[CB500Seattle]

I finally attempted a valve adjustment on my 76' CB500T, as the valves have been pretty noisy ever since I bought it.

Following the shop manual, I rotated the generator counter clockwise until the LT mark aligned with the index mark. Then because I thought the mark on the camshaft aligned with the mark on the bearing holder, I rotated another 360 degrees and set about adjusting the left side intake and exhaust valves. I set them to .0015" (rather than .0012") per some comments I saw on this site.

I spun the generator counterclockwise another 180 degrees (to the T mark), set the right side, and then put everything back together hoping for the best. The results were not good. Right side wasn't even firing and left side sounded terrible.

So after further reading on this site, I decided what I thought might have been the mark on the camshaft (which indicated to me that I needed to rotate the generator 360 degrees to get to TDC on the left side compression stroke) was not actually the correct mark (I can't seem to find a picture anywhere of what that mark looks like).

Following some further tips I read on this site, I put my finger over the left side spark plug hole when turning the generator. I felt a much greater push when approaching the LT mark one full turn (360 degrees) from where I had originally set the valves. Further, the lobes on the camshaft were now pointed away from the cam follower (before they had been pointed towards the follower on the side I was adjusting).

So in this new position, I set forth to re-adjust the clearances. Unfortunately, in this position I cannot get the clearances nearly small enough. The smallest I can get them is about .30 mm (10 times greater than the recommended .03mm). The same is true when I rotate to the T position and try the right side.

So, a couple of questions:

1. Did I have the pistons in the correct position the first or second time?
2. If I had the pistons in the correct position the second time, why can't I get the clearances small enough?
3. Does anyone have a picture of what the mark on the camshaft (that indicates whether you're TDC in compression or exhaust) looks like?
4. Any additional advice moving forward?

 

[J-T]

Do you have the factory service manual for your bike or one of the others?

 

[CB500Seattle]

I do. That's what I have been following to do the adjustments.

 

[76TWIN]

Are you sure you timed it on the compression stroke? Put your thumb over the spark plug hole as you rotate the crank to TDC. You should feel air pressure on the compression stroke.

 

[Lefty]

Forget marks look at cam and think about what's going on. Spring force exerts itself on the cam and it will slightly shift it certain ways

 

[J-T]

The DOHC bikes are a special breed, one of the folks who knows them will be along to help. Surprising to me that the manual doesn't have adequate illustrations but then, I get surprised quite regularly.

 

[66Sprint]

Forget cam indexes or thumb on the plug holes.....WATCH the intake valve..... it actuates (opens), then closes just as the compression stroke for it's cylinder begins.....
Once the valve fully closes, it is about 1/3 of a CCW crank rotation to the LT mark alignment (or T...depending on which cylinder's intake valve you were watching)

 

[CB500Seattle]

Thanks for the responses. Very helpful.

In terms of the lobes on the camshaft, is it true that they should be pointed away from the cam follower when the clearance is adjusted? They seem to be pointed towards the cam follower at one LT position and away at the other.

Pardon my inexperience here (I'm just learning), but is it the lobes contacting the cam follower that in turn opens the valves?

Thanks for any help.

 

[Lefty]

My experience has always been setting them and then you go back and they seem to be tight or loose. If you watch for the moment the valve closes, and then spin another 30 degrees or so and stick the biggest feeler you can in the gap, and then continue to spin the engine till the valve opens, you'll probably notice the feeler is tighter at some spots and looser in others. Cam might not be perfectly round/follower will have wear and makes contact on different parts of its face/the other valves spring tension will cause the cam to rock in its bearings. I suppose if you always recheck at the same spot you wouldn't notice but then what if it's too tight at a different spot? Probably cam wear. The factory clearances are very tight and hard to set if you ask me and that's why most recvommended to set them loose. Honda probably wanted quiet. Be careful setting them at first and spin the engine throughout the closed side of the cam and make sure they're not too tight. The opening and closing ramps of the cam are very gradual so probably no need to worry about 30 degrees or so before and after the valve opens and closes. These are mechanically busy engines bu after awhile you will learn what a loud tappet sounds like and just adjust it then. I check mine once in the spring and I'm usually good to go all year. When I first got it I was constantly messing with it.

 

[jd50i]

I adjusted my 450K6 valves in 1980 and then again in 2016, 11,000 total miles.
I haven't done the 500T, got it in 1994, 16,000 total miles.
Both run good and no abnormal noises.

 

[McReviver]

When I worked for a Honda dealer I had the job of servicing a few of this model. I made a piece of 3/4' aluminum bent into a "L" shape that was about three inches on the long side (with a sharpened point on the end), and 5/8"-3/4" or so on the short side. It was just the right thickness for the short side (necked down in width) to fit in the slot on the end of the adjuster. Then I put a white index card, shaped to fit behind the pointer end. I set the clearance to .002" and made a mark behind the pointer. Another mark at .001". Then it was easier to set up between .0012" and .0015" by the relative distance between the two marks. I think I still have that piece of metal in my tool box after 35 years.

 

[J-T]

In terms of the lobes on the camshaft, is it true that they should be pointed away from the cam follower when the clearance is adjusted? They seem to be pointed towards the cam follower at one LT position and away at the other.
You've got the idea. When you adjust the valves the piston is at TDC on the compression stroke and both valves are closed. When you rotate the crankshaft 1 full turn, with the piston at TDC the engine is transitioning from the exhaust stroke to the intake stroke and both valves are open slightly. Adjusting the valves at this point will result in them being very loose/noisy.

Pardon my inexperience here (I'm just learning), but is it the lobes contacting the cam follower that in turn opens the valves? Yes.
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And I had to add another line so the program would let me reply