It's been a productive couple of days in the ol shid and this project is now very close to finishing
Con rods are done and the final bits - the needle valve parts are near finished too.
Given current comments in other posts regarding lapping and thanks to Achim I spent a bit of time running through my old post on the subject. Nothings changed and these three, like all the other engines described before, have followed exactly the same path. No point in running over old ground in detail then.
One of the previously made laps was recycled by turning a few thou off
The liners were lapped before dealing with the pistons. Lapped with successive grit (320, 600, 1000) until the plug gauge would ease in to just below the exhaust ports.
A piston lap was turned until the liner plug gauge was an easy fit then split and drilled and tapped for a closing screw
The pistons were turned to a fine finish .05mm more than the plug gauge then lapped until they would enter the bore as the plug gauge ie just below the exhaust port.
They were then lapped by hand to their respective liner using minimal amounts of 1000 grit and plenty of lubricant. This is a slow, time consuming operation that cannot be rushed. Patience is the key and mine is usually just about running out just as the piston skirt reaches the lower exhaust face
As mentioned previously it was only after the second had been done that I noticed the top of one piston appeared distorted - I pushed it with my finger at the same time the brain realised what had happened
Three new ones were made with a slightly more substantial top thickness and lightening them by extra milling inside. These were then lapped as previous leaving them a tight fit at the top of the bore. Further fine lapping will get done on assembly.
Conrods were made from Alumec 85 a tough grade of ali via a local factory tool room. All above board unfortunately 'my supplier' has now retired so that will now become a diminishing resource
. Cut from a slab the pices were milled to square section before rough turning and drilling and reaming.
The big ends were formed first - using a previously made form tool. The position is set 'by eye' ensuring the lands either side of the hole are equal - hence the ink
A fair result for a home made cutter I'd say - always get a buzz out using a home made cutter when it works well. Simple milling and usual H&T - GFS quenched in oil and not tempered.
First stage ok
The little ends were done in similar fashion - the shank taper turned at 1* via the topslide
This gives a better idea of settiing 'by eye'
To finish the parted off pip a split tapered 'collet', a remnant from the ETA build was used to hold the shank.
It looks like the finished rods disappeared into their respective boxes
- may be tomorrow eh - but here are the last but one pieces - just the shim steel ratchet springs to make and assembly can begin
That's it from the ol shid for tonight - it's been a busy two days but tomorrow's a day off. Hopefully these could see some diesel fuel next week
Hope you've enjoyed this latest update
Regards - Ol Tug