Valve Clearances tightening

[bflint]

My exhaust valve clearances have tightened over time to the point they are at the minimum recommended clearance of .010. I thought they should loosen instead of tighten. Does anybody have any thoughts on this? Also, am I over expectant to think that the dealer/mech should have adjusted the Exhaust valves to their mid value of .011?

--------------------------------------------
Honda Mfg Clearances (Ex spec: 010-012, In spec: 005-007)
--------------------------------------------
10/18/2016 Mileage = 11,532
#1: Ex 012-012, In 006-007
#2: Ex 011-011, In 006-007
#3: Ex 012-012, In 007-007
#4: Ex 012-012, In 006-007
Note: 1st check.
--------------------------------------------
8/4/2018 Mileage = 29,181
#1: Ex 28-28 (011-011), In 18-18 (007-007)
#2: Ex 28T-28 (011-011), In 18-18 (007-007)
#3: Ex 28-28 (011-011), In 18-18 (007-007)
#4: Ex 28L-28 (011-011), In 18-18 (007-007)
Note: Exhaust a little tighter. Intake a little looser.
--------------------------------------------
3/17/2020 Mileage = 42,500
# All: Ex 010, In 006 } Service Dept front desk lost details
Note: All much tighter. Exhaust clearances at minimum tolerances.

[Inhouse Bob]

I'm interested to hear from the experts on this one. I've always been curious about how valves get outta whack.

[pekingduck]

The common thinking is that valve clearance clearances increase as cams and bearings, shims, and rocker arms wear. And it's true to a small extent. But the clearances usually come from valve seat inserts in the head getting their sharp edge surfaces constantly hammered by the edges of the valves. Over the long haul, the valve seats will get wider and the valves will lose shape, becoming "tulip" shaped in extreme cases.

[peterbaron]

If valve clearance is set perfectly = in the middle of its min and max tolerance by bucket/shim from the very beginning, good quality material, proper oil/intervals and fuel additives are used, there is very small chance that valve clearance will go out of specs. It does not mean skipping valve clearance checks.

Valve clearance set by screw/nut requires more frequent adjustments.
Hydraulic lifters, another story...

In general, most common failure are; wear, carbon build up around valve stem/ seat/lip, defect/failure, abuse, improper maintenance and unqualified personel servicing your engine.

[max]

Interesting to hear from someone who has extensive experience with valve clearance.
Nice insight Pekingduck

There may be a reason why new camshaft lobes are ground but not as fine as the bearing surfaces from new,
they may want them to wear some off on purpose and widen the gap as compensation for when the seats wear in and close the gap.



A major improvement over the old adjustment screw system;



Here is a link to a forum that describes what happens when valves wear to the point of no clearance and what the repair turned out to be;
https://bayarearidersforum.com/forums/sh...adjustment

This is why like peter said we keep an eye out and check with practical intervals ( spreadsheet ) for our bikes.

There is a small risk involved when taking the camshafts out and may not outweigh the benefit depending.....
Just my un-educated thoughts,thanks Bflint.

[Gone in 60]

For this reason, when my Bonneville hit 12k and I did its first valve check, I set them all toward the wider side of the range. Three valves were under spec at that point. I figure with the tendency for clearance to tighten over time, I would buy some mileage before they would need to be adjusted again.

As to the risk of removing the shafts, of course I dropped an alignment pin into the engine, so the thought of not having to do that again is welcomed.

[dave]

As to the risk of removing the shafts, of course I dropped an alignment pin into the engine, so the thought of not having to do that again is welcomed.

How did you get that alignment pin out?

[zirconxi_imp]

Interesting to note that the valve usually get tighter as mileage climb. The 1st time I check, my CB had been on the loose end limits and wondering will it get more loose or more tight, but riding privileges had been scarce lately and I can't clock enough mileage for next check.

When clearance getting smaller, will it make the top quieter or louder? Some old mech told me when valves clearance is out of spec, there will be baby bird chirping sound... But i read in some motorcycle forum and they claim tighter valve will be more quieter hence can't know when its too tight until too late..

[Gone in 60]

Dave- I put RLETs on the Bonneville and the pin floated back up the breather tube by itself.

[LakeWylieJoe_imp]

If they are going to charge you full price for the clearance inspection/adjustment job, they should set all valves back to the center of the spec range. If a cam or both have to come out, may as well get things exactly right. I always set my valves to the center of the range so if they drift one way or the other a bit, they'll still be fine.

Hypothetically, if a customer agreed ahead of time with the shop that if any valves were right at the edge of a spec limit (and the rest were within spec) they could be left alone in exchange for a lower cost, that would seem to be okay.

Pulling the cams adds a lot of work to the overall job. Especially since the cam chain isn't long enough to allow the intake cam to come out with its sprocket still installed.

I had one exhaust valve out of spec (loose and ticking) at the first check and none out of spec since then with 30,000mi on the clock now. However, I've swapped at least a dozen shims over the next two checks to bring borderline valves back to the middle of their spec range.