Author Topic: M32 Oil Pump Drive Dog  (Read 432 times)

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Offline Hamwic

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M32 Oil Pump Drive Dog
« on: 09 Nov 2021 at 11:52 »
Hi all, another M32 tale, and a question if I may?

After replacing the oil spray bar on the M32, we set off down the road again, and apparently all was well. Well, for at least the first 5 miles, but then a gradual tightening of the engine became apparent. The oil regulator was well open, and all the oil was being delivered, but it felt like either piston(s) or big end(s) were going to pick up. A roadside pause to consider my options. The bike restarted but soon warned me that all was not well, with a pronounced clattering, so a push home was called for. By the time I was home, the engine was cool, and turned freely again, but the clattering was audible valve gear perhaps?

A look inside revealed that the timing gear support plate was loose, allowing the valve clearances to vary from negative to positive hence the apparent clatter. There being plenty of oil where required within the cases, this plate was re-secured and a couple of clamping problems addressed. With the clearances reset and the cover put back on, the engine span freely and fired up readily. Off we went again. Within a few hundred yards the tightening again made itself felt, so we crept home again.

With the engine out and the front cylinder off, it was apparent that all was not well with the front big end, it feeling a bit stiff to turn, and the rear likewise. However, when taking off the timing chest cover, the rods dropped down freely. No signs of seizure in the bores.

It transpires that the oil pump driving dog locking screw had gently unwound itself, and was pushing the timing gear plate about. The driving dog had also unwound itself, and was bearing heavily on the pump drive gear worm in the timing cover. This had squeezed the flimsy crank endwise such that it had nipped the big ends between the crank webs. Once the dog was put back from whence it came, and the screw re-tightened, normal clearances are restored.

Perhaps a left-hand thread would have been a better idea for the drive dog, rather than the hard-to-reach and apparently ineffective locking screw?

Im not overly confident that the drive dog will properly stay put, although the thread engagement is very stiff, and the screw has gone further home this time. Is Loctite required perhaps, and if so, which grade? Any other suggestions as to how to secure this dog?

Cheers for now
Doug

Offline Hamwic

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Re: M32 Oil Pump Drive Dog
« Reply #1 on: 16 Dec 2021 at 11:48 »
The saga of the M32 and the loosening oil pump drive dog continues. The bottom line is that I think with the K and M32 crankshaft, Douglas took their eye off the ball, and the wrong i.e. a right hand thread, was turned on the end of the crankshaft. The half-time pinion is keyed to the end of the shaft, and it has a grub screw hole through the side. Once the drive dog is screwed onto the end of the shaft and tightened up, it is buried inside the half time pinion. The locking screw is put in, and engages with a groove in the drive dog. The rest of the timing gear is then assembled and the steady plate put on etc. All pretty standard stuff, except for the direction of the thread.

Unfortunately, after two long pushes home, it seems the load from the oil pump loosens the drive dog, despite flogging the dog up tight. The action of the locking screw tends to drag the half time pinion out off the crankshaft, because the screw is now following the groove in the dog as the dog rotates and unscrews itself. As extraction methods go, it's pretty effective. Eventually the dog is pushing hard up against the oil pump drive worm in the outer cover, and the crank becomes very stiff to turn. I did see another K32 timing cover for sale on flea bay a while back, and believed I could see some tell-tale cracks in it, and I think this explains what's been happening. The outer set of teeth on the half time pinion drive the dynamo, and these teeth are very badly worn away. I suspect this was caused by the half-time pinion escaping from the crankshaft along with the dog, and chewing up the dynamo gear, which is missing from my dynamo. I should imagine this was cast away in disgust by the previous victim!

There is no other available handy thread in the crankshaft or material left to change anything over to a left hand thread. I have tried changing the groove to a flat local to the grub screw contact point, and a drop of Loctite, but that didn't last long. Sadly I think the only alternative is to grind off the surplus damaged teeth of the half-time pinion and similarly grind a flat on the drive dog and then secure the two with a tab washer to prevent the initial loosening off. Hopefully that and a bigger dollop of Loctite might actually keep the assembly in place. I don't intend using the dynamo, and it's just filling up the hole in the cover, so the loss of yet more teeth shouldn't be a problem.

At this time of year, if you see a jolly red faced chap pushing a small motorcycle down the road - it might just be me....

Seasons greeting to all our readers!