1984 75Hp 4 cyl questions

"Hi to everyone, new to the si

"Hi to everyone, new to the site , and looking for some help with my 75 merc. I bought this motor with a 16 ft Starcraft ss 160 this fall. I did not get a lot of history with the the purchase. The motor looks in good shape, but the prop was pretty beat up and there are a few nick and gouges in the skeg. I ran the engine in a drum of water, but it was hard to start and idled very rough. It went into forward and reverse smoothly. I decided to replace the water pump as a percautionary measure. After removing the LU I noticed there was a fair amount of up and down movement in the drive shaft ( no preload pin). After removing the water and base I was suprised to find no shims. I mearured as per the manual and inserted the proper thickness of shims then the pump base and still hat roughly the same amount of up and down play in the frive shaft. I removed the pump and base again and this time pulled out the upper driveshaft bearing cone and it is very badly worn, no more shine just a dull surface. Is it safe to assume the bearings and gears worn enough that the shaft has dropped down not allowing preload on the bearings?
I also did a compression test on the powerhead today and found them to be starting from the top down 140, 130, 140, 140 is this good? The other thing I noticed was the spark plug in #2 cyl has erosion of the whiter ceramic around the electrode, is this normal, and what would cause it?
I have included a couple of photos. the second photo of the plugs #2 is the second from the left.
"

"1. The driveshaft's up an

"1. The driveshaft's up and down play is normal. (The plunger is the only thing holding the driveshaft down!)

2. Idling only in cold weather, plugs NEVER warm up.

3. It's impossible to get an accurate color read of those gapless plugs, that's why I never use them.

4. IF there's water getting into the cylinder, the most likely culprit is a hole in the exhaust deflector plate. Just had to make a new one for my similar Merc 350 twin.

Jeff"

"Thanks Jeff, What are you ref

"Thanks Jeff, What are you refering to when you say the "plunger", And What do you recomend for plugs.

Thanks again for your help Glen"

The "plunger" is what

The "plunger" is what most people call that spring loaded thingee-ma-bob at the top of the driveshaft.

Look for an equivalent plug that isn't gapless. A good NAPA tech should help you out.

Jeff

"Thanks again Jeff, My drives

"Thanks again Jeff, My drives shaft does not have the plunger/ preload pin in the top. How critical id the torque on the nuts for the water pump. I do not have an in lb torque wrench and my foot lb one doen't go that low.

Glen"

"Again, I'm an Olde Mercs

"Again, I'm an Olde Mercs guy. THe LUs I've seen up toi the late 70s all have the plunger. You can tell if it's broken off by looking for its remains in the top of the driveshaft.

Jeff"

"If the upper bearing cone is

"If the upper bearing cone is under the bearing, the shaft should have a plunger. If the cone is on top of the bearing, the pinion gear forces the shaft upwards, against the bearing cone. Adding shims on the latter would increase the play in the shaft.

The nuts on the water pump do not need to be torqued. Tighten them until you feel that the housing is making solid contact with the base.
Specs would probably be 5-8 ft/lbs."

"Those spark plugs look stran

"Those spark plugs look strange to me. If they have been used for any length of time, I would say they indicate a problem."

"Thanks for the info evryone.

"Thanks for the info evryone. Jeff there are definatlly no pieces of a pin in the top of the drive shaft, The motor is and 84. Tony, the Bearing cone is pressed on the drive shaft, then the bearing race slides down over top and is held in place by the water pump base. The ne water pump that came in the replacment kit was 10 thou thinner on the bearing support lower part than the old one. From what I could tell this was allowing the bearing race to move up and down in the LU. What type of problem could the plugs mean, Leaking exhaust plate?

Thanks agin everyone.

Glen"

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