however elastomeric parts such as seals do age chronologically in any gearbox.

Regarding the 6V-92 engines, @ 1,800-1,900 RPM they will serve well. As with all marine engine, from outboards to diesel inboards, internal corrosion of a microscopic nature occurs in the cylinder bores during periods of non usage, which is literally 99 percent of the time with recreational boats. This is a chronological time issue, not a running hours issue. The same is true of exhaust valves and seats. These problems affect all brands of recreational marine diesel engines with wet exhaust systems, and a twenty-seven year old engine of any brand will be affected accordingly.

The principal question you must ask yourself is, "Do I want any twenty-seven year old boat?" If the answer is yes, the combination of 6V-92 and an Allison gear is as good as any put in a recreational boat of 46 feet.

Ron Sparks

I used Jim for my rebuilds. He is great!! Years of trouble free running since.

Hello Brian: Good to know the existing problems were identified in a timely manner, prior to purchase. If you go ahead with a purchase of the boat, the repaired engine as well as the gears should serve you well.

Ron Sparks

Hello rcrapps: Thank you for your comment about posting #14.

I have an 89 Post 46 with 6V92s and Allisons.

Knock on wood, I've never had a problem with my Allisons. Never heard of any systemic problem with them.

I like the 6V92s because I the boat leaps out of the water when the turbos kick in at 1500rpm, and I have a lot more headroom at my normal cruise than I would have with the 71s. I'm a big believer in Jim Pascoe's position on not pushing performance diesels to the wall to get longevity. Parts are still plentiful and so are qualified guys to fix them. They are not as efficient as the 4-strokes, no getting around that.

As to the comment in #2 about not doing the engines any favors at 1800rpm, I cruise mine between 1800 and 1900 and they just feel "happier" at 1800. I also like the fact that 1800 puts me at a relatively economical place in the fuel consumption curve, and I get 18-19 kt which is usually plenty fast enough for me. I asked one of the best DD guys in the Mid-Atlantic (Jim Stitz) and he said "so long as they are at operating temperature, you're good".