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Onan Generators Restoring, operating and maintaining vintage Onan generators.

Onan Generators

Nice little job to do:


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  #1  
Old 08-01-2017, 11:36:19 PM
Troll Troll is offline
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Default Nice little job to do:

Buddy of mine refinishes wheels on late model cars at several dealerships being a mobile service. Currently he and wife work out of a Dodge "Sprinter" van performing the service. Using a 7500W "Quiet Diesel" Onan set he is powering a tire machine, balancer, compressor and single heat lamp for rapid curing of the wheels. He is expanding his operation and has purchased all new equipment including a 25KW Onan diesel genset, IR TR-30 series upright compressor, and four drying units for wheel refinishing. He is also bringing on two more employees. The new vehicle also purchased is a Freightliner van about 28' in length w/300 Cummins engine and it has a 10kw Onan "Quiet Diesel" buried in the side behind the drive axle. The van is a former SWAT team vehicle from a government auction and is very clean.

My part of this job is to build a suitable platform on the rear of the vehicle to support the brand new genset and compressor. By manufacturers prints I can build a 40" X 100" platform and have adequate clearance between the two units. He will be responsible for the enclosure but I'll make the platform from 8" X 13.5 pound per foot structural channel welded together with adequate crossmembers for the items to bolt down to via vibration isolators. Don't know if I'll extend his existing frame rails, or just go on the outer vertical sides of the existing and through bolt using grade 8 hardware, then weld the ends solid. Kind of a permanent install regardless but the frame is relatively unencumbered where the modifications/mountings need to take place. Looks to figure about 2700 pounds back there including the equipment and platform weight but a couple of knee brace and crossbucks to stiffen things up should be alright. He is dead set on the equipment hanging off the rear and inflexible to relocating it. If it lightens up the front end much, he may change his mind.....
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Old 08-02-2017, 03:28:26 AM
yellowlister yellowlister is online now
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Default Re: Nice little job to do:

Sooo.. he wants 2700 pounds of gen on the ass end of this swat van? That is just silly.. kindly.. those are built on 2 1/2 ton chassis if I'm thinking of the right one.. you should test mount it.. throw a few bolts to keep it from sliding around and drive it down the highway in anything but nice weather.. one good wind gust will send that brick on wheels into the wall Or another vehicle with all that weight on the tail end

I could be wrong.. but i would play with a few different configurations before deciding, is he going to ever tow with it? Think about maintenance and ease of fixing it access down the line..
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  #3  
Old 08-02-2017, 07:23:25 AM
MBB MBB is offline
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Default Re: Nice little job to do:

I agree with Yellowlister. I have a Sprinter 2500 and granted not the same vehicle. It is dragging when loaded heavy in the rear.I would bet he might have trouble at a weigh station the weight is unbalanced. Did you ask him if he would consider mounting it in a trailer?
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Old 08-02-2017, 07:26:18 AM
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Default Re: Nice little job to do:

Very close to my actual thinking also. I really didn't look too closely at the suspension or anything like that but it is single 8", .312" frame w/19.5" tires and there will be one hell of a negative cantilever effect on the front end IMO. I'm not for the idea at all but the equipment is set to be delivered today or tomorrow. My plan is to build a platform from scrap steel and set a 2500# concrete block I have upon it, strap it down good and have him drive the vehicle prior to getting knee deep into it. I do feel he is wrong but too stubborn or determined to properly evaluate the repercussions of what I consider an inadequate build. I'd like to see the generator and compressor mounted forward of the rear drive axle and his portable paint booth assemblies carried outside on a rear platform myself as they are quite light in weight. As far as it "washing out" behind him in inclement weather, I'm not really certain as I don't know the gross weight or placement of equipment inside this van project.

If he is willing to fund the engineering time I'll go for it otherwise I'm going to have to decline the job.
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Old 08-02-2017, 07:27:02 AM
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Default Re: Nice little job to do:

Not knowing what the vehicle and it's capability is, my first thought will be with that amount of weight hanging off the back it could be dangerous. Considering the moment arm of the weight will the rears be overloaded? Think of the weight as a pendulum and in a situation of sliding the rear it could make the van swap ends.

Or am I over thinking it.

edit:
Reading post #4 I'd put it on a trailer.
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Old 08-02-2017, 07:40:44 AM
Wayne 440 Wayne 440 is online now
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Default Re: Nice little job to do:

He will change his mind sooner or later. Buddy or not, if you do this, be prepared to hear all kinds of complaints later on. Have "I told you so" printed on a number of business cards, and get the agreement in writing before you do it.
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Old 08-02-2017, 08:15:16 AM
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Default Re: Nice little job to do:

Talked to a wrecker builder I've known and bounced ideas off of for many years and always follow their advice. After speaking with them I've sent off a letter to the vehicle owner declining the job citing many of the concerns brought up here along with a few extra. Seems like a severe liability exposure to me on the surface.

Hell, here is an excerpt of the letter:

I'm having difficulty having any of the truck body/frame builders I normally deal with give a positive blessing on this project. All cite the protruding weight from the rear of the vehicle causing stability issues. Not knowing what suspension is installed is another question but I'm told typically those box vans like that have a 12k rear axle and I can't remember what you spoke of in weight rating.

Building a sturdy platform is not a problem but with the amount of time and conversations I've had with others whom know more than I about this type application, I'm afraid I'll need to decline this opportunity. I would however be willing to build the platform and mount it to the truck, but can go no further as far as mounting equipment citing the liability exposure.

Thank you and I do apologize the application does not "feel" right to me.


Probably going to piss the guy off but at least I'm not looking at a lawsuit.

Thanks,
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Old 08-02-2017, 08:15:36 AM
dmeed dmeed is offline
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Default Re: Nice little job to do:

Do some quick math on weight on that rear axle. I had a 28' RV and figured that every pound added on the trailer hitch put 2 pounds on the rear axle (as it unloaded the front axle by 1/2 pound).

Check the tire weight ratings and put it over a scale (check front to back weight) while you have that test weight on... Then add all the other stuff he is going to put in it as a full shop. (Ideally check the weight distribution before and after the 2500 concrete block is dropped on).

(I see bike carriers and trailer hitch cargo decks on the back of cars and trucks and wonder what that is doing to their rear ends too).
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Old 08-02-2017, 09:58:56 AM
PnishrPW PnishrPW is offline
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Default Re: Nice little job to do:

There is an old saying: Discretion is often the better part of valor...

I've been a cert'd welder/fitter/rigger for 30+ yrs, my instinct would be to run away from this job. Not only is this unsafe, the liability is far to high. Even if the chassis would handle the load, vehicle dynamics would suffer greatly. I wouldn't even do the platform. Several times in the past I've declined ill conceived projects that went ahead via others and seen the results, one ended in a fatality - that one is still in litigation some years later. Go with your gut.
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Old 08-02-2017, 10:11:21 AM
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Default Re: Nice little job to do:

Yes and thank you. He is beginning to reconsider the relocation of the generator and compressor to the interior of the van amidships of the axles. The portable spray booths are looking to be carried on the platform as they will stand on their ends and take up less then the width of the platform so this may work out. I, like you, have many years of welding/fabrication experience but have always followed prints not being a design engineer myself. This job however does not set well with me as safe and glad to see others concur.
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Old 08-02-2017, 01:22:52 PM
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Default Re: Nice little job to do:

I agree completely with the above posts. Weight should be over the rear axle. With the weight on the back, the the steering control could be compromised. The guy needs a certified engineer to draw it up.
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Old 08-02-2017, 03:41:36 PM
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Default Re: Nice little job to do:

Within the constraints of GVW, and above/forward of the rear axle I wouldn't foresee any issues. Given the above caveats, I wouldn't think an engineer would be required. But, then again, my engineering degree is via Redneck U...
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Old 08-02-2017, 03:42:51 PM
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Default Re: Nice little job to do:

As a kid the city dumped a bunch of cobble stones in a friend's hole near us. Dad had me retrieve them to use as curbing for our house. After carrying them up 30 ft hill I laid them uniformly in back of a 1/2 ton pickup, then added 2nd layer. As I turned steering wheel to make a corner the front tires 1/2 slid over the road, not wanting to turn the truck. Felt !!!!!

And center of bed was over the rear axal, would be worse with weight beyond the bumper.
Saving grace might be that it's a long truck, but devil is in the details of weights, wheelbase, distance from load to rear axel. Assuming framing is of proper size, if bolting it up I'ld check shear and tension stress in the bolts. Don't want to use too small dia bolts.

Last edited by len k; 08-02-2017 at 09:44:28 PM.
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Old 08-02-2017, 04:35:52 PM
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Default Re: Nice little job to do:

He can always put a tow truck counter weight bumper on it.. would make a nice battering ram for people that cut him off and he can't stop being so heavy
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Old 08-02-2017, 05:04:16 PM
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Default Re: Nice little job to do:

Big load behind the rear axle is an accident waiting to happen. Ford found this out the hard way:

http://www.cbsnews.com/news/rollover/

GMC lengthened their wheelbase instead. I don't know what the Mercedes vans have done, but the amount of weight you are talking about would concern me greatly.

Run, don't walk.

tom
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Old 08-02-2017, 09:21:43 PM
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Default Re: Nice little job to do:

I'm out of the job complete with no hard feelings. He found a welding shop that will do the work as he desires. I didn't even have to piss him off to get out from under it which is good.

Hope all works his way as I never wish failure on anyone but this one didn't set well with me even prior to posting about it here.
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Old 08-03-2017, 12:19:47 AM
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Default Re: Nice little job to do:

You are a better person to tell the guy that you are not comfortable with the job HE wants you to do. You would feel like Hell if something happened and it was attributed to what you did. You will sleep better at nights
I have done automotive and equipment repair for over 40 years as a semi hobby and I have specific values and specifications as to how I will do the job.
My way is to do it ONCE, do it the right way and everyone is happy and SAFE.
I don't cut corners or Mickey Mouse ANYTHING. I also sleep well at nights.
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Old 08-05-2017, 02:19:44 PM
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Default Re: Nice little job to do:

I do truck mods at my shop. This sounds like trouble because of the front/rear loading AND the "teeter totter" effect of adding this behind the rear axle, above and beyond OEM. If you contact the chassis manufacturer, they will have prints and specs available for all of the dimensions, weights, loads, etc. and what's allowable. Most will provide this to you as a PDF file.

As for the frame and if the (OEM chassis manufacturer allows frame mods with welding), Use the same size "C" channels as OEM. Cut the stock ones on the rear of the truck at a 30-45 angle and make the opposite image on the front of the new frame rails being added. Once welded, add at least a 3' long section of "C" channel whose opening of the "C" fits over the outside of the frame's new weld. Now weld this on over the splice.

I prefer welding, but some chassis manufacturers don't allow it and DOT rules will go by their recommendation in the event of an accident due to a frame failure.
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Old 08-05-2017, 02:54:16 PM
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Default Re: Nice little job to do:

chassis manufacturers don't allow welding........ most likely their structural steel is heat treated for increased strength so they can use thinner steel for reduced weight ( gas mileage). Welding anneals the heat treat and can weaken the steel.
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Old 08-05-2017, 05:54:59 PM
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Default Re: Nice little job to do:

Troll I have walked off many jobs. Because I didn't feel safe being on them. From having drunks or druggies on the job. To the job not being safe. Having all that weight on the back end and something goes wrong. You would be the first one the lawyers would come after. You made a wise choice to refuse the job
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