Re: cam chain rattle...

Posted by sam on Apr 16, 2010; 6:57am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/cam-chain-rattle-tp461888p723295.html

IMPORTANT   the cam chain tensioner on the cb750 is spring loaded but spring is not strong enough after after years of heating. Its a basic flaw.  To get some room, remove the air filter assembly and the remove the 3 screws that hold the tensioner. Remove the tensioner.  Make sure that the mechanism in the engine that the tensioner pushes on moves freely.  Mine was stuck solid. I sprayed some penetrating oil and waited overnight and tapped on it with the end of a small vice grip and it loosened up.  Now disassemble and clean the spring loaded tensioner. Notice that there is a hole at the end of it where you can push an ice pick or small screw driver in to push the rod in that would normally be pushed by the weak spring. So first replace the tensioner mechanism , tighten the 3 screws, loosen the bolt, push the rod in from the hole in the end and while pushing tighten the bolt.    The tensioner mechanism is a weak design but the procedure I described will work.    Even if you disassemble your entire engine, replace the cam chain and the idler pulley inside the engine, the spring loaded tensioner will not work properly. If the wheels in the idler pulley are still in reasonable condition, the procedure I described will do wonders . It really doesn't matter if you do it with the engine running or not running. If you do it with the engine running you will hear the rattle decrease as you push on the rod in the tensioner mechanism. The idler wheel in the engine is made of black rubber.  When you change your oil, if you don't see any little pieces of black rubber, there is a good chance the idler pulley(this is what the spring loaded rod is pushing on) is still in reasonable condition.   Replacing the pulley is a big job because you need to remove the head and more so you want to avoid it if you can.  The procedure I described is actually very simple, the hardest part being the removal of the air filter housing. So you might as well replace the air filter.