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Author Topic: To rebuild or replace My DD8v71?  (Read 4134 times)
Antknee
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« on: May 19, 2010, 08:43:58 AM »

Howdy, I have been wondering if you guys have an opinion on this. I know thats a dumb question. Tongue

My Bus didn't come to me in a running state, the story goes like this , the charter service that owned the bus blew a head gasket and had the gasket replaced but after that some coolant got into the oil and scored the cylinder walls, Question is Should I Rebuild this engine my self, with the help of a friend who is also a Diesel mechanic and how much will it cost me, or... Should I remove and scrap the engine and replace with an already rebuilt 8v71 or 8v92, I have both available to me for around 3k each but what are the pros and cons of each engine?

I have built a few cars in my time but not a big diesel engine before so I  really don't know what I am getting into, although my Mechanic friend says we can do the rebuild for about 3k.

Do I want the experience of a rebuild under my belt or just a good price for a running engine?

I talked to John at Bus Service, Inc, (http://busfixx.tripod.com/busservice/index.html) he says to have someone do it "Right" it will cost me from 8 to 10k thats a bit steep in my book, he says he does not do rebuilds any more because there is no money in it.

What do you guys think?

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Anthony Brown
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« Reply #1 on: May 19, 2010, 09:22:14 AM »

Rebuilding your own engine is always the best way to know exactly what is in the engine and that everything is taken care of (with the help of your mechanic).  Exchanging it for a rebuilt engine ($3,000.00 sounds more like a reconditioned engine-which can mean nothing more than a new coat of paint and that it runs) has lots of chances for failure.  Your buddy at Bus Service is correct at a true rebuilt engine (where everything in the engine is replaced with new).  The advantage of you doing your own overhaul (where only the worn parts are replaced) is that you'll save money.  Remember-we aren't trying for an engine that will last 500,000 miles before overhaul.  Most will be satisfied with another 100,000 miles of use.

I like the 71 series since it has dry cylinder liners that don't leak over time, and that the coolant you use in the engine isn't especially critical.  As compared to the 92 series that you need to watch the coolant acidity level like a hawk so that the cylinder liners that are in direct contact with the coolant don't pit.

If you did go to a 92 series, there is a 99% chance that it is turbocharged.  The 6V-92TA (335hp and 1000lb/ft torque with 90 injectors) will put out more power then your 8V-71N (300hp and 800lb/ft torque with 65 injectors).  The 8V-92TA (450hp and 1400lb/ft torque) will put out the most, but you'll have to upgrade all cooling systems. 
I turbocharged my 8V-71 and installed an air to air intercooler with bypass blower.  I use 9G75 injectors and the engine was dynoed at 375hp and 1125lb/ft torque.  I've been very pleased with the performance, and while my fuel mileage has not really increased, my performance has, so I'm not concerned with fuel mileage as much (having an engine that is a slug up the hill, gets bad fuel mileage, and smokes at altitude is just not acceptable.  Now, just moderately bad fuel mileage).  So if you're going to rebuild your 8V-71N, consider rebuilding it into a turbocharged engine with air to air intercooling.  With 80 injectors, it can produce 400hp and 1200lb/ft torque-that's 50% more torque then the non turbocharged engine!  Good Luck, TomC
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« Reply #2 on: May 19, 2010, 09:28:25 AM »

Something else to think about if you increase hp and torque is to check that your tranny is capable of handling it.
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« Reply #3 on: May 19, 2010, 09:35:05 AM »

Having researched this to exhaustion my view has been refined to some fairly simple conclusions.

I do not have the specialty tools required to do a rebuild of my 8v71 and there are many that you need and they are expensive to buy around 25k in specialty tools is a realistic ball park.

The kind of knowledge that you need to rebuild one of these is around 50% the book and 50% hands on experience. Meaning guys learn half of what they need to learn outside of the book and alot of times they learn how to do it right after doing it wrong. If that's true I don't have the time or money to do it wrong until I get it right.

There are plenty of things that I can do with my own tools and knowledge (regular maintenance, rebuilding "systems" in the bus that don't require as much experience, things like rebuilding an air compressor, cooling system, water pump etc. to offset the costs of an eventual rebuild.

I think I am at the stage where I may be able to determine whether or not a motor is tired, worn out or running good. Learning by experience the things to look for has cost me thousands of dollars and alot of time and listening.
For me to actually learn how to take a motor from tired to good would require far more money, time and space than my life currently can spare.
Rick

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« Reply #4 on: May 19, 2010, 10:42:55 AM »

I am also looking at a dusted 8V71 and pondering options.  For me, pulling the engine would be the biggest and baddest part of the affair - MC-5C just isn't a totally user friendly bus from the excess space in the engine compartment point of view.  Plus my engine had bearings rolled in not long ago, and a new blower maybe 20K miles ago, so there are some decent bits and bobs that make it not a toss-away.

So I am most seriously considering doing an inframe and putting cylinder kits in, and maybe a valve job if the leakage on the valves shows it needs one.  In the race engine world we call this a "refresh", not a rebuild.  I see this costing no more than $3K, barring horror stories when I take it apart.  My goal is simple - stop using a gallon of oil every 500 miles.  Although you can buy a lot of oil for $3,000...

I'm curious about the $25K in tools needed?  I just don't see it.  I don't see, reading the manual, for a need for any tool that I don't already have or could make.  What am I missing?  What are the must-have special tools?

Edit - just did the math, I can buy, at todays prices, 100,000 miles worth of oil for $3,000.  Maybe I will keep killing pesky mosquitoes!

Brian
« Last Edit: May 19, 2010, 10:56:21 AM by bevans6 » Logged

1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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« Reply #5 on: May 19, 2010, 11:14:49 AM »

Brian, you are into tools about 2000 grand for the weekend warrior but with all the tools for DD you can get to 20G's easy Kent does not give the tools away they are proud of their stuff.
If the 8v71 has been ran hot more than likely it will need oversize liners and rebuilt heads if it has been run very long with antifreeze in the oil it will probably need a line bore and crankshaft grind also, you can patch or do it right and to do it right it will cost.
Some of must have tool is the ring compressor for a 71,wrist pin seal installer, liner puller,head guides,rack and injectors tools and a good vacuum pump with pads that fit the piston that's if you have a shop rebuild the heads but the very best tool is knowledge you can really screw a 71 up without it the 92 series are more forgiviing


good luck
« Last Edit: May 19, 2010, 11:27:21 AM by luvrbus » Logged

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« Reply #6 on: May 19, 2010, 11:55:50 AM »

I would say that if your friend is a DD mechanic or has successfully rebuilt one before, knows and has the necessary tools, and you have the time, you could do it.  Otherwise, I would fall back on the old wisdom that says it is better to learn to be a mechanic on someone else's vehicle.
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« Reply #7 on: May 19, 2010, 02:00:39 PM »

I have had both 8v71 and 8v92 no comparison in power...fuel is about 1 mpg more on 8v71... don't know about radiator if you like I can measure my 8v92 rad...do you have the four speed auto or 5 spd automatic?really huge difference in performance between two engines...In the new coach we are building we are going with the 60 series hope to get better fuel economy;maybe 8 plus..Bob
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« Reply #8 on: May 19, 2010, 02:20:50 PM »

luvrbus, I appreciate that advice.  I have or can make just about everything you mention, but I pulled the manual to see the piston pin seal checker - that is very interesting!  I wouldn't have thought of that!  I  might or might not be a typical weekend warrior, I have at least $100K in my tools, including a Bridgeport and a 16" Southbend lathe.  I was interested to see the picture of the piston ring compressor - I started making those for piston sizes I used a lot years ago, I thought I had dreamed up the idea myself, then I saw them in race equipment catalogs.  Nothing new under the sun, Detroit obviously came up with that type ring compressor before I was born!  Your advice about if it needs oversize liners, or a line bore is also well considered and noted - if I find anything like that on the teardown, then it's definitely not something I would take on as an in-frame.  But if I can get away with sleeve, piston and rings, and everything else is good, then I may have a plan.  If not, then I need to get another engine anyway.

What I think happened is the previous owner ran the oil type air cleaners dry for a while.  The thing runs perfectly, it just uses oil.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
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1972 NTM MK-4 B/SR
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« Reply #9 on: May 19, 2010, 03:12:19 PM »

Brian, if you do it by the book it will work for you fitting the liners in a 71 is art to tight a problem or to loose is a problem Don and Dallas are good at fitting the liners in a 71, it takes me forever it seems like every time I get a couple that have been laid on the side for a long period of time so for a 8v71 I order 9 lol.
When making the ring compressor make sure and cut a flange to hold it place 1 slip will cost you a set of oil rings and you will never know it till you start the engine fwiw some people cut a old sleeve to make a ring compressor never worked for me.
Pull a vacuum on the pin seals they cause trouble also on a rebuild.   


good luck
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« Reply #10 on: May 19, 2010, 03:23:01 PM »

Thank you.  I haven't decided to do it in-frame yet, one issue I don't have figured out is how to get my Sunnen hone (the manual kind you drive with drill motor) in there in the low engine compartment.  I think you really should hone the bores before you fit the liners.  I figure if nothing else it will be a ton easier to get the thing out if the heads and such are off, if I have to abandon the in-frame half way through...   Roll Eyes
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
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1972 NTM MK-4 B/SR
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« Reply #11 on: May 19, 2010, 03:46:45 PM »

Brian, I would roll the engine out to do the engine it is about a 3 hr job saves you time in the long run, build the dolly like in the MCI book it works good


good luck
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Just Dallas
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« Reply #12 on: May 19, 2010, 03:55:03 PM »

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« Reply #13 on: May 19, 2010, 04:58:05 PM »

Hey guys;
Isn't line boring seriously expensive? I seem to remember it costing 4-5 k because of the few shops with the equipment to do it.
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« Reply #14 on: May 19, 2010, 05:05:51 PM »

RickB, I have it done in Phoenix for 600 bucks with new main bearing caps with me removing the crank.
There is a guy here that has a mobile unit that does at your location for 500 bucks but for not enough trust in him for me .

good luck
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« Reply #15 on: May 19, 2010, 05:15:33 PM »

Clifford as usual thanks for separating fact from fiction.
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« Reply #16 on: May 19, 2010, 06:09:04 PM »

Brian,  "using a gallon of oil every 500 miles".   Are you trying to keep it up at the full mark?  Do you let it set for about 30 minutes after shutting down so the oil has time to get down into the pan?  I can run close to 2000 miles with the oil sitting right at the add mark or just a hair above.   If i try to keep it at the full mark i could probably also use a gallon every 500 miles or so.  You do know that these things will blow out any excess until they reach a certain level ?   My engine had 13,000 miles on it when i got the bus and now has about 50,000 miles and runs great. Took me the 1100 mile trip home with it to remember the thing about detroits and the oil level. Grin
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« Reply #17 on: May 19, 2010, 11:09:43 PM »

Quote
If i try to keep it at the full mark i could probably also use a gallon every 500 miles or so.  You do know that these things will blow out any excess until they reach a certain level ?

I didn't believe it until I experienced it for myself. Try running it at the lower end of your stick and see what happens.
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« Reply #18 on: May 20, 2010, 04:23:41 AM »

yep. i've tried all the easy stuff.  I run it kind of between the bottom of the stick and halfway between full and empty.  sometimes they seem to use oil because they are using oil!

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
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« Reply #19 on: May 20, 2010, 04:34:47 AM »

mine is equally moody on oil usage (leak or consume)..found my stick was marked wrong..should have been full mark 1 inch below block....8 V92
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« Reply #20 on: May 20, 2010, 07:21:10 AM »

Brian, if you can find the 1 oil ring piston kit for your 71 that is the best to use.( 1 large ring instead of the 2 small) 
I have a 8v92T in my Eagle I run 19:1 compression with 15lbs of boost no leaks I use about 1 gal of oil every 5500 miles and average 7.5 mph plus it produces 1550 lbs of torque at the rear wheels not to shabby for a old 2 stroke running with the 60 series. 

good luck
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« Reply #21 on: May 20, 2010, 08:14:45 AM »

Clifford, again thank you for that tip.  I have a question - when rolling the engine out is it feasible to leave the gearbox (a spicer) in?  One big reason I have been leaning towards in-frame is the fuss of disconnecting the clutch and shift linkages, and getting them back together again.  they are just really hard to reach on the 5, although I can take the bed out and go through the floor.  The downside of that is constructing a frame to hold up the gearbox after it's off the engine, I suppose.  Or am I making a mountain out of a molehill?

Part of my issue is that the powerpack (engine plus gearbox) weighs more than all three of my racecars put together.  i can rebuild engines - it's the rigging it in and out that intimidates me. I'm used to crankshafts that I can pick up with one hand... Grin
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« Reply #22 on: May 20, 2010, 08:26:44 AM »

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« Reply #23 on: May 20, 2010, 08:27:30 AM »

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« Reply #24 on: May 20, 2010, 08:28:15 AM »

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« Reply #25 on: May 20, 2010, 09:10:49 AM »

Clifford,

By the looks of your ast post on this subject it is becoming clear to me that you have never seen the movie "Broadcast News".

"I have a 8v92T in my Eagle I run 19:1 compression with 15lbs of boost no leaks I use about 1 gal of oil every 5500 miles and average 7.5 mph plus it produces 1550 lbs of torque at the rear wheels not to shabby for a old 2 stroke running with the 60 series. "

There is a seen in that movie where the guy who has everything going for him has a discussion with the guy who doesn't have a whole lot going for him says" What do you do when your real life exceeds your dreams?" to which the albert brooks character replies: "keep it to yourself"!!!

For a guy to have no leak, 1550 lbs of torque, fresh, no smoking, running perfect, passing series 60 two stroke has to qualify as a "keep it to yourself" moment to all us underpowered, leakers running at 20mph up the Rockies slowpokes like myself.

Just kidding of course. Your motor gives us reason to dream.

Rick
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« Reply #26 on: May 20, 2010, 09:32:24 AM »

RickB, there are several of the 8v92 in the bus world that will out preform mine, Don has a good 8v92 he gets better fuel mileage than I do but I weigh a little more than he does don't count the old 2 strokes out their not ready to die just yet.Who knows Don just passed the CARB emissions in Ca with his setup EPA may not like that.   


good luck
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« Reply #27 on: May 20, 2010, 10:42:05 AM »

Rick, just imagine what Clifford can do when he figures out how to get it out of second gear Grin Grin Grin
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« Reply #28 on: May 20, 2010, 11:56:11 AM »

Wait a second.... Are you saying there's another gear???

 Grin Grin Grin
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