McDonald Imperial Super-Diesel

Well today while in town I dropped off the valves and cast iron for the guides to the engineering shop. Slowly this young fella is coming around to these old engines and stuff as before it was a bloody nuisance. At least now he wants to know more about them so he is showing interest in them. I might and I mean might have time tomorrow to start to gap the rings and make a start in that area.

Today I got some play time and found an issue. Again I wiped out the bore and sprayed some Lanox inside and fitted the piston with no rings. I have a cylinder that is narrow in the middle of the stroke. Fromt between 45mm down from the top to 125mm down the piston sticks. But, if I rotate the piston 90' it does not. This may indicate an oval piston so I now have the piston in the chuck of the lathe and checking it with the dial indicator to see what is at fault.
I think that over time all that rust I removed from around the cylinder has maybe swollen up and caused the bore ID to shrink. More investigation.

Some pistons were designed oval, they return to round when they heat up.
Cheers Steve

Need to measure the bore with some calipers if you can
Between that and the piston in the lathe you should get a pretty clear picture

Paul

I reckon fair assumption there Cobba. A mate of mine had a tight spot in the bore of a horizontal Hornsby engine a few years ago. After pulling the head off, he put it down to excessive rust in the water jacket compressing the bore. He asked me about turning the piston down for him, but i suggested he borrow my cylinder hone instead, which he did, with success.

Getting a hold of a honer that suits the 3.5" bore is my next option. I feel the piston will be ok and as for the bore the piston slips up an down above and below the narrow section. If I give it a little bit of a bump with my hand it does go past the narrow area but rotate the piston 90' and it slides top to bottom no worries.
Next few days will no doubt be spent of our latest toy to come home, another caravan to update our 1998 GoldStream Coldlink camper trailer. So Ol Mac will be left alone again.

If you get stuck for a honing tool I have one I lend, I'll just pop it in the mail and send back when your done


Paul

Mrsmackpaul wrote: If you get stuck for a honing tool I have one I lend, I'll just pop it in the mail and send back when your donePaul

I think I have one just got to check ,I'm a lot closer so he can pick it up.

Cobbadog,
Blackduck59 has given you critical information. Do not turn the piston down. Do not hone the bore until you are absolutely sure that the piston should be absolutely circular.

I suggest you VERY carefully measure the piston, in line with the gudgeon pin and again at right angles to that. Unless the measurements are EXACTLY the same do not hone the bore.. If you MUST hone the cylinder, take off the absolutely least amount possible.

Thank you Mrs for your kind offer but oliver1950 has one for the job and I forgot to call him back this afternoon as I said I would so tomorrow it must be.

Morris, I never was going to machine the piston just check it using the dial indicator gauge and check it's shape. I feel that the piston should be round and not oval sa it is designed to be installed one way only and that is with the oil lubrication hole for the gudgeon facing up. It is in this position that the piston sticks and again my thoughts are that the solid rust and mud packed around the cylinder inside the water hopper has caused the bore to be out of round. Oddly enough turn the piston 90' and it does move up and down.
I know I am committed to getting the repalcement caravan set up to suit us over the next few days so the Mac will be lonely again while I build a spare wheel rack and sort out all the stuff that came with the van. Bloody thing scared me when we got home, I have around 200mm clearance between the 3 sets of carport posts to back between.