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After waiting until I finished rebuilding my back deck and got the wood &c out of the garage so I could move Mr.H there from storage and waiting 29 days for a front tire to arrive I finally moved the battery from the winter bike to the 'Wing and took it for the first 16 Km/10 mile ride of the season on Friday. The fan ran the whole while but I figured that was either because it was very hot out or maybe the new fan switch is turning on too low.
When I got home I drained the oil to change it and went indoors where it was cooler. I was in the garage for something later and, since I had to top up the coolant when I replaced the fan switch and I decided to look at the level in the recovery tank to see how much it had decreased when the engine cooled down after being at operating temperature.
Instead of dropping half an inch or so as expected it was nearly an inch higher.

Saturday, when it was a bit cooler in the garage I pulled off the seat and shelter so I could remove the rad cap and couldn't see coolant in the rad.
Spark plugs #1, 2 & 3 look a bit lighter than normal but not too bad but the electrode of #4 is very white and the ceramic part is very clean.
At least the oil I drained doesn't look milky...

Last fall, on a long trip on a hot night that ended up in city traffic in an unfamiliar area the fan switch failed and it overheated enough that I was leaving a trail of coolant when I arrived at the destination. Fortunately, I had installed a switch to manually turn the fan on so I was able to get home OK. At home I topped up the recovery tank and it gulped down quite a bit for a couple of days until the system was full again and the level stabilized. I ran with the fan switched on for over a month and the level in the tank stayed between the lines so I figured I'd dodged the bullet. And I ordered a new fan switch over the winter to install this spring (which is why I checked the level).

This has to be a leaking head gasket. These are the Athena gaskets from the kit I used when I had the engine apart before installing it in the bike 2 years ago (only about 1500 Km).

After I move the battery back to the winter machine and use it for the day's errands I'll transfer the excess coolant from the tank to the rad and use my "Hamilton tool" (airline adapter for spark plug hole) to pressurize each cylinder so I can watch for bubbles in the rad neck to confirm that #4 is the only one leaking (I'll try to take pics of this) so I know how many head gaskets I need to order.

Am I right in assuming that the gasket was probably weakened by the overheating but waited until now to let go or should I be looking for other problems?

Not speaking from actual GW experience here with head gasketz, I have read that if you do one head gasket you should do the other. I assume that you really cannot pin down the cause either by over heat or possibly with deterioration by age.

$0.02

just throwin' it out there..... did you re-check the torque on the head bolts?

I believe I re-torqued the bolts after a hundred Km or so.

I'm debating whether to order 2 of them just in case but I really hate doing any work on the side of the engine that faces the sidecar.....

I always do pairs...

sorry Bob, not the answer you are looking for.

In My short sidecar ownership, I removed said car for head gasket work.

I have had a couple bikes overheat and puke for a bad fan switch but never associated a head gasket issue with that. I did have one that over heated and melted the inter plenum gasket enough to close off fuel to the left bank. That took me a bit to figure out.

Not sure what to advise here but more testing is good.

Probably not your issue Bob, but I had a 1100 that would puke coolant.
I went thru the entire cooling system, everything was new and still it overheated.
the fan would come on at the right time so I thought it was working properly.

Long story short.......
Who would have thought that the fan could be wired to run in both directions?
The fan was plugged in backwards and was blowing instead of sucking.
Once reversed so the fan worked like it should, the overheating stopped.

That was a interesting discovery that I won't forget.

Reversed polarity will make a brushed dc motor turn backwards, fo sho!

77Gowing wrote:Reversed polarity will make a brushed dc motor turn backwards, fo sho!

Gonna steal your thread for just a bit Bob.

I always thought that but....... I recently converted Dad's 1945 2N tractor from a 6 Volt positive ground system to a 12 volt negative ground. I asked the guys on the tractor forum about the starter and they assured me it would be fine. Sure enough it was. I do not know why but it works.

Not to be too cheerful .... but my blown head gasket experience followed your pattern of symptoms.

Another vote for two ....

Gord(sorry)Jones

Rat wrote:Not to be too cheerful .... but my blown head gasket experience followed your pattern of symptoms.

Another vote for two ....

Gord(sorry)Jones

You are so gentle when delivering potential bad news Rat. We know you are here to help with the best of intentions.

Re the fan: I can see that happening but you're right, it isn't my issue. When I puled in I could feel the fan blowing hot air across my legs before I shut the engine off.

Re the starter motor: I haven't tried anything like that but I expect that it turned the right direction because the voltage was reversed to both the field coils and the armature so both were producing the opposite magnetic field.
I think the motors in fans nave permanent magnets so the field doesn't change when you reverse the polarity.

Well, the testing is done. Let's start with a pic of the plugs that I should have included in my first post. As you can see, #1 and #2 look pretty normal, #3 isn't bad but #4's electrode has definitely been steam cleaned. This is the "Hamilton" tool, named in honour of the late cx500forum member Hamilton, who invented it Here's how it is used. You set the cylinder being tested at TDC compression, screw the tool in, snap on the air line with about 90-100 PSI and watch the coolant in the rad for bubbles

Since the engine had stopped close enough to TDC compression of #4 that both rockers wiggled I tried that one first It is leaking so badly that the rad overflowed immediately, confirming the gasket failure and I immediately disconnected the air line.
I topped up the rad again, turned the engine to the next TDC mark and checked which cylinder's valves were both closed (#1 - pic below), then moved the tool to that cylinder and connected the air line. When no bubbles appeared after several minutes I disconnected the air, turned the engine to the next TDC, #3's valves were closed so I moved the tool to that one. A few seconds after I connected the air the level in the rad rose and then bubbles started to appear every few seconds. It is hard to take still pics of something intermittent. I gave up after a while; This is the best one I got So tomorrow morning I'll be ordering 2 gaskets.

Wow. Both rears? Well, "Off with her head(s)!"

sorry for your troublez side car.
Reg. PM motors. Reversing the voltage on a PM machine will reverse the direction of rotation aswell if it is a brushed DC macine. A brushless PM machine has magnets on the rotor and it depends on the dynamic waveforms fed it by the microprocessor controlled power electronic motor controller. I know, because I procured one for the US Army and tested it and its controller. Interesting phenomena I played with. Shorting any two phases on a pm machine produces a locked rotor situation. The rotor while static cuts no lines of flux, hence no torque, but the moment you try to rotate the rotor by hand the movement of flux cuts through the windings and maximum torque is delivered to resist your input. 20 yrs in Hybrid electric vehicle testing & research will teach a fella a thing or two. People dont get it from the telly anyway that research is really a training ground or schooling of sorts, even for the principle investigator or inventor. We do research to learn. & no white lab coats & clip boards...we got dirty and even scraped up and a little crispy at times.

dontwantapickle wrote:just throwin' it out there..... did you re-check the torque on the head bolts?

Great suggestion, but only when fully cooled down. Especially on aluminum blocks, they have a tendency to strip. I believe this block is steel however, but still best when cooled down.