Crankshaft grinding part two.
The journal was roughly filed and oil stoned to remove and smooth the major damage, especially any sharp edges. Forget any grooving, these will disappear later.
Two aluminium bearing shells were made as detailed.
Take two sections of 2mm aluminium plate and cut these 1 inch longer and 1/2 inch wider than the rod cap dimensions.
Using aluminium jaws in a vice, press the flat sheet into the cap using a small block of wood.
Using a hammer and another piece of wood, pound the living daylights out of the new shells into the cap, it must conform perfectly to the cap internal ID. Don't hammer the alloy directly, this will cause hard spots.....
Again, clamp the shells into the vice with the wood to hold it secure, and gently form the sides with a small hammer folding the edges down the sides of the cap, these will become the thrust surfaces. Do this gently, take your time with this.
This whole manufacturing process will take around 1 hour. See photo of finished product.
Now is the time to file the shell ends almost flush with the cap. . Leave them a tad proud to ensure they are firmly "squashed" into the rod when mounted.
The shells can now be inserted onto the big end journal, the thrust face width filed to allow them to fit. We need around 10 thou clearance here.
Cut small temporary shims from an old spray paint/flyspray can, these are to fit over the conrod cap bolts between the rod and cap. I used 3 per side initially.... around 30 thou. These allow a little "wiggle" room.
Fit the shells/shims to the conrod and cap, snug the nuts until the engine can just be stiffly rotated a few turns by hand, remove the shells, and with a pocket knife, scrape away the shiny high spots. Don't be too fussy just now, what we want is a reasonably large contact area over as much of the bearing surface as possible. Don't use oil at this stage..
Repeat this several times till a good wide contact patch is achieved.
Remove the dipper rod from the conrod cap, and use the hole as a guide to drill the oil hole through into the shells. Also with a sharp object, gouge the oil channels into each shell to distribute the oil.. Make these at least 1mm deep and fairly wide...say 2 mm. A broken hacksaw blade works well here.
Refit the dipper
Oil and fit the shells and as many shims as needed between cap and rod to allow the engine to turn easily/smoothly when fully tightened.
Refit the inspection cover and start the engine.
Run at a VERY slow speed, watching for oil smoke from the breather. When this appears, indicating bearing heat, shut the engine down for 10/15 minutes to cool and restart.
Do this repeatedly over several hours.
Again, remove the rod cap, and check progress. At this time, clearances will be very large, remove shims to arrive at a suitably small clearance and repeat the running procedure. Aim for around a sloppy 10/15 thou at this stage, we need LOTS of oil around the bearing. Loose is better than tight, and at this very low speed, it wont cause harm. A saving in time can be had by swapping upper and lower shell positions each time to equalise wear..
Any heat is caused by friction. The friction is due to metal to metal contact between alloy and journal. The wear is restricted to the journal high spots only. As the bearings and journal begin to mate, heat will be dramatically reduced, evidenced by less and less breather fuming, until eventually there will be no heating at all, indicating a full and continuous oil film.
Now is the time to recheck clearances and removing shims, also watching the shell end protrusion, . This is called bearing "crush", needed to preload the shells to prevent them spinning in the rod/cap. I reinstalled at 3 to 4 thou clearance.
Now, clean the engine internally with kerosene, change the oil, restart,and slowly bring up the revs, and increase load.
I rechecked mine after 10 hours running at half, then full load to find an almost visually perfect crank journal, and around 90 percent contact pattern on each shell.
Once a continuous and unbroken oil film has been established, there is no further wear on shells or journal.
Two engines repaired in this way have done many hundreds of hours without further troubles.
The final crank journal dimensions depend on initial damage. Mine, as an example, ended up 1 thou out of round, around 12 thou undersized, assuming it was standard to begin with. One groove remains, just detectable with a fingernail. The journal itself is slightly conical, differing each end by around .5 thou. This is very acceptable given the initial poor state of the journal, and money spent. This method is time consuming, but when taken in the context of a complete engine teardown, and conventional crank grind,I believe much quicker and certainly as effective, and ay NO COST financially.
As of today, engine has over 200 hours running after this repair, a quick look inside today reveals no detectable increased big end movement since the repair, and no sign of any further heating. A babbit type bearing would now operate successfully in this engine, but I'm happy to retain the alloy version!! It still has two tinplate shims of around 5 thou to allow for future adjustment if needed.
Purists may "shudder" at this unconventional approach, but as I am reliant on this engine, the repair has been done quickly and efficiently, very little down time, the journal now in even better condition than it was originally 20 years ago.