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Governor pulley belt

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BOB BLACKSHAW12/06/2018 15:10:00
116 forum posts
12 photos

I am having problems finding a belt that will spin the governor, all the things I've tried just slip, the worst being a belt used on the Mamod models. The governor spins ok as its got a ball bearing in the base so no tight spots.

I've tried nylon sting with a small knot at different tensions, a rubber band seems to work but judders. Dental floss is about the best I've come up with but that gives up after 30 seconds.

Any help please will be appreciated Bob.


SillyOldDuffer12/06/2018 15:23:28
3126 forum posts
628 photos

Could you post a photo of the belt in place please? The way belts run & relative size of pulleys can both make a difference. ( I guess the belt sits on the horizontal flywheel and crosses over to drive the vertical governor, in which case the ratio is probably the problem. )


Martin Kyte12/06/2018 15:26:49
1302 forum posts
9 photos

No suggestions to material but you may want to consider the size and shape of the pulley groove. But "off the top of my head" I would suggest you should aim at a round 'belt' that contacts on each side of a V rather than just sitting in the bottom of a wide circular groove. That way you get some wedging action which should increase the contact force.

I'm only saying round belt because that seems to be what you are using.

regards Martin

JasonB12/06/2018 15:27:11
13073 forum posts
1188 photos

Drive comes from the small pully that can just be seen from behind the flywheel, probably about 2:1

The Mamod belts run in round bottomed grooves as do the larger but similar spring type found on Stuart engines.


Edited By JasonB on 12/06/2018 15:33:10

roy entwistle12/06/2018 15:32:25
849 forum posts

larger O ring ?


Jim Nic12/06/2018 15:57:50
135 forum posts
56 photos

It appears to my old eyes that the drive pulley is made for a flat belt while the governor pulley is made for a round belt. How about remaking the drive pulley with a round groove similar in size to the pulley groove on the governor. If you use the existing drive pulley as a basis you would keep the hole you made to fit the crankshaft and the threaded hole for the grubscrew so it would then be smaller and result in a slower turning governor.

Your Mamod spring belt may then work.


BOB BLACKSHAW12/06/2018 16:25:07
116 forum posts
12 photos

Thanks for the replies.

I used a 1.5mm parting blade for the grooves, as suggested a round groove for a snug fit on both grooves will be a try, also a bigger drive. I shall remake them, I'm surprised that it didn't work as its so small and spins freely.


SillyOldDuffer12/06/2018 16:51:06
3126 forum posts
628 photos

I see the pulley now Jason's pointed it out. 2:1 is OK. How about the angle though? Perhaps it's the photo but the governor pulley looks high to me, perhaps putting the belt at an awkward angle.

Looks like a well-finished Potty. The governor finishes it off a treat. I'd be pleased if it was mine.


BOB BLACKSHAW12/06/2018 17:58:22
116 forum posts
12 photos

I've up loaded two more photos on my album on Mill engine governor for angles of the belt Dave. I've not finished the valve part yet, it mite work. I've made two of these and got them to run of a nebuliser, another good source of air power for small engines. Also the Mamod belt moves ok on the drive but not the governor.


Edited By BOB BLACKSHAW on 12/06/2018 18:06:57

Edited By BOB BLACKSHAW on 12/06/2018 18:08:01

mechman4812/06/2018 18:07:47
2019 forum posts
341 photos

Might I suggest dropping the governor pulley height, looks a tad high to me and the edge of the pulley is forcing the belt off also put a matching groove in the drive pulley.


Brian Sweeting12/06/2018 20:03:04
268 forum posts
1 photos

Yes, the governor pulley is too high, the belt is wasting energy trying to force the pulley downwards to level the drive line.

If the pulley cannot be lowered then consider making some idler pulleys to raise the drive line.

oldvelo12/06/2018 22:09:39
141 forum posts
44 photos

Hi Bob

The pictures tell the story The alignment needs to be addressed as Brian and George point out. The belt on the top of the crankshaft pulley needs to be parallel with the centre line of the engine and parallel to the horizontal center line of the engine.

Photos Two and Three in you Album explain the anomaly in the alignment.

Other than this problem this is a very well constructed engine.

This link may explain it better and is also useful for all sorts of power transmission devices




Edited By oldvelo on 12/06/2018 22:19:28

BOB BLACKSHAW13/06/2018 08:02:37
116 forum posts
12 photos

Thanks for these very informative replies, I shall have another go to get it working.


john carruthers13/06/2018 08:11:18
557 forum posts
171 photos

You might try a cassette tape recorder (or vhs recorder) drive belt?

They come in all sizes, in square or round section.

I used one on Lady Stephanie for the governor drive.

Ian S C13/06/2018 10:52:53
6909 forum posts
224 photos

I used a square section belt(may have come from a VHS recorder), on the governor of a Stuart Turner S9.

Ian S C022 (640x480).jpg

BOB BLACKSHAW14/06/2018 14:57:10
116 forum posts
12 photos

I made a new pulley for the governor with a rounded groove and it now works well on the Mamod belt. The drive has still got the flat groove but as it works I wont make a new one. Another bonus is that it has not added any more resistance so it will run on the nebuliser.

Again thanks for the replies, Bob.

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