Bobcat 720 Repower with Onan Diesel

[cadavi15]

Hello everyone,
I picked up this engine-less Bobcat 720 for a song back in November. The previous owner had pulled it because it had a bad leak and never had the time to put it back together. A couple weeks ago I found what I believe to be suitable replacement engine for this machine, a 1.9 Onan Diesel from a military Generator (MEP803A). The engine has very low hours and good compression.

I already have a couple stupid questions.

1. I'm not sure if my machine is missing a piece, but how do I safely tilt the cab forward haha? Seems like there should be a mechanism that either assists with the lift, or at least prevents it from falling forward once you get it past center? I have the manual but didn't find anything about this operation (maybe I missed it?) I know newer machines have gas struts to help and I may incorporate them in the future.

2. I'm planning on rewiring what little electrics are on the machine as the new engine is 24V. I was going to use a buck converter to bring it back down to 12V to run accessories (fuel pump, radiator fan, lights etc)

3. All I have to do is spin the pump right? Does anyone foresee problems I may run into? I have a small machine shop and some fab skills.

Thanks! Looking forward to hearing from your experience.

 

[cdmccul]

Fun project!

I'm here just to watch, mostly. I look forward to what you do with it.

Basically the engine just spins the pump, heats the cab if you have a heater, and is a good portion of the counter-weight.

 

[cadavi15]

Fun project!

I'm here just to watch, mostly. I look forward to what you do with it.

Basically the engine just spins the pump, heats the cab if you have a heater, and is a good portion of the counter-weight.

I live in Phoenix, no heater needed haha

 

[cdmccul]

Bring the Mercury!

Haha!

 

[volkswagenvan]

You might want to change out your starter and alt to 12V rather than try to add an extra battery. (Not much room)
I`m not sure if you have a cable stop or solenoid on your pump ether.
If you do decide to add an extra Battery you could just get 12v off one of the battery's for your accessories .

Cool Project!

 

[gearbox]

You are going to find out that the only way its going to work is if you drive off the front of the diesel . Originally the Wisconson drove the pump from the flywheel end . That would be clock wise looking at the flywheel .

 

[cadavi15]

Thanks for the feedback. Got off work a little early today and did some work on an engine mount. Although, after reviewing these pictures I realize I'll need to rethink it a bit to get to that big filter.

 

[cadavi15]

You are going to find out that the only way its going to work is if you drive off the front of the diesel . Originally the Wisconson drove the pump from the flywheel end . That would be clock wise looking at the flywheel .

I did have a thought about this. I would agree that the Wisconsin spins clockwise looking at the flywheel, however I'm pretty positive that the Wisconsin has the flywheel facing rearward in the machine. I actually have two of these old Wisconsins.

 

[cadavi15]

Spent some good time in the shop this afternoon. Finished tacking together the main frame of the engine mount. Also did a good chunk of work making a radiator frame. It's literally the cheapest all aluminum radiator on Amazon (Civic?). It has some bosses on the top and bottom so I used three rubber grommets on 1x1 tube as pictured in an attempt to give it some vibration isolation. I'll make the top cross member sandwich the radiator in the frame from the top and bottom. Added strapping across for hanging the fan.

 

[Atilathehun99]

Regarding raising the ROP -

20 series came with a screw jack lift located at the left rear (facing forward) of the ROP. Through time many of these were removed/broke. On my 722 I remove the retaining bolts and then hook a chain to the front top center of the ROP and then raise with my truck. One man can lift it (but anymore not THIS one man) and let it roll completely down to rest on the bucket. I like my method better as I lift just high enough to access whatever I want to do under the ROP. You could block it and remove the chain but I trust the chain more than the blocking which could get dislodged when working on the machine. I have no desire for the ROP to come crashing down on me.

 

[cdmccul]

Nice progress!

 

[cadavi15]

Something like this. I'd like to make so I only have to disconnect maybe throttle cable and electrical connector to remove the whole engine/cooling/fuel system

 

[jp8775]

You have done a great job, do you have any pictures of the engine side that has the u joint on it? I am curious how you did that as well. I am doing a Thermo king up grade soon V1702 to V2203.

 

[cadavi15]

You have done a great job, do you have any pictures of the engine side that has the u joint on it? I am curious how you did that as well. I am doing a Thermo king up grade soon V1702 to V2203.

Thanks!
I have a friend with a waterjet and my plan is to have him cut a plate that attaches to the flywheel with a large through bore. I'll turn a shoulder on the lovejoy for a snug fit, then weld it on. The ID and keyway on the coupler for the original Wisconsin engine are essentially abandoned. Here is a mock-up:

 

[cadavi15]

Hello again all,
I have taken a break from this project because I have to work on it outside and it's been +110F all summer in Phoenix. I've also been having second thoughts about some concerns brought up previously in this thread.

Member @gearbox mentioned that this engine may spin the incorrect direction. I was originally fairly certain it spun appropriately, however I had another friend stop by the shop and share a similar opinion as Mr. Gearbox.

Two questions for you experts:
1.
Is there anyway I can confirm the direction the pump is intended to spin from the factory? Does someone have one of these 720/721 that could peek inside for me?

2.
If it does indeed spin in the opposite direction, could a solution be to simply swap the A and B hoses of the pumps? Rather than reconfigure all the work I've done.

Thanks for your help!

 

[laurencen]

I do not believe the pump will run backwards, however if a vein pump you may be able to turn the insides around, did this with a pump some years ago but it depends on the pump

 

[gearbox]

I have a 700 and they definitely drive from the flywheel end

 

[cadavi15]

So in this view, I need to spin the pump the direction of the red arrow correct?

 

[Chris 8603]

So in this view, I need to spin the pump the direction of the red arrow correct?
View attachment 4531

If that's the original coupling, see if you can see which side has the wear on it. If you can see it, that's the direction it turns. If the wear is on the left side it turns counter clockwise, if the wear is on the right it turns clockwise

 

[cadavi15]

Good thought! Unfortunately it's not the original coupling. I have confirmed the spin direction of my replacement Diesel engine which does appear to be backwards