So I set about torquing the case halves together to get some bore measurements.
While overall things look round, even if I figure my measurements are just slightly off (due to user error), there is some variations in 1, 2, and 3 main and I didn’t even bother to look at 4.
I see no signs of case warping at the inner web seams, but the crank bore itself is someone off. It has to be.
The cam bores all seem fine.
I kept going back and taking measurements. I’m not all that great with these telescoping guages, but I think doing multiple sample measurements at different angles pretty much indicated that somethings off.
They are either within spec, very close to the wear limit for spec, or slightly off spec based on all the readings I took. I am pretty sure that though they appear round, they are slightly out-of-round enough to indeed impact the bearings.
In the future, I’ll invest in a dial bore gauge. That would have made this a far easier take I think. At least to determine the deviations in a quicker more concise manner.
I ripped it all apart and put in the bearings and the crank and lightly pounded on the flywheel.
With the flywheel on, I could turn the crank but I would not say it was a perfect spin.
I do believe that one or more bearings are in fact “crushing” a bit due to the slight out-of-round spec and are impacting the rotation of the crank.
At first I thought there was no loose end play (video), it felt tight, but as I worked the crank in the bearings more I got about a 2-3mm shift which is not good. Now I don’t have all the gears on so that may contribute. I’m going to try it with Murbella’s original crank which still have the gears on. I think the AS crank still does as well. We’ll see if that “slop” goes away.
However, that slop is not accounting for the tightness during rotation.
So. After reading, and some deep dives into Gene Berg documents, I think I’m going to get a new AS41 magnesium case. I noticed there’s sale on cases at AApistons and they have an aluminum case that is even less right now. Of course, the aluminum cases are a bit heavier than the AS41 cases.
I will shelve this case with Murbella’s stock stuff, and perhaps in the future have it align bored once so that it can be serviceable in an emergency situation should that come to pass.
The goal of this rebuild was to give Murbella an engine that will last another 100,000 miles. I’m thinking that a new case is in fact the way to go now.