It seems ages since I posted onto this topic, but now I have got the bling out of my system for the time being, I am pressing on with this rebuild.
The engine is now going together rather than having fixes done on it.
Today it was the time for the crank, and I think that this post might be of use to a few of you who build small engines.
This shot shows a normal crank build, and to me is one of the worst types.
What should be done, drill a slightly undersized hole, wack a pin in and hope it goes in straight? Or make a slightly oversized hole so that you have clearance for silver soldering, wack the end of the pin to deform it so it holds in the hole whilst soldering, and again hope it ends up square? There are many ways of doing it, but I will show you how I go about it to almost guarantee that the pin will be square and secure in the hole.
First thing I do is thread the hole, to about the same size as the normal plain hole.
Then I turn the pin up out of silver steel (drill rod) that is rather larger than the original sized pin.
First off you turn the length and size of the crankpin you want to go thru the big end. Make sure you end up with a nice clean shoulder where it joins to the main bar.
Then cut a length off the rod to allow you to form the other end.
Holding the crankpin in your chuck, you turn down the sticking out end to the size that is required for threading, and while you are doing that, form another shoulder, like shown. My integral 'washer' is about 0.025"(0.6mm) thick. Then thread the stub to whatever size that is in the crankdisc. Turn a small undercut on the thread, to ensure it screws all the way into the hole.
After that, turn down the diameter of the 'washer' so that it doesn't overhang the edge of the crank disc.
A little high strength loctite on the thread and it is then screwed into the hole tightly. The small shoulder will ensure that the pin ends up perfectly square to the crank, even if the hole was tapped slightly out of square and the thread isn't too tight a fit.
Dress off the back of the hole so the thread is flush, and put one or two very small pop marks around where the thread and hole meets.
If ever the pin gets worn, a good grip with a pair of pliers or vice grips and you should be able to screw it out, make a new one and refit it.
When I made the basic crank and disc, I made on the back of the crankdisc a 'rubbing face' to reduce friction, I left it overly long because I didn't know how thick my 'washer' would end up being. After the pin was made, I reduced the rubbing face by the thickness of my washer. So now everything has nice small running clearances.
But those damned big ends came back to haunt me yet again.
When I tried to turn the engine over by hand, I was STILL getting interferance, even though they were made to the modified drawings. The pic shows what I eventually had to do. Hack the corners off. Then the engine turned over very nicely thank you.
I just couldn't resist it, the basic bits for the engine were there, no gaskets or cylinder outer covers, so I wacked some oil into and gave it a small dose of air.
You guessed it.
It ran like a swiss watch, both forwards and reverse, and the throttle works a treat, and that was with a tight engine, when it get bedded in, it should run on a wisp of air (or steam).
So now on the run in, just a little work to do and it should soon be winging it's way back to the customer.
I will give you the final update to this post when it is completed.
Bogs
