4.6 con rods. Should they be blue at the wrist pin end?

[rich112]

Is this normal on a 4.6 Rover v8?

All my rods have bluing at the little end. I assume this is either to allow the wrist (gudgeon) pin to be pressed in or my con rods are all toast?

[stevieturbo]

I think most old Rovers were an interference fit pin ? So often the rod would be heated to allow pin fitment.

If they're all the same, that's a good sign. If some are very different from others..perhaps not so good.

[rich112]

I think most old Rovers were an interference fit pin ? So often the rod would be heated to allow pin fitment.

If they're all the same, that's a good sign. If some are very different from others..perhaps not so good.

They all look the same. I'll go with it being an assembly thing!

Cheers.

[Mc Tool]

Yes it is an assembly thing . The pins are indeed an interference fit . The small end of the rod is put in an induction heater untill dull red hot and the pin and piston is aligned and the pin quickly pushed in and the assembly is left to cool. They are fanarklinly tight , my 5 ton press wouldnt move them cold , usually wind up damaging pistons getting them off , cant really heat the small end with the pistons on so its brute force ......

[Richard P6]

They're not heated until a dull red, just until they go blue. Then you put them into place and push the gudgeon pin in. You do need to get it in the right place really quick as the conrod will 'grab' the pin within a couple of seconds.

[garrycol]

Sorry not following this thread - on a 4.0/4.6 the conrod does not grab the gudgeon pin as moves freely on the gudgeon - the bearing is in the little end and the little end moves around the gudgeon pin.

The gudgeon pin is fixed into the piston, is an interference fit and does not move - hence the risk of damage to the pistons if you have to change or force the gudgeon out - so the little end should not need heating at all.

Also be aware that the thickness of the gudgeon pin wall is thicker on a 4.6 than it is on a 4.0 - outside diameter is the same but the wall thickness is greater to handle the extra forces. When I build my 4.6 out of a 4.0 I decided to use the 4.0 pistons and had to change the gudgeons over - I was advised by the machine shop that there was a risk the piston could be damaged in the pressing process due to the forces needed - thankfully was not an issue.

Garry

[DaveEFI]

Sorry not following this thread - on a 4.0/4.6 the conrod does not grab the gudgeon pin as moves freely on the gudgeon - the bearing is in the little end and the little end moves around the gudgeon pin.

The gudgeon pin is fixed into the piston, is an interference fit and does not move - hence the risk of damage to the pistons if you have to change or force the gudgeon out - so the little end should not need heating at all. the piston

Also be aware that the thickness of the gudgeon pin wall is thicker on a 4.6 than it is on a 4.0 - outside diameter is the same but the wall thickness is greater to handle the extra forces. When I build my 4.6 out of a 4.0 I decided to use the 4.0 pistons and had to change the gudgeons over - I was advised by the machine shop that there was a risk the piston could be damaged in the pressing process due to the forces needed - thankfully was not an issue.

Garry

Did wonder if the larger engines were different. The BL manual for my SD1 just shows how to press them in - no mention of heat. But I'm confused. There is no bush in the connecting rod, so assumed the piston/gudgeon pin was the bearing?

[Richard P6]

Sorry not following this thread - on a 4.0/4.6 the conrod does not grab the gudgeon pin as moves freely on the gudgeon - the bearing is in the little end and the little end moves around the gudgeon pin.

The gudgeon pin is fixed into the piston, is an interference fit and does not move - hence the risk of damage to the pistons if you have to change or force the gudgeon out - so the little end should not need heating at all.

Sorry Garry, but I have to disagree. I have just fitted the pistons back onto the conrods on my 4.0L engine and the interference fit is the little end to the gudgeon pin. I made up a small rig to hold the piston and fitted the gudgeon pin with a little oil to check they slid in smoothly and turned in the piston.

As the pin needs to be able to float from side to side in the piston, I made up a 'stop' to ensure that pushing it in fully would leave in exactly the right place when the little end cooled. Then I pulled it out to leave a gap in the piston for the conrod, then heated the little end until it turned blue. Very quickly placed the conrod into the piston and pushed the pin fully home, then left it for a couple of seconds. Then applied a couple of drops of oil onto the pin and made sure the pin floated cleanly in the piston.

I also checked the distance of the pin from the outside of the piston when pulled to one side, and then compared it with the other side when pulled over there.

[garrycol]

So you believe the conrod is locked to the gudgeon and with the movement of the piston up and down the gudgeon turns inside the piston with no bearing material.

That is not how my engines are set up an how engine rebuild manual explains it.

[paul c]

My 4.6 also has interference fit in the small end. The gudgeons are floating in the piston.

[SuperV8]

Rover V8 4.0 4.6 gudgen pin clearence

From the Landrover 4.0-4.6 workshop manual - note the Gudgen pin 'clearance' in piston spec.

The Rover V8 pin is semi-floating like most OEM engines and is an interference fit with the connecting rod.

[garrycol]

Ok - I stand corrected - but it means there is something odd with the 4.0 converted to a 4.6 I have as it definitely has the gudgeon locked to the pistons - I guess the issue will show up sooner or later. So how is the correct position of the conrod little end on the gudgeon determined - just mid way?

[SuperV8]

Ok - I stand corrected - but it means there is something odd with the 4.0 converted to a 4.6 I have as it definitely has the gudgeon locked to the pistons - I guess the issue will show up sooner or later. So how is the correct position of the conrod little end on the gudgeon determined - just mid way?

Yes - just central on the little end.
When I re-build my 4.6 I pressed all my pins out - to measure and weight match the pistons/con rods. Turns out I didn't need to as they were all very accurate - weight wise - and following further research revealed the 4.0 and 4.6 engines had much tighter weight matching and balancing of rotating components due to improved production machines.

When pressing one of my pins out it 'picked up' on the alloy piston meaning that basically scrapped that piston - it made it stiff on the pin gudgeon and I needed to source another piston. The gudgeon pins should not be locked to the pistons - the pistons need to rock freely on the connecting rod assembly.