BANKS V.A. 0.4ccMILLS REPLICA REBUILD

Here's the engine as we received it from my good friend Richard Tapp in Ozzy.

 

This poor little engine has suffered an onslaught of poor quality in manufacturing or has been butchered by some Harry Homer at some point as the cylinder bore is very poorly finished showing little to no signs of having been lapped after machining, thus resulting in zero compression and a badly damaged piston to boot. 

So to rectify this sad state of affairs we will tool up for the small 7.20mm bore and relap it to achieve perfect roundness and the correct tapers in the bore. After that we'll go ahead and make a replacement piston and contra.

We have made up a set of tooling to make a new piston and contra and to relap the original liner but upon further inspection we have found that the original cylinder liners' fit into the crankcase has far to much clearance so that even with a perfect piston fit the engine is still unlikely to run so the decision was made to make a new cylinder liner to ensure a perfect gas seal between the cylinder liner and crankcase wall. 

Here's the first stage of the new cylinder liner being made.

And all finished. We took the opportunity seeing as we made a new liner to rectify the porting to allow a bit more usable power to be generated.

Now we'll get on and lap the new liner and make and fit the new piston and contra etc.

Here's the new piston and contra piston blanks all ready for final machining and lapping to final size and fit.

And all finished ready to refit to the engine.

Ready to go back into the engine.

Here's the crankcase all cleaned up with the bottom end also cleaned and reassembled.

Having received the engine already dismantled a twisted conrod wasn't discovered until we reassembled the cylinder assembly into the rest of the engine and found to our disgust that the blessed little gem was binding going in one direction and partially free in the other. So we removed the rod and checked it out.

The little end was raised off the parallel bars on one side by over half a mm. OH DEAR.

Oh well, time to make a new con-rod then.

We have made a new con-rod and added a lube hole to the big end.

Upon reassembling the engine to test that everything plays nicely instead of finding our binding problem gone we found that it had done the exact opposite in fact. BUGGER!! OK so what's actually going on here? 

So we rechecked the crank fit, perfect. Rechecked the piston line fit outside the engine, perfect. That leaves only one area in which the cause of the problem could lie in, the cylinder to crank pin center alignment, ie is the centerline of the cylinder in the center on the big end journal? Answer, well actually no its not, BUGGER. WOW how did this engine even leave the factory in the first place???

OK so having had a closer look at the case it appears that we can relatively easily machine the inside face of the case house out by another 0.5mm which will move the crank forward just enough to realign the big end pin in the correct location to remove our severe binding issue.

Before........

 

After.......

Now lets re-assemble this little gem of an engine and check he's now all ok.

Finally, all together and feeling ok. Now where'd the fuel bottle go.

2nd test run.