Thursday, March 22, 2012

CX500: Common Issues


A common problem with the CX500 is with it's timing / cam chain tensioner. The '78 models had a recall on this part, due to the guide bolt backing itself out.

"THE CAM CHAIN GUIDE BOLT MAY LOOSEN DUE TO THE PRESENCE OF A RUBBER COATING ON THE SURFACE OF THE GUIDE IN THE AREA WHERE THE BOLT SEATS. IF THE BOLT BECOMES LOOSE, THE ENGINE WILL DEVELOP A TICKING NOISE. CONTINUED VEHICLE OPERATION WITH A LOOSE GUIDE BOLT MAY RESULT IN BREAKAGE OF THE BOLT AND INCREASED ENGINE NOISE."

If your '78 model had the recall remedied by a dealer, you will see 3 punch dots on the engine casing in this location:


If your bike is a '78 and does not have these punch marks, you need to update the tensioner.

The manual requires that you check the timing chain at 20k miles. Doing so is usually an engine out operation and is referred to as the Triple Bypass. Triple because there are 3 elements to the CX engine that are common failures and all are engine out operations - thus, doing all three at once is preferred preventative maintenance. Them being the water pump mechanical seal, stator, and timing chain / tensioner. 

Here are some invaluable links for CX owners:

My CX has 26k miles on it, and has had the recall addressed. At the end of last season I suddenly got a metal slappidy noise coming from the engine. I rode it 2 blocks to the apartment and then had it towed from there. 2 blocks can do a lot more damage then I imagined.

What happens is the chain is either stretched beyond spec, or the tensioner lets go. In either case, this causes the now loose chain to run against an interior plate that blocks off the crankcase. 2 blocks of riding, at around 3k RPMs means about 3,000-6,000 revolutions of that chain grinding away at your casing.

Here's the aftermath of what it did to mine:

You can see it ground off most of the screw boss, screw head, and the lower casting protrusion.

Upper screw boss wear.

Broken right chain guide.

Broken left chain guide.


The semi-good news is the crankshaft bearing plate that the chain ate up is replaceable and not to expensive to pick up used. They pop up on eBay for around $20-50.

1978 CX500 microfiche
The amount of life your chain has left can be checked without removing the engine.

Using the dental mirror method, you're looking for the amount of travel the cam chain guide bolt (#15 above) has left to move in the channel of the guide plate (#5).

Here's a diagram explaining what you're looking for:


Now go check your tensioner and avoid garaging the bike while it's prime riding season.

8 comments:

  1. I've got a GL500i and have seen the photos per your link but have never got an answer as to what to look for. Your diagram is perfect. Thanks for the explanation!

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    1. Glad it could help. I had issues deciphering what to look for with the mirror trick as well, until I had the rear cover off.

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  2. Great post on the triple bypass!
    Sucks to see that the cam chain issues got the better of your bike.
    You might take solace in the fact that the damage shown probably didn't occour in just 4 blocks. The tensioner probably hadn't been doing it's job well for a while before you got the bike and it finally failed (terribly) and became noisy then.

    I've got a couple CB750 motors that have a good bit of the cam chain tunnel ground out from people not checking or setting their tensioner properly and probably missing a shift or two.

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    1. Yea, I'm willing to bet, judging by other areas of the bike when I bough tit, that the previous owner hadn't adjusted it regularly. All the parts I need to get it back up and running are on there way, so I should have my knees in the wind soon enough.

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  3. Great photos. I've been (on and off) performing the triple by-pass on mine as well, and had the same damage that you had from the slack chain.
    FYI, the left guide is no longer available, but the folks at the ChopperCharles forum are very helpful if you need assistance locating one (they helped me find one within a couple of days).

    While you're inside the rear cover, you might also want to upgrade to the ignitech system (replaces CDI unit) as the CDI units are supposedly notorious for giving out after 30 years of service--this requires upgrading your stator as well. However, the new ignitech and stator are (combined) cheaper than having to replace the original CDI or stator, so in some ways it's a no-brainer.

    Hit the front of the engine as well while you're at it. Easy enough to take off, and you'll probably find that your oil pump strainer has been clogged up with all those little pieces of metal and broken guides and tensioners caused from your chain slapping around.

    Best of luck,
    -ben

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  4. keep attention with the water-pump! still i got the same problem and it leaks!

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