Piston/rod concern - k series

[mahatma]

Just building up my engine, crank and main bearing ladder installed and I've beeen putting the spring clips and piston rings on the pistons and noticed something that concerns me slightly.

 

The rod does not appear to be central on the piston and I just wanted to ask what people though about this, I've got a couple of pictures one large, one small;

 

Small picture

 

Large picture

 

The image isn't quite square on, but you can clearly see the rod is not in the centre of the 'piston gap' that houses the little end.

 

I tried checking one of of the big end caps on the crank and there isn't any tolerance of to speak of, which I thought may be the case. The pistons were installed on the rods for me by a company but I couldn't see this effect until the spring clips were put in the pistons at the ends of the gudgeon pins.

 

Any opinions appreciated.

 

Andy

[Rob Walker]

If the gudeon pins are interference fit then you should not be fitting circlips. The gudgeon pin is suposed to be slightly offset and will find its own center IF its been correctly positioned on the rod end.

[mahatma]

The gudgeon pin is floating in the piston but an interference fit on the little end. Since the spring clips were installed, there is no lateral movement of the gudgeon.

 

Should have mentioned in the first post, the rods are standard and the pistons are accralite.

 

Thanks

 

Andy

[Paul McKenzie]

Oily will be along in a moment with the definitive answer, but I seem to remember something about the rods needing to be fitted a particular way round 😳, but I may just be confused

 

Paul

[Roger King]

You absolutely must NOT fit circlips with an interference fit rod. Unless you get the rod in exactly the correct position (and I mean exactly) on the pin, you will be forcing the rod to bend and the piston to tilt in the bore when you fit them in the bore.

 

The piston circlips are to be used when the rod is bushed and therefore is able to float on the gudgeon pin.

[mahatma]

Thanks Roger,

 

So the solution is to just remove the circlips then, right ?

 

Cheers

 

Andy

 

Edit ... Rob, along with the post from Roger, I think understand your reply. This is all still quite new to me. The advice is appreciated.

 

Edited by - mahatma on 6 Feb 2004 20:27:26

[oilyhands]

Second Roger's advice, circlips should only be fitted when the pin is fully floating in both rod and piston. If the pin isnt exactly central this is not normally a problem, provided that difference isnt greater than 1mm, there will be a degree of movement required when the rods are fitted and you may find that the rod eye is not completely central between the pistons bosses.

 

FWIW I would always fit forged pistons fully floating, it is possible to hone the small end of the rods to size to allow run the pin directly in the rod material, provided that an oil delivery hole is drilled in the top of the rod.

 

Oily

[mahatma]

Excellent, thanks all.

 

Andy