Valve adjustment question.

[nickajeglin]

I know, I know. This has been gone over a bazillion times, but I do have a very specific question. Several of my valves had clearances of less than .0015". That is my smallest feeler gauge, so I'm a little worried about what shim I should try to come up with. The current plan is to assume a .001" clearance, and go from there. I sure will be annoyed though, if I get a 280 shim (for example) then the buckets/shims snap up further because they were riding on the cams and I need to go and find thinner shims.

Another question I had: since I had the valve cover off, I figured it would be a good time to check on the cam chain tension. I had a he'll of a time getting it to tighten up. I finally got it a bit better when I realized that I shouldn't be holding down the rear brake while turning the engine, but it's still not super tight, there's maybe 1/8" play. Any tips on getting it a bit tighter?

[nickajeglin]

I'm sure most of you more experienced people know, but this is a DOHC.

Edit: also, what's the story on the recommended clearance? FSM gives .002 intake and .004 exhaust iirc, but the people over at the DOHC forums say .005 all round is the way to be. Thoughts?

Also, if someone with a lot more understanding of engines could either explain or point me in the right direction on why the clearance should be whatever it sould be I would be very grateful. What happens when it's too tight? Too loose? Pro's and cons of both?

[TOOLS1]

Can't help you on the valves, but the cam chain has a spring tensioner. It should provide all the tension needed to adjust the chain. Also the chain must have some slack!
TOOLS

[shinyribs]

If the valves are too loose it will be noisy. If they are excessively loose,or loose for an extended period of time,you can damage the valves and seats from the extra slack causing the parts to bang around harder than they should.This is worse scenario,but still a possiblity.Loose valves also hurt your performance by effectively making your cam ''smaller'' since it is not translating the full profile of the cam lobe into valve motion.

Too tight of a valve can causing poor sealing,resulting in ''burnt valves''. Burnt valves occur because the valve head only gets a chance to cool for the split second that it come in to contact with the valve seat in the head. It's a rough life being a valve,especially an exhaust valve! IMO, I'd rather be a touch loose(for cooling purposes) than too tight. Not too loose,just set on the loose side of specs. JMO,of course.

 I'm not really up on DOHC ikes,but this holds true for any internal combustion engine with valves. Hope this helps.

[RodneyCB750K1979]

You need to find out the thickness of the shim that is in there now.  Use a micrometer. Once you know the shim thickness that is giving you the 0.0015 inch clearance, you can determine the new shim thickness.

For example, the old shim is a 280 having a measured thickness of .112 inch.  Your target is 0.0035 inch. So, you need to get a new shim with a thickness of .112 less 0.002 inch (.0035 - .0015).  Or, you need to get a shim that is 0.110 thick.  It will probably be around a number 272 shim but you need to verify the thickness using a micrometer.  

[nickajeglin]

Thanks for the lesson shiny, I like to know why I'm doing things a certain way. And thanks tools, I was under the impression that the chains should be tight as a drum.

Rodney:  I pulled each shim one at a time and measured them. I ended up making a chart. My concern is that I can't actually measure the lash on 3 of my valves because the .0015" gauge doesn't actually fit.  So the gap is somewhere between .001 and 0. I think if the shims were actually riding on the cam, it could even be worse than that.

[icerigger]

If the clearance is less that 0, I guess that should be called interference, the cylinder will have less compression. If the compression is okay, assume the clearance is zero and choose the new shim from the table accordingly.
 

[nickajeglin]

That's exactly what I wanted to know ice rigger, thanks for the info, and for the terminology. Now I just have to go find a compression tester (grumble grumble)

[Lucky 1]

You need to start following the instructions in the workshop manual.

Cam chain adjustment is not about how tight you can get it.
Follow instructions.

[Lucky 1]

Stop taking information that you cannot trust. Just go read the book yourself.

.005 thousandths on intake and exhaust is incorrect.

[RodneyCB750K1979]

I learned fitting shims is by trial and error. You can measure and calculate all you want, but you'll usually miss the target.  Pickup a few shims greater and lesser than your estimate.  My Honda dealer let me rummage through his supply of shims, wrote down how many I took, subtracted what I returned, and only charged me for the number I actually kept. I kept some extras for future tuneups. Ended up spending about 25 cents per shim.  As far as the tight ones, I'd figure .00075 or .001 inch starting out and go from there. Make sure you are measuring with the cam lobe away from the shim.

[nickajeglin]

There's no need to be unpleasant. The factory manual is notably brief in areas, especially for someone as inexperienced as I am.

In any case, I found a great shop just five blocks away from my house, the old mechanic there was more than willing to swap shims with me, as well as give me some pointers.

I finished up the valve adjustment to FSM specs today, and I'm pleased to say that it's like a whole new bike. It must have never been adjusted, as there was definitely some interference happening. I ended up swapping a few shims twice because of that, but luckily, the serendipitous parts bike had exactly what I needed.

The bike now starts instantly, even though it sat all last week, it idles far far better (still a little uneven), and there is a surprising increase in power. I about fell off the back of the seat pulling onto a major road.

Next stop is the carbs to fix the rough idle. I think I will feed them some seafoam first and see how that works. I will probably stick a fuel filter behind the petcock first though, so no gunk gets washed out of the tank into the carbs.

Thanks for the help everyone!

[nickajeglin]

Yeah,  that's what ended up happening Rodney. I had a full sheet of notebook paper covered with messy graphs and conversions from mm to in,  bit once I actually started swapping shims, I just tossed the thing. I had 5 spares at first, and trial and error with those got me through 14 of the 16 valves.

[icerigger]

Where did you find that guy? My local stealership charges me $6 each for OEM shims.

[seestheday]

My local Honda dealership will charge me $7 if I want to buy a shim, but will do an even trade if I bring in an old one.

[seestheday]

Aren't there a few documented cases of clear errors in the DOHC FSM?  Like saying that the accelerator pump on the DOHC carb is adjustable when it isn't possible to actually do it?