Topic: Replacing Valve Guides

[dannyeven]

Hello...i have a bent valve on a 1977 cb550k.  the #1 intake is bent and i was looking for some tips on A. getting the valve out, and B. replacing the guide.  any tips other than taking it to a machine shop?

[nayto550]

In my experience, cutting the valve from the stem (behind the bend so the stem left is straight), then pushing it out usually works.  As far as replacing guides, I've never done it on a CB, but on heads that I have done, I put the head in the oven at 550 degrees for about 15-20 minutes and the guides will usually fall out or come out with minimal coaxing (the aluminum head expands faster than the steel guides).  Installing the new guides is the pretty much the same, put the new guides in the freezer for a couple hours, bake the head, and they should drop right in.  Just make sure you have the proper driver for tapping the new guides in in case they don't drop right in.  Reaming and honing the fresh guides is usually best left to a machinist unless you have the proper tooling for such a venture.

[dannyeven]

hey, thanks for the help.  how can i cut the valve without destroying the valve seat?

[nayto550]

The last time I had to this, I used a dremel and what seemed like a thousand of those tiny cutoff wheels.  Cut the valve head off the stem, then shoved the tool down the port and cut the stem.  In retrospect, I'm not sure if that would even be possible with the size of the ports on these motors.  Should probably try knocking the valve out with a drift before resorting to cutting it up.

[wrenchmuch]

If you can get the spring off the valve the valve might get looser in the guide as it comes out . You need to get the carbon off the guide tip where it protrudes into the port to avoid damage to the bore the guide fits into . If the guide is damaged and needs replacement you might want to consider taking it to a machine shop . You need a stepped drift to get the new guide in , a reamer or hone to cut it to final interior diameter , and the seat will likely need to be re cut the new guide will likely have a slightly different center from the old one . This would be a great time to fix up the other valves and seats in the head .

[nayto550]

and the seat will likely need to be re cut the new guide will likely have a slightly different center from the old one . This would be a great time to fix up the other valves and seats in the head .

I forgot that part , yes the seats should always be cut and lapped when a guide is replaced.

And wrenchmunch makes another very valid point:  a bent valve is always a good reason to rebuild the whole head!