Cam chain / timing chain guides

Suzuki DR350 motorcycles, 1990 - 1999.

Created: 2013 June 08

Updated: 2013 June 08

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13,000 miles ago, I replaced my cam chain and both sprockets. At the time, I did not replace the cam chain guides. Everything I read said the guides wear like iron, so there is no need to replace them. After installing a new timing chain and sprockets, I had maybe 5 mm or 6 mm of adjustment left on the cam chain tensioner. I did not think that to be very much in the way of adjustment, but figured that was the way it was.

After 13,000 miles, I discovered only one click left on my automatic cam chain tensioner. Not good. 13,000 miles seems a pretty short distance to me for a cam chain. Time for a new chain and sprockets. In hopes that I'll achieve a longer service life, I decided to install new guides. In comparing the new guides with the old guides, I learned a few things:

1. First off, the guides do seem to wear like iron, at least the portion that the chain runs against. I measured the overall thickness of each guide as well as the depth the chain wore within each guide. All measurements were very close.
   • Rear guide: Perhaps the old rear guide showed 0.08 mm of additional depth.
   • Front guide: I could tell no diffrence between the old and new front guides.
2. The old rear guide, however, showed a significant indentation where the automatic cam chain tensioner had pushed against it all these years. The depth of the indentation within the rubber was 0.76 mm, in addition to the overall reduction in height.
3. The old front guide also showed a significant flat spot on the round portion where it pivots, indicating it had been pressed up against the back side. This flat spot reduced the pivot from about 8.48 mm to about 8 mm.

All of these measurements add up and provide an overall reduction in the available travel of the automatic timing chain tensioner. In conclusion, I think there are good reasons to install new guides for the cam chain at the same time that you install a new chain and sprockets. Hopefully, I'll get a lot more than 13,000 miles out of this set up. Once my cam chain and sprockets arrive, I'll get them installed and see how many clicks I have left on my tensioner.