Bobcat 743

[antz]

Hello all, I have just purchased an 743 with 5500 hrs on it. Looks to have sat for some time. There is a couple of issue with it that i would like some help with in sorting out please! 1. The hyd pressure light is on. I think that that the unit is low on pressure somewhere as it screams when moving back and forth, and both sticks at opposite lock will cause an engine stall aftew a few seconds. I haven't changed the hyd filter yet (next day or so) but I have confirmed that it is full of oil. 2. The bobtach bucket locking pins are missing the plastic guides and make it extremely difficult to get the pins to lock into place. Not sure if there is a cure for this 3. The saftey lock out bar has no springs to stay in the upright position so needs to be held up with a strap which is a pain in the ass. 4. The radiator has black oily sludge in it that floats on the surface. The machine had little or no water in it when I picked it up but seems to be holding it ok now. The engine had at least a few litres too much oil in it, not sure if there is a way for cross contamination to happen with the cooling circuit. Initially I though a blown head gasket but it doesnt seem to be using water. I have only done about 1 hours driving since I picked it up though.

 

[SkidRoe]

Congrats on your purchase. The 743 is a legendary machine.
The hydraulic pressure light is for the charge pressure to the main hydro pumps. The gear/vane pump for the loader circuit provides a pressure tap to charge the hydro pumps. I take it the loader boom and bucket operate as expected? If so, it could be that charge pressure filters are blocked up. I believe that there is an aluminum block under the cab with hoses teeing out of it that holds the sintered filter blocks. Carefully remove them and wash them out with brake cleaner or mineral spirits.
If the machine has been sitting for quite awhile, I would do a full service on it: All filters and fluids, and lube everything. Two frequently overlooked areas are the chain case oil and greasing the drive shaft between the engine and the pump assembly. Two grease it, you will need a grease gun with an extra long hose and you may need a helper to operate the grease gun.
I would give the cooling system a good flushing until you are satisfied that you have got as much crud out of it as you can. Kubota engines do not tolerate over-heating at all.
As far as the safety bar goes, your local dealer should be able to help you get some new springs.
Not too sure about the Bobtach, but the dealer should be able to help you there as well. Parts availability for these machines is still pretty good.
Once you have everything sorted, make sure the engine temp gauge is working and keep a close eye on it for the first few hours of operation.
I am sure that I have missed something, but this should keep you busy until Tazza comments
Cheers - SR

 

[flyerdan]

Congrats on your purchase. The 743 is a legendary machine.
The hydraulic pressure light is for the charge pressure to the main hydro pumps. The gear/vane pump for the loader circuit provides a pressure tap to charge the hydro pumps. I take it the loader boom and bucket operate as expected? If so, it could be that charge pressure filters are blocked up. I believe that there is an aluminum block under the cab with hoses teeing out of it that holds the sintered filter blocks. Carefully remove them and wash them out with brake cleaner or mineral spirits.
If the machine has been sitting for quite awhile, I would do a full service on it: All filters and fluids, and lube everything. Two frequently overlooked areas are the chain case oil and greasing the drive shaft between the engine and the pump assembly. Two grease it, you will need a grease gun with an extra long hose and you may need a helper to operate the grease gun.
I would give the cooling system a good flushing until you are satisfied that you have got as much crud out of it as you can. Kubota engines do not tolerate over-heating at all.
As far as the safety bar goes, your local dealer should be able to help you get some new springs.
Not too sure about the Bobtach, but the dealer should be able to help you there as well. Parts availability for these machines is still pretty good.
Once you have everything sorted, make sure the engine temp gauge is working and keep a close eye on it for the first few hours of operation.
I am sure that I have missed something, but this should keep you busy until Tazza comments
Cheers - SR

The radiator being low on coolant with oily residue in it combined with a high oil level in the engine points strongly to a bad head gasket or cracked head which allowed coolant into the engine.
Chances are when you pull the drain plug on the oil pan, the first few liters out will be coolant.
Hopefully it hasn't been run long like that as bearings don't like antifreeze syrup for lubricant.

 

[antz]

The radiator being low on coolant with oily residue in it combined with a high oil level in the engine points strongly to a bad head gasket or cracked head which allowed coolant into the engine.
Chances are when you pull the drain plug on the oil pan, the first few liters out will be coolant.
Hopefully it hasn't been run long like that as bearings don't like antifreeze syrup for lubricant.

So when draining the engine oil, it was very thick, black and old. Didn't look to be any water in the oil. I changed the hydraulic filter last night and now the hyd pressure light comes on only under mid to low revs and under load. At full revs and load it seems to stay off.

 

[SkidRoe]

So when draining the engine oil, it was very thick, black and old. Didn't look to be any water in the oil. I changed the hydraulic filter last night and now the hyd pressure light comes on only under mid to low revs and under load. At full revs and load it seems to stay off.

Good to hear that you have not found any coolant in the oil.
Just a thought, based on what flyerdan posted - you may want to do a cooling system pressure test and a compression test just to be sure, especially if you don't really know the history of the machine.
Also, there should be a port on the hydraulic filter block that you can connect a pressure gauge to and check the charge pressure. It is good to here that it is extinguishing at higher revs, but it should go out almost immediately after the engine starts. Checking the pressure would help indicate whether it is a sensor issue or if it is a pressure issue.
Cheers - SR

 

[antz]

Good to hear that you have not found any coolant in the oil.
Just a thought, based on what flyerdan posted - you may want to do a cooling system pressure test and a compression test just to be sure, especially if you don't really know the history of the machine.
Also, there should be a port on the hydraulic filter block that you can connect a pressure gauge to and check the charge pressure. It is good to here that it is extinguishing at higher revs, but it should go out almost immediately after the engine starts. Checking the pressure would help indicate whether it is a sensor issue or if it is a pressure issue.
Cheers - SR

Thanks for your suggestions all. After some playing around and cleaning last night it seems quite likely that at a minimum it needs a head gasket, and probably a new head. The crank case is well pressurised, blew the dip stick out and the breather on the rocker cover is thundering out a whole lot of pressure that it shouldn't. Also using water. What a pain in the ass. On the plus side the engine has been swapped at some point in its life as it has a 1902 in there now.

 

[SkidRoe]

Thanks for your suggestions all. After some playing around and cleaning last night it seems quite likely that at a minimum it needs a head gasket, and probably a new head. The crank case is well pressurised, blew the dip stick out and the breather on the rocker cover is thundering out a whole lot of pressure that it shouldn't. Also using water. What a pain in the ass. On the plus side the engine has been swapped at some point in its life as it has a 1902 in there now.

Hi Antz,
Feel you pain. My luck usually goes that wat too. Hoping that it is only a head gasket.
At least you have a larger engine. I have seen guys shoehorn in V2203's as well.
Finger's crossed - SR