So, I got my block/case back from the machine shop. It was worth every penny to have a professional with a CNC milling machine do the work of drilling out the two broken studs. His work was incredible and he went as far as to countersink the holes slightly for the TimeSert barrel inserts. Nice, clean and straight holes, important details:
With that done, it was time today to tackle installing the TimeSert barrel inserts that will make up the replacement threads for the head studs on these two holes. I've spent more hours than I should have pondering this critcal step, but it wasn't nearly as difficult as I allowed my imagination to believe it could be.
TimeSerts are an elegant solution for replacing damaged in-hole threads in a variety of materials. They are in my opinion much better than Helicoil wound wire inserts. I ordered the TimeSert install kit from Clark's Corvairs and the recommended length (0.75 inch) TimeSerts from a local industrial supply shop. The kit contains all the tools you need to install these:
First step, drill out the hole to the correct size. The importance of having this hole straight can not be understated. Although drilling aluminum is easy, best to use a drill press:
The brand new bit that came with the kit was very sharp and made short clean work of the holes.
Next up, the shoulder countersink bit. The countersink the machinist put in was quite deep enough. The bit has a cutter which creates a countersink shoulder for the top end of the TimeSert allowing it to sit flush on the surface. Again, the drill press is the only smart way to do this:
Careful application of preasure on the very sharp cutter results in a nicely formed shoulder.
Next up, threading this aluminum hole with the tap provided in the kit. This tap (also brand new) has four cutting flutes and a flat nose to ensure the hole is completely threaded to the bottom. This is delicate work that is only done by hand, so it was important to make it perpendicular to the case, ensuring straight threads in the hole. I used lots of 3-in-1 oil to ease the tap through and keep the threads clean from debris. The secret is to cut 1/2 a turn, back out 1/2 a turn and repeat:
Once both holes are tapped, it's important to ensure they are cleaned out of any cutting debris. A blow gun and compressor is perfect.
At this point everything looks good. Next up is the insert mandrel.
What makes TimeSerts so effective, is their engineering. The bottom couple of rows of the insert are formed in a way that allows the insert mandrel to cold-roll the threads, pushing them outwards and into the surrounding material, locking the insert in place:
First, a couple drops of oil on the mandrel to ease the insert forming the new threads, then thread the insert partly onto the mandrel:
Once placed in the newly cut holes, the insert threads in easy, up to the shoulder stop. Continue moving the mandrel forward (in) until it bottoms out:
Back the mandrel out and the TimeSert stays in place, now permanently attached to the aluminum walls of the hole. Looks perfect!
Was it really that easy? YES!
After cutting the matching threads on the two upper (long) studs that will be used with these inserts, I test fitted one. A good clean fit that will be made real strong with LocTite 620 as per the conversion manual.
I can't explain how relieved I am to be past this part of the head stud saga. Next steps will be fastening all the studs in permanently with LocTite 620. Before that, I need to clean the block completely as there are still areas that can use some detail attention. The suggestions are to either hot tank the block at a tranmission shop, use varsol with stiff brushes and 3M pads or maybe media blast it. Ron has a sandblasting machine, maybe that would be easiest. More food for thought.
The other task I completed was the removal of the oil pick-up assembly. It is press fit into the aluminum:
A little gentle tapping from the oil passage end of the block witha pirce of dowel, and it came right out:
Overall, a very productive 3 hours. I'm tagging this blog entry as a milestone because it has been bugging me for months to get past it. Barring any further surprises, this will be my airplane engine.
Now back to making other airplane parts :)
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Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.