BMC 9/16 PTO speed question

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wol
Posts: 7
Joined: Mon Jul 30, 2018 10:38 am
Netherlands

BMC 9/16 PTO speed question

Post by wol »

Dear all,

Apologies up front for the perhaps silly question, however I still cannot understand in full the following. :o What engine rpm speed provides which PTO speed?

My 1965 Nuffield BMC Mini 9/16 (diesel) is a joy to play around with on our farm. Amongst others I like to mow a meadow every now and then, which requires 540 rpm pto speed.

My 9/16 has a dual speed PTO: 540 and 1000 rpm. The lever on left of the transmission casing, has 3 settings:
1. Lever to the front = 1000rpm pto gearing
2. Lever in mid position = off/disengaged PTO
3. Lever to the back = 540 rpm pto gearing

Furthermore, the tacho gauge shows 2 indicated areas.
A. Around 1300 engine rpm it says "PTO 540 rpm"
B. Around 2400 engine rpm it says "PTO 1000 Pulley 1315 rpm"

Can someone please say, if my reasoning below is correct:
If I want 540 pto rpm i put the lever to the back to select 540 rpm gearing, and apply full engine rpm (say 2400)
If I want 540 pto rpm, I put the lever to the front to select 1000 rpm gearing and apply 1315 engine rpm. (fuel economy setting?)
If I want 1000 pto rpm, I put the lever to the front to select 1000 rpm gearing, and apply full engine rpm (say 2400)
Any other setting does not provide correct pto speed (540 nor 1000)

Of course I tried RTFM https://en.wikipedia.org/wiki/RTFM before posing this question, however the manual I have of the 9/16 assumes it has only 1 pto speed (540)...

thanks a lot and take care,
Harmen

See photo tacho below:
Image


Nuffield 4DM
Nuffield 10-60
BMC Mini 9/16
Ford Dearborn
Nowtnew
Senior Member
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Re: BMC 9/16 PTO speed question

Post by Nowtnew »

I would say that your reasoning is correct, but your tacho is the incorrect version.
the two speed pto instrument is as per:
Image

(a poor photo because of the flash, but you'll see the difference).

Curiously, it seems that the single speed pto was the same gearing as the 1000 speed on the two speed.

With such a low power, the 540 speed at around 1300 rpm must have been all but useless.

Regards
Ley154
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Joined: Sun Apr 01, 2018 8:22 am
Location: Gloucestershire UK
Great Britain

Re: BMC 9/16 PTO speed question

Post by Ley154 »

Both of you are right. The tacho showing 540 rpm at 1300 is the original unit supplied when the first tractors came out with only the single speed 1000 rpm pto. The two speed pto became available in production and also as a free update for existing tractors in late 1966 but did not include a new tacho with revised readings on the face ( BMC cheapskates ). Newer tachos seem to have lost the 540 rpm at 1300 rpm marking.
If you select 1000 rpm on the lever you get 540 pto rpm at 1300 rpm engine and 1000 pto rpm at 2400 rpm engine. For the 9/16 engine this means you get about 8 BHP on the low setting ( virtually no use? ) and 15 BHP ( on a good one) on the high setting which will power a small accessory -topper mower etc. The only thing is, to get enough power ( by using 2000 eng rpm upwards )you are greatly overspeeding the accessory. Nobody seems to understand this, even Tractor Research who only seemed to test the single speed pto setup unless the accessories they used were built for 1000 rpm pto but I have never been able to confirm this.
In 1000 rpm the pto shaft connects directly to the layshaft in the gearbox which is permanently geared to the input shaft.
If you select 540 on the lever the drive goes through a set of reduction gears ( which can chip teeth or break ). On the later tacho is shown 540 pto rpm at 2250 rpm engine which is just above max torque and gives the strongest power to the shaft.

The late bigger engines 1500 and 1622 will run LIGHT loads such as finish mowing at 1300 rpm economically without stalling. John Poulter
wol
Posts: 7
Joined: Mon Jul 30, 2018 10:38 am
Netherlands

Re: BMC 9/16 PTO speed question

Post by wol »

Hi gents,

First of all, thanks for the clear and swift replies. Very much appreciated since it is great to have people thinking along.

And, very interesting as well.
So for me I should apply 1000rpm setting on the lever, and with 1300 engine rpm I can mow grass at 540 pto. That works fine power-wise (with apparently 8BHP). In case I need all the horses that are still in the engine, I can switch the lever to 540 and give full engine speed. So that's clear :-)

Even more interesting is, apparently my 9/16 must have had the free update of late '66. Considering the "old" type tacho. and the gearbox has on the right hand side numbers stamped, including what seems to be a date of 10-12-1965. Unfortunately, I cannot ask the previous owner to confirm it (who bought it new) since he passed away.

To end on a positive note, it means that my (original) manual is correct too, as that assumes the single speed 1000 rpm pto. Only it no longer applies in full to my tractor as it should have had an addendum to that manual. 8-)

Thanks again all, this thread can be closed in my viewpoint.
Nuffield 4DM
Nuffield 10-60
BMC Mini 9/16
Ford Dearborn
Ley154
Senior Member
Posts: 256
Joined: Sun Apr 01, 2018 8:22 am
Location: Gloucestershire UK
Great Britain

Re: BMC 9/16 PTO speed question

Post by Ley154 »

Just a little bit of irrelevant information. The two speed pto conversion was introduced in October 1966 and covered by technical bulletin 85 dated 26/10/1966. It was at the owners discretion as to whether the pto was upgraded or left alone. John P.
wol
Posts: 7
Joined: Mon Jul 30, 2018 10:38 am
Netherlands

Re: BMC 9/16 PTO speed question

Post by wol »

great :-) I love that kind of "irrelevant" yet very interesting detail
Nuffield 4DM
Nuffield 10-60
BMC Mini 9/16
Ford Dearborn
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