Topic: Valve clearances: What does your .004 "feel" like

[jessezm]

I've been setting my own valve clearances for years, but I've never really compared what I do to anyone else.  I was buttoning up my motor last night so I had it on the bench, where I've got much more patience for thinking about these things...

Clearances on my CB400f with the aftermarket cam is supposed to be at .004" intake and exhaust.  I set them so that there is drag on the .004" feeler, the .003" feeler slides right through, and the .005" feeler wont go in or if it does it hardly moves and feel like it's compressing the spring some (like I feel movement in the tappet when I pull it back out).  Last night I was really able to tell the difference in sound and feel between .004" and .005".   While rocking the rocker arm I could feel movement in my fingers at .004", the sound was a very muted "tap".  But at .005", there is an audible "click" when I rock the rocker arm.

For those of you who use .004" clearances for your bike, does this generally match with your experience?  I just want to make sure that I'm not setting them too tight...

Also, I noticed after re-checking my valves that the clearances had shifted a bit on some of them.  I rotated the engine several times, re-set the clearances, and rinsed and repeated till things stayed consistent.   I'm guessing this was because the head was just rebuilt and this could have been all the new parts settling in (new tappets and new keepers, valves, guides, etc)? 

[KJ790]

Stick your feeler gage in the middle of a phone book and slide it out. That is about the resistance you should have on a feeler gage to properly set the clearance. From your description it sounds like you are doing it right.

[jessezm]

Hmmm...  It actually sounds like I might be going too tight, then--I always thought if I could barely get the .004" in but not the .005" it was right, but that usually puts me with a little more resistance than you describe above.  That's more like what it feels like when I slide the .003" through...  In reality I'm probably somewhere between the two...  I wonder if I need to go back and loosen them up?

[KJ790]

I wouldn't worry about it too much, if you can get the .004" in and not the .005" then you are somewhere between the two, which is fine. It will always be a range that the valve clearance is supposed to be in, and anywhere between .004"-.005" is fine. being at .0045" vs. .0040" isn't going to make any difference.

[robvangulik]

What camshaft do you use, and what is the effect on the bike while riding?

[jessezm]

What camshaft do you use, and what is the effect on the bike while riding?

It's from Webcam, their #2 hardweld.  Described as their mild street cam.  I don't have anything to compare it to because I replaced the stock cam and bored the engine before ever riding it...  The description on the website says increased midrange and top end I think.

[70CB750]

I believe it is better error towards bigger than smaller space, correct?

[jessezm]

That's what I was thinking too.  I was afraid I'm actually somewhere between .003" and .004", which is why I was a little worried...

I think it's better to hear a little clatter than to hear nothing at all and then burn up your valves...

I'm running a hotter than stock cam and HD springs and hardened alloy retainers, I don't know how that effects what small differences in the clearances mean, though.  I would suspect that stiffer springs and lighter retainers would help prevent valve float at high RPMs, but I'm not sure if that's right or not.

[70CB750]

Maybe Hondaman will reply - btw I have the book coming and this is one of the things I want to learn more about.

[70CB750]

I found this: All four stroke engines have valves! The thing that opens them is called a cam or camshaft, (shown opposite). The term valve clearance or tappet clearance is referring to the "gap" between the cam and the cam follower, or between the top of the valve and the tappet or rocker arm that pushes the valve open. When an engine sounds noisy, rattly or "tappety" this is what they are referring to. Getting valves done, etc is all part of routine servicing.  There HAS to be some free play here as the valve will expand when hot and take up the gap, with disastrous consequences. The valve will not seal correctly and will overheat and burn, while causing pre-ignition, detonation,  valve and seat damage and less power.

All four stroke engines have valves! The thing that opens them is called a cam or camshaft, (shown opposite). The term valve clearance or tappet clearance is referring to the "gap" between the cam and the cam follower, or between the top of the valve and the tappet or rocker arm that pushes the valve open. When an engine sounds noisy, rattly or "tappety" this is what they are referring to. Getting valves done, etc is all part of routine servicing.  There HAS to be some free play here as the valve will expand when hot and take up the gap, with disastrous consequences. The valve will not seal correctly and will overheat and burn, while causing pre-ignition, detonation,  valve and seat damage and less power.

 
We are interested in power though. In an ideal world a valve would be instantly opened and closed. This way they could flow as much air or exhaust gas as possible for a any given opening time.

In practice this is impossible because valves cannot be instantly opened or closed.  Race cams try to get closer to this ideal, but in turn need heavier valve springs to close the valves faster and follow the cam.  One thing we can do to help power with a stock cam is to INCREASE the valves running clearance slightly. 

This works because camshafts are designed to run quietly in your road car, and have what are termed quietening ramps on both the opening point and closing point of the camshaft.  The problem is that for a good few degrees of engine rotation, the valve is S L O W L Y lifting off the seat, and the same in reverse as it returns.  This means that its not sealing so the effective compression, power, induction stroke for example is shortened, while at the same time the valve is not open enough to allow any meaningful gasflow to take place. Setting the valve clearances to the larger end of the allowable range therefore gives more power rather than the expected less power at the possible expense of some valve noise.

http://www.more-power.info/valve-clearances.htm

Makes sense, HM somewhere recommends higher values than the manual - adjust for power not to eliminate tappet noise.

[DYSKORD]

For what its worth, I tighten the valve lash with the correct feeler sandwiched until it doesnt slide. Then start backing off the clearance until the feeler will slide with a "scraping" sensation. Then double check that one size larger feeler won't fit.

[chewbacca5000]

For what its worth, I tighten the valve lash with the correct feeler sandwiched until it doesnt slide. Then start backing off the clearance until the feeler will slide with a "scraping" sensation. Then double check that one size larger feeler won't fit.

I do the same thing as you, but as I read more of these post I am thinking it makes more sense to err on the loose side.  Maybe .003 / .004 as has been suggested by some others.

[Kong]

You do not want to err on the lose side.  Set the clearance to what it is supposed to be, not too tight, not too loose.  The reason you don't want to set them loose is that it will beat the living hell out of the rocker and the portion of the lobe just above what are called the "acceleration ramps" causing premature cam wear and possible breakage and certainly excessive wear of rockers.

When pulling the feeler gage from the space it should feel like pulling a wet noodle out of a dog's ass.  Just a little bit of tug, but not too much.

[05c50]

When pulling the feeler gage from the space it should feel like pulling a wet noodle out of a dog's ass.  Just a little bit of tug, but not too much.

 ???Would that be a homemade noodle, or a store bought noodle?? Now that I think of it, What kind of dog??

.................Paul

[scottly]

You do not want to err on the lose side.
When pulling the feeler gage from the space it should feel like pulling a wet noodle out of a dog's ass.  Just a little bit of tug, but not too much.

I beg to differ. It is far better to be .002 too loose than .002 too tight. Too tight can burn exhaust valves in a very short time. I've never pulled a noodle out of a dog's ass, so I can't relate to that. (How did you get the noodle in there in the first place? )

[jessezm]

(How did you get the noodle in there in the first place? )

The dog ate it?

I will never forget this.  Thank you, Kong.

[crazypj]

When pulling the feeler gage from the space it should feel like pulling a wet noodle out of a dog's ass.  Just a little bit of tug, but not too much.

 ???Would that be a homemade noodle, or a store bought noodle?? Now that I think of it, What kind of dog??

.................Paul

 LOL, dat's funny

[bryanj]

The age old EXPERIENCED maniac er mechanic's adage was that you can just feel 2 thou play and just hear 4 thou play

[DYSKORD]

You do not want to err on the lose side.  Set the clearance to what it is supposed to be, not too tight, not too loose.  The reason you don't want to set them loose is that it will beat the living hell out of the rocker and the portion of the lobe just above what are called the "acceleration ramps" causing premature cam wear and possible breakage and certainly excessive wear of rockers.

When pulling the feeler gage from the space it should feel like pulling a wet noodle out of a dog's ass.  Just a little bit of tug, but not too much.

+1

I know some trusted mechanics who with set the tolerances a thousandth looser during the hotter summer time here in Texas. This is typically prescribed for early 70's and late 60's Hondas where the tolerances are pretty tight. As the years progressed the recommended clearances became a tad looser per the shop manuals. But really what Kong said is spot-on. Also these clearances effect more than just a "ticking noise". Your carbs are also effected and is the reason a valve clearance adjustment MUST be done before a carb sync.

[crazypj]

A few ten-thousandths of an inch isn't going to be a problem.
As long as correct size fits and next size up doesn't it will be fine
If next size up goes in, even if tight fit, it's too loose
Next size down should be very loose fit

[MoMo]

You are using the go/no go technique, which is the way every mechanic I worked with used.  After adjusting a couple dozen or so bikes you can get the "feel" without using the larger feeler gauge to check...Larry

[dave500]

When pulling the feeler gage from the space it should feel like pulling a wet noodle out of a dog's ass.  Just a little bit of tug, but not too much.

ha ha!years ago camping with some mates my big dumb dog ate some ones meat that was wrapped in like a long plastic strip,,i noticed "mack"rubbing his arse on the ground and doing donuts trying to investigate his butt,,he had a half inch piece of plastic poking out of it,i snagged it with a stick and got a mate to call him over and about two feet of plastic came out,,lucky dog,,,,,,back to feeler guages,i snip the rounded end off the finer ones squarely i use, then with a sharpening stone or wet and dry on a flat plate take off the burr and make the edge a little ramp both sides,makes it easier to insert them when youve got the setting correct but cant get the guage back in to double check.

[MRieck]

I would use new/very lightly used adjuster srews in those rocker arms. The quickest way to ruin new stem tips is to use beat up adjusters. I have seen some very chewed up ones.

[jessezm]

I would use new/very lightly used adjuster srews in those rocker arms. The quickest way to ruin new stem tips is to use beat up adjusters. I have seen some very chewed up ones.

I put in as set of brand new tappet screws, Mike, nothing but the best for my baby!

All--thanks for this enlightening conversation!  Fun for the whole family!  Dave I'm going to do that with my feeler gauge before checking the clearances again.

[DH]

If anyone is interested, "go/no go" type feeler gauges do exist and are available in sets similar to the standard ones. The tips of the blades are .001 thinner than the rest of the blade. I.E. an  .004/.005

[MRieck]

I would use new/very lightly used adjuster srews in those rocker arms. The quickest way to ruin new stem tips is to use beat up adjusters. I have seen some very chewed up ones.

I put in as set of brand new tappet screws, Mike, nothing but the best for my baby!
All--thanks for this enlightening conversation!  Fun for the whole family!  Dave I'm going to do that with my feeler gauge before checking the clearances again.

Nice. Good foresight on your part Jesse.