Seeking upper crank bearing for 25 hp Chrysler

[Motor Boater Bill]

My buddy has a 1970's 25 hp Chrysler. I think it has a bad upper main bearing. When we had the flywheel off you could see where it had been hitting the magneto. When running, it made bad "rocks in a can" noises above about 1/3 throttle. I have the parts list online, but the upper main bearing is NLA. The original part is 31-F458028. Any ideas where I could find one of these?

Many thanks!

Motor Boater Bill

 

[WillyBWright]

Re: Seeking upper crank bearing for 25 hp Chrysler

It's probably made by a bearing manufacturer like Timken. Get the numbers off the bearing itself (they'll be different than the Chryser numbers) and get from a bearing specialty supplier. There are businesses that sell nothing but bearings and seals.

 

[Frank Acampora]

Re: Seeking upper crank bearing for 25 hp Chrysler

Definitely a standard bearing! An automotive part. As above get at a bearing supplier.

Only thing is you need a press and a special puller to get it off. The puller is a massive flat split part with a gentle taper at the hole to get under the bearing outer race.

To put the new bearing on, place it on a 100 watt light bulb for about 15 minutes. Use a glove and it will slip right on. The bulb gets it hot enough to install easily but not hot enough to damage it.

 

[Motor Boater Bill]

Re: Seeking upper crank bearing for 25 hp Chrysler

Thanks for the information, Frank.

Do I understand you to be saying that changing the bearing requires a complete disassembly, or is it possible to change the bearing without tearing the motor down? I've never worked on a Chrysler.

Many thanks!

Motor Boater Bill

 

[Frank Acampora]

Re: Seeking upper crank bearing for 25 hp Chrysler

Unfortunately, the upper bearing is held between the two crancase halves and is a press fit on the crank. Complete disassembly is required.
Tools needed are: 9/16, 7/16, 3/8 wrenches. Flywheel nut is (Ithink) 3/4. Con rod cap screws are 12 point 1/4 inch socket. You will need assorted screwdrivers, and a flywheel puller would be nice but not an absolute necessity. It is possible to remove the flywheel without one. To reassemble, con rod cap screws must be torqued to 165 to 175 inch pounds. Flywheel nut is 55 to 65 foot pounds. All other bolts take standard torque values for their sizes.
Disassembly and reassembly is relatively easy: This is a simple engine. But before going through this, try to rock the shaft back and forth. There should be no play in the bearing side to side. A worn magneto plate bearing (bronze bushing) or loose screws holding the magneto to the plate will let the magneto core(s) hit the inside of the flywheel.

 

[Motor Boater Bill]

Re: Seeking upper crank bearing for 25 hp Chrysler

Thanks for the tip on the magneto plate, I'll check that for sure.

No worries on the tools--got plenty of these toys, as well as inch-pound and foot-pound torque wrenches. By the way, there are no holes for a puller on this flywheel, it is apparently designed for the prize-it-up-and-tap-the-crank-nut method, which does work. Of course someone doing this with less than finesse can wreck havoc on the innerds.

I've been looking at this parts list:
http://www.mercruiserparts.com/Show....1/16.png&inbr=1726&bnbr=120&bdesc=POWER+HEAD

On this diagram, part #3 is a "crankshaft bearing cage" which I was thinking holds the bearing and could just be unbolted. Not so?

Many thanks!

MB Bill

 

[Frank Acampora]

Re: Seeking upper crank bearing for 25 hp Chrysler

Yes and no. This "cage" holds the top crankshaft seal, and holds the bearing down and in between the crankcase halves. This top ball bearing is the only ball bearing on the crank and locates the crank properly in the crankcase. That's why it is a tight press fit on the crank and held down by the cage. If I remember correctly the cage is held on with four fillister head screws and it is also part of the magneto carrier plate bearing. Depending on model, it will also have either a gasket or O ring seal.

On top of the flywheel there should be a pressed steel ring for the rope starter. This ring has three dimples on the bottom which fit into three shallow holes on the flywheel. These holes can be drilled and tapped for a puller. (with the wheel off the engine)

 

[Motor Boater Bill]

Re: Seeking upper crank bearing for 25 hp Chrysler

Yes I saw those dimples and had that thought of drilling them, but obviously in it's original configuration it isn't made for a puller. There is a nice solid boss on the case to pry on and the nut is big and solid with a reasonable striking surface, so clearly the design does not assume the use of a puller, although that is always my preference. It did come off easily last time with a series of pretty light taps as I rotated the flywheel a third of a turn at a time, but of course I don't know if the nut had been torqued to specs previously. I torqued it to spec when I replaced it after the initial inspection and point adjustment.

Thanks for all the help, Frank. If we determine it is the bearing (not the magneto) I'm sure I'll be back in touch. It will wait until we find a day that I don't have too much other stuff on my list and he can bring the motor over here (he lives a half hour away). And in the meantime, he can use his old Evinrude 15!

Regards,
Bill