1952 G9 Connecting Rod Question

[Duncan]

Hi, Just some additional info on the twin con rods (Yes they were polished and weight matched). When rebuilding an engine it is imperative to match the conrods with the correct crank.
Early rods (1949 - 1951) had a small cross section rod and were very light. These must be matched to the early (Light) cranks with the large centre main bearing.
Later model cranks had three different weights (Different balance factors ) and must be matched with a choice from three different (weight) types of conrods.
It should be noted that as the factory increased the capacity from 500 to 550 to 600cc, the cranks were increasingly made heavier, consequently, you will find the con rods were made heavier to equalise the balance factors.
Even though all the twin conrods have the same part number, Do not mix any of the earlier rods with later rods, otherwise, the engine will be out of balance.

Regards............David

Hi David, do you have a source for your information, I have always understood that the crankshaft is balanced to a percentage of the weight of the connecting rod, piston, rings etc.

Looking at the 1960 parts list both the 500 and 650 have common connecting rods.

1960 Extract crankshaft and connecting rod.PNG

[matchless]

Hi Duncan,
Sorry for such a late reply but I have been off the air for a while.
The parts list shows 024438 however, if you go back a couple of pages and look at the image of the con rod assy, you will see listed two numbers; 014221 and 024438, these represent the 500 and 650 respectively.
Unfortunately, the 014221 number does not differentiate between early and late model manufactured rods (500 / 550 and 600 variants).

There is no data (other than experience) to show how to visually match rods with cranks. So it is left up to the restorer to have the crank and rods professionally balanced to 50% (early cranks) 60% (600 engines) and 65% (650 engines) and somewhere in between for 550 engines. I have no balance factor figures for the Matchless G15 engines (Not Norton).

I hope this helps
Regards............David

[Duncan]

Hi David

The way I read it is that from the start the twins had the same connecting rod 014221 up to 1959 when 024438 was introduced, the difference was the chamfer at the trunnion ends for the 650. The 1959 parts list differentiates between both the 500cc and 650cc variety, by 1960 the penny had dropped that 024438 could be used in either engine and were listed for both models. Unfortunately the graphics department was a year behind in updating the pictures. Other than the chamfer I have not come across any differences in the connecting rods I have seen.

[matchless]

Hi Duncan,
The later model rods are heavier than the earlier ones and can be used in all the twin motors as long as they are balanced to the type of crank they are fitted to.
I have found 5 different castings of the same rod and each have a distinctive weight difference. there are 3 variants of the 014221 and 2 variants of the 024438 rod. As long as you have a matched pair, you should not have any trouble with the assembly.

Good luck with your assembly............David

[matchless]

Hi,
Just recapping:
Early rods for 1949 - 1951 had a thin 'H' stem section and not much metal around the small end
Series 2 from 1951 - had the 'H' stem section thicker but still with not much metal around the small end
Series 3 had the series 2 improved with more metal around the small end
Series 4 - had more metal again on top of the small end
Series 5 - for the 650 had series 4 rods with chamfered edges.

Regards............David

[Duncan]

Hi David

That's interesting are you able to provide photographs and weights to aid identification? I could be something for the Jampot.

[matchless]

Rod00000092.JPG

Hi,
I had a rummage through my back shed and found a couple of Rods to show the difference.
I have a 1949 early rod, clearly showing the reduced 'H' section in both profile and elevation.
The other rod is from a late model twin with thicker 'H' section and more metal around the small end.
Both rods are quite different yet they have the same number.
I hope this helps in your identification.

Rod00000093.JPG

Regards..............David