M T f U! I'll do it myself.

The J&T guy was not kidding about the part supply issue.
Seems MTU has contracted lots of it's part mfg in China.
I don't need to explain the China issues (Do I?).
On top of way behind in schedule, what later MTU liners were used, had problems and were recalled. Some of these still waiting for replacement parts.

J&T, MTU, FLDDA and other "factory" shops are not going to use non MTU parts.
They have no say over these parts and can not warranty them.

Don't listen to the talking heads on other web sites, McBee has had Detroit part issues also.
Including liners.

Here is your #1 problem;
71 use dry liners. You may think that is great but one thing, there still has to be a correct fit between the liner and the block.
If there is an error, this fit is achieved by honing the block and installing the new liner by measuring tools & feel for proper fit.
At the factory, 3 different sizes were available for use (Standard, #1, #2). On the block top, near the lungs, a stamp notes what the factory used.
The replacement liners OD are in a set A thru F in size. Ordering a stock size will not work.
So, you have to have the block tore down,
inspect the block,
examine the block for liner to block chatter and wear/damage,
correct if needed by honing,
measure for the correct sized liner,
THEN order the liners and wait.
& wait & wait & wait,,,
There is no standard liner.

Unless somebody pored sand in the crank case, it is hard to damage a straight-71 crank shaft.
It usually checks good and std bearings are re-used.
A new head and turbo, rebuild the blower * and that completes the in-frame for another 4000+ hours.

* That $30k estimate may have also included a new blower, cam bearings, cams, new gear sets, shaft seals, pumps and time on a Dyno.

So, let us re-think your needs, what is wrong with this motor exactly?

IMO, purchase a new long block or a low hour RTO.

Anybody looked into the lung yet to inspect the piston, rings and cylinder walls yet?

Carbon?? What else did he see? Glazed cylinder walls?

Tell me about the new injectors;
What problems were you having to replace them?
Did they fix that problem?

When did this cold starting issue start?

How much sump oil is consumed?

Under load, matches the performance of the other engine?

How wet was this carbon? Oil or fuel?

I know we have gone over a few things before, I can not remember your details from before. To many projects and hootch have gone by since we last chatted.
Please excuse me if you have answered these questions before.

First, I know I have discussed this many times before to all; New injectors mean squat to me.

I've used lots of parts from Interstate Mcbee and never got any bad ones but if you order liners from them, be sure and give them the actual bore diameter of the cylinders and not just the stamp number off the old liners because they don't always match up. ( a "2" stamp Detroit and a "2" stamp Interstate Mcbee may be as much as .003" difference) And make sure you measure each of them individually against the bores as you install them.

I have always thought 671 Ns, and 871 Ns were bullet proof, great engines. Might this thread indicate that it is no longer wise for a mechanical idiot like me, who will always call in professional help, to buy a boat with these engines unless I want to repower?

Relax
71s are bullet proof.
When set up correctly, they are near idiot proof.
There continues to be factory support.

But China was making 71 parts for MTU.
China has problems
China is a problem.

India also makes parts for Mtu as other world wide places.
I look forward to other places stepping up and replacing China.

Now, 2 stroke Detroit designs are over 90 years old. Other than DDEC, no other upgrades have been made in over 50 years.
This dependable design is installed in the greatest numbers and many, many are still in use. They will be available parts and support.

Although most parts are interchangeable from a later engine to one made during WWII, It is a pile of technology not compatible or interchangeable to any other engine mfg or family.
Sadly, in this narrow vertical market, supply chain is going to be slow, support is getting smaller.
In the big picture of all the other mfg's and their offered models, the old Detroit is in a smaller share every day.
I typed there will always be parts and support, this market will be getting smaller also.
It is there, parts and support always will be, just patience is required when dealing with it.

When shopping for your next boat, engine options are to be a concern no matter what mfg.
This should not be a shocker, even some Cat engines you want to run away from.
But what were new engines from Cummins a few years ago, their 8.3 is a great engine and cheap now days.

Old DDC, Cat, Cummins & VP engines require a through conversation with your heart considering all aspects of life and future of the boat you are shopping for.
I luv some engine models from all mfg's, I'll never be scared of a DDC 71.

By the way;
Was talking to my Volvo Penta shop the other day.
They have boats around Jax waiting for parts.
Some for near a year waiting for VP parts.

I enabled my block heaters Friday morning in prep for the weekend. I left the saloon deck hatch above the engines open also.
Last check yesterday afternoon, Saloon nice and toasty even with ER vents un-covered.
Not near as bad as the rest of the country, we were down to 25 last night for over 6 hours.

Mechanical temp gauges do rise just a bit. Expansion tank recovery bottles do fill a couple inches more.
After sitting for several weeks, we usually start quickly with one puff of smoke and clear after that, Then nicely.
Before our block heaters, in any COLD weather, we would smoke a bit and idle after several minutes.
Were around 40° outside (or last nights 25°) , I can just touch those starters and it would be like cranking them up warm,,, well they are warmed up.

We use 1000W immersed Hot-starts with thermostat controls.

If Cleanslate has fuel wet lungs from a dribbling nozzle, he will still smoke a bit but they should start faster.
Un-burned fuel blown into the exhaust manifold takes a while to burn out and stop smoking.
IMO, where his carbon build up is coming from.

Agree on all
But many of us can not afford these fancy MAN, and Cats you mention and have to stay with the ole mechanical engines.

I have also witnessed the aftermath of a later 8.3 ending up getting shoveled into a scrap pile from a blown oil hose.
Did not take long even with an ECM.