6v91 versus 6v92

I am looking at buying a trojan 13 Meter Express. I boat on the great lakes. I have narrowed my search down to two boats that I really want to explore further. One is currently in the great lakes and is powered by Detroit 6v91 engines. The other is in salt water and powered by 6v92 engines. This will be my first boat with diesel engines and I really know nothing about them. Can anyone offer me any advice on wich of the models would be the better choice?

As time goes by, guys owning either one of these engines will face more and more difficulty finding parts reliably and reliable mechanics to help. Both are "obsolete" in that they are no longer in production. I don't quite recall when the 71 series stopped being made but it was superseded by the 92 series and they stopped making the 92 somewhere around the year 2000.

Having said that, if you were to buy either and get to know them, you will probably fall in love. Well, love/hate anyway.

For my money, the 6-71 series engine is, most likely, the best damn engine ever made. They take a lickin' and keep on kickin'. First built in 1938 as an in line and reconfigured in 1954 as a V, They have been around for EVER and enjoy an excellent reputation.

The 92 is the natural progression of the design with the same stroke and bigger bore piston. First introduced in 1972, it had some problems and you really don't want one built before 1985 or so. Around that time, they had gotten all the kinks out and they too became a very successful story. Make sure you have them carefully dated before you buy.

The 92 is supposed to provide more power and better fuel efficiency but, for my money, I love the elegant simplicity (if you can call a 2 stroke diesel simple) of the 71. If you do end up owning one or the other, you will probably want to find one of the mountains of used parts that are stashed around the country and up in Canada. Very helpful when things break and you need a place to turn that won't break the bank. But, the guys that own those mountains are getting old too and their heirs are selling off the remainder for scrap. Sad but true.

Thanks for the very thourough reply!

Someone at my marina told me they thought one of these engines had a very short rebuild time on them. I want to say they thought the 6v92 had something like a 1500 to 2000 hour between overhaul time on them where the 6v91 had a much longer life expectancy. Is this accuarate?

Well, I don't know that to be true. Engine longevity is so subjective and based on so many variables that it would be hard to give you a hard, fast number to hang your hat on.

As an example: if the engine is turbocharged, then it will make more horsepower and burn more fuel over it's life. The increased cylinder pressures associated with this simple, taken for granted these days, fact will increase wear rates and usually does result in shorter OH intervals. Almost all 92's were turbocharged while many, many, many 71's lived as naturally aspirated engines...apples to oranges.

Factor in oil change frequency, air filtration and full throttle operation and you can see that the equation is a moving target based on who is doing what and how in what latitude.

Your source is, most likely, referring to the 70's and early 80's version of the 92 that I already spoke of. That era gave that engine a poor reputation. Later versions and replacement part improvements changed all that.

I ran them in a fleet of 150 buses, for many years, with good reliability and "nominal" lifetime characteristics. Of course, they were subjected to a rigorous maintenance schedule during that time and, adherence to that, more than anything else, was supremely responsible for our success in my opinion. As they say on TV though, your results may vary.

I can't thank you enough for that info. I appreciate it very much. I suppose after that explanation I am not really going to use the engine model on the two boats as a serious factor in my decision making process. I will now likely look more at engine hours, maintenance history, boat quality and price.

thanks again.

You are welcome.

Yes, that is probably the best way to make your selection. If you can at all afford it, try and find the best Detroit Diesel guy in your area to look the hardware over. It will be expensive but will pay big dividends by identifying problems BEFORE the sale.

A good mechanic should be able to offer a few different "options", based on what your budget will bear.

Ideally (and most expensive) would be a thorough visual with cooling system pressure check and inspection covers removed. Followed by a compression and valve lash check as well as an injector timing and governor wear inspection. An engine oil sample sent for analysis is also useful to identify any "wear trends" or contamination.

This might take an honest, competent and fast tech the better part of two days to accomplish and he will undoubtedly charge handsomely for doing all that. It won't seem that expensive a year from now when the engines are still purring but it does hurt for a little while.

And, something is better than nothing, so, when you pick yourself up after the "extensive inspection" estimate and catch your breath, start negotiating for something you may be able to swallow.

Good luck with your decision and I hope you are more than pleased with your "new" boat!

Once again thank you!

I have a Detroit Diesel guy out of Detroit (oddly enough) who is very reputable who has been highly recommended to me by two different people. I am going to contact him in the next day or two and start the process. I will use your list of inspection criteria to start the discussion with him.

This information is very valuable to me and much appreciated.

I will re-post as the process progresses and let you know how I am making out.

THANK YOU!

Well, I'm out here pulling for you and I hope the guy treats you right. I'm also hoping to hear back about some good results and a happy new boat owner.
Once again herdbull,
Good luck.