McDonald Imperial Super-Diesel

Might be time for a 20L drum , a fire and boil that piston for a bit then see how it goes when it is hot.
Cheers Steve

Now this is getting really intense - go for it cobba . . .

Pistons are "cam ground oval",to a Van Norman E contour,because a round piston will load at the edges of the thrust face and seize.......the reason for this is that heat from the crown is conducted into the skirt by the heavy pin bosses.,so the sides expand more than the thrust surfaces.This is the theory behind the cut away slipper pistons used in Red Holdens and the V8s.....The sideplate Holdens had ordinary trunk pistons ,and were consequently cam ground oval.....The "E" contour reduces the sides by about .010" compared to the thrust faces.

Hi Blackduck, I just can't imagine what it would taste like after boiling. How long do you suggest before serving?
I think my next move is to continue with the rigid hone that seems to be getting the job done and with the new stones fitted is really tossing out some grey kero sludge. I will work mainly down the bottom of the stroke but still drawing it back and forth.
Have even had it suggetsed to make an adjustment on a block of wood and a rubber mallet. Sounded like 'railway engineering' but was something I was prepared to try until I heard of this 'cam grinding'.
So after brekky and our last caravan which we sold gets picked up it will be back to the honing department while sitting on my arse up plastic bucket. I will also make more use of the internal gauges on loan but checking the gap from the bottom end instead of going down from the top which is almost to my elbow. It does feel good to be back playing with it again even though I have not won the battle yet. Just hope it is the light at the end of the tunnel and not a bloody train coming.

Think the old Galah recipe might work.
Boil it with a rock, when the rock is soft chuck the Galah and eat the rock.
Cheers Steve

Being a bit of a "Galah" myself I resemble that remark!

And the winner is.....cobbadog! I got the bastard!
There was definitely 2 different issues, the bore for what ever reason was undersized at the bottom end and believe or not there was a bump on the piston skirt. So with a long time honing, washing it out and then checking it was time to go to the lathe.
As suggested I set it up using the dial indicator and this time with the piston top in the chuck and at that point it ran true. As I went down the skirt things were good but then I rotated the chuck and presto a lump on the skirt. So no amount of honing would fix this issue and would make the bore completely the wrong size if I didn't machine the piston. So yes something must have been dropped onto it and caused this problem. Now I have the same clearance top and bottom and that is 0.010".
In the pics you can see the hone in position ready to have the drill connected to it which is a socket on an extension with a slot to engage the small lugs to drive it around. Liberal amounts of kero was used and it certainly hooked into cleaning things up and it works far better than the spring loaded hones.
You can see the high spot on the skirt and as I took 0.01mm off at a time it slowly progressed towards the oil ring land then from there up all was good.
A picture of the Australian made Somers brand rigid hone.

Thats a result

Paul

Work got pushed aside for a while while I played to get to this point.
Got the rings onto the piston and gapped them using the cut off wheel of my grinder. (that will be a talking point).
Fitted the piston then the crank into place and connected the big end to the conrod and then to the crank. Made a new gasket out of 1.5mm paper for the side cover that houses the other crank main, fitted a new oil seal and then put the cover on and tightened it. The rings a have a good hold of the bore but once I have it moving I can move it with a struggle by turning the crank by hand. Once the flywheels are on it will be a lot easier.

The picture of the gaping process is not how I did it but was safe enough and the rings were well supported at the time of "adjusting".

I wonder if anyone ever followed the note on the casting.

Read the Instruction book!

Good to see a result.

Noise and action shouldn't be too far away.

Grinder is fine I reckon
The proper gizmo is a little grinding wheel type job so you should be pretty close to that when using a Jenny Craig wheel

Paul