My Second $500 K75 Project

[Smudgemo]

Good call on the fan motor - I'll wait until it's running and I service the cooling system.  But I'm going to order a new fuel vent line and the wires because I'd rather mess around with fuel once and be done with it.  I'm not in a hurry.

This weekend I mostly just cleaned things up some.  While giving it a wash, I was reminded that the rear cowl lid had a broken tab and a PO held it in place with gorilla tape.  I got this idea somewhere, and it worked perfectly for a non-abs bike.


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It's just a bit of kit to mount a fender on a bicycle that I bent 90*.

[Smudgemo]

So I got it running today.  Lots of smoke initially (I did shoot some fogging oil in the cylinders last weekend), but it seems to run as well as my RT.  Who'da knowd fresh gas vs old gas/varnish/water was the ticket?

The one thing I'm not clear on is why so much moisture exited the muffler when it was running.  I noticed some dripping where the header and muffler connect before I tried to start it, and assumed it was somehow accumulated from sitting outside, but it seems kind of like oily coolant.  I need to get some distilled water to fill the system and let it get up to temperature, I guess. 

[Smudgemo]

I decided to add distilled water to see what would happen, and there's coolant getting into the oil.  The level in the sight glass was milky looking and went up, and the watery exhaust didn't quit.  I'm going to drain the oil and coolant and take a look at the pump.  Maybe the prior rebuild was done poorly or the shaft was reused in poor shape.

The engine had good compression when I checked, so wasn't ready to blame the head gasket, but the wet and smoking exhaust is making me think maybe.

[Smudgemo]

This morning I dropped the oil pan while investigating the pump, and yeah, that ain't so great.


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Still not sure this is the smoking gun, but the pump drive shaft is damaged, though not terribly.  Anyone have experience?  The weep hole had a blob of sealant in there, but wasn't attached and didn't seem like enough to block drainage.


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I also found a thread this morning where someone was getting large amounts of coolant into his engine and he apparently had a cracked block.  https://motobrick.com/index.php?topic=11379.25 Figured I may as well try and eliminate that as a problem so I turned a plug to fit the block, disconnected the radiator hose on the left side and poured a liter or two of water into the radiator hose.  The plug doesn't seal perfectly so I put a cup in the catch pan to segregate it from any real problems and went in to have lunch.


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So at this point, the engine had compression, it runs well, but it's getting a lot of coolant into the oil.  Is it possible the pump rebuild was done poorly and it really is the issue?  The only thing that looks iffy so far is the pump shaft and my desire to spend $200 on a replacement part, not to mention $50 for another rebuild kit.

[TriSpark]

Yay, it's running! Congratulations on getting that far with it so quickly. It's a great feeling when they come back to life again.

Re-reading the initial posting, and looking at all that water in the exhaust gas and the sump, I'm leaning towards the water pump repair being a bodge job. I think you are on the right track with that. Someone here who has done a water pump overhaul before should have the necessary know-how on that job.

Will the pump shaft polish up to remove the damage, or is too far gone? Did the seller say who'd done the pump seal work - them, or a bike shop?

[Duckbubbles]

I don't believe the water/oil pump can introduce coolant into the engine oil system.  If you will notice there is about a 10mm gap in the cavity between the waterpump seal and the oil seal inside the combined pump.  That cavity is where the coolant or oil leakage past those seals drains from at he bottom front of the oil pan.  The only place I see where that can happen is through the head gasket or a cracked block as mentioned before.

Frank

[Smudgemo]

Yeah, I think this one isn't the pump.  I pulled the exhaust and it was full of water.  The #1 pipe looks less carbon-colored, and using my cheap HF borescope, the #1 cylinder looks to have a bit of water in it, whereas the others are clear. 

I ran a leak down test again, and using about 50lbs of air I got:
#1 46/51
#2 46.5/51
#3 43/50

At this point, I'm leaning toward pulling the head off.  I'm already sort of questioning the state of the bearings as I have no idea how long the PO ran it overheated and with coolant in the oil, so other than a head gasket and a pump rebuild kit, I'm not planning to throw much money at this engine.  It looks like I can potentially grab a used one in a couple of places locally.

Things looked wet around the forward oil return.


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Moisture in the #1 cylinder.  Not the best unit, but it worked.


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[Smudgemo]

Saturday morning rolled around and I decided to start taking the bike apart and figure out what's wrong.  BMW was right, it is a pretty easy bike to work on.  Sure is nice to have access to the shop manuals and online knowledge as opposed to something newish that a dealer is required for help.

I got things stripped down pretty quickly so I could figure out what went wrong.


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As far as I can tell, the head gasket had a breach at the bottom of #1.


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Once I got it cleaned up, it looked like the casting was questionable.  Like the surface area in this spot was minimal, so maybe the overheat event didn't take much to create the problem?  I don't know, I'm spitballing.  I never opened up one of these engines before, but this looks pretty iffy for QA.


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I was also concerned that the head was warped, and maybe it is, but I have a granite surface plate in my shop, so I glued down a sheet of 1000 wet or dry and gave it a look.  Not shown, but I painted the surface with Dykem just to see.  It looks pretty good other than where some corrosion occurred.


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Everything else I took apart looks good, so I'm going to order the new head gasket and the pump rebuild kit, and see what happens.  I didn't notice any damage to the cam journals or the cylinder walls.