There should be no play at the radial drive. If the radial is installed properly (bored .003” undersized), when it is tightened in place it should not move. The key only serves as a secondary fixture to prevent the drive from turning on the post if the interference clamping is damaged. The key should also be stainless for strength and to mitigate corrosion. Brass or bronze keys are soft and not appropriate. It is possible to damage a rudder stop or bend a radial through an accident or misuse, but that would not effect the centering of the wheel. Only the position of the chain on the sprocket can do that. Damaging a rudder stop may allow the chain to become derailed from the sprocket at the chain to wire joint if the chain runs off the end of the sprocket. Pulling it back the other direction could result in a misalignment if the chain.
For what it’s worth, jumping one tooth on a 13tooth sprocket will result in a 20 degree wheel offset... Chuck Sent from my iPhone > On Jan 24, 2018, at 2:33 PM, Michael Brown via CnC-List > <cnc-list@cnc-list.com> wrote: > > > > True, though note that very little play at the radial wheel keyway is > required. > If your rudder swings 80 degrees and that takes 3 turns lock to lock ( no > idea, just an example ), > then 1 degree on the rudder is 13.5 degrees on the wheel. If your rudder post > is 2.5" diameter then > 1 degree is less than 1/32" of play. > > Other than taking everything apart on Windburn I have only looked at two > other drives > systems. Both had been damaged and had some play in them. On one it was > a similar observation, the center mark on the wheel was no longer straight > ahead. My guess > is while in full reverse the wheel was let go and slammed over against the > stop hard > enough to shift the radial on the shaft. The key was brass or bronze and was > damaged. > On the other one the keyways were not the same size, maybe out by 0.02" or so. > > It is not always easy to get in and make good measurements. > > That allowed the radial to move, polished the fit a bit and the drive system > slipped > down enough to cause alignment problems. > > I take it from your advise that everything was engineered to be a very tight > or interference > fit. The ones I looked at were not but I couldn't tell by hand. Still, 20 > degrees is a lot. > > > I did take the plate and idlers off of Windburn, had them sandblasted and > coated them > with POR-15. Came up as hard as rock and looks to be a good solution for > rusting steel. > > > Michael Brown > Windburn > C&C 30-1 > > > > > > From: "Chuck Gilchrest" <csgilchr...@comcast.net> > > Michael, > > A 20 degree deviation on wheel centering is an AWFUL lot of wheel travel with > no explanation. I suspect Bruce?s boat has a 44? diameter wheel which means > at 20 degrees of travel, the Turk?s head knot would have moved roughly 7 ?? > to one side or the other. Generally speaking, if my hand moves the wheel > that much, the boat changes course dramatically, even with a big wheel. > > Most C&C Yachts had radial drives that are held in place on the rudder shaft > by an interference fit of the two halves of the radial, machined undersized > by .003? for a machinist clamping tolerance and then a keyway is cut in the > radial drive to accommodate a stainless key that locks the drive wheel in > place on the rudder. Generally, even if the boat is run aground on the > rudder, the radial drive wheel or rudder post may bend, but it won?t slip on > the post unless it is not clamped tightly at the hub of the wheel. > > I too suspect a weakened idler assembly that is allowing the idlers to pivot > after tensioning. The next step is the idler wheel letting go and dropping > various bits into to the bilge whilst the cable goes completely slack. Boat > handling suffers when this happens.. > > Chuck Gilchrest > > Half Magic > > 1983 Landfall 35 > > Padanaram, MA > _______________________________________________ > > Thanks everyone for supporting this list with your contributions. Each and > every one is greatly appreciated. If you want to support the list - use > PayPal to send contribution -- https://www.paypal.me/stumurray >
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