PS Advisor 03/01
Gearbox Seepage & Sealants
A friend and I both own Pearson 424s with Walter gear boxes for the “V” drive. The gear box has a water passage on top for cooling. It uses sea water. When we bought the boat in 1997, the top of this water box was nicely sealed, with no seepage. After removing the top plate and cleaning out the scale, I added a zinc to an available plug hole. When replacing the cover, I used a new gasket from Walter and coated it with RTV. Now both my friend’s gear box and mine have what appears to be a white salt line around the joint of the cast iron top plate. My friend’s dipstick fell off. Mine is starting to show a similar problem. The dipstick goes through the top plate and in a corner of the gear box. My question: What sealant should be used when joining cast iron parts exposed to sea water?
Don Chaternuck, an engineer at Walter Machine in Jersey City, New Jersey, said no sealant should be used with the gasket, which is a seal. He said RTV (besides not being needed) becomes hard and brittle and can shed particles that damage the gear box. He said Walter recently saw one on which RTV had been used that in six months scratched up the bearings so badly that it looked like they’d had 20 years of hard usage. Chaternuck said your friend’s dipstick problem is not related to the sealant. He said the dipstick is aluminum, sealed and isolated by an O-ring. After simple wear from years of use (he figured your Pearsons were about 20 years old), the dipstick and the O-ring should be replaced. If you have problems, give Chaternuck a ring at 201/656-5654.
Do you have a recommendation about starting a diesel engine that has not been run for several days? Some friends recommend cranking the engine with the kill switch engaged for a few seconds to distribute oil to the cylinder walls and other wearing surfaces. My yard manager suggests instead to crank the engine for a few turns with the compression levers open to relieve pressure before starting, while others scoff at both practices. Are either of these techniques helpful and worth the effort?
I don’t think there’s much to be gained by turning over an engine to throw oil around when it has only been days or a week since the last start. It can’t hurt, but seems like kind of a pain.
When we attended a Perkins diesel school some years ago, the instructor (from Perkins) said you could start the engine and let it run for 5 seconds and shut it down. Wait 10 minutes and start again. It would probably make more sense to throw the compression levers, but that necessitates opening up the engine box, etc. It also means turning over the engine from the cockpit (presumably), and having the engine turn over with someone nearby (risk of hand in belt, etc.).
We wouldn’t bother with any of the above. Just change your oil and filter often, plus fuel filter, and you should get long life from any engine.
Questions on your article in the October 15, 2000 issue. 1. Are the quoted “Amp-hours @ 20-hour rate” the TOTAL (100% capacity) rated amp-hours, or down to 50% of capacity? 2. What are CCA and MCA?
Amp-hours, 20-hour rate is the amount of energy that a battery can deliver over a 20-hour period, at a constant rate of discharge, before the battery drops to 10.5 volts. It’s an industry standard test. CCA means cold cranking amps (number of amps a battery can deliver for 30 seconds at 0°F); MCA is marine cranking amps and is similar to above except at 32°F. Sorry we didn't explain this in the article.