Topic: 1981 CB650 Camshaft Installation

[imandrewparks]

Hey everyone! After replacing the starter clutch in my 1981 CB650, I finally got it started to then realize Cylinder 1 and Cylinder 2 weren't firing. I've checked the carbs, and ignition. I'm definitely receiving fuel and creating spark. I then checked compression and Cylinder 1 and 2 read slightly low, so I'm curious if there is a screwed up valve, or bad rings. Let be me forthcoming in saying this is going to be my first engine teardown.

I have successfully removed the head cover, and the cam. Once my buddy comes over I can get him to hold the cam chain that I have wired to the frame while I remove the head.

The reason I am posting this is because I am nervous about the re-installation of the camshaft. I have a basic understanding of how the engine works, but am certainly novice when it comes to correcting timing, etc. Please excuse the potentially stupid questions I am about to ask.

1.) How do I make sure I am putting the cam in correctly? Is there a certain way the lobes should be facing up vs down vs horizontal? Does it matter as long as the notch is horizontal with the head?
2.) Is there a certain way the sprocket should be installed? I don't mean which side do you slide on to the cam, or which side of the sprocket faces out/in, but what I'm asking is rotational direction. Is there a top or bottom to the cam sprocket that needs to face up or down?
3.) Is there such thing as the cam being at TDC determined by how you install it? If so how do I achieve it? Or is that simply just referring to the pistons?

Please drop any tips or other suggestions you may have for a noob like me. Thanks so much!

[scunny]

1 notch horizontal to head, doesn't matter which way
2 sprocket has 2 dimples to align with head, no up or down
3 #1 piston at top, timing advancer on the T timing mark
be very sure the bottom of the cam chain tensioner is seated in it's slot when installing it.
good luck and don't stress it, these are simple machines.

[Flyin900]

If your doing this without a service manual and are a noob then that is not the best choice IMO. While many on these forums are very knowledgeable, there is no substitution for a service manual to give you the correct specs for torque, head gasket, valve adjustment and correct assembly procedures.

If the compression is slightly low then that may not be the cause of the bike not running on those two cylinders. If the two good cylinders are 150PSI for instance and your two low ones are 130PSI then the bike should still run and usually not too bad given two cylinders are low.

Since you have already pulled the motor apart you may as well look further into the valve/ring condition. Doing a leak down test is by far the best way to check a motor before getting into tearing it apart, as that will tell you the condition of your valves and rings quickly.

If you don't have a service manual there maybe one online for free; or there is a website that sells OEM Honda factory manuals in a PDF download costing under $15US. I believe it is called www.servicerepairmanualonline.com where you can check your model availability.

[calj737]

Low compression in #1/#2 is more likely due to incorrect valve adjustment than anything necessitating an engine teardown. If you're popping the rocker cover off, hopefully you're releasing the valve adjusters before so doing. If not, you can bend a valve...

It's also possible you have the plugs/coils incorrectly routed. Left side coil runs plugs 1/4 and right side coil runs plugs 2/3.

Can you confirm these things are correct?

[grcamna2]

Welcome to the forum Andrew.