Valve clearances

[icerigger]

Hi all,

I bought a '79 CB750K a couple of weeks ago and have been looking at a couple of other forums. This one looks a lot more friendly.

Anyway, one of the other forums recommends nominal valve clearances to be set at .005" instead of the FSM recommended .003" and I thought I'd ask your collective opinion before starting.

Right now I've got a couple that I can't get a .0015 under, so it really needs it.

Thanks,
bob

[TOOLS1]

Welcome to our friendly forum. I always adjust my valves to .002" intake, and .003" exhaust as per the factory recommendations. However some feel that they should be adjusted a little looser, so that the valve will have more time to dissipate heat into the head, but I feel that Honda knew what they were doing, and I can't stand valve noise.
TOOLS

[cdaiscool]

Running them loose also causes the cam to wear out much faster, as its slapping the shim, versus just pressing on it.

I x2 on the run 'em per the FSM.

[seestheday]

Tools, what doesn't the valve noise sound like?

All of mine are set between .004 and .006 and I am trying to eliminate some of the rattles.  I'm starting to become a little too obsessed with my bike running smoothly.

I had one valve that was at .008 that I just fixed and it improved things, but not completely.

[TOOLS1]

It is a constant tic, tic, tic, tic... and speeds up with RPM. I don't know what the clearance is supposed to be, for DOHC engines. I have only done the SOHC engines.
TOOLS

[cdaiscool]

Those are the right clearances.

[seestheday]

Ya, I have a little tic tic tic that is going on that speeds up with the revs.  Now, why does that get caused by having clearances that are too big?  I'm trying to think logically and it seems to me that it would be caused by having clearances that are too small.

[icerigger]

The thinking on the other forum is that .003 is too tight and once the metal expands the valves may not fully close, causing compression loss, burnt valve faces etc.

Sounds like you guys have never had this problem.

[icerigger]

The tic tic tic would be the cam lobe slapping against the shim face, louder because of the shallow angle of impact and higher speed farther from the centre of the cam.

[seestheday]

Ah, that makes sense.  Thanks.
I guess I could reduce it significantly by making all of my clearances around .004 instead of leaving the ones that I have that are currently at .006.

[icerigger]

Yep, I  think I'm going to go with the FSM spec of .003, +.002, -.001 or somewhere between .002 and .005.

Thanks,
bob

[icerigger]

Sorry, the above specs are for DOHC, my sig should read '79 CB750K

[robs750]

Did you get them adjusted?

I have four exhausts that will not accept a .0015" gauge.I'm going to grind the shims to get the correct clearance.

I also have been to the other site I think you are talking about.They are sticklers for  not following the rules but have been very helpful.

[Re-run]

I open mine up .001 on both sides. This tip came from a racer in the 70s that really knows his stuff about the sohc bikes. Heat will cause these parts to expand, which is why you put in a gap in the first place. Adding a bit more actually reduces wear on the train, at least in the sohc. The amount of extra noise in negligible.
Some bikes these days actually give a RANGE to have the vales set in. For instance, my rebel, is something like .005 to .008 so I see absolutely no reason to not open your settings by .001, I would do it too.

[Lucky 1]

You cannot be too obsessed about how the bike runs. LO...lol

[Lucky 1]

Many people adjust the valves and think they are done.
WRONG.


Now go back and check the exhaust valves that are supposed to be .003
insert a .004 thickness gauge in the exhaust valve tappet.....un huh.... fit right in didn't it?
Then take your .002 and see if that will slip in. It SHOULD slip right in.

Do the same with intakes..002 check with a .003 see what I mean.

That is how we did it at the Honda dealer that I worked at.
So when the customer said, " I did it like the book said and I still hear a noise."
Then after we checked them and re-adjusted, the customer said, "Gee you guys are good."

All we did was make sure they WERE right.

[Lucky 1]

Yes not a bad idea. Then you know it is protected.

[icerigger]

Yeah, finally got them within spec, although most are at the upper or lower tolerance. Lucky's right, it's a moving target. Had several that wouldn't take a .0015" like rob above, replaced a 290 with a 285, should have given about .005", measured over .007". Most took several iterations, and at $6.00 each from the dealership an hour away it was a costly process. At least I've got a few that I can have ground down to size for next time. Luckily my brother-in-law is a toolmaker and can grind them down for beer.

[robs750]

I removed all of the exhaust shims yesterday.I replaced the shims with quarters so I could move on to the next.
I had a little trouble with the Motion Pro tool on the number one valves.The tool would slip off to the left only compressing the bucket on the left side.I had to place a small screwdriver in between the lobe and tool to make it work,all the others were good.
By doing the math,there is only one shim I can swap to get a good clearance.

Icerigger,The difference between a 290 and 285 shim is only .0019"!

The math.....devide the shim size by 25.4 to convert to inch.So 2.90mm devided by 25.4 = .1141".
A 2.85 shim is .1122".Hope this helps.

[icerigger]

Just pointing out that the math doesn't always work. I put together a spreadsheet based on measured gaps & installed shims targeting .08mm. Then went to the dealer to buy the recommended shims. BTW, the dealer I went to had shims in 0, 2, 5 & 7 increments, so it should have been a snap to get within a thou of nominal. Only 3 out of 8 that needed adjusting were okay after replacing the shims, the rest were on the high side. Apparently this is the machines way of telling you to bring it more shims. Another trip to the dealer and shuffling more shims, I actually changed another 8 with swaps to get them all into spec. I pray I will never have to do this again.

I had the same problem with the MP tool on the number 2 ex, it's a real pain if it slips after you take the shim out.

bob