Sonic’s Workshop: Honda CX500 Autopsy

Well here I am at yet another Sonics Workshop, who’d a thunk it? I’d like to thank all of those who took the time to write, phone, fax, and E-mail me in regards to the article. I’m glad to see so many of you are finding it enjoyable reading. As you can see, the name is still the same, but as promised I did pick a winner for the oil and filter. The envelope please, and the winner is, Rob Harris?? Nice try, you have to watch this guy like a hawk folks. The real winner is Bob White of Ajax. One of the many who sent in Surgeon Sonic.

Update. The XR200 is still running although it’s still having carb trouble in the form of running too rich, all the regulars have been checked, replaced if needed, and set up to original specs. I’ll let you know as soon as I know. The other patient, the 750 Katana, is still going strong, although I heard that she’d had a minor fall during the later stages of the recovery, tearing open all of the plastic surgery, as well as adding some additional grazes in the process. Sigh, oh well, can’t cry over busted plastic, at least not until you’ve seen the bill for the new stuff.

This issue’s patient is the ‘reliable’, however not so popular, Honda CX500, of 1980 vintage. As happens sometimes, this issue’s bike didn’t just drop into my lap, as did the other two, I actually had to work to find this one by flicking through the local rags in search of a suitable purchase. The pickin’s were slim but I finally found a CX500 in the Toronto area.

It was still for sale when I called, so I figured it was worth a drive for a look. The bike was parked in the underground of a building and had a cover on it, (always a bonus) and was owned by a woman, who’d had it since new and was selling it because she hurt her back at work and was unable to ride much anymore. After a thorough inspection and the usual chit chat, we reached a mutually satisfying price of $450.00.

Once at home in the lab of Dr. Penniless, I set about the usual physical check to determine exactly how much skin would be coming off my knuckles this time. The odometer had 41687.9 km showing and, except for the bad case of flesh eating disease on the tank, the overall appearance of the patient was good. The mufflers had been replaced at some point with the Honda originals and the seat had been recovered. A new battery resided in the battery box and a large bug killer adorned the face of the patient. All things considered, so far it looks as though this one would pull through nicely. Don’t count your chickens before they’re hatched comes to mind.

Engine: Hondas first V-twin, complete with push rods, liquid cooling, five gears, and shaft drive. Reliable enough, although two common failures, the water pump seal, and the rear cam oil seal, will require the engine to be removed in order to replace them. Other than that the motor is easy to do most regular maintenance to. Note – On pre 1980 models there was a recall to replace the cam chain tensioner. Once replaced the dealer placed three punch marks beside the serial number on the left hand side of the engine to show that the newer tensioner had been installed. Our patient’s heart was in good shape, with the compression in the 140’s on both cylinders, with the exception of an oil leak from around the drain bolt. At first glance you’d think it was just the washer on the bolt, but with the bolt removed a crack in the front case cover was plain to see. This cover would have to be replaced or welded.

Suspension: Both fronts and rears were in good shape with no apparent signs of leaking.

Frame: Good shape with very few chips in the paint.

Wheel and Tires: Rims are the nicer mag style and are both in good shape, the rubber however only had about a year left to live.

Chain and sprockets: The beauty of shaft drive – The fluid in the diff was up, and that’s all folks.

Brakes: Both front and rear had been done recently and were in good shape.

Plastic: Not much on these older ones, both side covers a bit faded but still intact. The tank however will need to be stripped and painted.

I started by pricing out the welding of the cracked front cover. All the estimates were in and around the $50.00 range, but came with no guarantees. T.O. Cycle had the best price for a used replacement at $58.00, and with only a few dollars difference, I opted to replace the part and the gasket.

With that job done almost painlessly, I replaced the oil and filter and then stripped, cleaned and reinstalled the carbs. The valve clearances were then checked and found to be right on, no adjustments required.

It was start up time. Connecting up the battery and turning the key, I hit the starter button and varooooom! The CX came to life and after a quick and easy carb balance, sat smoothly idling in the garage. With nar a knuckle barren of skin there sat another (? – Ed) Sonic success story, in fact the only success story thus far. I mean, without the usual ordeal first.

After about a month and 700 or so kilometers of tiddeling around on the CX, a slight knock had developed somewhere in the engine. This slight knock quickly grew into an obnoxious banging. After some consulting and conferring with those in the know of such guttural groanings, it was guessed to be either worn cam journals or big end bearings. The price of fame keeps going up!

Now I had to make a decision, to either fix what’s wrong, which would require complete gasket kit, bearings, potentially a crankshaft, rods, or cam, or replace the engine with another used motor (hopefully with fewer miles on it) or to simply part it out. As always, it comes down to cash. It was considered cheaper, and much less time consuming, to simply pick up another motor for an engine swap, than to rebuild the motor I already had. Now because I do this sort of thing as some what of a hobby gone terribly wrong, I just so happened to have such a motor laying around. Very fortunate, otherwise it would’ve cost me about $500.00 at a wreckers, $50.00 more than the bike itself cost.

The motor swap on this bike, with its back bone style frame, is relatively simple, however I strongly suggest a shop manual and a good pair of strong hands to help lower this slug weight out.

In and out was about four hours all told. Now with new oil and fresh antifreeze I fired up the patients new heart, and other than a slight coolant leak from the right hand cylinder head gasket, (which I replaced over the next few days) the motor was running fine.

After about a month and 700 or so kilometers of tiddeling around on the CX, a slight knock had developed … somewhere in the engine, which quickly turned into an obnoxious banging …. Hee hee … baaahaaaa … aghhhhhh!!

The autopsy of the first heart that I removed from the patient revealed a very worn and spun connecting rod bearing from the left hand cylinder. Upon consulting with colleges on the matter we concluded to burn it, er, I mean, that the noise in the new/used engine was most likely the same problem. Now I was faced with same problem I was faced with earlier, to either rebuild or get another motor from somewhere. Both options this time are going to cost a pretty penny. I feel that this episode of Sonic’s Workshop will have to be put on the back burner for the time being, as I’m low on cash, the job doesn’t pay very well and my word count is approaching the cut off point ….

Thanks for reading, anyone out there got a cheap CX 500 with a good motor?