743 U-joints

[kap258]

I can confirm that these u-joints will break. I just replaced the engine in my 743 and inspected the u-joint and greased it real well before I put it back together. I have put 4 hours on it since the new engine and today the u-joint broke. There was a very loud noise and then then nothing worked, but the engine runs great. When I opened up the back I found some pieces of the u-joint in the engine compartment. I am not looking forward to taking the engine out again.

 

[skidsteer.ca]

I can confirm that these u-joints will break. I just replaced the engine in my 743 and inspected the u-joint and greased it real well before I put it back together. I have put 4 hours on it since the new engine and today the u-joint broke. There was a very loud noise and then then nothing worked, but the engine runs great. When I opened up the back I found some pieces of the u-joint in the engine compartment. I am not looking forward to taking the engine out again.

Did the ujoint break or did it come loose or unbolted then fly apart?
ken

 

[Tazza]

Did the ujoint break or did it come loose or unbolted then fly apart?
ken

Removing and replacing an engine in a 743 is a snap. I have done it too many times......
Un-bolt everything and use a small hoist with a chain attached to the lifting points on the head, slowly lift and pull back wards and presto! Reverse to install, but you will need a second person with bars to push the engine forward while you lay on the hydro pump lining up the drive shaft to the hydro pump.
I may think its easy because i have done it so many times before. More still to come!
I too do agree they do break, the ones i replaced had one U-Joint's needle rollers fused together, the other was fine. It didn't break, but it was very sad indeed.

 

[skidsteer.ca]

Removing and replacing an engine in a 743 is a snap. I have done it too many times......
Un-bolt everything and use a small hoist with a chain attached to the lifting points on the head, slowly lift and pull back wards and presto! Reverse to install, but you will need a second person with bars to push the engine forward while you lay on the hydro pump lining up the drive shaft to the hydro pump.
I may think its easy because i have done it so many times before. More still to come!
I too do agree they do break, the ones i replaced had one U-Joint's needle rollers fused together, the other was fine. It didn't break, but it was very sad indeed.

Often I find that if a u joint failed so soon after instalation that there was a problem with how it fit or that it was not torqued down properly.
We have alot of the mechanix style ujoints with 2 bolts in each corner and often I find if we retorque them a hour or so after being put into service that they are no longer as tight as they should be.
Ken

 

[kap258]

Did the ujoint break or did it come loose or unbolted then fly apart?
ken

I finally had a chance to get the engine out. I found that the 4 bolts that attach the u-joint to the flywheel have snapped. I suppose the u-joint failed then the bolts were sheered off. It took me about an hour and half to get the engine out, so I would say it is probably worth pulling the engine every 250 hours to grease these fittings. I would much rather do this than have to replace the rear end of the hydrostat.

 

[Tazza]

I finally had a chance to get the engine out. I found that the 4 bolts that attach the u-joint to the flywheel have snapped. I suppose the u-joint failed then the bolts were sheered off. It took me about an hour and half to get the engine out, so I would say it is probably worth pulling the engine every 250 hours to grease these fittings. I would much rather do this than have to replace the rear end of the hydrostat.

Thats not too bad for you're first engine removal.
While its out, take the time to clean and junk that has been sitting behind the engine before you re-install the engine.
When you grease the U-joints, do the part which engages the splines on the hydrostatic pump too, it makes removal and installation easier.
Take you're time installing the engine, you will need to get the engine in the engine bay, with it sitting as far back as possible. Lay on the pump and try and fumble around to get hold of the drive linkage (not easy i know) get someone to gently bar the engine forward to get it to engage. You may need to turn the snout of the crank shaft a bit to get it to line up.
Any problems just yell!

 

[skidsteer.ca]

Thats not too bad for you're first engine removal.
While its out, take the time to clean and junk that has been sitting behind the engine before you re-install the engine.
When you grease the U-joints, do the part which engages the splines on the hydrostatic pump too, it makes removal and installation easier.
Take you're time installing the engine, you will need to get the engine in the engine bay, with it sitting as far back as possible. Lay on the pump and try and fumble around to get hold of the drive linkage (not easy i know) get someone to gently bar the engine forward to get it to engage. You may need to turn the snout of the crank shaft a bit to get it to line up.
Any problems just yell!

Be sure your new u joint mate perfectly flat on the yokes of the drive shaft (we had on where the center "keyway" on the u joint cap was to tall by .070", causing bolt failure), that there are no burrs,dirt or anyway they can seet themseves tighter after operation, causing the bolts to lose there torque. Retorque the bolts a hour or so after startup if this is possible, or conside loctite if its not.
Ken

 

[kap258]

Be sure your new u joint mate perfectly flat on the yokes of the drive shaft (we had on where the center "keyway" on the u joint cap was to tall by .070", causing bolt failure), that there are no burrs,dirt or anyway they can seet themseves tighter after operation, causing the bolts to lose there torque. Retorque the bolts a hour or so after startup if this is possible, or conside loctite if its not.
Ken

Thanks Ken. I was planning on using Loctite. I have been a fan of it for a long time. Kirk

 

[Tigerotor77W]

Thanks Ken. I was planning on using Loctite. I have been a fan of it for a long time. Kirk

Mark, do the competitive units with a U-joint need greasing also? How do the directly-driven machines connect the engine to the pumps?

 

[WebbCo]

Mark, do the competitive units with a U-joint need greasing also? How do the directly-driven machines connect the engine to the pumps?

All u joint units need grease, no matter the make. Connections for pump to engine in transverse units are belt driven. Its funny to think how a skid steer is driven with a belt but in 10 years of selling bobcat parts, I dont sell more than say one or two a month, counting for 600s series machines that had belt issues thats nothing!

 

[Tazza]

All u joint units need grease, no matter the make. Connections for pump to engine in transverse units are belt driven. Its funny to think how a skid steer is driven with a belt but in 10 years of selling bobcat parts, I dont sell more than say one or two a month, counting for 600s series machines that had belt issues thats nothing!

I thought the exact same thing, all the drive power is transfered via 1 single belt. I can see no real problem for the smaller machines that have say 46 HP or so, but say the larger S300 you are looking at almost double that figure. It obviously works though.

 

[skidsteer.ca]

I thought the exact same thing, all the drive power is transfered via 1 single belt. I can see no real problem for the smaller machines that have say 46 HP or so, but say the larger S300 you are looking at almost double that figure. It obviously works though.

My 753 and 773 40 and 46 hp, used a triple v belt with one backing, all made into one belt.
I got the 753 at 2100 hours and runit until 33?? and never replaced the belt, tightened it once.
I got the 773 with 1500 hrs and the tensioner failed at 2000 hrs, or I believe the belt would have lasted awhile yet. Not sure if it had been changed since new.
853 uses a quad v belt all made into one. 58 hp. I replaced the belt when I got it because the back was starting to separate between the V's it had 2160, but the belt starting to crack from old age. Also it had been totally bathed in hyd oil from a leak that had been ignored.
The belts wrap more then 180 degrees around the engine and the pump pulley, which makes for a maximum hp rating for a given belt and pulley configuration. Although the pump turns faster then the motor (overdriven) which reduces it some. But Bobcat claims this is some sort of hyd advantage, Also you can't overdrive the pump if you use a straight inline drive.
I woud think as the hp rises the belt would have to get even larger. And the spring loaded tightener is a big plus in insuring the belt stay tight for a long time. Shortly after I got my 753 it would make a horrible squeal, only when I was lifting and driving up a small hill. I was glad to find (after it dawned on me) the it was just the belt needing adjusted. With both the pumps working hard, it was enough to slip the (begining to loosen) belt
My Nh Ls 160 is a inline drive, the manual says nothing about greasing u joints in it, they must use a straight shaft to couple the pump to the motor. It seem to work just as well imo.
Some of those new "poly chain" syncroness belts are rated over 200 hp, so I;m sure bobcat will stay on with its belt drive. I not really sure if it is an advantage though, or just a way of setting yourself apart from the crowd. It does help make a more compact machine, and move the engine weight a far back as possible.
Regards Ken

 

[Tigerotor77W]

My 753 and 773 40 and 46 hp, used a triple v belt with one backing, all made into one belt.
I got the 753 at 2100 hours and runit until 33?? and never replaced the belt, tightened it once.
I got the 773 with 1500 hrs and the tensioner failed at 2000 hrs, or I believe the belt would have lasted awhile yet. Not sure if it had been changed since new.
853 uses a quad v belt all made into one. 58 hp. I replaced the belt when I got it because the back was starting to separate between the V's it had 2160, but the belt starting to crack from old age. Also it had been totally bathed in hyd oil from a leak that had been ignored.
The belts wrap more then 180 degrees around the engine and the pump pulley, which makes for a maximum hp rating for a given belt and pulley configuration. Although the pump turns faster then the motor (overdriven) which reduces it some. But Bobcat claims this is some sort of hyd advantage, Also you can't overdrive the pump if you use a straight inline drive.
I woud think as the hp rises the belt would have to get even larger. And the spring loaded tightener is a big plus in insuring the belt stay tight for a long time. Shortly after I got my 753 it would make a horrible squeal, only when I was lifting and driving up a small hill. I was glad to find (after it dawned on me) the it was just the belt needing adjusted. With both the pumps working hard, it was enough to slip the (begining to loosen) belt
My Nh Ls 160 is a inline drive, the manual says nothing about greasing u joints in it, they must use a straight shaft to couple the pump to the motor. It seem to work just as well imo.
Some of those new "poly chain" syncroness belts are rated over 200 hp, so I;m sure bobcat will stay on with its belt drive. I not really sure if it is an advantage though, or just a way of setting yourself apart from the crowd. It does help make a more compact machine, and move the engine weight a far back as possible.
Regards Ken

Thanks for the replies. I've heard a ton of stuff about belt vs. directly-coupled, and I've got to admit, without having owned one of each, I really have no idea if there is a "better" one. But then again, it's impossible to operate two machines exactly in the same manner for thousands of hours (realistically -- perhaps I had a ton more money...), so perhaps it simply doesn't matter, either.

 

[skidsteer.ca]

Thanks for the replies. I've heard a ton of stuff about belt vs. directly-coupled, and I've got to admit, without having owned one of each, I really have no idea if there is a "better" one. But then again, it's impossible to operate two machines exactly in the same manner for thousands of hours (realistically -- perhaps I had a ton more money...), so perhaps it simply doesn't matter, either.

My father and I have said that often, the only way to know if something was a good or bad design would be to have about 10 of each then when a trend developed you would know it was not merely a fluke or a "friday" machine.
So us little guys will never know for sure, just like the troubles that pop up on this forum, you have to wait for a trend. And buy then they change the design anyway
Ken