MK1 - Possible Rear Crank Gear Play

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Paul_Linden
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Re: MK1 - Possible Rear Crank Gear Play

Post by Paul_Linden »

Sounds like the fitter over did it.
When I changed my clutch sprocket recently the new dowels were a slack fit as they pushed in with very little force, so I re-used the old ones.
Square 4 mk1, Square 4 mk2, BSA C12.
john.whiting
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Re: MK1 - Possible Rear Crank Gear Play

Post by john.whiting »

the clutch centre dowells must have been too great an oversize ......any experienced fitter should have realised the holes needed to be reamed before pressing in dowells .......just because a man has a hydraulic press doesnt make him anything more than a bodger with much greater ability to wreck things......Personally,I d go for the guy through the small claims .......repairers are automatically guilty in these consumer courts ,so you will have no trouble getting your money and damages .
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Re: MK1 - Possible Rear Crank Gear Play

Post by camstevens »

any experienced fitter should have realised the holes needed to be reamed before pressing in dowells .......just because a man has a hydraulic press doesnt make him anything more than a bodger with much greater ability to wreck things......Personally,I d go for the guy through the small claims .......repairers are automatically guilty in these consumer courts ,so you will have no trouble getting your money and damages .
Hi John
I guess I struggle with what many other on here struggle with..........I live in West London, and other than the odd car mechanic (charitably titled) there are few or no engineering workshops left...there is one in Hounslow, but he is so busy doing churn and burn auto machining (where he can earn without needing to think) small tricky jobs are of no interest to him. So....unless you have your own machine shop and the necessary real estate, you're stuffed. Even the small city of 50K near where I grew up in NZ had 3 auto-machining operations...now there are none, so it's the way the world has moved.
I weas even lucky to get an auto machinist to do the MK1 machining....because it's a bit different it was seen as a loss maker. But I was grateful that he did do it, and he did a good job.

Cam
Julian Murphy
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Re: MK1 - Possible Rear Crank Gear Play

Post by Julian Murphy »

I know its a few miles out for you, but perhaps give Terry at Stotfold Engineering a call. He is located in Biggleswade, right off the A1. All motorway for you.

He is a good 'general' vintage motorcycle engineer, with a lot of tooling around him at his workshop.

I'm sure he would come up with a solution.

I was there yesterday whilst he trued up the braking surface of my NH wheels.

He previously trued up the brake on my 1984 BMW ST, and the brake was as smooth as butter. Even the MOT tester commented.

Here is a link:

http://www.stotfoldengineers.co.uk/
JohnnyBeckett
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Re: MK1 - Possible Rear Crank Gear Play

Post by JohnnyBeckett »

hi i have used him to skim a NH rear wheel brake hub when my big lathe was in bits and he done a good job and he and his son are very helpful look up his weeb site and you will see what they do 8-) :D i did put a post on the forum under suppliers about 3 years ago
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Re: MK1 - Possible Rear Crank Gear Play

Post by camstevens »

Thanks Julian
Much appreciated.....worth the trip, no doubt.

Cam
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Re: MK1 - Possible Rear Crank Gear Play

Post by allan.walker »

Hi Cam,
I'm watching this with interest. I've started stripping down my Mk1/2 (Mk1.5???) I discovered that, whilst the front crankshaft coupling gear was very tight, the rear one barely needed the extractor to pull it off. The key was tight in the shaft and a sliding fit in the gear.

When I replaced the gear on the shaft without the key, it went on easily with hand pressure and a bit of side-to-side waggling. When pushed home it rotates on the shaft. This may be causing the knock I am hearing.

Thinking about it, fitting the coupling gears on a parallel shaft is probably the worst bit of engineering design on these engines. A key is meant to locate the components in a specific position and not to carry a load. The shafts/gears connection should be a taper so that tightening the fixing nut secures it positively.

The rear crank is a hopeless setup, since there is no solid, threaded fixing to hold the gear in place. The large nut holding the shock absorber in place serves the purpose of keeping the gear pressed against the crank, so is 'spring loaded.' My only surprise is that any of these engines are still running with a secure, silent rear crank/gear connection.

(Just a thought, perhaps we could dispense with the sprung shock absorber and replace it with a solid connection securing the sprocket and everything else lying 'behind' it. Then, find a clutch with a built-in rubber cush drive and modify it to fit in place of the existing clutch. Has anyone done this?)

Allan.
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Re: MK1 - Possible Rear Crank Gear Play

Post by john.whiting »

Its rather obvious that the key transmits drive...to have a cylindrical surface transmit drive ,the interference fit would be in the order of 10-15 tons push on/off......The simplest way to fix the fit would be with a thin deposit of electroless nickle in the gear bore ....which you can do yourself.......Its unwise to plate crankshafts ,due to hydrogen embrittlement,however with a bit of ingenuity ,you could deposit electroless nickle on the worn part of the crank. without dismantling the motor.
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Re: MK1 - Possible Rear Crank Gear Play

Post by john.whiting »

Thinking on it,the only instance of a smooth surface cylinder transmitting drive is the D Series Ford "suitcase gearbox",where the layshaft gears are fitted so tight keys arent used .......the layshaft is unservicable ,as pushing the gears off scores both shaft and gear bores.........I suspect the gears are shrunk on in production.
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Re: MK1 - Possible Rear Crank Gear Play

Post by allan.walker »

john.whiting wrote:Its rather obvious that the key transmits drive...to have a cylindrical surface transmit drive ,the interference fit would be in the order of 10-15 tons push on/off......The simplest way to fix the fit would be with a thin deposit of electroless nickle in the gear bore ....
Quite so, John and hence my statement about it being poorly engineered, particularly regarding the rear crankshaft where there is no secure fastening to prevent movement.
I am considering using a home plating kit to plate the internal bore of the rear coupling gear. I have a couple of spare gears which, when trial-fitted, show up the wear on the rear crank in the same way as the existing gears.
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