Originally Posted by Iceni John
The 6V53 is a little screamer - it revs higher than the later 71 and 92 series engines, and because it's a two-stroke it sounds like it's turning twice as fast as a four-stroke. Torque isn't high, so you'll need to keep its speed up, but like any Detroit they can be run on the governor all day, provided their cooling system can keep up with it. The US military is still using them more than half a century after they were introduced, and Crown used them in some of their rear-engine Embree buses. For a 30-foot bus you should be seeing 10 MPG or better: folk with 35-foot Crowns with 71-series Detroits, even converted ones, are seeing 10 MPG or slightly more, and when I helped bring a friend's 40-foot 10-speed 6-71T Crown tandem back from Northern California it also was getting 10 MPG over the 500 miles, including going over Tehachapi.
Is the engine a turbo? You called it a 6V53T. If so, they're better than the gutless non-turbo 6V53. What transmission does the bus have? In those days there was a six-speed Allison HT70, but they're getting very rare now. Was the cooling system replaced when the 6V53 was installed? All two-stroke Detroits need an effective cooling system in top condition, or they WILL overheat: you need to carefully check the bus's radiator etc., otherwise you'll be having constant overheating problems.
Good luck, John
I'm the guy that bought ALL the Embree Fleet number 60 Series Crowns and still have two of them in perfect factory delivered condition and equipped. They were all 35 ft two axle full air ride suspension with immense amounts of extra cost charter options added. They were rear mounted 6v53 non-turbo 195hp engines which was totally unheard of for Crowns at the time(1962), totally custom engineered and spec'd by and for Embree Buses. They all had an Allision 6 spd transmission the exact model I can't seem to remember now(MT66X??). The engine/transmission combo was extremely popular at the time for use in Trash trucks and if you were around then you surely heard the screaming demons in the morning waking you up with all the racket. But boy did they sound nice, nothing like the smell, and sounds of a Scream'n Jimmy.
All this previous advice is spot on and should be heeded as the gospel truth.
I noticed something that got my curiosity up. Did you say weather this Blue Bird was originally a front engine bus and this guy swapped ends and mounted the '53 in the rear??? It sounds like that when you mentioned how he extended all that structure to the rear to accommodate the new '53 engine installation. If this is the case I would be much more concerned with the overall vehicle weight distribution, chassis loads and axle weights on the ground. I'm thinking of center of gravity, turning moments when underway, possible light loading on the steering axle and much evil flowing from that. All in all swapping the engine from end to end on a somewhat lightweight school bus chassis could be too much excitement for even me to want to deal with. If it was already a rear engine vehicle and all he did was add the heavier diesel then you should be able to manage but make sure you check the axle loading and suspension tuning to insure safe handling at all speeds. Weight behind the rear axle is nothing to ignore and should be considered.
If cared for and driven like you're always mad at it.....that's no joke, then you should get many happy years of service and enjoy the notoriety you'll garner. Oh, and don't expect to get any more than about 6-7mpg out of it.
One other thing to be aware of and this could be crucial, now that I think of it.......Be sure to check and make sure if the block is aluminum (Military only) or a real solid Cast Iron commercial Block. If it's a Military aluminum block they really don't have the expected lifetime of a cast iron block. The Military M113 APC used an 8v53TT (twin-turbo) with a designed rated lifetime of only about 300 to 400 hours.....no joke. You can get them around and about in crates as stated before, but if you really want one bad enough you better get several for when they break and die so you can swap in another new one from a crate, which is of course what the Military expected and always did......Commercial cast iron blocks didn't have these built in life-ending quirks and would run and allow for in-frame repairs and rebuilds, Commercial don't you know. Long lived, repairable, efficient, cost-effective, Capitalistic, Profit generating, unlike a Combat Vehicle engine life cycle measured in hours. I'm not really sure if there was ever a Military Aluminum 6v53 or not, just a random thought I wanted to throw out to consider.
Detroit Diesel 2-strokes are truly a fun adventure with all sorts of excitement but you must be prepared for all the hilarity and ups and downs, and mechanics are getting very hard to find who still really know how to work on them correctly. Pure mechanical and will come through an Atomic Zombie Apocalypse along with the VW beetles and cockroaches. Have fun.