1981 CB750 How to check your valve clearance or valve lash

Demonstration of how to check your valve clearance. Also called valve lash.

[@Mechanicalcircus1]

The bolt thingy you turn is the Rotor. It’s the bikes charging system and the thingy hanging down is your stator. When the motor spins, it turns the rotor making contact with little brushes housed inside the stator cover generating AC volts. Your rectifier converts the AC to DC to keep your 12VDC battery charged. Hence the Regulator/Rectifier. Awesome stuff. Checking the valve lash and replacing shims on these are easy peasy compared to other bikes. 👍🏻

[@Toehead698]

Thanks for the video, very helpful

[@TheSeestheday]

glad you found it useful :-)

[@R3d1100f]

removing the plugs also allows for a quick indication of the piston is on the compression phase or not.

[@WoodrowfolloweroftheMessiah]

Thanks! 👍🏻🙏🏻😀

[@bfpeake933]

good vid Simon, just too bad you ended it without actually SHOWING the shim coming out, OR explaining the use of the chart for selecting and replacing the proper SIZE shim... but a good vid, need more people doing this (DOHC) motor. ~ps. its not a wise idea to use a magnet on the shims in case they become magnetized and attract metal fragments :(

[@matthewzotta7577]

Hey Simon, great video! I am going through this process on my 1981 CB750 Custom as well. I have seen many people saying that .005 inches is optimum but when I look at the service manual, it suggests .003 in. is optimum with -.001 in and +.002 in. As .005 does fall in the high range, what is the reasoning for going to the high end of this spec? It is causing me probably too much anxiety but I was just wondering if knew the reasoning/advantage to going to .005 in? Thanks!

[@ryanmcgehee9817]

Maybe a dumb question, but I went to do this today, I removed the valve cover bolts(8) and the speedo, valve cover doesn't want to budge...am I missing something?

[@TheSeestheday]

Good idea regarding the pen magnet. I have been meaning to pick one of those up. Now I have a good reason. I guess pulling the plugs would make the engine turn more easily. Other than making the job a little easier is there any reason to pull the plugs? I'm always super paranoid about anything falling into the combustion chamber.

[@alexokp]

Two questions: When you turn the wrench "forward", is that clockwise? Also, where do you find shims to fix the valve adjustment? Thanks for the video, ton of help.

[@jonfranchi4446]

Good: helpful video. Bad: Really hard to hear.

[@rodneypopper666]

Great video very helpful. So, for example with the one that was too tight, you add a thicker shim to create more clearance? And vice versa for the sloppy one? Also when doing this do you need to put in a new valve cover gasket and bolt seals? Thanks.

[@TheSeestheday]

rodneypopper666 thicker shims create less clearance. The shims are filling a gap.You may or may not need a new valve cover gasket and bolt seals. If they are in good shape you can re-use them.One thing I would recommend, is that you get a genuine Honda valve cover gasket. I've had trouble with aftermarket ones leaking.

[@TheSeestheday]

you can gets shims from your honda dealer. ask them if they will swap you with your old ones. they often do a straight swap, ot do it for cheap.

[@caroltenge5147]

This is what I mean,, If my bike needed a swap of these shims, over 30 years old, I would have to stop working, look up a dealer, then call to find they dont have any, or swap if they did.... again Ill say if its running smoothly, just leave it alone. Have a nice day.

[@trevorwolters4065]

Let me try this again are u sure that DTC the lobes in the cam are facing away from the plugs My cb900 DTC 1-4 the lobes face towards the plugs timing and everything else is based on that

[@scal760]

Do they wear out. I tried with .005 and went in fine on intake side but not exhaust side. How do I know which to use. And I hear knocking on the exhaust #4 side what do you think it is? Cam chain is fine having trouble with point. And spark plug looks like it is richer than the rest

[@TheSeestheday]

Yes they wear out, that is why you need to adjust them. Do you only have a. 005 measure? It sounds like you are probably too tight exhaust side, but your comment is sparse on details so I can't be sure. If you get too tight, you will hear a ticking sound when the engine is running. Is that what you mean by a knock? If not, then it's likely something different.

[@johnwellybobs]

+Simon Austin They get tight through the valves wearing into the head, making the gaps smaller. Too tight and when the engine is hot the gap is taken up by expansion of the metal and the valves no longer close correctly, leading to poor running. The gaps should be 0.08mm (+0.05/-0.02) or 0.003inch (+0.002/-0.001) for both inlet and exhaust. (more for scal760)

[@andreasn]

How did you get the gasket off without taking the motor out? Please answer :)

[@andreasn]

Sorry, i see youve uploaded a video. Subscribed.

[@trevorwolters4065]

de I think dead top center ithe lob should be facing the spark plug 1-4 cylinder are u sure cb 900c lobe face towards plugs

[@Ronniegodfrey67]

speak up bro!

[@orazioolracid9577]

whats with the gay low voice?