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Author Topic: New Vintage Project, 250cc M-VG, Reconstruction of a 1933 French Jonghi 350  (Read 25786 times)

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Offline thefrenchowl

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No worries, Tom...  :-D

I've done the same time and time again...

Do you have as well a steering tube goin' through that window? or are top and bottom trees just held top and bottom w/o a tube in between?

Patrick
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...What exactly are we trying to do here?...

Online Koncretekid

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Patrick,
I have a 3/8" S.S. threaded rod which has been turned down to the root diameter, around 5/16", which applies the required preload on the tapered roller bearings.  It does not impair my vision.  The only problem is loss of peripheral vision between the sideline flags which I believe are 1/4 mile apart.  With a bit of side wind, this can unknowingly move the bike across the course.  The event I now attend (World of Speed) has a centerline painted on the course which keeps me aligned.

Tom
« Last Edit: April 21, 2019, 09:25:57 AM by Koncretekid »
We get too soon oldt, and too late schmart!
Life's uncertain - eat dessert first!

Offline thefrenchowl

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Now you see me   :-D now you don't!!!

Great!!!...

By the way, the guy who redid my paint has a Metisse framed B50 that he races in classic moto cross events...

Nice bike...

Patrick
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...What exactly are we trying to do here?...

Offline wobblywalrus

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Patrick, type "nowhere faster sprint motorcycle" into google and look at the images.  That bike is in the UK.  Another example of a very low frame.   

Offline thefrenchowl

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Hi All,

Easter weekend spent kicking the bike to death, even breaking the center stand!!! To no avail, not even the smallest fart...

Verified everything, had the carb and magneto in a 1000 bits...

So tonight, a friend, Alan, came to help me for a pushing cession...

I live at the bottom of a hill, in town... So we headed up for a bit, then turned into the cemetary that has an even more pronounced gradient.

OK, 1st push, a few farts but nowt conclusive... So we go up again...

2nd push, the bike starts well in less than 5 meters, but it sounds fluffy and too rich. I open the auxiliary air fully and she picks up nicely now, clear and deep raging sound... and the flywheel takes off!!! Sheared key...

I'll chase a few bits tomorrow and will reassemble as fast as I can!

A few shots taken by my friend Alan:..











So long, Patrick
Flat Head Forever

...What exactly are we trying to do here?...

Online Koncretekid

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Sorry to hear that, Patrick, although probably better there than at the Salt Flats.
Tom
We get too soon oldt, and too late schmart!
Life's uncertain - eat dessert first!

Offline comet

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That sucks. Sorry to read that Patrick. Good luck sourcing the replacement parts mate.

Offline thefrenchowl

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Thanks for your concerns!!!

Happily, all the Jonghi engineering drawings (over 900 of them at the last count...) are on the web thanks to two friends of mine...

dgr 2112:



I'm off in a minute either finding one or materials to make one,

Plus serious fine grinding in with lapping end passes with toothpaste if I can't find a bit of sulphur...

Plus loctite press and moding a touch the flywheel nut and its cover, they are slightly too thick for the space available and maybe the initial cause for the shearing...

So long, Patrick
« Last Edit: April 26, 2019, 03:43:09 AM by thefrenchowl »
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Offline Interested Observer

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Patrick,
From the photos it appears that the flywheel is fitted to a tapered shaft.  If so, you may want to take a close look at that fit, since that is probably the primary connection means between the two.  Relying on the key alone may not carry the day.

Online Koncretekid

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Patrick,
From the photos it appears that the flywheel is fitted to a tapered shaft.  If so, you may want to take a close look at that fit, since that is probably the primary connection means between the two.  Relying on the key alone may not carry the day.


x2. On the BSA main shaft, a lot of lapping is required, especially after the hub has sheared a key.  Then the nut must be well torqued with at least medium thread locker, maybe the stronger thread locker would be good insurance.  I imagine that flywheel is a bugger to keep tight, especially during engine braking.

Tom
We get too soon oldt, and too late schmart!
Life's uncertain - eat dessert first!

Offline thefrenchowl

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 :-D All ready to assemble again, photos to follow later...

Yes, key is just there for location, not to hold the assembly...

Both flywheel and shaft were lapped together for a long time, but what happened is the flywheel nut was tight between flywheel and its cover...

All were assembled with loctite but when the flywheel started to shear the key, the movement unlocked the nut and it all flew away.

Could also be that too tall a key will prevent tapers to mate properly, I'll never know since it's now in 2 pieces!!!

Sorted now, 1mm play between nut and cover, new key made, more lapping...

Thanks for the pointers,

Patrick
« Last Edit: April 26, 2019, 10:49:13 AM by thefrenchowl »
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Offline saltwheels262

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Your build looks great ,have been following it.

Couple of questions----
 
No safety wire on that nut that came off motor shaft?

Where did flywheel end up when it separated from engine?
No ballistic type cover on flywheel?
What happens if flywheel fails and separates into numerous bits?
bub '07 - 140.293 a/pg   120" crate street mill  
bub '10 - 158.100  sweetooth gear
lta  7/11 -163.389  7/17/11; 3 run avg.-162.450
ohio -    - 185.076 w/#684      
lta 8/14  - 169.xxx. w/sw2           
'16 -- 0 runs ; 0 events -- made a 2 state change in ZIP codes

" it's not as easy as it looks. "
                            - franey  8/2007

Offline thefrenchowl

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Quote
Saltwheels262: Couple of questions----
No safety wire on that nut that came off motor shaft?
Where did flywheel end up when it separated from engine?
No ballistic type cover on flywheel?
What happens if flywheel fails and separates into numerous bits?

That's actually four but I'll let you off!!!

- Trying to find a way to fit hefty safety wire or split pin in that tiny space between flywheel and nut cover...
But if flywheel can break a key in half, what are my chances with safety wire or split pin  :? At point of contact, key is 5mm wide x 19mm long = 95mm2...
- Engine runs "backwards", CW from flywheel side, so it passed my legs et went uphill on the road... Big enough, easy to find!!!
- No cover on the flywheel...
- Me thinks it would have to rev way way way past what this engine can do (say 6000rpm) before exploding...
There are 3 ball bearings on the narrow crankshaft (IE this is NOT a nitro fed British twin with nearly a foot between the mains and a gigantic weight bobbing for its freedom in the middle!!!!!!!!!!!!!!!!! I've seen these explode, nasty... Everything was broken or bent including the frame...)

Thanks for your interest...

Patrick
« Last Edit: April 26, 2019, 02:23:12 PM by thefrenchowl »
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Offline thefrenchowl

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Hi,

Found slightly bigger keys at the ball bearing dealer, plus some BlockPress...



A small 1/2 hour to slim one to the required dimms:



Paste lapping:





Then tooth paste lapping:



Lathe small trim for a good contact with the nut...



I reassemble it all tomorrow......

So long, Patrick
« Last Edit: April 26, 2019, 02:45:17 PM by thefrenchowl »
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Offline rgdavid

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    • fancy metalwork
After lapping put a small chamfer behind the flywheel hole, just in case there is a tiny ridge on the shaft from lapping,
Is the flywheel balanced ?
Is there any wayto hold the flywheel back when tightening so it doesnt stress the key ?