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Topic: Prevost engine swap possible?
Posted By: DonHutchins on 05/21/16 08:03am

I'm looking at a used Prevost that's a beautiful unit in nice condition, but it's got the old DD 8v92 motor, which I'm really leery of. It's got a rep as a dripper and fuel guzzler. What are the chances it could be swapped for the newer DD Series 60 motor? I know this is off-the-wall, but I really do like this unit and might go for it if this is do-able...

Don Hutchins
Kingston WA

Posted By: rgatijnet1 on 05/21/16 08:15am

Personally I would contact Prevost directly. I'm sure that they can be of help. Prevost chassis buses are used in fleet applications and they are designed for major repairs and engine swaps with a minimum amount of downtime, if you have the right equipment. You should be able to find a used engine out of a wrecked chassis.

Posted By: mowermech on 05/21/16 08:20am

Yes, that chassis was built to accommodate several different engines, depending on the specifications of the original purchaser.
But why go for another Detroit Diesel? Why not a Cummins?
All it takes is money and time...

CM1, USN (RET)
2017 Jayco TT
Daily Driver: '14 Subaru Outback
1998 Dodge QC LWB, Cummins, 5 speed, 4X2
2 Kawasaki Brute Force 750 ATVs.
Pride Raptor 3 wheeled off-road capable mobility scooter
"When seconds count, help is only minutes away!"

Posted By: Kayteg1 on 05/21/16 08:53am

I just sold 1972 Prevost with 8V72 and made 400 miles delivery trip with it.
Detroits are consider drippers as lousy mechanics don't pay attention to them.
I made my Detroit dry. All it took was new valve cover gaskets and paying the attention to alignment. Problem was that with 2 center bolts, the covers can play about 1/2" around and if you don't pay attention, miscenter covers will drip.
Bare in mind beside valve covers the 44 years old engine is likely on all original seals.
Fuel economy? I keep the log book and over the time my mpg on 16 tons coach were 5.5-6.2 mpg.
The only complain was HP/lb ratio as with 318 HP that thing was slow on grades, but will cruise 70 mph on flat.
Than why Cummins?
Put Mercedes in it. [emoticon]




Posted By: westernrvparkowner on 05/21/16 09:05am

With a big enough hammer, all things are possible.

Posted By: RLS7201 on 05/21/16 09:37am

The old DD silver 8V92 was dry. At 500+ HP it should get you down the road well.
How about a 1998 45' Blue Bird with a Detroit 60 at 55,000 miles?
One of my FMCA chapter members has it for sale.

Richard

Posted By: Golden_HVAC on 05/21/16 09:48am

Greyhound ran the 8V71 and 8V 92 in many applications from coast to coast, for many years, until enviromental regulations made a cleaner engine a requirement.

The 8V92 is 92 cubic inches per cylinder and there are 8 of them! IT is also supercharged and two stroke, so it makes power on each stroke. It is a little more fuel costly than a 4 stroke, but if you get a quote of $25,000 to install a rebuilt inline 6 and adapt to your transaxle, you will be lucky.

The inline 6 will be about 8 feet long, while the V8 is a compact 5 feet long. You might not have enough space. You will never save $25,000 on fuel. You might get 7-8 MPG with the most fuel efficient engine and transaxle, while this one has a lot more slippage than a modern transmission, but still was built with fuel efficiency in mind.

The 8V92 can be turned up to about 500HP. The 8V71 mentioned above is much smaller - giving up 168 cubic inches with smaller cylinders. They also came in 6V71, 6V92 and inline versions. I worked on a 16V92 generator, rated at 1500 HP and 750KW power output! It turned 1800 RPM and roared! The most that many road engines are allowed to run at is 1700 or 1800 RPM, before the governor kicks in.

The advantages of a 2 stroke engine over the 4 stroke is more compact size, lighter weight per HP, and less internal friction per HP rating. The disadvantage is a little more fuel consumption. It will use about 20% more fuel than a 4 stroke engine. But they are fun to drive! My buddy has one, and he said he took it in for a check up - they hooked it up to the computer. Said it was rated at 450 HP and they could turn it up to 500, but he said no, it is fast enough. They stated the maximum road speed was 87 MPH. I suggested that his poor little Honda was hanging on for dear life to the back of the RV!

Good luck with your decision! I think you will end up liking the 8V92. Drive it hard, the engine can stand to be wound up to it's max RPM rating. At slow engine speeds, it will not put out the HP that you will need for getting over a mountain, but it will cruise along with no problems.

Another friend had a 8V71 in a 18 wheel tractor. He ran coast to coast with it but had poor performance in the mountains. He ended up turbocharging it, and installing fuel injectors from a 92 cubic inch engine. Then it would make lots of power, got 10 mpg empty and 6 full. Just check the fuel and fill it with oil. Because it is two stroke, the air is blown into the engine, then into the slots in the cylinders. IT can take in oil and burn it with the diesel fuel. So it can burn a lot of oil at higher RPM range.

The generator that I took care of had a specific over RPM shut off, that closed off air to the supercharger in the event that the engine started to burn it's oil, and not slow down. In come cases, they would shut off the diesel fuel, but if overfilled with oil, and over the rated RPM, it would splash enough oil into the cylinders to keep running at the higher RPM. It was a sort of panic switch to close off air to the engine on the generators.

Good luck, happy camping!

Fred.

Posted By: Kayteg1 on 05/21/16 09:55am

Yeah, my 8V71 has fighter jet-style switch that close big flapper on intake in case of run away. Never had to use it, but tried out of curiosity.
It also had 2 fire sensors in engine compartment and loud bell under driver floor. It worked fine as I tested it.
Funny all-metal coach had fire alarm, while wood and fiberglass newer coaches don't

Posted By: DonHutchins on 05/21/16 10:00am

Wow! That's a LOT of great input in almost real-time. I think I'm gonna like this forum!
Plenty of good suggestions here - including the vote to go with the DD as is, because it is a very reliable rig. I've heard of them running happily with a holed piston, though I certainly would hope never to be in that position! Believe I'll talk to Country Coach (it's their conversion) about the motor swap, as they've done all the maintenance on the rig since new.
Thanks again for all the good poop. I'll keep the forum updated on how we do with this search. We're moving up to a tag-axle pusher so I can mount my big BMW moto on the rear, and move up from the 5'er we've pulled it around in for several years.
Best regards to all.
Don Hutchins

Posted By: Bill.Satellite on 05/21/16 10:05am

It can be done but everything has to change. Engine, transmission and electronics. I was quoted north of $60,000 to make the change. You will be better off buying a newer coach. My current 1988 has the 8v92 and gets 5.5 MPG. Changing to a series 60 can up that to 7-8 MPG so that's not going to pay for the change. The 8V also has more torque and can often out run the newer 60 series up a hill. Yes, the slobber tubes drip some oil and I burn about a gallon every 1000 miles but that's OK, too. There are even ways to catch the oil from those tubes if you just want to keep the underside of the coach cleaner.
There certainly is no reason to swap engines if you are concerned about reliability as the 8V92 is a long haul work horse that will last nearly forever. Even if you needed to swap one out, there is a company in MO that can do it in 2 days for about $15,000 compared to an in-bus full rebuild for about $30,000.
My only caveat would be to ensure that the bus does not have the DDEC 1 electronics (1988 and earlier). I would recommend that it have at least the DDEC 3. If that's the case, buy it, drive it, love it!

What I post is my 2 cents and nothing more. Please don't read anything into my post that's not there. If you disagree, that's OK.
Can't we all just get along?

Posted By: Mr.Mark on 05/21/16 10:14am

DonHutchins wrote:

I'm looking at a used Prevost that's a beautiful unit in nice condition, but it's got the old DD 8v92 motor, which I'm really leery of. It's got a rep as a dripper and fuel guzzler. What are the chances it could be swapped for the newer DD Series 60 motor? I know this is off-the-wall, but I really do like this unit and might go for it if this is do-able...

Don Hutchins
Kingston WA


Mr. Don,

Brian was at one of our 'know your Prevost' seminars. Nice fella and the company he works for would know what is best.

-------------------------------------
Brian Stanton 417-865-4420
2441 E. Jean St. Springfield , MO 65803

[email protected]
http://www.americanfleetinc.com

American Fleet Inc. specializes in Detroit Diesel Engines and repairs for the motorhomes, entertainer coaches and any bus application. We offer Allison Transmissions for the same applications. Most engines and transmissions are available to ship within 3-5 days. Feel free to call or email with any questions.
-------------------------------------


MM.

* This post was edited 05/21/16 10:23am by Mr.Mark *

Mr.Mark
2021.5 Pleasure Way Plateau FL Class-B on the Sprinter Chassis
2018 Mini Cooper Hardtop Coupe, 2 dr., 6-speed manual
(SOLD) 2015 Prevost Liberty Coach, 45 ft, 500 hp Volvo
(SOLD) 2008 Monaco Dynasty, 42 ft, 425 hp Cummins

Posted By: DonHutchins on 05/21/16 10:37am

Thanks Mark,

I've emailed him...

Don

Posted By: Bill.Satellite on 05/21/16 11:29am

That's the company in MO I was referring to. Excellent folks who do excellent work.

Posted By: hanko on 05/21/16 12:28pm

Id take that old Jimmy any day,compared to those smog choked def cumaparts

2014 Tiffin Open Road 36LA,Banks Power pack,sumo springs, 5 star tune, magnum invertor

2013 Ford Focus Toad

Haigh Superstar


Posted By: Sea Dog on 05/21/16 03:18pm

hanko wrote:

Id take that old Jimmy any day,compared to those smog choked def cumaparts


Aint that the truth?

I spent my career running 871s in commercial fishing boats.
They will spit out most of the rings and keep running.

No one wanted a Cummins, too temperamental, kinda hard
to pull a boat off to the side of the road and wait for a mechanic!

Life is short,Death is long,
Take a vacation.

Posted By: mpierce on 05/21/16 04:13pm

Love the 8V92 in our 1990 Bluebird. 475 hp, goes right down the road. Buy the two stroke, love it!

Posted By: Ivylog on 05/21/16 04:41pm

Yes the 2 cycle GM's love the fuel but unless you are putting 100K miles/year on it... you can't be serious about swapping. Because of the higher pressure on the crankcase you get more oil out the slobber tube/crankcase vent. You can make a catch bucket out of a gallon jug with steel wool in it to catch the oil and yes you could even recycle it. I have a 8v71 in a dump truck that's very dry (agree valve cover gasket/alignment) and they are still fairly inexpensive and easy to rebuild... used to be $100/hole. A complete OH kit for a 8v92 is only $3000.

How many miles on it?

This post is my opinion (free advice). It is not intended to influence anyone's judgment nor do I advocate anyone do what I propose.
Sold 04 Dynasty to our son after 14 great years.
Upgraded with a 08 HR Navigator 45’...
Posted By: slickest1 on 05/21/16 05:09pm

I ran many Detroit 2 strokes over the years. The last one i had we up tuned it. We changed it up from 80 or 90 injectors to 110 injectors and a Detroit v12 pump. They are interchangeable. The cost i can't quite remember but was not real expensive. That gave out upwards of 500 HP and actually improved the fuel mileage. Yes they use a little oil but the harder you drive them the better they ran. They are noisier than most engines but are very cheap in comparison to maintain or rebuild.
That truck that I had that engine in was pulling 63000 kg loads and was hard to pass. The Cats and Cummins of the day could not touch it.

The engine swap you suggest would be very expensive to do. I changed on truck from a 8v71 to a Cummins and the costs went through the roof when you started having to replace radiator and all hoses including hydraulics fuel lines and wiring and it goes on and on.

1998 Holiday Rambler Imperial 40 ft.
Dennis and Marcie and Pup the Jack Russell

Posted By: Mike Hohnstein on 05/21/16 09:12pm

Major problem with 2 strokes, as with 3208 Cats is the emission regs knocked them out of the market 20+ years ago, it's getting pretty difficult to find a tech who can deal with them considering the fact that Detroit and Caterpillar don't support them service wise.
That being said, mechanical engines are less likely to leave one marooned, as the Dedecs are obsolete and as stated above, not supported.

Posted By: 11178adm on 05/21/16 10:21pm

if it is n good shape the 8v92 will give you good service. when they were a common engine in trucks a quick way I would use to check the condition was to start the engine cold after sitting over night and watch the smoke out of the exhaust at idle if any white smoke clears up within 30 to 45 seconds then the rings are probably ok take a infrared thermometer and check the exhaust temp at the manifold ports if the white smoke persists the port that is colder will be the smoker these engines with high mileage are bad about breaking the top ring
also check the amount of oil coming out of the air box drains (slobber tubes)if it drips it is somewhat normal if it runs out probably piston pin retainers or piston crown to skirt seals are leaking, major repairs. also make sure there is no coolant in the oil quick check with the engine hot stick your finger up the breather tube if it comes out foamy and watery major repairs. 92 series engine main bearings don't like anti freeze. most common cause would be the head gaskets or the liner seals. yes finding a tech that even knows what a 71 or 92 series Detroit is let alone how to fix one is getting more difficult every day.

good luck with it

Posted By: Sea Dog on 05/22/16 09:45am

We have lots of them.
The guy who bought my boat
had a complete rebuild including magna flux
on a 8-71 last year.

Posted By: potentialrvers on 05/29/16 04:19pm

Don,
You might join www.prevostcommunity.com, www.prevostownersgroup.com, and or www.prevostgurus.com. Those boards are directed to Prevost and potential owners of Prevost. A wealth of information and knowledge on those boards.

Reese

Posted By: Jarlaxle on 05/30/16 07:51am

DonHutchins wrote:

I'm looking at a used Prevost that's a beautiful unit in nice condition, but it's got the old DD 8v92 motor, which I'm really leery of. It's got a rep as a dripper and fuel guzzler. What are the chances it could be swapped for the newer DD Series 60 motor? I know this is off-the-wall, but I really do like this unit and might go for it if this is do-able...

Don Hutchins
Kingston WA


I'm sure it's possible...will probably cost between $20,000 and $40,000 to do.

The 8V92TA is fine...I suspect it is a "Silver 92", with the leakage problems solved. In a Prevost, I would expect a pretty high power rating, probably 450HP or better.

John and Elizabeth (Liz), with Briza the size XL tabby
St. Bernard Marm, cats Vierna and Maya...RIP. ">
Current rig:
1992 International Genesis school bus conversion

Posted By: Jarlaxle on 05/30/16 07:54am

Mike Hohnstein wrote:

Major problem with 2 strokes, as with 3208 Cats is the emission regs knocked them out of the market 20+ years ago, it's getting pretty difficult to find a tech who can deal with them considering the fact that Detroit and Caterpillar don't support them service wise.
That being said, mechanical engines are less likely to leave one marooned, as the Dedecs are obsolete and as stated above, not supported.


Pablum. Off the top of my head, Cat still rebuilds 3208s!

Posted By: Mr.Mark on 05/30/16 09:17am

DonHutchins wrote:

Thanks Mark,

I've emailed him...

Don


Mr. Don,

Any updates? What did Brian suggest?

MM.

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