Bertram 50 repower

I agree with your synopsis on the 92 series. The 71 series are reliable and get enough longevity to warrant a rebuild, but I would swap for C18 cats also. The problem is the factory DD parts for the 2 cycle engines are no longer good quality. The injectors are now rebuilt and not good quality for example as well as many other hard parts.

Back in 1998, when DDC began phasing out production of two-strokes in favor the 60-series four-stroker, they didn't also quit making parts...at the time, there were ~800,000 engines out there in mining, military, and trucking, not to mention all the boats.
There are still all the OEM DDC parts available, plus Reliabilt remanufactured parts that, over the years (as well as today) were offered with a 12-month warrantee--as compared to the new stuff which used to come with a six-month policy. As of about three years ago, both new & used bits are warranted for a year.
There are other companies that claim to make parts to OEM spec but are not your gen-yoo-wine Detroit Diesel parts.

The only problems I've ever seen had to do with Chinese knock-off 92-series liners (as evidenced in the post-mortem teardown by the lack of a DDC logo) which caused an 8V-92 to puke on seatrial.

Maybe you have to tow extra fuel tanks behind you. Or bolt a shuttle fuel tank to the hull.
Dockeffer, should be "gph", right?

i just went through a rebuild on a 12v71, not once but twice......the only injectors that could be found by two dealers in different sections of the country were reliabilts and the same for a cylinder head, it too was deemed bad by DD and had a couple of valve seats not installed correctly. The second time they rebuilt it, they had to overnight cylinder kits from the west coast because nobody had them on the east coast. 5 out of 12 reliabilt injectors were deemed bad by DD and were 4 months old with 150 hours on them and caused a liner to be washed out and 3 that were right behind it.

To the original poster, I've always felt the 50 was underpowered with 8v92's, but if you're happy with the performance that the 50 had with the 8v92's then consider repowering with QSM-11 Cummins. I've been on several 46 Bertrams that had 8v92's then repowered with the QSM's and they've run fantastic.

correct, gph

Am new to this discussion, but we have had some experience with this exact issue. We bought a 1990 Bertram 50 Conv. galley down, no tower, had 8-92s. We have refurbished her above and below decks, including a pair of new 2008 1100 CRM MAN engines. The 50 is really good hull even though the 46 and 54 get most of the "press". Our boat ran great, 27-28 kts @ 1850 rpm burning 64 gph, about 70% load and 35 -36 kts WOT with 30X39 4 blades. Right up until the MANs acquired a serious smoking habit at a bit less than 400 service hrs., at the tender young age of 9 months, resulting an embarrasingly sooted over tramsom. Unfortunately, after 12-16 months of wrangling the best we are offered is to pay $10,000 USD for two sets of rebuilt injectors. As a result I have a couple of thoughts: If possible repower with newer/new engines if possible, we threw away the 8-92s for a reason(s) ie. too slow, high maintenence, uncertain reliability for multiday trips over long offshore distances. The Cats previously discussed sound like good options, we've owned older CATs with good results and CAT stands behind their products. I would suggest a minimum of 1000 hp./motor which allows one to " keep up with the Joneses" espescially if appreciable distances are involved. Although we liked the MAN performance their atrocious post sale support would keep me from recommending them. Good luck with your effort, I bet you'll like the 50.