Cam chain replacement without breaking engine

I did that about 15 years ago to one of my Hondas.  My only regret is that I failed to mark the link that I re-riveted.   I make a point of checking the chain when I have the valve cover off to set the valves, but I can't tell which link I pressed.  I guess that's a good sign but if I had marked it, it would have made checking for anything unusual a lot easier. 

I didn't trust myself to break the old cam chain and install joining link in new one, over the engine - even with the sump off there was just too many places for those tiny link plates to hide if they slipped past the rags, or fell through when removing the rags. So I did everything in front of the engine. After threading the new cam chain through (on end of the old chain, after breaking both) I had both ends hanging down over the front of the engine. Then made up a simple platform with wooden blocks, a few centimeters below the top of the engine cases, so I could work on the ends with one hand while manipulating plates and pins with the other. Hopefully the photos will help explain (recreated using old chain and stuffed joining link). Hold both ends together with fingers of one hand, insert joining link through first couple of plates, then insert first of the three intermediate plates so that it is aligned but resting on the joining link pins. Hold that plate in place with a third finger, pressing down slightly, then gently ease back the joining link until the inserted plate pops down and giggle the joining pin through this to next couple of plates, repeat for second and third plates. As the final outer plate of the joining link is a press fit, it wont easily sit in place so I used a dab of assembly grease to hold it there. The platform was also handy for resting the riveting tool on so you didn't need a third hand. And I used small fine grinding wheel on the Dremel to take the heads off pins before pressing them out to break the chains - made it a lot easier. Hope all this helps the next person. Oh, and if you think your old cam chain is just on the service limit (length measured between 20 links) like mine was, it will be ok, check out how worn the pin is from my old cam chain! [attachment=12308]

I would have been nice to compare the old link plate to one of the new link plates. What I see in the pic is the bore in the link plate in the upper left is getting really thin to the edge of the link plate and I would be more worried about that thinning more so than the wear on the pin.

One also has to remember that when the cam chain reaches the service limit, the stretch in the cam chain will retard the camshaft timing by as much as 8 degrees retarded. Add that to the stretch in the primary chain and you end up with more camshaft  retarded timing, maybe as high as 13 degrees total retard. The adverse effect of retarded camshaft timing is that the intake valves will close late, reducing the amount of charge compression . It also upsets the timing of valve overlap to the position of the piston at top dead center resulting in less volumetric efficiency . All bad.

The effect the wearing of the primary chain has on valve timing is surely something that the designers of this engine must have thought about, surely, yet they went ahead with this flawed design. It would be interesting to check the valve timing on an engine that has covered about 20 thousand miles.   Are you intending to engineer some means of adjustability into your camshafts, Kawboy?

Yea, I got plans for an adjustable camshaft sprocket. Life just keeps getting in the way. If isn't one thing, it's another.the CRF450 camshaft sprocket is the only camshaft sprocket that will work. A minor mod will need to be done to slip it over the cam lobes and a backing plate will need to be machined to attach the sprocket to the camshaft after the original sprocket is machined off.Ape makes an adjustable sprocket for the CRF450 and also Falicon. I have both of these waiting for some time to play machinist.



 

 

This is a pic of a stock non adjustable CRF450 camshaft sprocket that one would remove to install either the APE or the Falicon sprocket. I came up with this idea 8 years ago and haven't found the time to work on it.

biltonjim wrote:

The effect the wearing of the primary chain has on valve timing is surely something that the designers of this engine must have thought about, surely, yet they went ahead with this flawed design. It would be interesting to check the valve timing on an engine that has covered about 20 thousand miles.   Are you intending to engineer some means of adjustability into your camshafts, Kawboy?
 

All cam chain engines suffer from chain stretch affecting the valve timing to some degree.  You'd think that the Engineers would have built some level of chain stretch into the design, i.e. the timing for a new engine would be advanced (from ideal) and as chain stretch occurs (at least the initial stretch - which is probably the most pronounced), the timing move more towards the ideal.