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Sunday, 5th June, we went out for a run from home up into the Angus Glens and Southern Grampians, with the Duke (’74 450 MKIII) and the Bros. Clear skies, easterly breeze, keeping the flies off and the midges are no out yet. Away from the main road from Blairgowrie to Glenshee (A93) that is a time trial for many “Rocket Pilots”, the roads are twisty, narrow, and gravelly and my preferred place to go at a steady 30 – 40mph, with the odd stretch where 50 -60mph is possible.

So, after a grand day out, with a picnic, we were heading home and having left the speed restrictions of Blairgowrie were heading towards Meikleour (Muckcluer) down the A93 that has a couple of long straights. At the end of the 50mph limit on the first straight, I opened up the Duke and overtook an Army lorry cruising at his 45mph limit and her singing along between 60 -70mph through a left and right dip and onto the next straight, when there was a noise like your visor vibrating, when the wind gets between it and the helmet. I was sure it was secure, checked and all was well. But that “Brrraaap!” had me worried and decided to turn right off the A93 at the x-roads into Meikleour. I stopped to let oncoming traffic pass and then turned right. The clutch was still working, but was a bit harsh and I took a look down to my left. My boot was running with oil, the whole of the left-hand side of the bike was covered in oil, there was a piece of the outer case attached by a bit of flapping gasket and the clutch adjusting cover plate was smashed at both ends and bent, with only one countersunk head screw holding it place.

Kat, on the Bros, had a film of oil droplets all over the front of the Bros and herself, apparently this had appeared at the start of the second straight. So the Duke had covered about 2 km (1.3 miles), with oil coming out of the cases. The clutch had operated on 6 occasions and was still driving. Whilst the engine hadn’t missed a beat!

So, nothing for it, but to push the bike down to the Meikleour Arms car park, have a pot of tea and shortbread; await recovery to home, whilst Kat rode home once the recovery had been arranged.

Today, I started stripping and cleaning the engine and the bike and from the attached images you can see the carnage. It would appear that there has been a long time fracture at the bottom of the clutch spring screw retaining post in the bottom of the clutch hub and after 85,000 + miles it had enough and “let go”! Punching its way sideways, having caught the edge of the outer case and making its exit from the case, along with the retaining screw, washer and spring still affixed, never to be found.

At first I thought that the retaining screw had become slack and ejected itself along with the washer and spring. But, it was after removing the pressure plate, with mangled spring cup in situ and the clutch plates that the true culprit, the clutch spring screw retaining post, was revealed.

So, I will now be having a look through the “useful bits”, speaking to some engineers, to see what might be salvaged, how big a strip down will be required (the out-rigger bearing has alloy flakes in it and is “lumpy”). There were very few little alloy shards within the case and none came out from the sump when the oil came out. The engine turns freely and there is no excessive play between the helical gears and no end play on either the crankshaft or the mainshaft. So, I think that the oil pump will need a strip and inspection to see if there are any marks on the pump gears. If there are no marks, I think that the crank could stay in situ. A flush out of the sump with brake cleaner and a sweep with a flexi-magnet and then a rebuild, would be a nice option.

Has anybody else experienced this failure, under any circumstances?

Would you strip the motor and split the cases!

I am just thanking the fairies that the bits didn’t get ingested and lock the primary drive at 60mph +!

Good health, Bill

Ouch !!, You do lead an exciting life . I would follow your plan , In my case the bike could otherwise be in bits for years. Life is too short. When you think about it the orriginal design was for a much smaller motor and add the milage --------. Get it back working and out there before the season is over.

Hi Bill,

I agree (but I'm no engineer) I would get everything as clean as possible, replace the damaged parts and do a couple of oil changes. And cross my fingers!

Colin

I suppose that it is not surprising that the pillar fractured, the clutch must have been lifted millions of times in the bike's life, and those 450 springs put a greater strain on them too.

Good morning Bob and Colin,

Thank you for your thoughts.

I don't have a "season", unless the ice and snow are lying on the road! So, I shall be delving into the guts of the oil pump and swilling out the sump. After which I shall probably have a quiet chat with a soothsayer, who after much sucking of teeth and pondering, may opine the quality of my scrap metal!!

As for 450 springs putting a strain on the spring pillar/post, I would have thought that the force should be in a vertical plane, down into the base of the hub casting, with no lateral/twisting forces, but then I am no engineer.

Have a good day, Bill

Hello Bill,
Loose pillars are not unusual and pillar failures are quite common with race bikes. I would say that the 450 springs are part of the reason and the failures are far more common on bikes using 450 springs. Part of the problem beyond aging is attempts to secure loose pillars by welding or braising from my experience exacerbates the situation. I think the heat and uneven or rapid cooling causes embrittlement. I would say you have been particularly unlucky that it has punched a hole in your cover, mostly the first time you notice you have a pillar failure is when you remove the primary cover to find heavy scoring around the inside and the absence of a pillar, screw, washer & spring.
Regarding whether it is possible to fix, it is. I used to stock replacement pillars which overcome the problem. Part of the problem with the existing pillars is that they are only 5 mm diameter where they pass through the hub and then they are rivetted over. The replacement pillars involved removing the riveting, drilling the 5mm holes out to 8mm and then pushing the replacement pillars in from the back and then silver solder them in place. The picture below shows one of the replacement pillars, the hub on the right has a set installed and the hub on the left has the rivetted area welded to secure the pillars. I removed the welded one from an engine I built as it had signs of cracks.



I no longer have any pillars in stock as I never had any more made but hopefully it shows a potential repair. Whenever I was rebuilding race engines I always carried out this pillar modification as I did not trust the original set up for race use. In particular on 350's and 450's using the 450 springs.

Hope this helps

Nigel

Good afternoon Nigel,

Thank you for your comprehensive reply in answer to my query. Also, for correcting my assumption that the stresses on the pillars were mainly vertical, rather than lateral.

May I ask if you have a dimensional sketch or drawing that I might use, of the improved pillar?

I shall contact you, with regard to other parts that will require replacement.

Good health, Bill

Bill, firstly that's a bit of bad luck, however it could have been worse with the serious loss of oil or a transmission lock up, I'm not sure but I may still have a standard clutch hub in my spares stash, let me have a rummage to see.........if I still have one (and you want to risk another standard "old" spare) you are welcome to it for the cost of postage.
Cheers,
George

Bill,
Had a check there......I do have one PM me
George

If you are stuck looking for a side case I have a few but post from Australia might be expensive
Graeme