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Big end diameter
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SpacedMarine
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March 22, 2019 - 5:57 pm
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Hi all.

I'm just wondering if anyone knows what the exact internal diameter of the big end hole on a d14 crank web should be.I have 4 big ends 2 new ones from Rex and the ends of the shaft where they press into the webs are all bang on 19.06mm.The old one is 19.075 one side and 19.09 the other which Is why I have a majorly sloppy hole I'm guessing.Would a hole exactly 3/4" or 19.05mm have enough friction or would it need to  be slightly undersized.Does anyone have factory drawings or anything like that?I'll have a look in my Haynes manual later but I'm the other end of the country at the moment and I'm sure it wont have that info but I could be wrong.

I'm looking for an exact figure and the +/- tolerance not "as tight as you dare!".I'm sure someone will know.

Many thanks.

James.

What's 7/16 in mm again?

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neddyo
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March 22, 2019 - 7:31 pm
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Hi James,

I have made a few Bantam crank pins but  I'm not sure

of what the original interferance fit would have been.

I havd asked various engineering firms and they all

said much the same thing, a round .002" per inch of diameter.

What is most important is the surface finish of both thr crank pin and 

the hole in the flywheel. I always lap the hold on the flywheel but

polishing with fine emery paper would be ok.

Nick.

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SpacedMarine
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March 22, 2019 - 7:44 pm
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Thanks so by my back of an envelope calculations make that 0.00015" or 0.0038mm 😂 on the total diameter.so the hole would need to be 19.0562mm?What that is in inches I'm guessing is 3/4".

I'm quite new to this and was looking at engineering documents going on about h7,c11,etc fits and couldn't quite get my head around it. I'll have to sit down when I have a bit more time and try to digest it 😁

What's 7/16 in mm again?

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Mags 1
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March 22, 2019 - 8:17 pm
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Various engineers books or booklets will advise about fits, + 1 thou per inch is first and + 2 thous is next, but I forget the exact nomenclature now.

Somethink like running, interference and another I can't remember. I seem to remember Bantam crank fits to be + 2 thous, but don't quote me as I cannot even remember where I read that, sorry. 'Motorcycle Mechanics magazine' maybe.

Four now on the road and at least several in bits.

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SpacedMarine
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March 22, 2019 - 9:09 pm
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Mags 1 said
Various engineers books or booklets will advise about fits, + 1 thou per inch is first and + 2 thous is next, but I forget the exact nomenclature now.

Somethink like running, interference and another I can't remember. I seem to remember Bantam crank fits to be + 2 thous, but don't quote me as I cannot even remember where I read that, sorry. 'Motorcycle Mechanics magazine' maybe.  

ta mags consensus is 2 thou looks like.From what I was reading the closest is a force fit for stuff that doesn't come apart the one before that is the closest you can get with cast iron,cant remember what it's called though.

What's 7/16 in mm again?

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sunny
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March 23, 2019 - 7:37 am
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  try     B S A ONERS    CLUB  if   your  a  member     or   BRITISH  STANDARDS   

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SpacedMarine
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March 25, 2019 - 9:29 pm
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For future reference 20190325_212516.jpg20190325_212537.jpg

H7/s6 is tightest you can go with cast iron and pin diameter is 19.06mm so work it out 😁

If hole is bang on +0.035mm so 1.38 thou.

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What's 7/16 in mm again?

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