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Panigaliscious
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9,103 Posts
Discussion Starter #1
After more time has passed than I care to mention, I finally swapped the engine in my 1990 851 with a used unit from a 1991. I originally was going to rebuild my old engine with undamaged cases after a broken chain runied my alernator cover and left side case half, but as luck would have it a good used one became available.

Many months ago I had removed the water pump and alternator cover and stator to assess the damage. Yesterday I finally got around to pulling the old engine and putting in the new one. Quite a job for one person but with a little forethought (and a couple of jacks) the engine is now in place with all electrical hooked up, except two things.

1) For the life of me I cannot find the connectors for the alternator leads. I may just be tired after spending hours in a hot garage but I have looked and followed the rat's nest of wiring harness. I know they must go directly to the regulator/rectifier (red wires I believe), I just can't find them. If anyone can tell me precsiely where they are on your bike I would very much appreciate it.

2) On the back of the engine, right side, is a sensor of some sort. If you were looking at the clutch cover it is at about 11 o'clock position with the wire leads exiting toward the back of the engine. I disconnected this one as I removed the engine but failed to note how it connected to the pair of wires. The sensor has one wire green/yellow and the other red/white. What is this sensor and how does it match up to the wiring harness?

Thanks in advance.
 

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Senior Member
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2,737 Posts
The sensor on the back of the engine is the neutral switch.
Theoretically it shouldn't matter which wire connects to which pole on the switch.

As it's a 90 vintage I'm sure it's a single phase stator. Same thing here. Both generate AZ power and pass it to the rectifier. Note that the red on most rectifiers is the DC output and is not to be connected directly to the stator.

Check your schematic to be sure on both issues.
 

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He with the senior member
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5,671 Posts
On the 748/916/996 motors, there are 2 sensors with the same connectors, that can be inadvertently swapped - the neutral sensor and the oil pressure sensor. If the 851 is similar, and you see an oil pressur elight when you start up, but then go off when you click into 1st gear....swap them! :)
 

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Panigaliscious
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9,103 Posts
Discussion Starter #4
Got everything hooked up tonight. Neutral switch was as everyone said. Finally found the male end of the alternator wiring tucked under the main harness on the left side. They were right at a joint in the trellis frame and so happenned to also be right where a tie wrap was holding everything to the frame.
 

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Panigaliscious
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9,103 Posts
Discussion Starter #6
Update

The engine is in, fuel lines replaced in and out of the tank with a new fuel filter.

Filled cooling system with distilled water to check for leaks rather than leaking antifreeze everywhere. Luckily nothing leaking.

Fuel pump wasn't running (it was dry in the tank, probably gummed up with varnish). A couple of days soaking in new gas and it is running fine.

The bikes hasn't started in years, so with some trepedation and a new (to me) engine I double-checked everything and hit the starter.

Whump whump whump whump whump for about 30 seconds.

Engine finally caught and settled down into a nice idle after nursing it for another minute or so. Let it warm up. A couple of oil leaks, but they were just the plug where the oil pressure sensor on my 1990 was (different location on 1991 engine) and the banjo bolt on the oil line to the vertical cylinder. Tightened them up after it was warm. No more oil leaks.

Water seems to be circulating fine. Temp gauge working. Oil pressure light off (it was leaking from vertical cylinder as well so I assume good pressure). Alternator charging as it should.

Time to take it for a spin around the neighborhood with just the tank and seat on it. I had forgotten how tight the legroom was on this thing. At 6'2", this was not designed for me. Compared to my 999 I just sold, the newer bike is a sport-tourer. I forgot how raw and primitive the 851 is, it crackles when you chop the throttle and where the Termi on the 999 was throaty at low revs and got progressively louder as revs rose, the FBF pipes on the 851 go from merely loud to pounding. At idle I wouldn't be surprised if it was louder than the 999 at redline. It is that big of a difference.

Front end feel on the 851 was just as good as I remember. Even with the old M1R forks (but new Bridgestones), I really think the 851 has better feel the 999. I might even lower the forks a bit (taller front end) to find a balance between how it falls into turns now and what the 999 felt like.

One problem remains that I will hopefully rectify this week. One of my front calipers is leaking, so a rebuild kit from yoyodyne will be needed and a couple of hours later I can put the bodywork on again. I'll change out to antifreeze and probably replace the battery although it seems to be working fine, but just to be sure.
 

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Panigaliscious
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9,103 Posts
Discussion Starter #9
This morning I'm looking for the rebuild kit. Typical sources are out of stock at the moment (Brembo kit p/n 120.2799.10). I can find the pistons several places, I found another place (racing kart site) that has them listed. We will see if they are available. Yoyodyne gave me a month lead time minimum :banghead
 
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