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Author Topic: New Vintage Project, 250cc M-VG, Reconstruction of a 1933 French Jonghi 350  (Read 7330 times)
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Harold Bettes
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« Reply #90 on: June 18, 2018, 06:56:49 PM »

Patrick,

Looks like a fun project. The challenges of recovery, restoration, and performance improvement are time consumers but provide much in rewards. cool

Question on the balance of the single cylinder engine: What % of reciprocating vs rotating weight are you trying to do? Seems I recall that a number of 36% to 40% was often used on performance poppers but do not remember exactly.

Although the tungsten material (Mallory metal alloy) is good to use, it is expensive. shocked

Good Luck on your interesting project. cheers

Regards,
HB2 smiley
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thefrenchowl
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« Reply #91 on: Today at 04:16:05 AM »

Hi Harold, I do not know the Jonghi balance factor.

The only thing I can say is that they are not known to be boneshackers!!! And I know the balancing weight I removed as lead.

I leave the crank alone for the time being as it is not too urgent...

Continuing work on the cycle parts... Handlebars decision time soon.

TT 2 had quite a wide set up to cope with the pains of a 24 hour run.

I want it tighter for smaller run lengths on the Salt Flats.

The outside bits in the horizontal plane:



Vertical plane:





In between:



With fork stops to limit the steering to allowed 15 degrees:



I'll leave it for a while before welding for good!!!

So long,

Patrick
« Last Edit: Today at 04:22:38 AM by thefrenchowl » Logged

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wobblywalrus
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« Reply #92 on: Today at 11:17:04 AM »

Alpha Bearings in the West Midlands helped me 46 years ago with my Matchless and they are still in business.  They specialize in the crank work you need.  The typical procedure is to figure out the weights while dynamically balancing the crank/rod/piston assembly.  Really, one cannot be done without doing the other.  They might be the help you need.
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thefrenchowl
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« Reply #93 on: Today at 11:57:44 AM »

Hi wobblywalrus,

Yes, I know Alpha Bearings, they have done work for me in the past, mostly obsolete crankpins or rod races.

I have done quite a few Harley Sportsters and K/KH cranks in the past, always used the race shop 50 % of the reciprocating weight rather than the there about std 60 % the factory use on their street models.

The race 50 % factor on these V twins seems to push the dreaded "around 4500 rpm" vibration out of the available rev range, so I like it, but I'm not sure at all it'll be the same factor on a single!!!

I'm not too worried anyway, as I said, I don't know the balance factor, but I do know the weight I've taken out as lead!!!

I might spend tomorrow weighting all the bits of the crank assembly, and then, I can have a go at calculating the factor they used in them days!

Thanks again,

Patrick
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