Cummins Diesel Upgrade to Classic MH

Wayne Olson · 10-13-2006, 12:38 PM

Several people have asked that I start a thread on the Cummins Diesel upgrade that we have in our '85 345 MH. This is the first MH we have owned and the previous owner had the diesel conversion done at a diesel shop prior to our purchase. However, when the PO started on the complete MH restoration they quickly got into more than they had expected and purchased a new MH so that they could take off on their trips.

We have now finished the complete frame up restoration which we spead over several years. We started by stripping this 345 MH leaving only the outside skin and the frame. All the windows, interior, and inside skin were removed including the floor. Most of our friends did not believe that we would ever get all the pieces back together again. I think it is important to note that the wife allowed this project only on the basis that we had another Airstream 345 ready to go until this one was completed. So, we quickly purchased our second 345 which we were lucky to find already in great shape. We have now completed several 345 restorations for resale but this 345 with the diesel conversion is our pride and joy.

The engine is a Cummins Diesel 6BTA5.9 with 457 lb-ft torque and 180 HP connected to a Allison AT542 4-speed Transmission and a 3.54 : 1 rearend. The conversion cost the PO over $16,000 and the engine had less than 20,000 miles on it when we purchased the MH.

The advantages are:
1) This combination has proven to be very powerfull allowing us to travel at any speed desired. Just set the cruise, sit back and enjoy the ride.
2) I do not believe that the diesel engine gives off any more noise than the 454 gas 345 MH's we have owned.
3) The milage is great getting 11 to 13 MPG.
4) Another advantage is that the Cummins starts quickly EVERY TIME.
5) The diesel requires much less maintenance than a gas motor with a service life of about 250,000 miles.

This disadvantage is:
Price of conversion. This conversion would be for someone who loves their Airstream MH and wants to keep it for a long time and / or travels a lot of miles. You will only have to do it once but it will not be cheap. It sounds expensive but it also has a significant impact of resale value. We would not have done as extensive a restoration if it had been a gas MH!

I will be happy to provide more details if requested.

GlenCoombe · 10-13-2006, 04:13 PM

Wayne, first ...thanks for starting this thread.
Do you know if the P.O. did anything to the front end to support the added weight of the new combo?
What do you turn for RPM's at 70mph? 3.52 is a great rear end for a motor with the torque numbers you have!!
As my coach is a daily driver I'm interested in the improved economy. That said I am turning 8-9.5 mpg and am always looking for better. I'm currently looking to go with GearVendors to reduce the rpm's at highway speeds, and to eek out the best fuel economy I can.
I'm just back in from a two week swing of over 1600 miles so my ROI is faster than the average MOHO owner.
Does the coach have a diesel generator, or did you go propane there?
Thanks again for this interesting new thread.

bake315 · 10-13-2006, 06:11 PM

I would absolutely LOVE to see some pictures of the restoration process!

ralley · 10-13-2006, 06:15 PM

THANKS Very Much for this. There are a few of us who are just diesel fanatics, and would like to investigate the retrofit of diesels into the 345-370 series AS MH.

Wayne Olson · 10-14-2006, 02:44 PM

There was some modification to the front cross member in order to aid installation however nothing drastic. I would be happy to privide any details and photoes to anyone who is doing the conversion. I am sure that the 3:52 gears would be just fine.

I realllllllllllly want to change the generator to diesel as well but the 7000 Kohler just will not die and has always worked great. I took it to a Kohler Service Center in Indianapolis to be checked and serviced when I purchased the MH. They rebuilt the carb, put new 'O' rings in the fuel pump, and put in new brushes before doing a complete adjustment of all settings. It took them 3 hours and I have not had any problems. The service tech said that many times the 'O' ring in the fuel pump will break down and the pieces get into the carb. The 'O' rings are very cheap and easy to replace. However, getting the pieces out of the carb can be difficult. The funny thing is that we took one of our other 345's to the 1st NASCAR race in Kansas City and had that exact problem. Went to John Deere and found an 'O' ring of similar size and fixed the fuel pump. The hard part was cleaning the carb at the track. All those great auto shops all around us and I only had basic tools. I sure wanted my shop at home. We were camping for 3 days inside the track with over 100 degree temps. Not fun without electricity. Less than a $1.00 in parts, a couple skinned fingers, some funny looks form my wife, some cold beer, and we were back up and having fun.

I can start putting some of our restorations pictures in if people are interested. There really is no part of a 345 that I have not gotten personal with.

Minnie's Mate · 10-14-2006, 06:22 PM

I am no mechanic nor am I a motor home expert or owner, but I do have my first diesel 3/4 ton truck that I have come to admire more the more I drive and think if I ever went motor home, I'd go diesel for sure. I'd love to live vicariously through your process along with others in this thread.

toddster · 10-14-2006, 08:15 PM

Wayne...........I've always been an advocate of diesel technology especially in motorhomes. Many times I too have envisioned a late 80's to early 90's Airstream Classic motorhome diesel conversion. I found online where someone converted an old GMC motorhome to run with a GM 6.5L diesel (what an undertaking!!!):

http://www.gmcmhphotos.com/gallery/s...d=marc&aid=432

I would love to see photos of your restoration as well as any that the PO may have passed along of the diesel conversion.....

Happy Trails

-Todd

fastrob · 10-14-2006, 08:23 PM

Quote:

Originally Posted by Wayne Olson

.......The service tech said that many times the 'O' ring in the fuel pump will break down and the pieces get into the carb. The 'O' rings are very cheap and easy to replace. However, getting the pieces out of the carb can be difficult.
....
I can start putting some of our restorations pictures in if people are interested. There really is no part of a 345 that I have not gotten personal with......

Wayne,
We love pictures, especially those of us who must wait to Airstream.
Why not put a fuel filter in between the pump and carb?
I almost bought a 4 cyl cummings in an aluminum van the other day but rationality won out.
R

ALANSD · 10-14-2006, 08:24 PM

there used to be a member here with a cummins diesel classic installed AS motorhome. I will have to look up the old posts.

Geophilist · 10-15-2006, 11:37 AM

Wayne,

Please post some of your restoration/conversion pictures. There appears to be quite a bit of interest in the topic. The trouble with PMs is that they are so .. well, private. Please share with us all, and that way they can live a long time for those who come later.

Steve

Wayne Olson · 10-15-2006, 05:16 PM

I will try and start a thread on our restoration but I have a question for all of you. My question is: 1) should it be a single thread covering all subjects or 2) break down the restoration into major subjects ie. Interior / cabinets, furnace upgrade, plumbing, AC / vents, and the Diesel conversion covered in this thread. I think the exterior finish and window seals have been covered very well in the other threads. What do you think?

wascobob · 10-15-2006, 09:52 PM

Wayne ----I think that there is interest in two very seperate topics, it certainly calls for a split in the thread. I would follow both branches, but personally, I would be most interested in the under the hood thing.

If you are handy with a digital camera and know how to post photos, I would love to see very detailed photos of the instalation under the hood and under the moho that shows as many details as possible. It would be great to be able to see such things as the crossmember mods. as well as turbo and exhaust routing, the whole nine yards.

-------I will follow this with interest...Thanks Bob

jking · 10-16-2006, 06:54 AM

Thanks for an interesting and meaningful idea. I would reiterate the front suspension comments: Airstream did not do any changes to the front end when they installed diesels back in the 80's and there have been numerous ball joint failures owing to the increased front end weight (ask how I came to know this). Keep on with the thread - it's a great one. Jamie ('84 310 turbodiesel soon to have a gearvendors added)

Geophilist · 10-16-2006, 10:58 AM

Wayne,

I agree with Bob, two threads would be good. It would make following the engine swap eaiser as many folks appear to be keen on that.

I'll bite, how do you know about the weak front ends, Jamie? Have you done anything to augment the suspension, or do you just carry around extra ball joints like I carry around an extra alternator?

Steve