Re: '76 Merc 850 Wrist Pin Needle Bearings Question
Those crank ball bearings are pressed on pretty hard. I've had success in the past removing the lower bearing with a gear puller. If I recall, I had to grind a flat in the end of the jaws so they'd fit against the back side of the bearing.
The upper bearing is quite tight and I don't think there's any way to pull it off without the 'wedge plate' type of puller. You can find a very basic one of these for fairly cheap and use it with a harmonic balancer puller.
When you're installing these bearings, don't drive them on. They must be heated then installed quickly. Lightly oiling the crankshaft will help them slide on easily. As soon as they hit the crankshaft they will cool and form an interference fit on the crank journal.
If you don't get the bearing fully seated, all is not lost. You can drive it home but you need to get a piece of pipe or other suitable driving device which only touches the center race. Never put pressure on the outer race or you'll ruin the bearing.
I use an old toaster oven to heat up bearings, be sure you use some thick gloves! If I recall I heated them up to around 200 deg F, don't go hotter than 250 as you can damage the bearing.
The bottom bearing is a "206" (aka "6206") unshielded, the top is a "5206". You should be able to get these thru your local auto parts store or local bearing supply.
If you find a smokin' hot deal on eBay or elsewhere on shielded bearings, just pry out the shields and wash out any grease you find. They'll work as well.
The Merc bearings are great but more $$$ and aftermarket bearings such as BCA or SKF are of no less quality.
Here's some interesting info on bearings:
http://www.hartheat.com/docs/Bearing Failure Information.pdf
HTH & Happy Rebuilding.........ed
