Post by: Smudgemo on August 18, 2026, 02:30:31 PM
I just happened to see the CL post one day, and it just happened to be a couple of miles away, so I went to look.
Seller stated: K75 Was running nicely until about a year ago. Turns over but won't start. Best theory of an non professional is this: Began to overheat determined that a seal on the water pump was bad (coolant in the oil), the seal was replaced and it ran again but poorly. More coolant in the oil and then it wouldn't run again. Best guess was the head-casket went bad during the orginal overheating.
Don't have the time or skills to attempt a fix. Lots of nice parts. Oher than the major engine issue it is in good shape. The seat and cases are probably worth the price of admission.
So the seat is a Corbin and appears to be in okay shape for the amount of time it probably sat outside uncovered, and the plastics (not all shown) at first glance are okay, but I don't think the cases are original because design and different key (school me if I'm wrong.)
Anyhow, first order of business is to remove the plastic, drain the tank and start poking around the oil/coolant pump to see what clues I can find. Seller's son apparently bought it from a friend less than two years ago, and rode it all of about 40 miles before it crapped out. Probably lucky for him. The tires are nearly 25 years old and I noticed a large sidewall crack on the front when looking for the date code.
The plan so far is get it running properly, and then decide. Either I go through things fully and make it really nice, or I just do enough to make it a safe and reliable beater. Knowing me, I'll probably take it too far. I usually do.
Oh, and props to Uhaul and their $30 moto trailer rentals. Complete enablers in this hobby we have.
Post by: Edward on August 18, 2026, 03:25:11 PM
Post by: Laitch on August 18, 2026, 05:10:15 PM
Anyhow, first order of business is to remove the plastic, drain the tank and start poking around the oil/coolant pump to see what clues I can find.Do a compression test. Probe into the pump weep hole to verify it isn't clogged.
(https://motobrick.com/gallery/4/1601-220726134848.jpeg)
Post by: Smudgemo on August 18, 2026, 06:15:43 PM
Just sitting on it, I like not having my knees hitting the RT's fairing, that's for sure.
Post by: Edward on August 18, 2026, 08:07:13 PM
Post by: TriSpark on August 19, 2026, 11:33:12 AM
I'm sure you can get it running again and enjoy some riding time on it. It looks good, maybe just a bit neglected. How many miles on the clock?
Also a thumbs up from me for U Haul and their cheap to rent bike trailers, I've used them many times to pick up my next money pit around here.
Post by: Smudgemo on August 19, 2026, 12:24:04 PM
I pulled the fuel filler cap and I can see rust down low, so I'm going to clean it out and look for damage. Maybe the filter is clogged and the coolant wasn't the problem. That would be funny.
Then I figure I'll drain some oil as it's at the top of the site glass to see if there is coolant present. That will make me feel better about turning it over to look for spark and checking compression.
After that I'll dig into the water pump and see what sort of mechanic the PO was.
Post by: Edward on August 19, 2026, 01:05:32 PM
Post by: TriSpark on August 19, 2026, 03:18:46 PM
Looking forward to hearing what happens next.
Post by: Smudgemo on August 19, 2026, 03:26:38 PM
Yesterday I ran a bit of brazing rod up in the weep hole and a couple-three drops came out. Dumped the overflow tank into a jar and the coolant is very blue and has lots of particles slowly settling (bottom of the tank has white-ish gunk to be cleaned out which is what the particles are, I think.)
There doesn't appear to be any oil as I'd expect it to be floating on top. I did get a gallon jug of parts store anti-freeze that isn't very old in the sale, and it is down just about the amount I have in the jar. There are also some used parts that suggest a pump seal kit was installed.
Makes me wonder if the overflow bottle was empty and it was the only thing that got refilled. The whole system takes less than a gallon, so I would expect most of the bottle to be used up unless the old stuff was dumped back in after the pump was worked on. Not sure why anyone would do that, though.
Puzzles are fun, aren't they? I'm dying to dig into this project, but there's too much work to do the next few days. And I have to get over to DMV for the title process - worst part IMO..
Post by: Edward on August 19, 2026, 05:19:26 PM
Post by: Smudgemo on August 19, 2026, 06:04:37 PM
I gave the coolant hose that runs through the crankcase cover some squeezes and I didn't hear anything that would suggest there was coolant in there, which would explain why the jug of coolant was still 2/3 or more full. So I pulled the hose at the pump and got 10-12oz of pale coolant with some crud, a stale smell and a bit of oil. For comparison, I got about 16oz from the overflow tank so I don't think the PO bothered to refill the system, or just thought he did. Does the pump burn up when lacking coolant? Might be good that it didn't run for him.
I just did the actual math - the title says 32,068 and the odo shows 32,086, so the PO got all of 18 miles of riding before things shut down. What a bummer. For him.
Post by: Edward on August 19, 2026, 07:50:02 PM
Post by: Smudgemo on August 20, 2026, 11:19:25 PM
Compression and the fuel delivery next. Maybe compression first because it's fast and I'd like to know why the seller mentioned a head gasket in the ad. Hopefully clueless instead of coy?
On the plus side, I was led to believe the bags were on a different key. Turns out I got two folding keys and one regular and they fit all the locks (though two bag locks are missing), so yay! I also got in and out of the DMV fast (!) for only $59 for non-op when the online calculator primed me for a $390 hit, so shout-out to the PO for not letting the reg expire.
The only hiccup was the DMV guy spelled my name on the title with an n instead of m. Upon noticing at home (of course) the DMV chat person said I could get it fixed only in the office and once the title arrives by mail, so I typed "thank you" but was actually thinking "No thank you." Close enough.
Post by: Laitch on August 21, 2026, 07:40:53 AM
Post by: Smudgemo on August 22, 2026, 08:24:52 PM
I also noticed the crankcase breather z-pipe was wrapped with electrical tape, so I guess I should replace that and remove it from the potential issues.
I drained the fuel and there was quite a bit of goo in there, possibly water it seemed when the siphon first started, but now it's in a bucket and I can't tell. I need to clean out the tank, but the pump looks fairly new (clean and shiny, and the rubber damper isn't all melted looking.) Fuel cap is crusty and needs a new gasket and rebuild kit.
20260822_174044667_iOS.jpg (68.65 kB . 768x576 - viewed 193 times)The valves are all tight, so that's not ideal, but nothing looked smoked. I took the time to measure the shims and I'll order some replacements.
The oil that spilled out from the cover didn't look great, and the cover had the gunk in the photo in the upper rear corner. Strange.
20260822_213049544_iOS.jpg (61.92 kB . 768x576 - viewed 208 times) 20260822_212929878_iOS.jpg (74.28 kB . 768x576 - viewed 194 times) 20260822_212906190_iOS.jpg (93.58 kB . 768x576 - viewed 197 times)Post by: Edward on August 22, 2026, 09:54:58 PM
Post by: Smudgemo on August 22, 2026, 10:22:08 PM
alright I'm done
Something I said?
I pulled the cap, it's a bit crusty and there's no coolant in the system. There's no sense in buying parts and refilling it yet as there's no rush to get this thing going. I'm just taking inventory of what I find and putting together a shopping list.
Post by: Laitch on August 23, 2026, 09:44:47 AM
An Italian tuneup—as you have suggested—might sort out this Brick. Stranger things have happened. 112350
Post by: Smudgemo on August 23, 2026, 03:03:52 PM
We're probably seeing the effects of condensation during prolonged periods of disuse, even the gunk in the cover. Consider obtaining a good quality gauge for compression and check the calibration of your homemade leakdown gauge so you, and others, can have confidence in their results.
An Italian tuneup—as you have suggested—might sort out this Brick. Stranger things have happened. 112350
This got me to thinking that my compression gauge is of pretty decent quality, and getting solid readings in a leakdown but nothing for compression was not logical. And if the tool is assumed to be serviceable, then it must be the dope using it incorrectly. I'm pretty sure I removed the presta valve years ago to do a leakdown on the CB550 I was working on, and never replaced it so I'm the dope - my fault.
Readings taken three times with a clean air filter and throttle open are 185/190/230. Someone with more K experience can interpret these numbers. I also noticed that there was what seemed to be water that smelled of fuel exit my compression tester when pushing the release button. The tank was off so must be residuals in the injector bar.
Anyhow, the plastic is off and not in too bad of shape, though this thing needs a bath.
20260823_162200868_iOS.jpg (107.43 kB . 768x576 - viewed 204 times)I also took the opportunity to address the intake shims and get them in spec using two of the shims from my RT and moving one from cyl 1 to 3. Saved me the cost of two shims.
And I did notice the fan is not as smooth as my RT or as the descriptions I've seen indicate it should be. But it did run with some jumper wires. I was thinking I found the reason for the overheating, and maybe it was stuck until I manually moved it and then applied power, but either way it's likely on the way out. The thermostat opened in a hot water bath, so that probably wasn't part of the problem.
Post by: Laitch on August 24, 2026, 04:41:06 PM
Get a new hose size dedicated to the RT length. The attached photo shows the correct layout.
(https://motobrick.com/gallery/4/1601-240826163032.png)
Post by: Smudgemo on August 24, 2026, 05:35:17 PM
I've got the tank taken apart and partially cleaned. The pump seems to work, though I do want to carefully test it. The screen is damaged and the filter unknown, so replacements are on the way. The rubber vibration damper is a bit soft, but it didn't leave any residue in the tank and for $75, plenty good enough for now.
For posterity, if a fella wanted to make a sending unit block-off for any reason (like protecting the sending unit while using cleaning solutions), the holes work fine drilled with a 1/4" bit and 54.5mm apart. Having some scrap and a milling machine made that pretty easy.
20260823_231833993_iOS.jpg (88.14 kB . 768x576 - viewed 164 times)Post by: TriSpark on August 25, 2026, 11:34:38 AM
Yes, you have a K75s like mine, and that coolant hose routing is correct. I had to get in and replace the pump and filter in mine this year also. And the fuel level sender, which cost a packet from EME. Like you, I had to become very familiar with fuel pumps......
Post by: Smudgemo on August 28, 2026, 06:25:28 PM
I rebuilt the fuel cap, which the need was debatable, I suppose, but it was pretty crusty. This is the second time I have noted that the EME rebuild kit screws are not quite right, in that I think they are too long or don't have a slight taper. But no matter, a quick shortening in the lathe and a touch-up with a file and we're all set.
The tank turned out to be pretty clean. Normal corrosion and varnish, but it actually rinsed out with water. I decided not to mess around with the corroded spots since it's just really discoloration at this point.
20260828_220228355_iOS.jpg (49.79 kB . 768x576 - viewed 103 times)But then when I was reassembling the fuel pump, of course..
20260828_220305010_iOS.jpg (62.25 kB . 768x576 - viewed 118 times)Guess I'll need to wait until next weekend for some fuel-rated wiring to fix this. Just as well, the breather line for the strainer is original and barely hanging in there. And the rubber mount for the fuel pump is soft and not really holding the pump very well, so get out the wallet.
I also replaced the Z breather tube that I've read will prevent a bike from running. I can see what a previous somebody was thinking here, but even I'm not THAT cheap.
20260828_220341597_iOS.jpg (102.72 kB . 768x576 - viewed 112 times)I'm on the fence about the motor for the fan. I know it's going to need replacement, but I'm ordering some stuff anyway..
Post by: TriSpark on August 30, 2026, 02:29:03 PM
Unless you're planning on sitting in traffic the first time you ride it, I'd clean the cooling fan up and try to get some lube in the motor part, then see how it does with 12V on the terminals. Replace it if dead, otherwise let it be for now - you won't need it to spin while you are just running the bike in the garage.
That Z hose is nasty, but if it works for now.......
Post by: Smudgemo on August 30, 2026, 10:48:55 PM
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.
20260831_022449495_iOS.jpg (56.66 kB . 768x576 - viewed 125 times)It's just a bit of kit to mount a fender on a bicycle that I bent 90*.
Post by: Smudgemo on September 05, 2026, 04:01:39 PM
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.
Post by: Smudgemo on September 05, 2026, 04:24:06 PM
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.
Post by: Smudgemo on September 06, 2026, 04:00:19 PM
20260906_182359645_iOS.jpg (88.31 kB . 768x576 - viewed 136 times)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.
20260906_182431574_iOS.jpg (60.97 kB . 768x576 - viewed 145 times)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.
20260906_193809174_iOS.jpg (83.31 kB . 768x576 - viewed 132 times)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.
Post by: TriSpark on September 06, 2026, 08:17:34 PM
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?
Post by: Duckbubbles on September 07, 2026, 12:05:18 AM
Frank
Post by: Smudgemo on September 07, 2026, 03:38:43 PM
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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Post by: Smudgemo on September 12, 2026, 09:50:07 PM
I got things stripped down pretty quickly so I could figure out what went wrong.
Block.jpg (102.06 kB . 767x576 - viewed 99 times)As far as I can tell, the head gasket had a breach at the bottom of #1.
Cyl1.jpg (81.87 kB . 767x576 - viewed 101 times)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.
20260912_225651801_iOS.jpg (59.61 kB . 768x504 - viewed 102 times)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.
Head.jpg (74.33 kB . 767x576 - viewed 100 times)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.