743 drive problems

[bandjoeman]

Hello, I have a 743 that has broken u-joints, broken the attaching bolts and now the splines (inside and outside) at the pump all at separate times. Could anyone help me with a possible fix or has anyone had this problem before. I have a new engine (20 hours) and I have not had any problems other problems with the machine in 5 years. Thanks

 

[Tazza]

What sized engine are you running? is it still the standard V1702?
As all these problems relate to the connection between the engine and pump, i would start by ensuring that the height of the pump shaft is correct. If its not inline with the centre of the engine it will make the U-Joints to do more work. The limit out of straight was only about 1/4”. This measurement is in the service manual, i don't have it on hand though.
If the engine is different, its possible its sitting too high or low?

 

[bandjoeman]

What sized engine are you running? is it still the standard V1702?
As all these problems relate to the connection between the engine and pump, i would start by ensuring that the height of the pump shaft is correct. If its not inline with the centre of the engine it will make the U-Joints to do more work. The limit out of straight was only about 1/4”. This measurement is in the service manual, i don't have it on hand though.
If the engine is different, its possible its sitting too high or low?

The engine was replaced with the v1702 as original. My mechanic told me today that he was going to replace the engine mounts while he has it out this time. If they are worn could this cause the alignment problem. He has talked to several people at Bobcat and no one knows of this problem. Thanks for your help. I know you have a 743 and you seem to like it as much as I like mine.

 

[Tazza]

The engine was replaced with the v1702 as original. My mechanic told me today that he was going to replace the engine mounts while he has it out this time. If they are worn could this cause the alignment problem. He has talked to several people at Bobcat and no one knows of this problem. Thanks for your help. I know you have a 743 and you seem to like it as much as I like mine.

The 743 machines are excellent, simple to work on too.
Its possible the mounts could have caused the issues too. Its just weird that the splines striped out. They aren't a loose fit, it just seems odd to me that it would go. Mounts i can see causing the U-joints or bolts to go as they would be working harder to keep the power going from the engine to pump.
Its also possible you just had a bad run of luck. There was another member that re-built his lift cylinders, ran the machine and the vane pump lost a vane and took out the pump and shaft. It wouldn't have been caused by the cylinder repair, it was just bad timing... Hopefully your bad luck is at an end!

 

[bandjoeman]

The 743 machines are excellent, simple to work on too.
Its possible the mounts could have caused the issues too. Its just weird that the splines striped out. They aren't a loose fit, it just seems odd to me that it would go. Mounts i can see causing the U-joints or bolts to go as they would be working harder to keep the power going from the engine to pump.
Its also possible you just had a bad run of luck. There was another member that re-built his lift cylinders, ran the machine and the vane pump lost a vane and took out the pump and shaft. It wouldn't have been caused by the cylinder repair, it was just bad timing... Hopefully your bad luck is at an end!

Yep, the whole chain of events is weird. The reason I have a new engine is I let a friend use it and his brother checked the oil and left the dipstick out. Pushed all the oil out and threw a rod through the block! I bought a re-man engine and everything was fine until this! Any how my mechanic should have the parts in a week or so and we'll go from there! Thanks for your help and advice!

 

[Tazza]

Yep, the whole chain of events is weird. The reason I have a new engine is I let a friend use it and his brother checked the oil and left the dipstick out. Pushed all the oil out and threw a rod through the block! I bought a re-man engine and everything was fine until this! Any how my mechanic should have the parts in a week or so and we'll go from there! Thanks for your help and advice!

Ouch....
This is why its hard to loan anything out, you never know what they will do, something so simple can cause thousands of dollars worth of damage....
With a bit of luck, this will be the last time you have issues *crosses fingers*.

 

[frogfarmer]

Ouch....
This is why its hard to loan anything out, you never know what they will do, something so simple can cause thousands of dollars worth of damage....
With a bit of luck, this will be the last time you have issues *crosses fingers*.

If they replace the engine mounts make sure they do the pump mounts as well. The drive couplings are a neglected service item as they are hard to get to and require patience to ensure they are properly greased. So many factors going on its hard to pin point what happened. The splines may have been sheared when the motor blew as RPM can change drastically when parts detonate. Likely something was changed along with the new motor that may have led to an alignment problem. The new motor may run much better and possibly faster than the old engine causing more stress on worn parts. Check the alignment and mounts install the new parts and all should be well. Many things could be at fault on a 20 year old machine.