Tuesday, August 7, 2007

Let's Back Up a Moment

In my continuing series on the Stroker Flathead Engine Build I find that I have inadvertently skipped a couple steps that I should have mentioned. My most recent post in the series, Stroker Clearance and Flywheel Balance , brings us to the point of assembling the flywheels. However, I never did get around to explaining what was done to "fix" the problem with the rods that I mentioned in the post on Joe's Flathead . So if anyone is actually following this series, they are likely wondering why I would balance the flywheels with rods that were too narrow not to mention cracked!

Well, the answer is that I wouldn't. Knowing the high cost of replacement rods ($513 from V-Twin) and the likelihood that the new rods would also need to be honed to round before use, we decided to do the best we could with what we had. I sent the old rods to be magnafluxed by a local gentleman who specializes in aircraft engines. This showed cracks as I had suspected. My aircraft engine specialist recommended having the cracks welded, re magnafluxed, and then shot peened. That was the coarse we chose to take. Hind sight being 20/20, if I had realized at the time that the rods had been ground narrower, then I likely would have gone with new rods.

Once the rods were repaired, new races installed, honed to round, and bearings fit, it was time to do an initial assembly of the flywheels to determine the width of the flywheel assembly. It was during this initial "mock up" that I discovered the huge rod end play.

The reason that I needed the crank width info had to do with the Pinion race in the crankcase which I also talked about in my post on Joe's Flathead . The race needed to be removed from the case due to being spot welded into the case; not exactly an approved procedure. I have found over the years that once you start replacing case races in these old motors, there is a pretty good chance that you will have no flywheel end play even with the thinnest of end play thrust washers. This is due to the replacement races having a wider inside lip than the originals. I often wonder if the manufacturers of these replacement parts never had an OEM part to work from, or if they just lack any measuring instruments.

In any case, I knew that with a new race going into the right side, flywheel end play had to be taken into account. My first thought on the rod end play was a shorter crank pin, (one is available) but that would not bring them together enough. My next thought was thicker flywheel washers (the ones that are staked into stock flywheels on each end of the crankpin). Of course the S&S flywheels don't have washers there, but I knew that the flywheels could be machined for them, so I called my S&S tech rep. He suggested that it would be just as easy for me to send the wheels back to S&S to have the tapers machined deeper into the flywheels to bring them closer together. So that's what we did.

Now by the time you add up the cost of machining the flywheels, magnaflux, welding, shot peening, and shipping, suddenly the new repop rods don't look quite so outrageous in price. Like I said about hindsight....

As for the right side case race, that also posed a problem. After cutting through the spot welds, the race came out very easily; obviously that was the reason for said spot welds. Upon measuring the race and case, it became apparent that this would take unusual steps to repair. The race was already a +.025 and loose. The only good solution I could think of was to bore out the case and sleeve it for a new standard race. That was accomplished by bolting the right case to the table on the mill with the cam side down, bolting the left case to the right and then indicating on the left case race. Once the table was locked down the left case could be removed for easy access to the right side bore. Then a steel sleeve was fabricated to be a press fit in the case as well as give a press fit to the new standard race. By the time the new race was line lapped to size, we had perfect alignment of the two races.

So that should bring us up to date with my most recent post in this series. In my next post in this series, I will try to get into some issues having to do with eliminating piston scuffing.

1 comment:

Jack Hester said...

I have an old Ammco rod alignment tool that my buddy Pat (local machinist) ground to fit the smaller diameter motorcycle rods. I also have a Van Norman magnaflux kit that I used, until the switch broke. Haven't replaced it yet. Don't know if the switch is still in manufacture, as the tool is very old. Like most of what I have for tools.

Anyway, I'm interested in the picture of the slotted female rod, and your reasoning behind doing it. I like the fact that the female rod slings oil up into the cylinders. I'm thinking that you slotted it for reasons of drag. That is, reduction of drag.

Jack Hester