Greg Rudzinski, a liveaboard sailor in California, sent this note about the dangers of buying parts and why its a good idea to bring the old part with you and match it up with the new part.
“Here are two routine boat maintenance projects that went very bad for me as the result of incorrect labeling and cross referencing of parts. We will start with what happened when a shaft zinc was changed. First I double checked my shaft size at 1 1/8” then went to West Marine to procure a 1 1/8” collar shaft zinc ( Martyr brand made in China). To the eye the collar zinc looked about right but it split into pieces when I tried to tap it down flush to the prop shaft. Close inspection revealed the zinc was only 1” but marked 1 1/8”. When I checked West Marines inventory all the 1” Martyr collar zincs were identical to all the 1 1/8” collar zincs. Something was very wrong here. I got my money back but lots of people are going to get frustrated when they spend half a day doing something that should only take minutes. Changing an oil filter on a M50 Universal resulted in trouble as well. The filter on the engine was a Kubota 70000-43081 which are no longer made. The cross reference chart replaces it with a Kubota 15213-32090. This filter did not seal properly onto the Universal M50 flange and blew a few quarts of oil all over the engine and engine compartment. I am now using Baldwin B-163 filters with better luck.
“So what did I learn out of these experiences. Well do not trust size labeling or cross referenced parts without triple checking size and fit. The new boat maintenance plaque now posted aboard reads if the part doesn’t look exactly like the right part then it isn’t the right part.
“There is no substitute for the right part and the right tool. I was finally able to install the correct collar shaft zinc on my second try. This time I took the correct old zinc to the chandlery to be absolutely sure of size when purchasing a replacement. Over the years I have noticed that zincs with a lock washer and nut perform better than those with just a bolt that goes into a tapped portion of the opposite half. Here is my latest blog post showing a 1 1/8” zinc (the correct one with nut bolt and washers. To avoid losing the all important nut to the ocean depths place a pinch of Handitack (superglue product) into the nut pocket on top of the nut.”