Interesting problem just arose:

I have recently put a different gearbox on one of my 1275's, clutch and fly looked great, chucked it all together and it was running nice, shifting nicely etc.

Anyway, i was tweeking the timing and fuel, and it putted to a stop - low idle. I restarted, and it started and imediatly stopped, and froze solid.

I was at the top of a hill, so i rolled to the bottom, all attempts to roll start resulted in clutch slip...interesting. I assumed i had melted a ring, or spun a bearing.

I walked away for a couple of weeks.

Lifted the head yesterday, and found Hepolite pistons - happy But it then turned mayby a 1/8th of a turn, but there was a grinding from the clutch housing, which i then removed, and found to be full of shavings:

I could feel a groove arround the edge of the ring gear, so i pulled the fly off:

The ring gear has moved on the flywheel and was fouling on the housing, locking the motor solid!

Easily Fixed, but ive never heard of this happening, anyone got a cause for me or is mini voodo getting me?

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speed costs....how fast do you want to go...

Check you put both dowels in the flywheel housing when you changed things. If not, it can move and hit the ring gear.. apart from buggering your idler bearings etc.

Only other cause I can think of is a dud ring gear, been made with the bore too big. They usually have something like .010" or more interference fit, so just can't move once heated and shrunk on.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks Doc,

Yup both dowels are in - i remember as i had to change one..

Ive just had another look, there is some spot blueing on the ring gear, and Machine marks, my guess is that it has been changed, using an Oxy torch....Interesting.

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speed costs....how fast do you want to go...

You do need an oxy torch to fit new ones, they need to get to a straw colour before they will fit on.
Best way to remove them IMO is an angle grinder and cutting disc, carefully so you don't nick the flywheel. When you get near cut through it goes BANG!! and is off.

<edit> who's the dill who makes nick appear here with capital N all the time if spelt normally...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I blame nick.

nick is not a mod... so maybe his lover/mistress/concubine??

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Ah ha, so you have finally learned the secret.

1100 S clutch housings have different size dowels to Most others, Are you using a 1100S housing and standard Dowels .1100S Housing Will have 3 numbers stamped into clutch housing near starter motor Hole

If the ring gear was heated up too much when it was being installed they dont shrink back to size properly and will be loose. Every time you operate the std mini starter the pinion bashes into the ring gear and eventually the ring gear moves on the flywheel & sometimes even falls off. Like the Doc says, they should be heated up untill they turn a straw color, any hotter and they'll fall off. I linish/sand 3 spots equaly spaced on a new gear, that way i can tell i have an even heat all the way around when i heat the gear up with an oxy.

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Have a Nice Day.
If already having a nice day please disregard.

I do the same ^^^ I polish the whole side.

If they get to blue colour, they are then too soft...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Its a UK 1275GT (78) lump, with a very early (78) A+ CR Box as per UK spec, NZ 1275 GT's.... It all fits nice and tight.

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speed costs....how fast do you want to go...