Converting early gas MH to Duramax? Possible?

[FamilyTimeRV]

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.

How's your conversion working out -- no updates in the last few months.

Also, are there any 20-20 hindsights that would benefit a similar conversion?

Kevin H
still in planning & prep stages

[BigRabbitMan]

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.

How's your conversion working out -- no updates in the last few months.

Also, are there any 20-20 hindsights that would benefit a similar conversion?

Kevin H
still in planning & prep stages

Hi Kevin, sorry for the delay in responding. Had things happening that kept me away. I am glad to assist you in your information gathering. The first thing to understand if you are looking at any older motor home, you need to be at a minimum a mechanic to some level as there will be things that need attention/repair/upgrading and it would be cost prohibitive to have that stuff done by a regular shop in most cases. Since you are on this site, I expect that you are covered in that respect.

As to things that I would have done differently, the only one of significance is that I need a larger fan. Another person is in the process of doing the same conversion to his FMC that I did and has secured a better fan. I expect that at some point I will be getting that same fan, but in the meantime I just have drive conservatively going up grades. You can visit both my complete photo album and his (still in progress) on the FMC Owners Club website. The link is: [URL="http://www.fmcowners.com"] . His coach number is 1027 and mine is 1046. He is up to 227 photos in his album and I have 371 in my album. There is also a discussion of both projects in the forum area in the Mechanics section. Feel free to register on that site so that you can post questions in the forum area. He is doing somethings differently than I did but no two people do something like this the same. Not better or worse, just different. He will be doing some suspension things as well as the engine change in his case.

Two major things that I like about the FMC is the low profile and the quietness with the engine in the rear. The GMC also has the low profile, but you do have the engine up front on that one with the attendant engine noise. If you want to convert one to diesel, I think it would be much more of a challenge with a GMC. I am not aware of a compatible engine/tranny for the GMC. There may be one, but I am not aware of one. When you say "efficient engine", I don't know how you define efficiency but if it is more than 8 or so mpg, diesel is the only way you will get there.

There are FMC's that have already been converted to diesel that come up for sale from time to time, but you need to ensure that the conversion process was done properly. That is particularly true of the heavier diesels like the Detroit 8.2 or the Cummins 5.9. Length with the Cummins also causes some issues that have to be addressed.

Traveling with four children raises some questions in my mind. The first is the ages of the children as that will be a factor in how much "space" each one needs. The "A" or dinette model with the optional bunk beds is set up to be able to sleep six people. As they get larger, some have had the teenage children sleep in a tent adjacent to the coach when camping for more than one night.

I haven't had any updates to my thread here as I haven't done anything additional to the coach. In Feb I did travel about 800 miles south to Buellton, CA for a coach rally and back - just had to take it easy going up six percent grades! On the way back I did get 13.6 mpg measured which is very good for a motor home. It is sweet to drive and very quiet with the rear engine and the sound proofing that I did to the firewall. I can hear that it is running, but that is about all.

I am in Oregon, in what state are you located?

[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