The Fordson Tractor Pages Forum

Hi all,
We recently got this compressor that Davie has been charging marvellously (we also got a cultivator and mounted box), but we're hoping Billy can do it so he uses his PTO (it's also rather heavy for Davie to carry around).


Having read about all the stories about PTO castings suffering from running at 1200 rpm I was hoping to see what whoever is used to using their Major's PTO thinks about it.
Thanks very much.
Sandy

The castings break with overloading. This compressor wil hardly be able to let the tractor work I imagine. I wouldn’t have any doubts with it.

The reason I mention this is that someone was commenting on how at 1200 rpm there was a kind of motion that would cause a much earlier failure than the same load (on the idler gear) at 1600 rpm, hence one of the many good reasons for a raised PTO. This might be in connection with the max torque being at 1200 rpm, and might also be related to balers, but I'm saying this from fairly distant memory.
We need to find out if the compressor is ok at a speed higher than 540 rpm, but I rather suspect it's designed for 540 rpm, so preventing Billy doing it at 1600 rpm. We'll keep it at 540 for now and see what we find out.
I agree it's not what you would expect to be a heavy load, compared to the Holman compressors used by many industrial tractors at any rate.
Any more comments or corrections highly appreciated.
Sandy

Hi Sandy, used a PZ mower, tedder and baler on a major, as well as a pto sawbench and pto driven hydraulic log splitter. Used them at various RPMs and as the tractor never had a working rev counter I used to set the revs by 'feel'. The only issue I ever had was using a 6ft single blade topper, at low revs and with no load it would start to over run causing the engine to hunt and break the shear bolt on the pto shaft. The log splittrr was home made and we never used it at high revs, it would definitely put a load on the engine but we never had a problem

Thanks John, that's comforting to know, I know all about setting the revs by feel too, as Billy doesn't have a tachometer. I think it was hunting that would eventually cause the casting to fail, and I seem to remember someone pointing to a particular baler that was notably bad in that sense but I could be very wrong.
Very keen to see what others think too.
Sandy

I can see how it could damage the casting but a pto shaft with a shear bolt coupling should give enough protection though, I used to have to carry a pack of spare bolts and a spanner in the toolbox when topping

The issue with the early tractors that ran at 1200 rpm to give 540 RPM at the PTO was that with shafts and gears in the PTO train running at relatively low speeds, this set up exceptional torque stresses in the shafts and gears which in turn caused exceptional shear stresses in the castings. This was further enhanced in situations involving surging loads such as a PTO baler, where the torque stresses in the shafts were constantly surging then dropping more than once every second, and particularly so with vacuum governed pump engines where engine speed variation under surging load would be much more than the later minimec pumps. The end result was sometimes an occasional failure of the PTO gearbox casing, where the 2 lugs carrying the intermediate gear would shear off. Horsepower equates to Torque times Speed, so to deliver a fixed horsepower you can see that to deliver it at higher speeds means that the torque level needed is lower. This is why the 1000 rpm PTO setup is used for high horsepower implements. This is why the raised PTO for earlier tractors was also geared so that the engine ran at 1600 rpm giving faster speeds in the internal PTO system before the raised PTO reduced the output speed back down to 540 rpm. This is why the New Performance tractors ran at 1483 engine rpm with faster internal shaft speeds, effectively the gearing of the raised PTO was incorporated into the new PTO gearbox which also had a considerably strengthened casing.

The official workshop manual, in the section covering the PTO on the New Performance tractors, has a warning that for "earlier tractors maximum power at the PTO should be utilised only under conditions of steady load", that is avoid surging loads. This was also a tacit acknowledgement that there had been failures of the PTO system on earlier tractors without actually saying so!

In your case with the compressor, the horsepower needed should not be particularly high, and the load should be fairly constant and when it does change it will be gradual. Many industrial tractors were fitted with rear mounted compressor setups, such as the Holman Tractaire, and I don't think that there were any particular issues with them. If the tractor does not appear to struggle with the compressor then all should be well I would think.

The intercep (see here: viewtopic.php?p=60364#p60364) is the same, and usually once a year as far as having to replace it. The compressor shouldn't cause hunting as it runs pretty fast compared to the PTO shaft, but it's worth knowing this. I'm not sure how we could find a yoke with the bolt to fit on the PTO shaft (the shaft we're using isn't actually very big), having said that we've got another much bigger shaft that needs a new yoke, but that is something we need to look around for.

Thanks Shepp, I knew someone had mentioned balers before! I think Billy already suffered this problem a very long time ago, as he doesn't have his original PTO casting (a newer Ebro one instead). If I'm not wrong about this the Holman types were massive compared to this one, which was one reason for me to think that this one would be ok. The fact that Davie can do it easily means that it's not going to be a problem with power.
I would like to think that someone will say that this will work fine at 1000 rpm when we ask, but rather suspect that it won't be the case, if it is alright my plan was to run at 1600 rpm, so the PTO would be going at roughly 720 rpm. I'm hoping to ask the manufacturer, but it seems they're long gone.
Sandy

Yes, the Holman was a pretty useful compressor which could easily run 2 breakers simultaneously!

Just to be devil's advocate on this one, we've run majors for 1000s of hrs and have not knowingly encountered any breakages in the pto driveline. We've run NH 268 and 276 balers, drum and disc mowers, rotavators and all kinds of pto powered equipment without any bother. Equally we have been breaking and selling bits for majors for 25yrs at least and in that time the only time we've sold the pto pot for a blue orange tractor is when someone is fitting a pto where one is not fitted. We have however sold maybe half a dozen np pto pots and each time it is because the post/support for the idler gear has broken off on the pto pot. Whether these were all 4 cylinder tractors I couldn't tell you. Other than that I have seen the splined shaft at the back sheared off or badly worn and the splines on the input shaft where it engages with the clutch disc worn right down.

Hi Roadless, I think we have had a bit of a discussion before about this topic! I personally have never known anyone running a Major of any type to have problems with the PTO gearbox case failing. However I personally have bought in at sales at least 3 blue orange Super Majors in the 1970's that turned out to have smashed PTO gearboxes, and another 2 from main dealers who disclosed to me that they had broken PTO gearboxes. If you went to a collective sale in those days and there was what looked like a nice clean Major in but with either a flat battery or a battery missing so that it could not be started, everyone would suspect that the PTO gearbox might have gone amongst other possible things and that would be the general conversation. Frank Rowland, who today is big into the hire business with about 250 John Deere tractors, 150 JCB telehandlers, and hundreds of tankers and trailers in his hire fleet, started off in the late 1960 's by dismantling tractors, and these were mainly Fordson Major types in those days and then later mainly David Browns. I bought gearboxes off him and he always said, one item that was regularly being asked for was the PTO gearbox for the early tractors, but contrary to your experiences not for the NP tractors as they never failed. I also knew contractors who ran Power Majors and early Super Majors on PTO baling work, using progressively MF 703, NH 278, NH 268, NH 276, NH 376, NH 940, and they also ran NP Super Majors on similar work, they never had any issues with any tractors. But failures DID happen, and the workshop manual DOES carry a warning about PTO use on the early tractors.

We've now tried it and we seem to be fine.





A bit smokey as we're so dry that we can't really plough much as it's loose dust and it just ends up just as solid as before, and it's not that much of a load for Billy anyway.
Sandy