750S/GT - cold straightening con rods??

[mikeb]

I know cold straightening con rods in old British cars was fairly routine, but I was surprised to see this in the ‘operation and maintenance manual’ of the early 750S:

Place two shims perfectly smooth and equal on the base
supporting the cylinder (Fig. 39). Insert the gudgeon pin into
the eye of the connecting rod, and then put said gudgeon Pin
upon the shims. If both holes of the connecting rod are parallel,
the gudgeon pin will rest on both shims. If it should touch
only one of the two shims, it will be necessary to straighten
the connecting rod, pressing appropriately on one side or the
other, till the gudgeon pin rests on both shims.

There are similar but slightly different instructions for later models (eg SF2..).
So… will any one admit to doing this?
On the scale of risky ideas, is this a ‘1’ (certain disaster) or 100 (legend best idea ever).

thanks

 

[Paul Marx]

I know cold straightening con rods in old British cars was fairly routine, but I was surprised to see this in the ‘operation and maintenance manual’ of the early 750S:

There are similar but slightly different instructions for later models (eg SF2..).
So… will any one admit to doing this?
On the scale of risky ideas, is this a ‘1’ (certain disaster) or 100 (legend best idea ever).

thanks

Which service manual is that?
Paul

 

[piranha-bro2]

Which service manual is that?
Paul

The std SF owners manuals (I have SF1 and booksSF2) and they both show the procedure for checking in pretty pictures! I actually had a crack once, but don't think I was successful, so passed the rods onto my reboring man and general smart guy, who had them done by a quality automotive engineering place. They apparently had a slight S-bend, but came out straight. So proof positive. No way I'd attempt it myself in the bench vice, that's for sure.

 

[Paul Marx]

The std SF owners manuals (I have SF1 and booksSF2) and they both show the procedure for checking in pretty pictures! I actually had a crack once, but don't think I was successful, so passed the rods onto my reboring man and general smart guy, who had them done by a quality automotive engineering place. They apparently had a slight S-bend, but came out straight. So proof positive. No way I'd attempt it myself in the bench vice, that's for sure.

The procedure for checking I remember, but I'd forgotten the mention of the procedure for straightening
However, I seem to remember Phil Todd mentioning it.

A friend of mine once straightened the rod on his Velocette like that in a field by the application of well measured force.

Paul

 

[sfcpiet]

Standard routine.

I've straightened dozens of bent and/or twisted rods, I use vee-blocks and dial indicators to check once the crank is disassembled. You'd be surprised just how many distorted rods show up.

piet

 

[1200ts]

I have straightened a few British bikes with steel connecting rods with the motor still together and in the bike. On some bikes such as a Velocette, a stuck piston can bend the rod a little bit. The side load while straightening the rod does not damage the roller big end bearing at all.

 

[mikeb]

thanks for your comments - encouraging. I was half expecting someone to say straightening 50+ year old rods was the surest way to next have to replace the cases. I might have to have a go at this...

also intersting the later SF1-2 operatonal manual dials it back a bit to only say:

If the connecting rod is straight the gudgeon pin will rest with both its ends on the rods. If only one rod should be touched by the pin the connection rod needs straightening.