743B intermittent heavy shaking / metallic knock

[mograine]

Hello all,

Yesterday all of a sudden my bobcat 743B intermittently started making this metallic knocking noise and shaking pretty badly. I limped it back into the garage.
I've checked the drive chains but they're okay (quite sloppy but not overly so that they can cause this problem.)

The sound matches the frequency that the motor is running on, so i suspect something going on there? Any ideas?

Kind regards.

 

[mrbb]

is the sound coming from drive train, or the motor itself? only make sound when machine is moving or while parked?

 

[mograine]

is the sound coming from drive train, or the motor itself? only make sound when machine is moving or while parked?

It was coming from behind the drivers seat, when standing still and driving it kept going the same.

 

[brdgbldr]

Hello all,

Yesterday all of a sudden my bobcat 743B intermittently started making this metallic knocking noise and shaking pretty badly. I limped it back into the garage.
I've checked the drive chains but they're okay (quite sloppy but not overly so that they can cause this problem.)

The sound matches the frequency that the motor is running on, so i suspect something going on there? Any ideas?

Kind regards.

First thing that I would check is the drive shaft. It's one of the most neglected greasing points (there are three grease zerks on the shaft).

 

[mrbb]

if its making the noise while its standing still/parked, I doubt its a drive train issue,as in order for it to be making noise in drive train it would need to be moving
so, that might mean its something inside the motor, like a bearing going out some where
which could be a major problem about to happen
, if I was you, I would try starting it, and then listening to where the sound is coming from on the motor/engine

also, how many hours are on this engine/moor?

things do wear out over time and use!

also are you sure motor oil is at correct level?

 

[ZekeSkyree]

Would you post a video? Might help to diagnose the issue.

 

[spitzair]

That sound and vibration is most likely your u-joint between the engine and hydraulic pump about to fail. DO NOT START YOUR ENGINE until you have checked that u-joint because if it does let go completely it WILL do considerable damage! Like Brdgbldr says this is one of the most neglected maintenance items, it needs to be greased every 100 hrs or so, most don't do it because it's a bit of a pain to get to.
My suggestion is to pull the engine out and replace the u-joint assembly, pulling the engine on these machines is not a major undertaking. All you do is undo the coolant lines, some fuel lines and your throttle linkage, a bit of electrical, the intake and exhaust pipes, pull the 4 bolts that hold the engine subframe to the main frame of the machine and the whole thing comes out. On my 732 I can have the engine out in less than an hour, your 743B will be similar, the biggest difference will be you have a Kubota diesel engine. Once you have the engine out the u-joint will be easily accessible on the flywheel, I'm willing to bet it is shot.

 

[mograine]

That sound and vibration is most likely your u-joint between the engine and hydraulic pump about to fail. DO NOT START YOUR ENGINE until you have checked that u-joint because if it does let go completely it WILL do considerable damage! Like Brdgbldr says this is one of the most neglected maintenance items, it needs to be greased every 100 hrs or so, most don't do it because it's a bit of a pain to get to.
My suggestion is to pull the engine out and replace the u-joint assembly, pulling the engine on these machines is not a major undertaking. All you do is undo the coolant lines, some fuel lines and your throttle linkage, a bit of electrical, the intake and exhaust pipes, pull the 4 bolts that hold the engine subframe to the main frame of the machine and the whole thing comes out. On my 732 I can have the engine out in less than an hour, your 743B will be similar, the biggest difference will be you have a Kubota diesel engine. Once you have the engine out the u-joint will be easily accessible on the flywheel, I'm willing to bet it is shot.

What would a worn out U-joint look like? I'm planning on pulling the engine out since it doesn't look too complicated / involved.

 

[spitzair]

You'll know. It'll be very sloppy and loose feeling and might even feature some obvious broken / worn pieces. I wish I had a better picture I could send of mine for comparison...

 

[mograine]

Well, i got it out (getting it back in might be a bit harder...). And i have a suspicion the U-joint is the problem.
Now to figure out where to get a new one in Europe / the netherlands. Any suggestions are most welcome!

Also: the splined coupling was fairly worn, would it be worthwhile to replace while i'm at it?

 

[spitzair]

Wow, lucky you caught that when you did! When the one in one of my 732s went it did major damage to both the pump and the engine! They are still stocked at Bobcat, your local dealer should be able to get it in for you. If it was me I would also replace the splined coupling since you're already in there.

 

[mograine]

Noticed the ring gear was also quite worn, that would explain the difficulty starting sometimes. I'll probably replace this aswell.

Which models share parts with the 743(b)? not having a whole lot of luck finding parts for the 743.

 

[Dave1234]

It was coming from behind the drivers seat, when standing still and driving it kept going the same.

 

[Dave1234]

Sounds like the u joint between the motor and pumps to me

 

[ByggareBobby]

How on earth do you grease those zerks when everything is mounted back into the engine bay?(!!!)

 

[spitzair]

The ring gear might be a tough one, I'm not sure if the flywheel on the engine is a Kubota part or a Bobcat part. I've honestly never dealt with a 743, my experience is on the 732 with the Ford gasoline engines. On those, the flywheel is a separate part from the blower fan, hard to tell from your picture but it looks like the fan and flywheel are one piece?
As far as what machines use the same parts, most parts off of a 741 or 742 will work on a 743. Really the only difference between these machines is the engine, and unfortunately you're dealing with engine interfacing parts here so it's unlikely that parts from another 74# series machine will work for you here but I could be wrong. Your best bet would be to look at the Bobcat online parts catalogue and compare the different drawings and part numbers. I don't know how to post a link from my phone, but I know Brdgbldr knows how, hopefully he'll be along to help soon.

 

[spitzair]

Oh, and to answer your question ByggareBobby, those grease fittings are greased from the front side of the machine. It's actually not that big of a deal. You first have to remove the seat (630, 631, 632, 730, 731 and 732 machines) or raise the operator's cab (640 and 740 series machines. Next, you find your grease gun and install a long hose on it. A pistol grip grease gun with 3 feet (1 meter) of hose works best. Now you lay yourself down on top of the hydraulic/hydrostatic pumps. This can be a bit awkward but it isn't bad. Reach your right hand in past the pump towards the engine inside the blower housing and feel for the grease fittings. You may need your wife/son/beer drinking buddy (pick one) to rotate the engine slowly by hand so as to get the grease fittings into a position you can reach them with your right hand. Once you can feel them with your right hand you can pop the grease gun coupling onto them with your right hand, and with your left hand you squeeze the grip on the grease gun a few shots. Repeat for the other grease nipples, then extract yourself from the machine. Once you've done it once or twice you'll see it isn't bad at all, the biggest pain is either taking the seat out or lifting the cab depending on your machine. Hope this helps.

 

[mograine]

Good news: I've got the replacement parts in and am working on getting it back together. I also noticed the bolts that hold the hydraulic pump were loose? I tightened them, not sure if the pump needs to be aligned at a certain height?

 

[alice.smith097]

That metallic knocking noise and shaking usually point to an issue with motor mounts, bearings, or even a connecting rod. It might be best to check these areas and, if you're not comfortable with it, consult a professional.

 

[spitzair]

Good news: I've got the replacement parts in and am working on getting it back together. I also noticed the bolts that hold the hydraulic pump were loose? I tightened them, not sure if the pump needs to be aligned at a certain height?View attachment 7248

Excellent! The pump height should be fine where it is, that u-joint you're replacing is there to compensate for any slight misalignment between the engine and pump.