Sticking Automatic Camchain Tensioner

Some of Honda's automatic camchain tensioners have a propensity to fail to take up the slack in a camchain as it wears. I have not personally experienced a problem on my CXT's, but I know that other Hondas have. I bring it up, in part, because our bikes do have automatic tensioners. Mainly, I bring this subject up in light of a report from Colin Goodall at his Web site, as reprinted in Turbo News #27. In a nutshell: With 75,000 miles on his CX500TC (big pat on the back!) he found the need to replace his camchain. The bike had steadily developed a louder and louder rattling from the engine cases. The upper camshaft sprocket had also worn well beyond serviceable limits, and required replacing. Mr. Goodall noted that the lower sprocket, which is part of the crankshaft, was in fine shape. His analysis of the situation is twofold: A) The camchain wore, causing the upper sprocket to wear out. B) The upper sprocket wear may also be attributable to its location farther from the oil bath below. Perhaps these are valid points.

However, my experience with camchains in the CX engines has been very favorable. I currently also ride a CX500 Deluxe which has racked up over 130,000 miles on it's camchain. I closely examined the camchain and sprockets at 120,000 miles, and found no abnormal wear. The chain is the same type as found in the Turbos, but instead of an automatic tensioner, my CX500 requires me to manually tension the chain every 3000 miles. The system is whisper quiet to this day, with never a hint of rattling sounds. Oh yes, there is one occasion when I heard MAJOR rattling sounds from the rear of the engine. That was at 87,000 miles, when the righthand camchain tensioner guide suddenly broke, allowing the chain to rattle about freely with way too much slack. This rather points the direction in which I shall go in my analysis of Mr. Goodall's experience.

I believe Mr. Goodall's camchain/sprocket problem was not caused by wear, or lack of upper engine lubrication. A rattle is always an indication that something is loose, but not necessarily worn. Camchains have a wonderful record of reliability, but they do continue to stretch over their normal life. This is why I must continually take up the slack in the camchain on my CX500D every 3000 miles. And this is also what you are blindly hoping the automatic camchain tensioner is doing for your Turbo's camchain. I believe that all indicators suggest that the automatic tensioner in Mr. Goodall's engine became stuck. The chain gradually kept stretching, while the tensioner failed to take up the slack. This would bring about his observation that "the bike had steadily developed a louder and louder rattling from the engine cases...". The more the chain stretched, the looser it got, the more it rattled. Period.

Yet, what could cause the upper sprocket to wear severely, while the lower sprocket remains fine? Could it be a deficiency of lubrication in the upper reaches of the engine case? It is not entirely impossible. Yet, imagine what a loose camchain is doing within the engine. Imagine viewing the crankshaft/chain/upper sprocket from the rear of the engine. The automatic tensioner push rod presses against the tensioner slipper, which is ideally kept snug up against the righthand vertical run of the chain. From the rear, the pistons rotate the crankshaft counterclockwise. This naturally keeps the lefthand vertical run of the chain taught, pulling against the tension created by the valve springs. All slack in the chain will always be manifest in the righthand side of the chain run This is why the tensioner is situated there. As the chain stretches gradually, the tensioner should push gradually, increasingly inward to maintain a constant tension on the righthand chain run. Now imagine the tensioner hanging up in it's travel, refusing to push to the left any further, while the chain gradually continues to stretch. Excessive slack is now becoming present, and it is this slack which causes the chain to now slap violently up against the upper camchain sprocket. Such continued abuse will rapidly wear both the chain and the upper sprocket. Anyone who has observed the action of a loose chain knows that the sprocket receiving the loose chain bears the brunt of the beating, in this case the upper sprocket. The crankshaft sprocket remains relatively unaffected since it is pulling the chain downward from the left side of the run, constantly under back tension from the valve springs. This keeps everything on the left side taught.

Should anyone's Turbo experience the symptoms which Mr. Goodall's did, suspect first the tensioner. I would certainly have sympathy for anyone who goes to the great trouble to replace a camchain and sprocket worn, unbeknownst to him, from the slack created by a sticking tensioner, while failing to recognize the tensioner itself as the source of the problem. If Mr. Goodall overlooked this possibility, hopefully the very process of replacing the chain freed up the sticky tensioner, since it must be fully removed in order to replace the chain. The proper initial examination procedure, should one ever have access to the area, is to press in on the steel ball within the tensioner with a screwdriver, allowing you to assess the presence, or lack, of unrestricted motion in the push rod. I would further completely disassemble the tensioning system and inspect for wear and galling on all moving parts. Particularly if you are already experiencing symptoms, be certain to check for breakage in the spring hidden inside the tensioner which wedges the small steel ball into the rear of the push rod. See page 23-10 of the Honda service manual.

Disclaimer

© Turbo Motorcycle International Owners Association