I snagged my son for some 'quality time' this afternoon, and we did the chain replacement together, using my new tool. More on that in a moment. As promised, here are the dimensions for making one. Referring to the drawing, and the earlier shots of the unit, I'll add a few notes on how it was designed.
I first cut out the pieces from thick cardboard, the stuff picture framers use as 'mat board', to make the cresent shaped top part. After verifying the fit, the cardboard was used as a template to mark and cut the steel, which was scrap about 1/16" thick. This was tack-welded together.
The objective is to get a nice tight clearance, absolute minimum, between the top of the chain on the gear and the inside of the loader tool's curved top. I taped 1/16" cardboard inside the steel top piece to establish this clearance, as it sat on the chain/gear.
After making up the lower bracket pieces, I marked the position of the uprights relative to the top piece sitting on the chain/gear. With the spacers inside, that meant that the finished piece would have just enough clearance to allow the chain to ride inside, but impossible for the links to leave the gear teeth.
The rear support rod may have been overkill, but in use, the chain definitely smacks the inside of the top piece as it tries to jump out while the valve springs jerk the camshafts forward. Thicker metal would have made this rod unnecessary, but then the cutting would've been harder. I cut this out on my bandsaw and using a jigsaw BTW.
So, as my boy and I found out, it would be easy to jump a tooth or 2 if not for something like this tool, or very tedious using visegrips or tie-wraps. I maintained constant upward pulling pressure on the old chain as it rolled out, and even pushed down on the new chain as it entered the tool top piece as he slowly turned the engine crank. I left the rocker arms in, sparkplugs and tensioner were out. We finished the load in about 20 minutes. All my timing marks line up and the balancer pointer is at '0'. I'm ecstatic!
One more piece to replace (tensioning rail) and the oiler plastic thingies and it's button up time.
Last pictures are of my modified vice grips, for holding the cam solid while undoing/torquing those big bolts (100nm). I couldn't find a picture of the MB tool for gripping those nubbins. All my books show a square block and large end wrench.
