Converting early gas MH to Duramax? Possible?

[convert2diesel]

Thanks for all your efforts and information. We're looking to add an affordable way to rv with 4 children. The FMC (possibly GMC) is our choice with an efficient power plant. We may follow your example.

Kevin H
still in planning & prep stages

Kevin:

Just a few thoughts. I am going through the same thought process as you are. Mind you, I don't have to factor in 4 kids.

Currently I am leaning towards the GMC. The original design was not only brilliant but it has survived the test of time with a large and active owners community. Having said that, for your purposes, shoehorning yourself, significant other and four kids into a GMC would be tough with any of the available floorplans.

Additionally, the front drive system comes out of the Olds Toronado/Cadillac Eldorado of the same vintage. Without major surgery, that means you are stuck with the THM 425 transmission (basically a 400 with the torque convertor and front pump attached to the engine with a chaindrive to the rest of the tranny turned around and going forward. Still a great transmission, especially if you can find a "switch pitch" trans from a 67 or 68 car. Essentially gives you a 6 speed tranny.

The bell housing is a "BOP" bolt pattern so if you use any other engine you would have to get an adapter plate, modify the engine oil pan to accommodate the right hand drive axle and fabricate a front mounted engine mount. There are a number of 6.5 turbo conversions out there as well as a couple of Duramax conversions.

If you are still interested in the GMC, I would suggest you look into the GMC Co-op in Orlando Florida. Jim Bounds is the by far the most knowledgeable person in the community.

http://www.firefightmarine.com/gmccoop/

This thread has me looking at the FMC as an alternative. Love the concept of the independent rear suspension and pusher engine layout. This plus the added room for the family would make sense for your uses and open up your options for engine trans combinations. Unfortunately they are not only the same vintage as the GMC but there were far fewer manufactured. I would question the availability of parts, specific to this platform.

I have also started looking at the Airstream Motorhomes. Lots of them out there with a 40 year production run including some pusher versions later on. Even today, they are still manufacturing a motorhome based on the Mercedes Sprinter platform. Still trying to get some information on the various versions and separating the good from the bad.

From a cost point of view, I would seriously analyse how you are going to use this motorhome and specifically, how much you are going to use it. Upgrading any of the powerplants in these vehicles to a newer engine is far easier and cheaper with a gas conversion than the diesel. In other words, you are going to have to pack on lots of miles to justify a diesel conversion from a cost point of view.

The new "LS" series GM gas engines are plentiful, with an extensive aftermarket support system in place. Properly configured, they can be programmed for very acceptable fuel consumption and with reasonably inexpensive "go fast" parts can lay down some very respectable power. Based upon my research into the GMC, I could do an LS conversion for about $5,000 less than any decent diesel conversion, plus, it can be fixed on the road by any reasonably equipped garage. Even Bubba in lower Buttkiss is probably conversant with this engine family.

Myself, I am leaning towards a GMC with either an AMG 6.5 or LS engine and a switch pitch transmission, upgraded suspension and brakes and a total re-working of the body. I expect the cost to be in the 30 grand area, including the initial purchase. Not much more than a reasonable tow behind trailer.

Hope this helps.

Bill

[BigRabbitMan]

I expect the cost to be in the 30 grand area, including the initial purchase. Not much more than a reasonable tow behind trailer. Hope this helps.

Bill

Bill has done an excellent evaluation. His cost estimate is very good for a conversion done properly. In my case, I spent more than needed in some areas and already owned the coach and I ended up with a total cost of about $27,000 for the Duramax conversion. The other person that is currently converting an FMC to a Duramax expects his cost to be the $30,000 number including the purchase price of his coach. I expect that number will be very close to what his actual turns out to be.

In the case of the FMC, a conversion/upgrade to modern gas engine/tranny setup would be much cheaper and that is what I would recommend for most people as most motor homes will not get the mileage on them to begin to justify the cost of the diesel conversion. With the FMC, a gas conversion is fairly straightforward with few complications. Mainly engine/tranny mounts and gauges. But again, it takes many miles to justify a conversion verses, in the FMC case, just doing a rework of the existing 440 with possibly upgrading to a fuel injection system. With the 440, I pulled 6% grades at 45 mph passing many other motor homes!

As to parts availability, with both the FMC and GMC there are support groups out there and sources of parts have been identified for most things. As an example, I have just ordered all of the steering linkage parts for my coach as with 160,000 miles it is time for work on that end. They are all off the self items still today as they were/are used on many other vehicles.

Rollin', rollin', rollin',

Stephen H. , FMC #1046