Oil or Grease?

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Seamule

Cadet
Joined
Apr 21, 2002
Messages
16
I'm rebuilding a 91 50hp Yamaha and my Clymer's manual says to oil the crankshaft bearings before reassembly. My question is would it harm anything if I greased them instead with a high temp grease vice the oil? Pro's and cons would be helpful. Thanks!
 
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russthemuss

Petty Officer 2nd Class
Joined
Jan 16, 2002
Messages
101
Re: Oil or Grease?

VERY HARMFULL!<br />The engine relies on its lubrication from the oil fuel mixture which is floating around inside your engine crankcase.If you grease parts ,it prevents this lubrication.Grease will not stay where you put it as the FUEL droplets in the vapour will wash it out.You will have a fuel/oil/grease mixture burning in the engine.Wow think of the smoke!and the big bang later!
 
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Seamule

Cadet
Joined
Apr 21, 2002
Messages
16
Re: Oil or Grease?

I thought the same thing but wanted someone else to tell me that! It just baffles me that the oil injection system on these motors is enough to lube the crank bearings and even the needle bearings in the rods. I guess I've just worked on too many car engines and still expect a bath of oil on the crank! Thanks for the reality check!
 
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Spidybot

Lieutenant Commander
Joined
Apr 4, 2002
Messages
1,734
Re: Oil or Grease?

This is why good quality oil is needed. I got one once, for a high-performance two-stroke (cart) that did not keep the specs on the can. The oil evaporated (burned) at too low temperature. This meant, that already in the crank the oil disappeared and after a few minutes killed all bearings, bushes, shims and whatever moved inside.
 
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DJ

Guest
Re: Oil or Grease?

Seamule,<br /><br />Actually, two stroke engines are very well lubricated. Most die of neglect or clogged carburetion systems long before they wear out. There are folks on this board that have outboards with 2000+ hours on them.<br /><br />Good oil is the key. Use a marine TCW3 rated oil ONLY. You can use some of this to lube your needle bearings during assembly. It will also help keep them in place while you're working. A bit messy.
 
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petryshyn

Commander
Joined
Oct 3, 2001
Messages
2,851
Re: Oil or Grease?

The real danger of using grease as a assembly lube is cause it won't wash out quickly. If grease is allowed to reside on the crank, it tends to stick the needle bearings in place and promotes sliding rather than turning. This results in flats being formed on the needles which causes premature bearing and crank wear...
 
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