offset gudgeon pins

Seight-V8 · Post by **Seight-V8** » Sat Sep 13, 2008 4:24 pm

hiya all,

Anyone like to explain this in more detail??

Been trying to understand whats in the 4.6 overhaul manual, but it just aint helping.

I know there's an arrow on each piston and a dot on each rod, which then face each other in the engine.

But which part is actually offset???..is it how much the pin is from one side of the piston.

As i've had my new pistons installed on my rods, but the pins are all installed slightly different from the edges...

Hope this make sense to someone.

cheers

scott

minorv8 · Post by **minorv8** » Sat Sep 13, 2008 4:48 pm

The pin bore in the piston is not central but offset slighly. An ancient CCC magazine article states 0,60 mm offset.

HairbearTE · Post by **HairbearTE** » Sat Sep 13, 2008 5:11 pm

The offset of the piston gudgeon pin is an effort by Rover to reduce "piston slap".

Seight-V8 · Post by **Seight-V8** » Sat Sep 13, 2008 5:32 pm

hiya,

still having bother trying to understand what it means in terms of the how the pin is installed.

This is the text from the overhaul manual on page 31 of the 4.6 engine overhaul manual.

Set torque wrench to 16 Nm (12 lbf.ft), and
using socket on large nut, pull gudgeon pin in
until flange of LRT-12-126/1 is distance A
from face of piston.
Distance A = 0.4 mm (0.016 in).

Sorry cant post the picture

Or is this a completely different issue.

thanks again

scott

stu8 · Post by **stu8** » Sat Sep 13, 2008 6:03 pm

Just a guess,;

LRT-12-126/1 must be a pin fitting tool, consisting of a sleeve, long bolt with flange on one end and a large headed nut fitted on the other.

To pull the pin through the piston you tighten the large nut which pulls against the sleeve and on the bolt pushed through the centre of the pin.

The measurement they are talking about will be the gap between the flange on the bolt head and the side of the piston, the size of the flange will have been set so that when the gap is 4mm the pin is centred in the piston.

You probably don't have the tool so non of the above is relevant, except the pin should be centred in the piston I would think.

.

mgbv8 · Post by **mgbv8** » Sat Sep 13, 2008 9:30 pm

How can the position of the pin affect anything?
Surely the important thing is to make sure the con-rods are fitted the right way round?

minorv8 · Post by **minorv8** » Sun Sep 14, 2008 6:37 am

Acc. to factory manual the pistons are fitted in room temp. Since the pin is interference fit in the rod small end one needs to use brute force to fit the pin. Hence the tool LRT-12-126/1.

Most shops fit the interference fit pins by heating the small end with blow torch or induction oven. Heat expands the small end and the pin slides easily in the bore.

With offset pin the only main thing is to ensure that the pistons are fitted in correct orientation, offset directed where it is supposed to be. The pistons are marked accordingly, some with arrow, some with a groove or whatever. Some manufacturers specify the marking towards the flywheel, some towards the front of the engine. My copy of factory manual states that there is an arrow that points to the front of the engine. Interestingly, same manual quotes the offset at 0,2 in. Sounds a bit excessive...

Ian Anderson · Post by **Ian Anderson** » Sun Sep 14, 2008 8:27 am

Not of the R8 but on other diesel engines my previous employers used to sell the offsets were big enough to see by eye - like half an inch

these were in long stroke diesel engines and the offset was to stop the con rod snagging on the bottom of the cylinder wall.

Now I believe in some engines the offset was on one side and the other way on other engines - depending on angles between cylinder and crank i.e. in v configuration the con rod may touch on either the 9oclock side of the stroke or the 3 oclock of the stroke

Ian

Seight-V8 · Post by **Seight-V8** » Sun Sep 14, 2008 4:04 pm

hiya all,

Yes think i understand this now, i was trying to understand the A dimension, but this has nothing to do with the offset pin, as this is set by the piston direction.

getting close now to building back up my 4.6 block and i need to make sure i understand as much as possible.

Thanks for everyones help.

scott

ChrisJC · Post by **ChrisJC** » Mon Sep 15, 2008 7:40 am

Don't forget that the rods are also asymmetrical. The pistons should all be mounted the same way on the rods.

This is so you can tell by just looking at the big ends that all the piston offsets are correct.....

Chris.