These are pictures that have been taken over a period of time when I felt like doing a bit in the shop over the last week or so.
The last post finished off where I had made the perfectly true running nut, and then found out that the ali boss had been welded onto the outer case way off centre.
This shot show just how far off centre it really was. Whoever did it had no thought about getting the two critical parts centred to each other, and because of that, has caused this complete rework. Damned amateurs!!!
I stripped the crank out of the case, and got the case clamped to the table using the strongpoints already on the case half.
Then using the main datum on the engine, the crank bearing, I zeroed up the mill to it.
Zeroed up and the table locked up solid.
Because the case has oil galleries drilled all around it, plus the open main bearing, I sealed everything up with pure aluminium tape. This tape will not be removed until every bit of swarf from the machining has been cleaned up.
Luckily, the outer cover has two datum pins built in, so the cover should always go back into exactly the same place each time. The cover was bolted to the already clamped crankcase half.
Then it was just a case of rough boring until all signs of the old thread had been removed.
Once the threads were machined away, I did a very fine bore to clean everything up and get it to an easily remembered size.
This shot shows how close this job had come to being a complete failure. If the block had been welded 1/8" further away from central, it would have been almost impossible to rescue by using this method.
A recess was made to as large a size as I dared go, without the risk of breaking thru the edge of the boss, taking into account I will be dressing up the boss a little later.
It is a bit of lathe time now. A lump of ali was turned down until it was a nice sliding fit in the larger recess I had just bored.
A spigot was then turned onto the end of the bar, 0.002" (0.05mm) smaller than the thru hole I had bored, and of the correct length to fit thru the casing. The smaller size is to allow clearance for the loctite I will be using.
The plug was parted off, all parts to do with the assembly were given a good spirits clean down. Then it was assembled using hi strength loctite and left to cure a while.
As you all know, I throw away nothing that might have a use in my shop. This time it was an old ali knitting needle. I have found that the metal in them is a lot more rigid than normal ali bar, and once the outer coating has been cleaned off, it makes great pins for holding ali bits together.
So, I hand drilled two holes roughly 90 degs apart that penetrated well into the plug, then with loctite on the end of the pins, they were hammered into position. This is a belts and braces way of fixing. That plug is going nowhere fast.
Then it was just a matter of putting the cover back onto the still zeroed case, and drilling out with the right sized drill (7/16") for cutting a new 1/2" BSF thread.
Everything perfectly square and the new thread was cut.
The final act was to skim the top face with a fly cutter.
So except for blending this welded on boss into the case to make it look like it has always been there, it is just a matter of machining up the drive nut and takeoff.
Hopefully.
Bogs
