Project: 1987 Honda CH150

By this time I've forgotten all the story, but are your valve guides OK, and the valve seals? There's oil on top of the head that could be sucking in on the intake stroke, and exhaust could blow by on the exhaust stroke. That would put oil in the combustion chamber and exhaust in the crankcase. Your compression would be OK. The rings and bore would be OK too. You'd think the exhaust would go out the port and pipe, but there is some backpressure from a Honda muffler.

Guides look great, no deposits or oil starvation. Seals were just replaced after the first tear down and reassembly. Backside of intake valve looks spotless, no debris or deposits in the intake port either. Exhaust valve was the gunky looking one, mainly on the valve face, and port leading out to the muffler joint, caked in sticky black soot. My newest theory was that exhaust gasses were slipping between the layers of the MLS head gasket and into the timing chain tunnel, thereby overpressuring the entire engine case, and maybe forcing too much oil up into the combustion chamber?

this has become the greatest Detective Story in all of ADV...

Ha! As tempted as I am to feel honored about that, I think I would much rather it have simply been a cool restoration thread. Oh well, lol.

Factory replica head gaskets showed up finally, and from what I can see, Gaskets To Go did a stellar job!

Installation and rebuilding of the scoot starts tomorrow, as soon as it's warmer than 40F outside, haha.

I give up. I'm listing it on CL as running, but needs work. Hopefully I'll at least get back what I paid for it. Anyone think it's worth parting out on eBay?

I need to replace the front brake lever and the same side mirror assembly, and that's it, getting rid of it.

If anyone has a front brake lever they feel like giving away, part no.
53175-KM1-830

I'd be very grateful, thanks. Only the levers from the 87 and 88 fit.


I also need the right side mirror assembly. Same side as the front lever. It was broken and taped when I bought it, I want to replace it before I sell it.

HA! Decided to tear into it again today and it looks like I've got the head gasket issue solved! New head gasket, modified firing ring, and Copper Coat gasket sealant. It lives!!

Took it for a test ride and the head gasket seems to be holding up OK. The motor is getting quite hot, but not overheating. It's still got a lot of pressure in the crankcase, and after talking to a couple people, the only think I can think of is that something is up with the timing...Either valve or spark. Apparently the CDI units go bad on these scooters all the time, right?

Also, the fan works if you jump the leads from the switch unit that threads into the radiator body, but it never turns on. If that sensor is dead, can I just install a switch between those leads, and manually turn it on whenever I ride? The system still has a fuse for that circuit, so that should be safe, right?

My reaction is to tell you, screw it and just ride that puppy for a while. Overheating is rare for these scooters, but the sender unit for the gauge can be faulty. It's the same as senders for Honda cars of that era, so take it to a car parts store and get a replacement. The sender is on the thermostat housing and has nothing to do with the fan on the radiator, which can run without you knowing it because it's not too loud. That has it's own sender and, yes, you can wire around it and use a manual switch. Or, just set it up to run whenever the key is on.

Anyway, I still say, ride it. Report back after 3 tanks of fuel. You should get between 60 and 70 mpg unless you really hammer it or ride only with a wide open throttle.

The head gasket blew again while test riding it for 30 minutes at around 45mph, could look down and see bubbling coolant coming out of the reservoir. I have one more I can try installing, but I'm burnt out on working this thing.

I have not put a volt meter on the thermosensor, which I bypassed with aforementioned switch today, but I have tested the thermostat, and the sender unit for the engine temp that is part of the thermostat housing. I have been riding with the front panel off, so it's been easy to just look down and see that the fan has not been spinning, the whole time I've owned this scooter, until I installed that switch. Indicated engine temps stayed in the low range until I rode for a solid 15 minutes at about 75% throttle, ~45mph. The Scooter used to do an indicated 63mph, but was struggling to hit 55 today, so I went easy on it. Didn't matter apparently...

On the bright side...! I met another ADV member today who owns a shop here in town. Picked his brain about some stuff, and probably ate up way too much of his time, lol (Sorry, man!) Good to know there are service places besides stealerships around here though.

Ever flush the engine both oil and water passages just in case there's something plugging one up?

I've done a couple coolant flushes, but as someone pointed out, I never checked the pickup line from the reservoir tube...I know at least all the external hoses are fine, as I've taken them all off at one point. I flushed the oil line that bolts to the outside of the motor, and blew compressed air through some of the passage holes that I could get to...

Maybe tomorrow, but I'm going to clean, and try re-using the MLS style gasket, this time coated in Copper Coat, and with a .020" shim washer under the head stud acorn nuts, in an effort to generate more clamping force on the gasket...

My 150 overheated once, when the radiator cap came loose and the coolant boiled. It needs pressure to raise the boiling point.

I'm just about out of ideas to help you. The only other weird thing that a Honda scooter ever did that caused it to fail was when a piece of gasket from the gasket that seals the crankcase halfs came loose and floated down to the bottom of the case, covering the oil intake on the floor of the cases, behind the oil filter. The result was oil starvation and a camshaft bearing failure that brought everything to a halt. It was about the oddest thing I ever saw happen in an engine, but another guy on the Yahoo CH250 group had exactly the same experience.

You really should join that group and see what the folks there can suggest.

Thanks, I still appreciate people bouncing ideas around, as it gets me thinking outside my own experiences. I'm going to tear the motor out again today, and see if the MLS style gasket, with Copper Coat on it, does any better than it did last time. I basically have nothing to lose at this point, since I probably can't sell it as it is.

Pulled the motor again today, 6 hours later I'm done for the night. I think I got distracted when rotating the crank back to TDC on the compression stroke to re-install the timing chain, and mistakenly did it at TDC on the exhaust stroke.

Good news is the install of the Copper Coat-ed MLS head gasket went OK. Won't know how it holds up til tomorrow though.

There is no exhaust or comp. stroke if the timing chain isn't attached to the cam its just TDC. The cam decides which stroke it is.

I guess that's true, huh...Seems a silly thing to say now...

Now it seems I'm not getting any spark. Battery was just charged overnight, motor turns over with the starter, but it won't fire...

Keep up the ghood work Nihon! You'll figure it out eventually. I can't offer any advice but I can say that a well sorted 87 ch150 is an absolutely awesome scooter! Mine has been through HE11 and back but it still takes me wherever I want to go.

Here we are at the top of the mountain in the Sequioa Natoinal Park in Californina last winter.

Man, that is awesome!! I will get it sorted eventually, but I'm in the middle of buying a real motorcycle, so all my scooter funds are gone for the moment. Someday...

So, after messing with the wiring loom, and trying to get spark, I think something is actually wring with the CDI box, or it's flat broken. I'd like to have one to test that theory with, so I'm going to see about borrowing one from an Elite owner around my area, to see if that fixes my "no spark" issue. Any recommendations on aftermarket CDI units?