Con rod alignment

[Greig Smith]

I've got 4 sets of Mr Betts finest slipper pistons here in the Colonies, no fault found on any of them & I run those at 6000++ in the race cars

Aye
Greig

[John Cornforth]

Heres a picture of a slipper piston.  I don't have the exact measurements, but the "full width" section above the gudgeon pin is only about 11/16 inches deep, i.e. about one third of the bore diameter.  

If for example the bore was 3 thou bigger in diameter than the piston, it would be able to cant over enough to give about a 10 thou slope on its crown when just touching the bore at two points.

A conventional "deep" piston would not allow this much angular movement, but with a misaligned gudgeon pin/little end I guess the con rod would bend instead and be placed under stress.    

[Colin Reed]

Hi Leaf,
Take a good look at Terrys photo this is the quickest way to check the rods.
all you need to do is remove the block, leave crank in crankcase  remove pistons and use a 1/2 inch ground rod ( ie ) Silver steel

this will check for the following
center to center between Big end and small end
any side to side bend
and twist in the rods
which will confirm any problem with the rods

with the block off check that the top and bottom is parallel and that the  bores are at 90 degrees to the bottom face
one other tip when checking piston height leave rings off 

Hope this helps
Colin
NZ

[Tony Press]

From your description it appears that one of your rods has the little end white metal bored in error at a slight angle (about a quarter of a degree if my maths is correct).


????

[leaf200]

I have now removed the rods and measured them on the jig shown.

The difference between each side of the pin is:

1- less than 0.5tho
2- 7 to 8 tho
3- 4 to 5 tho
4 - 6 to 7 tho

I believe the issue is with the white metal but any suggested ways to resolve this issue would be welcome. The current suggestion is new little end bushes bored to suit the white metal

---

   

[Charles P]

I have now removed the rods and measured them on the jig shown.

The difference between each side of the pin is:

1- less than 0.5tho
2- 7 to 8 tho
3- 4 to 5 tho
4 - 6 to 7 tho

I believe the issue is with the white metal but any suggested ways to resolve this issue would be welcome. The current suggestion is new little end bushes bored to suit the white metal

---

The proper way to fix it would be at the white metal end, if that's the problem.
A length of 1/2" silver steel as Terry illustrated but without the crank will prove that the little ends are fine, because if they are, the rods will sit tightly together, like bee eaters perching on a wire. 

I had to get the big ends of a new set of 1.5" shell rods resized and honed because the bearing tunnels weren't round. By the time I discovered the problem I couldn't be bothered suffering the delay that a complaint and argument would probably have created.

Charles

[Greig Smith]

As those look to be new rods, my question would be if there is any recourse with the seller ??

Aye
Greig

[Peter Johnson]

Thank you all for your help. Will post an update when we have decided what to do next.

Great day out today at Stonehurst Farm for the annual PWA7 club rally. Managed to pick up a few remaining parts for the rebuild.

Peter