Drive shaft trouble (updated)

[GWGAllisfan 86]

I went out to mow the lawn this morning with my 712S and while going along- Bang the engine to fiber disk drive shaft bolts snap off at the engine, again. This happened last year one time. That was almost the same. There I assumed a bad set of bolts, or long term wear, so I replaced the bent drive shaft and disk and bolted it back up with new grade 5 bolts and now this. I would guess less than 20 hours of run time on it.

So now it's done it again, bent my only spare drive shaft and put it out of commission. Even worse this was the only mower on ready duty sine the others are in various states of disrepair.

There was no warning, no obvious engine sound change, hit nothing.

Both bolts are snapped clean through.

OK so what could be the causes of this?

I'd like to make sure I have the cause fixed before I try another shaft and bolt set.

[jdwilson 14]

Is it the original engine? The reason for this query is my son has just recently replaced the 12hp in his 2012 with a 10hp. The driveshaft appeared to be 1/4 - 3/8 too long. I think the difference was that the 12hp had an impeller, or fan on it. He tried to buy a couple of shorter bushings at the local hardware store, but ended up finding them online. This made the driveshaft butt right up flush again, with no binding.

We tried putting the impeller on the 10hp flywheel, but the holes were bigger. I think the PO had a hole strip out, so he made them bigger.

[427435 0]

One SWAG. These bolts might be failing because they get a little loose. The first failure may have led to some wallowed out holes in the engine flywheel--------allowing the new bolts to come loose quickly.

[BLT 461]

Next time you install the driveshaft, install discs and tighten them to drive shaft. Roll driveshaft on a flat service and observe for any disc wobble, if there is none shaft is absolutely straight. Loosen the BGB yoke so you can slide it freely, and then engine mounting bolts. Assemble and tighten driveshft and to engine and BGB yoke. Spin engine over 15-20 times. This will allow the engine to square up with the shaft eliminate any forward and reverse tension on the discs.

[MysTiK 3]

Bob, thanx for that, answered questions in the back of my mind for a long time. Do we have a "post of the year" award? That's what I come here for.

[johnmonkey 4]

I Thought about the washers and the "curve" on one side. In other words the washers go on one way with the curve towards the disc. If the flat side goes towards the disc, the flat edge can cut into the disc. jh

[HubbardRA 11]

John, I put the washers on backward on the disks that I put in the 61 Wards over 20 years ago. That was a tractor puller for many years and has since been used for a mower, or whatever I needed it for. The washers are still on backward and I have not had any trouble with the disks. This makes me think that just putting the washers on backward will not cause a bolt breakage problem. I would say that the bolts probably fatigued and broke because they came loose.

Randy, I have found loose bolts on one of my tractors. I tightened them before having any real problems with it. Once it is fixed, I would recommend checking at least the bolts on the flywheel, because those are the ones that have come loose on me and they usually have some type of spacer on them to make the driveshaft line up right.

[GWGAllisfan 86]

OK, Thanks for all the ideas and suggestions. I need to get a new drive shaft first to check any of it. Interestingly, when the bolts broke last time the remaining part was so loose in the flywheel I could run them out by hand. This time the won't budge. I plan to remove the screen and drive adapter to get them out.

Also, the fiber disk did not come apart. What ever happened just snapped the bolts. They show a perfectly clean break right across them. I'm fairly sure the drive shaft bent where it hit the rockshaft.

There seems to be quite bit of play in the BGB yoke, could this jam up and cause this?

I'm just concerend that if i do put it back together, again, this will happen again, if whatever the root cause is isn't fixed.

[D-17_Dave 11]

You'd better check out the gear lash in the BGB. Sounds as if you have some dead load being applied at low speed.

[Willy 0]

If you have play in the BGB that may be your problem.

It could set up a vibration and fatigue the bolts.

I would replace the needle bearing and seal in the BGB also,

you can ruin and expensive set of gears and shafts by letting

them get sloppy.

I had one come loose on me one time,Make a heck of a racket

don't it?

[GWGAllisfan 86]

It gets worse. Last night I crawled under and looked a little closer at the BGB. I has, best I can tell from laying under it using a measuring tape, at least 3/8" of play at the yoke. That is the yoke can slide in and out of the box at least 3/8". Side to side or up and down it's something like 5-10 degrees of wiggle, and turning it there is almost no slack.

I have two BGB on the shelf one for a 410, but it has a messed up driven shaft on the PTO end, and one from a 7119, which has a bad driving shaft...Maybe to two together can make one decent one.....

[HubbardRA 11]

Randy,

Sounds like a bearing failure may have seized up the driveshaft suddenly. This could produce enough load to bend the driveshaft and snap the bolts. A small sliver from a fractured bearing can wedge under the adjacent ball or roller and put the brakes on very suddenly. As soon as the load is removed, the broken piece usually falls out and relases the jam. If it were me, I would now pull the BGB apart and check all the parts. Any BGB that you put back together should definitely have new bearings installed.

[DanD 9]

quote:Originally posted by HubbardRA

Randy,Sounds like a bearing failure may have seized up the driveshaft suddenly. This could produce enough load to bend the driveshaft and snap the bolts. A small sliver from a fractured bearing can wedge under the adjacent ball or roller and put the brakes on very suddenly. As soon as the load is removed, the broken piece usually falls out and relases the jam. If it were me, I would now pull the BGB apart and check all the parts. Any BGB that you put back together should definitely have new bearings installed.

---

id="quote">

id="quote">I agree that a BGB going bad can seize suddenly. Years ago (I was a kid yet...will turn 39 on Monday to give you some idea of how many years ago it was) I was mowing with my 7016, just going along without a care in the world, when all of sudden with no warning the engine just died...there was no opportunity for the governor to open...it stopped that suddenly. We assumed the engine blew up in some fashion, but it was the BGB. I remember we replaced all the bearings and seals but I don't think we did anything with the gears or shafts. Fortunately it didn't cause any harm to the drive shaft or discs. The repaired BGB is still working well after this many years of service. I think it's usually worth the money to rebuild the BGB in these tractors, unless something else major is wrong, since it will still last longer than many new mowers. I just wanted to agree with the above post concerning how quickly a BGB can fail.

[1Litre 0]

The discs should have no tension on them when installed. Use washers

to correct this. I have never had to use more than two extra std washers per bolt. Is the engine loose in the frame? Check the bevel gearbox mounting bolts in the front frame. I have seen those come loos and the tractor is missaligned with the shaft. What grade of bolt are you using. Should have three dash marks on head for Grade 5.I think they came with grade 5 . Grade 8 will have six dash marks

and would be stronger yet.

[GWGAllisfan 86]

Well after nearly a year, I have this tractor back to riding. To all those who talk about doing a quick BGB replacement. How? It took me all of a day to dig down to it, pull it, removing all those linkages. Rigging a way to hold the two halves level while I put the bolts in was interesting. Then it took me 6 months to get back to hook up the driveshaft. It is together now, though. Still needs a little more shuttle adjusting, and I found out my regulator rectifier wasn't working, so i ordered one, but maybe, I can get to mowing with it soon.

I am fairly sure the BGB was always marginal in this tractor. The new one is MUCH quieter, no howling sound.Some time when time and ambition collide, i will disassemble the old one and see what it's like inside.

It's a problem, when I have time to work on it I don't have desire, when I have desire I don't have time.....oh well.

[phtann3 0]

you guys refer to the BGB I'm new to this so dumb question maybe but just what is the BGB?

[jlasater 114]

Bevel gear box.