(Note: Donations are not tax deductible)

This is a public forum. The opinions expressed here don't
necessarily reflect the feelings of The Folks That Run The Site (that's us)
unless we explicitly say so, ok?


Forum's been "upgraded".
Things will look a bit different.
A *few* posts might have gotten lost in the crossover.
PM bobc with problems, or post in "Website Suggestions".

Author Topic: New Vintage Project, 250cc M-VG, Reconstruction of a 1933 French Jonghi 350  (Read 33395 times)

0 Members and 1 Guest are viewing this topic.

Offline Harold Bettes

  • Sr. Member
  • ****
  • Posts: 404
  • Age: 76
  • Location: High Country (6672'MSL)
  • Firebase High Country
Patrick,

Looks like a fun project. The challenges of recovery, restoration, and performance improvement are time consumers but provide much in rewards. 8-)

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. :-o

Good Luck on your interesting project. :cheers:

Regards,
HB2 :-)
If it was easy, everybody would be doing it.

As iron sharpens iron, one man sharpens another.

Offline thefrenchowl

  • Sr. Member
  • ****
  • Posts: 376
  • Age: 68
  • Location: Great Britain
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: June 22, 2018, 04:22:38 AM by thefrenchowl »
Flat Head Forever

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

Offline wobblywalrus

  • Hero Member
  • *****
  • Posts: 5007
  • Age: 66
  • Location: backwoods Oregon
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.

Offline thefrenchowl

  • Sr. Member
  • ****
  • Posts: 376
  • Age: 68
  • Location: Great Britain
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
Flat Head Forever

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

Offline sofadriver

  • Sr. Member
  • ****
  • Posts: 518
  • Age: 68
  • Location: tacoma, wa
there's no steering degree limit any more.
Mike in Tacoma

"aww, what the hell - let's just do it".............

Bike #833
100cc A/G, A/F and APS/G (in 2019)

Offline thefrenchowl

  • Sr. Member
  • ****
  • Posts: 376
  • Age: 68
  • Location: Great Britain
Hi, Sofadriver,

 :-D I'll have to find meself another rule book, the latest I have is 2014!!!

But I'll need the stops if I go for the extreme look:

Just tacked with silver braze to have a good look at it...





Before and after, nothing like elbow grease and a small polishing mop!!!



Assembled the AMAC levers on their perches and fitted with locking wire, good looks...







So long,

Patrick
Flat Head Forever

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

Offline thefrenchowl

  • Sr. Member
  • ****
  • Posts: 376
  • Age: 68
  • Location: Great Britain
Hi,

Done some calcs yesterday for evaluating crank balance. Balancing the rod on horizontal edge to find its equilibrium point:



This to find the two distances that allow the calcs of rod rotating weight and reciprocating weight.



Then calc sheet "a la" Harley KR, assuming a 50% factor (factor at this stage is unknown for this single)



I'll check more today to see if I can easily determine repartition of masses on the crank itself, not that evident!





Patrick
Flat Head Forever

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

Offline Old Scrambler

  • Sr. Member
  • ****
  • Posts: 690
  • Age: 72
  • Location: Wherever I park the RV
  • Going Fast - Slowly
Patrick..........I run a Triumph T20 Cub at the AMA-sanctioned BMST. I began with an early model but converted the big-end crank bearing to a later roller-cage and used the original crank-weight. Because the 243cc piston is heavier, the balance is slightly changed from original. It begins to buzz at 7,000-rpm :|but so far has held together for more than 2-dozen runs on the salt.

I see in your pics a few 'nicks' along the rod.  Your plan to increase the rpms will obviously stress the rotating masses..............My experience with a small single versus a twin is to keep the crank near its original weight/balance. I like your project and watch with great interest...........carry-on 8-) 8-) 8-)   
2011 AMA Record - 250cc M-PG TRIUMPH Tiger Cub - 82.5 mph
2013 AMA Record - 250cc MPS-PG TRIUMPH Tiger Cub - 88.7 mph
2018 AMA Record - 750cc M-CG HONDA CB750 sohc - 136.6 mph
2018 AMA Record - 750cc MPS-CG HONDA CB750 sohc - 143.005 mph
2018 AMA Record - 750cc M-CF HONDA CB750 sohc - 139.85 mph
2018 AMA Record - 750cc MPS-CF HONDA CB750 sohc - 144.2025 mph

Chassis Builder / Tuner: Dave Murre

Offline thefrenchowl

  • Sr. Member
  • ****
  • Posts: 376
  • Age: 68
  • Location: Great Britain
Thanks, Old Scrambler!!!

I had a few diffuculties finishing the handlebars recently!!!

Nearly there at last!!!

Kill button and main ignition switch:









Few more bits made for the magneto:



Tried to whiten the alloy cases with caustic soda, not entirely satisfied, will try to find some acid, works much better!!!



Also dropped the hight of the steering damper knob, so had to move the star spring from top to bottom. Done a small spring for the knob, that job is normally done via the spring holder which is now discarded.





So long,

Patrick
« Last Edit: July 01, 2018, 03:49:31 PM by thefrenchowl »
Flat Head Forever

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

Offline Old Scrambler

  • Sr. Member
  • ****
  • Posts: 690
  • Age: 72
  • Location: Wherever I park the RV
  • Going Fast - Slowly
The safety 'kill' switch must be lanyard operated.........
2011 AMA Record - 250cc M-PG TRIUMPH Tiger Cub - 82.5 mph
2013 AMA Record - 250cc MPS-PG TRIUMPH Tiger Cub - 88.7 mph
2018 AMA Record - 750cc M-CG HONDA CB750 sohc - 136.6 mph
2018 AMA Record - 750cc MPS-CG HONDA CB750 sohc - 143.005 mph
2018 AMA Record - 750cc M-CF HONDA CB750 sohc - 139.85 mph
2018 AMA Record - 750cc MPS-CF HONDA CB750 sohc - 144.2025 mph

Chassis Builder / Tuner: Dave Murre

Offline thefrenchowl

  • Sr. Member
  • ****
  • Posts: 376
  • Age: 68
  • Location: Great Britain
It will be, Old Scrambler, all mechanical, operated from the twist grip on the left hand side, auto spring loaded tap plus 2nd kill switch behind the tap.

Similar to what I did on my KHK in 2011:





The wedge that keep the cable tentionned and the valve open has a strap to my left wrist. If I fall, the wedge goes out, valve closes and kills ignition as well.

See ya,

Patrick
« Last Edit: July 03, 2018, 04:20:25 PM by thefrenchowl »
Flat Head Forever

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

Offline thefrenchowl

  • Sr. Member
  • ****
  • Posts: 376
  • Age: 68
  • Location: Great Britain
Hi,

Still no wheels, so small jobs only these days......

I dismantled the cylinder and head from my other Jonghi since I had lots of work done on them, I'll use these on the record bike...

Standard Cylinder with flat deck:



Cylinder with sunk valves and channel dug between seats and bore...



Standard head without work done:



The standard cylinder and head use a copper/aspestos gasket. Not ideal on a fast side valve since the squish is bigger and variable depending on gasket compression. So, like on KRs, no gasket used and replace with high temp paint, a lot more durable than what you might think. The piston is slightly domed, so small interference and material removed till I measured 20 thou clearance.



Channel with piston at TDC:



Piston and its pin with PTFE keepers:



Curved transition around valves:





Patrick
« Last Edit: August 04, 2018, 12:48:24 PM by thefrenchowl »
Flat Head Forever

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

Offline konon

  • New folks
  • Posts: 14
  • Age: 65
  • Location: Iowa
Does the intake have a hollow valve stem ?
Sherman racing  M/PG 750

Offline thefrenchowl

  • Sr. Member
  • ****
  • Posts: 376
  • Age: 68
  • Location: Great Britain
No, it's just very "tuliped" as we say in France...

ie shaped like the flower, or a trumpet end, or a saxophone end. :mrgreen:

VG for an OHV/OHC, but not at all the right shape for a side valve, should be much flatter with 30 degrees seats, but I don't know if my finances can stretch to a pair of forged stainless valves...

Patrick
Flat Head Forever

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

Offline thefrenchowl

  • Sr. Member
  • ****
  • Posts: 376
  • Age: 68
  • Location: Great Britain
Good day today...

1st a little packet with some 20 Widthworth nuts from my friend Frederic in France, thanks again!!!



And 2nd, a MASSIVE box with my two 21" wheels in...







Not goin' straight on them, I've ran out of Argon for the TIG welder, off to swap the bottle...

So long, Patrick
Flat Head Forever

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