Honda DOHC Cam Chain Tension

So, here's something we've never found much information about, either from Honda, or online. Starting in the 1980s, Honda switched design for most of their motorcycles from manual cam chain tensioners to automatic models. Once they went automatic, it became a lot harder to know what was going on with the system when you started to hear cam chain noise. There is good information for some bikes on how to tell with the automatic tensioner, but not much on the DOHC inline fours. How can you tell if your cam chain is stretched? And how can you tell if the tensioner has reached its limit?

Having just successfully diagnosed and fixed this problem on a 1983 Honda CB650sc Nighthawk, here is what we learned:

* The bike in question had approximately 31k miles. There was noticeable, very loud rattle, almost like a buzzing/gurgling sound throughout the rev range. It wasn't bad when the bike was cold, but got much worse as the engine warmed up.

* The stock cam chain has to be broken to remove both the chain itself, and the tensioner. However, both jobs can be done with the engine in frame, and only removing the valve cover.

* The tensioner is known for the spring to become weak and/or fail. Also, the spring and the complete tensioner have both been discontinued by Honda, for the CB650sc and CB550sc models with hydraulic valves.

* It may be possible to remove the tensioner without removing the cams, but certainly very difficult. We had to unbolt both cam sprockets from the cams and then remove the intake cam before there was enough room to remove the tensioner.

* The only solution that doesn't require engine disassembly down to the crankshaft is to break the old cam chain at one link, also break the replacement cam chain at one link, temporarily attach to each other and run the new chain around the crankshaft sprocket by manually turning the engine, then remove the old chain and fasten the new chain with a special cam chain masterlink.

* If done this way, be sure to run the new cam chain through the cam chain tensioner before fixing it with the masterlink, much easier than dealing with the tensioner slipper clips!!!

* We replaced the original cam chain tensioner with a unit from a 1983 CB550sc with 10k miles. The tensioner is the same design for both models as far as we can tell.

As far as measuring cam chain wear, we sadly did not take photos or measurements of the old chain before removing it from the bike. However, here are some photos of a new chain and low-mileage tensioner. Photos are with crankshaft positioned at TDC. Note the following that can be used to measure wear:

* Deflection of the chain is very minimal between the cam sprockets, estimate less than 4mm.

* The tensioner has a rod that runs through a center hole in the fastener plate; the closer this rod gets to the upper hole, the farther out the tensioner is (hence, the closer to its limit). As you can see in the photos, the rod is far below this upper hole in our new setup, estimate approx 10mm gap.

Hope this helps some of you out there, good luck!