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Old 06-18-2002, 09:31 AM
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Cam Chain Tips

Cam Chain Tips
by various authors
Cam Chain Replacement
Cam Chain Tensioner Leaking Oil


Adjusting the Cam Chain Tension

An out-of-adjustment cam chain can cause the bike to run poorly andvibrate. To adjust the tension, locate the tensioner on the front of the engine between cylinders 2 and 3 - it's that little do-hickey protruding from the cylinders with a bolt sticking out the left side. Remove the engine case cover over the timing plates and use a wrench to manually rotate (clockwise) the engine until the timing pointer aligns with the "C" on the timing plate. Then loosen the locknut on the cam chain tensioner, loosen the bolt, then retighten the bolt and then the locknut (specified torque is only about 5 ft/lbs so don't overtighten), and replace the case cover. That's it.

David Hansen
Last modified: September 24, 1996


Cam Chain Replacement

I replaced mine at 70,000 because the adjuster was at max. The thing would probably last longer, but I love tinkering and did not wanted to take a risk on the upcoming long trip. Few mechanics told me not to worry until you hear it slap around. I thought that this was lousy advice, especially since you would then need to change the chain guides as well, and that is much bigger job requiring removal of the head.

I am monitoring the stretch of the chain right now and it is stretching fast. I measure it by inserting the bottom end of a vernier caliper through the cam chain adjuster, after popping the end seal off every time.

You don't have to split the cases even if the manual says so. The earlymanuals also say that the chain is a "continuous (endless) chain," but Yamaha sells a length of chain with a rivetable master link for about $60. The procedure is not described in the manual, so pay attention, the order of procedure is extremely important:
  1. Follow your manual for cam removal up to the point where you have both cam sprockets off the cams and the chain of the sprockets. From this point on DO NOT MOVE CAMS OR CRANK until step 13 when required by the manual. Otherwise you will loose your timing at best or you will crack the top end at worst.

  2. Remove the cam chain tensioner adjuster assembly off the engine


  3. Remove the bridge chain guide between the two cam brackets


  4. Attach a length of steel wire between the cam chain and the frame of the bike in two places close to where the chain disappears into the engine. You will be cutting the chain between these two points, so give yourself room for the operation. The steel wire is necessary because you do not want to drop one end of the chain into the engine after cutting it. If that happens, you have to split the cases.


  5. Put a large rag or towel between the chain and the rest of the engine. That will prevent small parts of the chain or otherwise from falling into the engine.


  6. Use special $80 tool (I will loan you one for the price of postage) to brake the chain by pushing out one of the pins.


  7. Attach the new chain to an end of the old one with some temporary pin. Make sure the temporary pin is good enough not to fall out in the middle of the engine. The chain will sometimes jam during the feeding and you will be jerking on it. If you just stick a nail and bend it, the increased width will jam inside. I used the pushed out pin and riveted it back in to make this temporary connection. Use the same tool to do it.


  8. Hook up the other end of the new chain to the frame with a steel wire.


  9. Remove the steel wire from the end of the old chain where the new one is temporarily attached.


  10. Really take your time feeding the new chain while pulling on the old one on the other side. In my experience, if you feed too much of the new chain it will jam. If you feed too little it will hang on the crank sprocket. When it jammed on me, I did wiggle the crank just a bit, enough to loosen the jam. Keep in mind that some of the valves may be only millimeters from the tops of the pistons! If you put the cam sprockets on the cams in their normal position and drape the chain on them, they may allow you to guide the chain right under the crank sprocket without it jamming. Too bad I got that idea too late.


  11. When enough of the new chain emerges on the other side (I fed it from intake to exhaust), hook up the emerging new chain to the frame and then and only then unrivet the old chain from it.


  12. When you buy the new chain make sure that it comes with all the necessary pieces of the rivetable master link. Mine didn't and they had to reorder it for me. Now change the attachment on the special tool that you just borrowed from me and rivet the new master link in. I recommend doing one pin half way, then the other all the way and then return to the first. PRESTO!


  13. Remove all the wires and reassemble following the manual.


An alternative method that actually may be safer and easier (that I did not try) is to remove the cams completely (allowing the valves to retreat into their seats) and then turn the crank with a wrench to feed the chain through while maintaining tension on it. I did not do that and had problems with the chain getting stuck probably between the crank sprocket and the bearings.

Jurek Zarzycki




According to the manual, the crank should be set with the ignition timing mark on the "T" mark and the cams have a dot on them with an arrow on the cam bearing cap ( next to the cam sprocket ) that are lined up when the thing is in time. Thus the 2nd part of Jurek's instruction would be the most logical. Removing the cams and turning the crank would sure help in horsing that chain around. Either way it seems like it can be done with patience and swearing. One warning in the manual - the cams have an area right next to the center caps that you can put a wrench on and turn the cams to get them in the proper position, you will be turning against the valve spring pressure and don't have much room, here's the warning - Use extreme caution when rotating the cams. Two possible dangers exist. First, the wrench may contact the head and fracture it. Or second, a valve may become bent if the cam is turned the wrong way (I would guess turned into a piston).

Norm Kokes




It would not be easy to un-rivet the old chain and rivet the new one with cam sprockets and "bridge" in place. The bridge actually just pops out. It would be even more difficult to feed the combined chains with the cam sprockets obstructing the opening.

There is really no worry about of irrevocable loss of timing since the manual has a good procedure to set it up. The biggest worry is manipulating cams (and therefore valves) and crank (and therefore pistons) independently and the possibility of their crunching collision.

And here is another word of caution: do not attempt to rotate the crank with the cam chain tensioner removed or completely contracted even when the cam chain and sprockets are on (like during reassembly, when the manual asks you to completely contract the tensioner before bolting it back to the engine). In such condition, the cam chain is so loose that the crank may jump a tooth or few on the sprocket without moving the cams. If you are luckier than most you will be able to finagle the crank back by the same number of teeth. If not, the cams must come out and you must follow the Tmark/arrows/dots procedure. Do not rotate the whole thing if you know or suspect that the chain is off by a tooth or more! If you are unlucky, while you are "finagling" the piston crunches into some valve, stems bend, aluminum casting cracks and you are trying to recollect the phone number to the nearest dismantler.

The manual tells you to stick your finger through the tensioner hole and tighten the chain by pushing on it during any movements of the crank or cams. Seems minor, but it makes all the difference.

The cam chain has 142 pins/rollers on about 7mm pitch. When the NEW cam chain is laid flat on a table it is 998.5 mm compressed and 1002.3 mm stretched. The OLD cam chain is 998.5 mm compressed and 1006.0 mm stretched! As you see the difference is less than 4 mm only on the length of the chain! And that causes the tensioner cam to be extended to maximum.

If you have a standard model similar to 78/79 and are curious about the degree of your cam chain tensioner extension, measure the depth of the hole behind the rubber plug on it's tip. The bottom of this hole is actually the back of the shaft that pushes on the shoe that pushes on the chain. At the maximum extension (no more range) this hole is 20 mm deep. My bike with a brand new chain (no miles) had this hole 14.6 mm deep.


After 5,000 miles it increased to 15.2 mm.

After 9,000 miles it increased to 15.5 mm.

Jurek Zarzycki



Cam Chain Tensioner Leaking Oil


Two problem areas on the tensioner are the rubber plug @ the end of it, and the gasket between itself and the head. Replace both and you should have no further problems. Use some good silicone sealer (high temp) on the plug.

Justin Lassy



The oil leak is minor in terms of oil loss, but given the location
it is major in terms of the mess it will create. The leaking oil
will make it's way between the cylinders and in the back of the
engine, where it will accumulate dust and dirt.

If the oil leaks just from under the adjusting screw (are you sure
of that?), the fix will be easy.

  1. Follow the manual procedure for cam chain adjustment up to
    the point where it tells you to loosen the adjusting screw.

  2. Remove the adjusting screw completely

  3. remove and discard the small o-ring

  4. clean the o-ring seat well

  5. put NEW o-ring in place

  6. screw in the adjusting screw remembering the flat washer which squeezes and seals the o-ring

  7. tighten according to the manual procedure


You are done - no more leak.

You have a slightly bigger problem if the gasket under the whole
assembly leaks and much bigger problem if the oil leaks from under one of the engine studs and just surfaces around the adjuster (like in my bike).
Jurek Zarzycki



I used aviation gasket cement because it doesn't dry out. I removed the complete chain tensioner system and recut a new gasket (you can just buy one if you want) from gasket material. I then used this cement to set this gasket into place. The leak I had however was from the small seal (dime-size) at the front of the tensioner. I pushed the plug out the front, from inside the hole where the spring loaded plunger would go. In other words, if the piece was on the bike and you were in front of the bike, the seal was pushed from the engine side towards you and the front tire. confusing enough? The way I fixed this was to use some of the sealant around it's edges after pushing it out with a small brass drift (easy). The sealant then set up overnight to a thick consistency and kept the seal from leaking. 10,000 K later it's still tight. The brand name of sealnt was Gaska-Cinch No 3. Aviation Type.
Courtney Hook



Don Gringo (78E) had this same problem. I wasen't nearly as sophisticated as Courtney, I simply cleaned the inside up with sovent, dried it well, and injected a glop of JB Weld. It solved the problem.

A word of warning- restrain the tensioner when you remove the side adjustment bolt/nut. The tensioner has a pretty good spring inside and, as I found out, can launch itself a considerable distance .

Phil Stewart
 

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