Reinstalling flywheel question

[VaSteve]

I failed to mark the flywheel and crank for relation before I took it off as per the clymer manual.  So I followed the instructions for a "new" flywheel....line up the OT with the mark on in the inspection hole after setting the cylinders to TDC*.  Well, the cylinders are off, so it was rather easy to ensure they were all the way extended.  

But, its hard to use that mark in the inspection hole as an "exact".  It didn't line up perfectly.   Then again, there's only 5 bolt holes, so I'd be at least 72degrees off had I used any other mounting position.

Am I overthinking this?



* Also, the book says to use the allen bolt on the alternator to crank the engine.  I have it "blocked" per everything I have ever read...Odd a repair book wouldn't address that.  ?

[Barry]

Am I overthinking this?
 

Maybe - finding TDC accurately to within a few degrees is near impossible without using a dial gauge with the heads off or a piston stop and degree wheel. The reason it is so difficult is because as the piston approaches TDC it  only moves .014" over the last 10 deg of crankshaft rotation.  Over the last 3 deg of rotation it moves only .0015".

The piston stop method works more accurately because at say 40 deg before TDC the piston is moving almost 3mm for the same 10deg crankshaft rotation.

Edit

Steve

There is a recent thread on the ABC airheads list which mentions the flywheel fixing bolts having to be centered in the holes so presumably there is some slack perhaps enough for the flywheel to be a degree or so off either way.

BTW I've never seen a published figure for the conrod length. If you still have the barrels off could you measure/estimate the length centre to centre. Just curious for an approximate figure as it has an impact on the piston position vs crank angle calcs and I had to guess the length.

[nhmaf]

I agree with Barry.  If you can, I would suggest putting each of the 5 flywheel bolts into place and just snugging them up finger tight first before torquing them in a cross-pattern sequence.  That way you're most able to get them all centered before tightening things down.