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Hey everyone. New to the forum. Bought a 1978 CX500 last week and ran into a few problems this weekend that have me pretty bummed and searching for a place to start to get this machine roadworthy again. I'm going to be as detailed as possible about the situation in hoping one of you will spot any possible errors on my part.

I've owned a CB650 before this and a few CMs, but this is my first water cooled Honda. I've always loved these and have been on the search for a nice 78 and found this.

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I read a few recommendations on this forum for preventative maintenance when buying a new CX and don't know where the problem may have developed.
Previous owner was a nice elderly guy I've known from the area who picked up this bike, cleaned the carbs, and flipped it for $1000 to me last week. 21k miles.
When I checked out the bike the oil was clean, the temp gauge was working, and it had a very slight coolant leak from the weep hole, a few drips on start up and then stopped completely. Lower coolant pipe got warm, no smoke, and ran and shifted through the gears and had no problem on a short highway ride. My plan was to ride it around for 100 miles or so, and if the weep hole leak didn't clear up, sort it out using the Shep Mech Seal Method.

This week it sat out front of my house, I started it up and took it around the neighborhood a few times but haven't gotten the chance to take it on a good ride yet. I took some time to pull and clean the easily accessible bullet connectors with some sandpaper, and check brakes and fluids. As it did have a small coolant leak, I pulled the tank so I could check the coolant level at the rad.
Radiator looked a bit low, so I let the bike idle with the cap off, and filled it with coolant. After the T-Stat opened and it dipped an inch or so, I topped it off and put the cap on, shut the bike off.

The next day it rains so I don't get a chance to ride.

Today, the temp gauge isn't working when I start up the bike, and I'm feeling the lower coolant hose and waiting for it to warm up. Take it around the block and still nothing on the gauge. After about 15 minutes, the coolant hose still feels like it hasn't heated up. Turn of the ignition, check the oil and holy mother of god it looks like thick coffee and I'm livid.

Did the mechanical seal completely fail in the 4 days I owned it? Head gasket? Did rainwater somehow find its way in to the coolant? Am I an idiot and didn't follow the proper procedure for topping off coolant at the radiator? Any help or a place to start to diagnose this is appreciated. I'd like to tackle it myself if possible.
 

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if there is no white smoke out the exhaust it does sound like the mechanical seal and oil seal have failed. If you remove the spark plugs do they have the same color deposits on the electrodes, or does one look fresher, as if it was steam cleaned? that may indicate head gasket. a compression test may show a weak gasket seal also. it sounds at the very least, like the mechanical seal was having some issues, unfortunately if coolant has worked past the oil seal you are looking at removing the rear cover to service the oil seal and the mechanical seal. while it is still together and running definately check the stator output as this would be the time to service that as well. I hope this helps although not a good way to start riding season.

Steve
 

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if there is no white smoke out the exhaust it does sound like the mechanical seal and oil seal have failed. If you remove the spark plugs do they have the same color deposits on the electrodes, or does one look fresher, as if it was steam cleaned? that may indicate head gasket. a compression test may show a weak gasket seal also. it sounds at the very least, like the mechanical seal was having some issues, unfortunately if coolant has worked past the oil seal you are looking at removing the rear cover to service the oil seal and the mechanical seal. while it is still together and running definately check the stator output as this would be the time to service that as well. I hope this helps although not a good way to start riding season.

Steve
thanks for the quick reply Steve, very helpful as I was just looking for a place to start. I didn't pull the plugs before so I can't say if either is cleaner than before the issues, but the LH cylinder is much lighter than the RH, as seen below. I'll try a compression taste later today when I have some more time to see if that provides any more clues.

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Here is a quick shot of the milky situation:

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Is there any way I could have caused this by not appropriately burping while adding coolant? This bike just seemed to be in such great shape before its short stay with me, and there are so few things I have actually touched on the bike :mad:. Also in the temp gauge suddenly malfunctioning, is this a symptom of air in the system with these bikes?

Am I correct in thinking if this does end up pointing to the mechanical and oil seal, that the Shep method wouldn't be useful here as the rear cover would have to come out to access the oil seal? 3, 11, 12, and 13 if I'm correct?

cx500pump.gif
 

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Is there any way I could have caused this by not appropriately burping while adding coolant?
Am I correct in thinking if this does end up pointing to the mechanical and oil seal, that the Shep method wouldn't be useful here as the rear cover would have to come out to access the oil seal? 3, 11, 12, and 13 if I'm correct?
1.That is pretty unlikely
2.That would be my approach
 

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Hey Phillycx I as well just joined the forum this march, as I bought a GL650I a week or two ago and have the same issue with coolant in the oil. And have been continually researching the mechanical seal repair while working on stripping it down to the frame to drop the engine. If your unfamiliar with these bikes, like I am, I would suggest doing a little research. But I dropped the engine today and it was a lot eaiser than I thought when I first got it. Now I am in the process of taking the rear cover off.

But If you haven't already, get a copy of the FSM (Factory Service Manual) for your application because it almost tells you everything you need to know. You can find it on the wiki page as a PDF.
 

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I had the same problem on a GL500 last year. It was running fine, and one day I noticed the chocolate milkshake oil. I did a compression check-no problem, then a leak-down test-again, no major issues. I tried to insure that the weep hole was open with a piece of wire. (Difficult to tell, sometimes), and then decided to just bite the bullet and remove the rear cover.

I had done a few of these, so I wasn't intimidated by the project. What I found was that there was some debris in the coolant that migrated to the space where the weep hole is and it was acting like a one way valve. The wire I inserted must have just pushed the debris father into the hole, and then it fell back down and closed the hole when I removed the wire. This allowed pressure to build in the space between the back of the mechanical seal cup and the oil seal. Thirteen psi of coolant was more than the oil seal could handle backwards, and the oil went into the rear case.

A new oil seal, mechanical seal and good coolant flushing fixed the problem. I also checked the cam adjuster and stator color while there and replaced all of the O rings and cover gasket. You are probably looking at about $100 for all the parts. (Seals, O rings, coolant, oil, gaskets, etc) Plan on a full day plus to get this done, as you are invariably going to run into issues like removing the exhaust, carbs, drive shaft, etc. Just take your time and use lots of PB Blaster, followed by heat from a mini torch to break loose stubborn nuts.

The wiki has a section on "triple bypass" that lists the parts needed for this. You may not need the cam chain tho. Good luck!
 

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I sure sounds like the mech and oil seal have gone, hard to tell about the head gasket just by the plug pics. I know if it was me (many here hate this) I would taste the plug ends for any trace taste of sugar, which would indicate coolant in the cylinder (do this even though I have a borescope). Is there any indication of oil in the coolant (rad), as that can sometime be do to a head leak. You will need to pull the rear cover to change the oil seal, plus its a good time to check inside. Many would pull the cover and replace the seals, but I myself would drop the engine and open it up. This way I can clean the inside, see what else may need doing, and make sure everything else was good to go. The main difference in the two methods is time and the cost of a full gasket set. Price difference between a full set and just the rear ones (rear case, impeller, etc) is around $50-$80, which is small compared to having to go back in later. This allows you to

Check the chain and guides
clean the inside and check for damage/shards/gunk
check the oil chain

Also, unlike most here I ALWAYS pull the heads at least ONCE on a bike I get, even if it doesnt need it. It allows checking the cylinder condition, and more important to me, doing a valve job, which costs me about $5.00 (new seals and gaskets come with the full engine kit anyway) for some lapping compound. Makes a difference to the overall performance.

Your call, and about the only thing I can say that I know all will agree with, is dont run it in the state its in.
 

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Discussion Starter #8
I sure sounds like the mech and oil seal have gone, hard to tell about the head gasket just by the plug pics. I know if it was me (many here hate this) I would taste the plug ends for any trace taste of sugar, which would indicate coolant in the cylinder (do this even though I have a borescope). Is there any indication of oil in the coolant (rad), as that can sometime be do to a head leak. You will need to pull the rear cover to change the oil seal, plus its a good time to check inside.
Thanks Stern. I haven't started the bike up since I saw the milky oil. The coolant in the rad and overflow both look clean. I do however plan on running it for a few minutes to use a Combustion Block Leak Tester I borrowed from a friend (just picked it up this morning hence the lack of updates) to definitely rule out head gasket before I moved on to the Mech and Oil Seal. Looks just like this:

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Other than that I should be dropping the engine ASAP and taking on the Water Pump Oil/Mech Seal and possibly stator. I must say I am slightly intimidated by boring out the 78's 27.5mm Mech Seal hole for the 28mm Seal itself. Wish me luck.
 

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Not familiar with that tool, looks interesting.
If coolant is clean, how about starting it and running it for a minute with the radiator cap off to look for exhaust gas bubbles coming up thru the coolant?
Will that work before the thermostat kicks in, anyone?
Or is it too risky to run it at all with water in the oil?
 

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Not familiar with that tool, looks interesting.
If coolant is clean, how about starting it and running it for a minute with the radiator cap off to look for exhaust gas bubbles coming up thru the coolant?
Will that work before the thermostat kicks in, anyone?
Or is it too risky to run it at all with water in the oil?
Hey Thumper. That is essentially what the Combustion Leak Detector does. It sits over the radiator cap opening and you squeeze the air pump to pull in vapors with the engine running. The liquid that comes with the kit changes from blue to yellow when exposed to combustion gases. According to my friend (Snap-On dealer) a lot of shops use this to take the guesswork out of diagnosing a head gasket leak.

I am changing the oil just to run the test.
 

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Sounds like a good plan, and replacing the oil with new stuf will help displace some of the coolant in tight places. Let us know how the kit works out
 

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Another quick question to those with mechanical seal experience (as this has been on my mind and I am currently unable to get anything done on the bike while at work) since the mechanical seal hole must be enlarged to a certain depth, is it possible to reuse the original cup and the guts from a new seal even though I am pulling the engine?

I'm talking about removing the rear cover, replacing the oil seal and replacing the guts of the mechanical seal while leaving the cup in place, and in turn avoiding all possibility of error enlarging that hole and the host of problems that inexperience has in affecting the actual seating of the cup. There seems to be a lot of room for error in the process (I've seen tutorials that show rear cover heating in the oven while some simply use a home made press). Opinions?
 

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Yes, the replacement of the seals "guts" and using the old cup is basically what they call the Shep method. This method is used to replace the seal guts without removing the rear case, but can still be used even if the rear cover is off. As for entire replacement, enlarging the hole sint hard, just takes patience (using a flap wheel just a tab bigger than the hole, and ONLY enlarging the mech seal 1/2 of the hole as the oil seal side needs to stay as it is. Weel hole is a safe depth to go to). If the entire seal is replaced it must be pressed in with a press. NOT hammered in. As for heating the rear case, I would never ever do it, as these are 30+ year old case and can be fractured easily with heat (also deformed). Some times heat is used before pressing things in (like bearings), BUT the item the bearing is being pressed into is almost always solid steel.

So, enlarging the holes isnt hard, do it in short bursts (5-10 sec) and then checked. Longer it takes you the less chance of messing up, with the end point being when the cup will finger push in almost up to the band on the cup and then stop. If you prefer to not do this, the the shep method will detail the steps in removing the old guts from the cup, removing the new guts intact from the new seal, and them installing the new guts in the existing cup.
 

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Discussion Starter #14 (Edited)
Yes, the replacement of the seals "guts" and using the old cup is basically what they call the Shep method. This method is used to replace the seal guts without removing the rear case, but can still be used even if the rear cover is off. As for entire replacement, enlarging the hole sint hard, just takes patience (using a flap wheel just a tab bigger than the hole, and ONLY enlarging the mech seal 1/2 of the hole as the oil seal side needs to stay as it is. Weel hole is a safe depth to go to). If the entire seal is replaced it must be pressed in with a press. NOT hammered in..
Good deal. Thanks for all the info Stern.

I got a chance to run the combustion leak test and it was pretty straight forward. The test came up negative, so it looks like the lesser of two evils and I'll be tackling the oil and mechanical seal soon. Here's a quick rundown of how the tester worked/works for any one new to this stuff as I am or anyone reading this in the future who decides to go a similar route to check for combustion leaks:

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Here is the slightly inappropriately shaped tester filled with the testing fluid (blue) which turns yellow upon exposure to combustion gases. As a recommended test to be sure the fluid is actually working, the box recommends exhaling into a closed fist and pumping some of that carbon dioxide up from your fist through the tester, which will turn the fluid yellow, as such:

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After being sure the tool actually works, I emptied the chambers and refilled with some new blue fluid. The tool fits just on top of the radiator cap opening, and I made sure the fluid was low enough for the tester (sucking coolant into the tubes will ruin the fluid and it will not give a reading). Got the engine up to operating temp (and changed the oil prior just for this test which is already once again milky afterwards) and gave it about five solid pumps. Saw it pull some bubbles but did not change to yellow like it had when I tested it with my exhaled breath.

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So that's that. If anyone in the Philadelphia area has ever done this before, you could be paid handsomely in beer or pizza if you are willing to spend a bit of your Saturday afternoon watching me wrestle this engine out. More updates to follow.
 
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