Valve clearances too loose/tight.

[alhendo1 3,031]

Okay...just been reading Staningrimsbys post re how to adjust valve clearances. ...I've read a few instances where the nc clearances all seem to be slightly too loose or tight from the factory....as the video in the thread shows.....am I right in saying Honda don't specify checking these till the 2nd service/16k and if so...as a mechanical noob question......what damage can be done if they are out of tolerance?

[Dunnster 1,650]

I think too tight is much worse than being loose, but being loose won't do the engine any favours. 

I checked mine at 16k 

cyl 1 IN & EX were on the tight side

cyl 2 IN was tight but in spec EX was tight. 

Reset to spec and will check again at 24k. 

[Tex 36,816]

Valves (like Baby Bear's porridge) are best when they're 'just right'. If you can't get them right (?!) then you want them a little on the loose side.

 I'm camping in Yorkshire (Yay!!) at the moment with only sporadic internet so I can't go into much detail. But you don't want tight valves. 

 

 

[Guest Hati]

The 700 NCs have valve clearances prescribed every 12k (8k miles) service. The 750s changed to 24k (16k miles). Obviously Honda decided that there is no need to do it more frequently.

[Graham NZ 1,186]

2 minutes ago, Hati said:

The 700 NCs have valve clearances prescribed every 12k (8k miles) service. The 750s changed to 24k (16k miles). Obviously Honda decided that there is no need to do it more frequently.

 

Even that is twice as often as the Jazz 1340cc called for.

[Guest Hati]

Yes, but the NC engine is only a distant relative of the Jazz donk, with only a few parts and mostly the principals common, Graham.

[Graham NZ 1,186]

Yes, Hati, but surely the con rods, pistons, valves, rockers, adjusting screws and cam profiles will be common?  If so why would clearance conditions differ?

[Guest Hati]

IIRC it's only the con rods and pistons... Been a while since I read about that.

[Tex 36,816]

I thought that Jazz had hydraulic lifters? The valve train is completely different anyway.

[Graham NZ 1,186]

8 hours ago, Tex said:

I thought that Jazz had hydraulic lifters? The valve train is completely different anyway.

 

The 1340 has screw and locknut.  The 1500 may be different.

[trisaki 2,029]

I've done a few nc700 at 8000 miles now and I would say don't ignore  the service  because  everyone  has had to have at least 2 valves adjusted and one needed all the valves adjusting  

[Tex 36,816]

5 hours ago, Graham NZ said:

 

The 1340 has screw and locknut.  The 1500 may be different.

 

By jove, sir, you're right. The Fit (which I always thought was the Jazz with a different badge) has the different system. Or something.. I understood the first valve check was 105k miles, but a search on Google shows all sorts of different (and confusing) information.

 

 I guess the NC needs more frequent checking over the Jazz because motorcyclists tend to rev their engines to the red line more than the average car driver? But I'm probably wrong about that too!

[embee 7,288]

Different markets for the Jazz/Fit used different engines. Also the earlier UK Jazz had the 2 plug engine, the NC uses the technology from the next generation 1340 which I think in the car was a VTec, so different valve train detail.

[Slowboy 20,359]

20 hours ago, alhendo1 said:

Okay...just been reading Staningrimsbys post re how to adjust valve clearances. ...I've read a few instances where the nc clearances all seem to be slightly too loose or tight from the factory....as the video in the thread shows.....am I right in saying Honda don't specify checking these till the 2nd service/16k and if so...as a mechanical noob question......what damage can be done if they are out of tolerance?

Too tight and you risk burning out the valves and damaging the seats, especially on the exhaust side. Too (very) loose and the engine will run worse rattle really badly and you might damage the valve gear. Either way a little loose is better than too tight.

Its worth doing, it's not too hard to do, or worth getting it done at the right time if your not sure.

[alhendo1 3,031]

Thanks for the replies folks....I won't be doing anywhere near 16k in 24 months but is this something that you think would benefit from doing earlier....or am I just creating another issue for myself?...I'd imagine Honda specify it this way/time as they're confident that when the engine leaves the factory they're set correctly. ...by the looks of it some aren't! 

[Graham NZ 1,186]

10 hours ago, Tex said:

 I guess the NC needs more frequent checking over the Jazz because motorcyclists tend to rev their engines to the red line more than the average car driver? But I'm probably wrong about that too!

 

I think you're correct, Tex.  It takes some time to alter the habit of revving bike engines.  To me the NC is a cruiser but one which is truly comfortable and has enough cornering clearance to be safe.

[Tex 36,816]

14 hours ago, alhendo1 said:

Thanks for the replies folks....I won't be doing anywhere near 16k in 24 months but is this something that you think would benefit from doing earlier....or am I just creating another issue for myself?...I'd imagine Honda specify it this way/time as they're confident that when the engine leaves the factory they're set correctly. ...by the looks of it some aren't! 

 

I'm struggling with the concept of Honda building an engine with adjustments out of spec. I just don't see it happening.

 

More likely (to my mind) is 'enthusiastic amateur' mechanics not understanding 'go - no go' or 'sliding fit'.

 

'Back in the day' I had to do all sorts of adjustments to Moto-Guzzi, Ducati, Triumph & Norton bikes on PDI. The Hondas were always perfect. Every time.

[SteveThackery 3,090]

4 hours ago, Tex said:

 

More likely (to my mind) is 'enthusiastic amateur' mechanics not understanding 'go - no go' or 'sliding fit'.

 

 

On my course we were told that you can't use feeler gauges to measure a gap exactly, nor to set it.  The idea is that ALL dimensions everywhere in engineering have a tolerance - there is no such thing as an exact dimension.

Suppose our clearance is supposed to be 0.17mm - it should have a tolerance specified, such as +/- 0.02mm.  So the gap is allowed to be anywhere between 0.15mm and 0.19mm.

The correct check for the clearance is to confirm that a 0.15mm gauge slides freely, and a 0.19mm gauge won't enter.  That is the go - no-go test Tex refers to.  What you don't do is check for a "sliding fit" with a 0.17mm gauge, because almost every valve clearance will fail that test unless it is within a few microns of 0.17mm.

You can try that sliding-fit method when setting the gap, but you should still use the go - no-go test to confirm it afterwards.  By the way, there's no reason why you couldn't use +/- 0.01mm when setting the gap (assuming you've got feeler gauges that fine), because you know it will then comply with the +/- 0.02mm test.  

At least that is what I was taught at uni.  Does anyone know different?

Edited June 15, 2017 by SteveThackery

[Tex 36,816]

Anyone who says different is on thin ice..

[Dunnster 1,650]

3 hours ago, SteveThackery said:

 

On my course we were told that you can't use feeler gauges to measure a gap exactly, nor to set it.  The idea is that ALL dimensions everywhere in engineering have a tolerance - there is no such thing as an exact dimension.

Suppose our clearance is supposed to be 0.17mm - it should have a tolerance specified, such as +/- 0.02mm.  So the gap is allowed to be anywhere between 0.15mm and 0.19mm.

The correct check for the clearance is to confirm that a 0.15mm gauge slides freely, and a 0.19mm gauge won't enter.  That is the go - no-go test Tex refers to.  What you don't do is check for a "sliding fit" with a 0.17mm gauge, because almost every valve clearance will fail that test unless it is within a few microns of 0.17mm.

You can try that sliding-fit method when setting the gap, but you should still use the go - no-go test to confirm it afterwards.  By the way, there's no reason why you couldn't use +/- 0.01mm when setting the gap (assuming you've got feeler gauges that fine), because you know it will then comply with the +/- 0.02mm test.  

At least that is what I was taught at uni.  Does anyone know different?

Spot on, Steve 

[Taipan 110]

Checked mine ta 16k and 6 were too tight and one too loose. I didn't bother to check how much by though, just reset them correctly.

[embee 7,288]

Just to add a little background behind cam profile design for understanding.

Taken fro Google images

 

The lift (red), velocity (green) and acceleration (blue) curves look typically like this. The values are given relative to engine speed in some way, depending on units used, so lift is inches (or mm), vely is in/deg, and accel is in/deg^2. In metric you'll see units like mm/rad (same basic idea as in/deg).

The opening and closing have "ramps" which are there to take up the clearance and load the system on opening, and to allow the elastic compression/deflection to unload on closing in a controlled manner before the valve actually touches the seat at a relatively low velocity.

The system needs to compress slightly to take up oil film clearances and flex in the rocker and camshaft etc in order to overcome the spring seat load. Similarly on closing the deceleration of the valve system requires loads which deflects the components and this then unloads and the deflections release, which can induce vibrations before the valve actually touches down, This can result in more than one contact event, or chatter, which will give noise and wear and is to be avoided. The ramps take this into consideration.

Ramps are typically "constant velocity", though sometimes a constant acceleration opening ramp is used, often where hydraulic elements are used. This diagram shows such a case, you can see the closing ramp is a constant velocity design. The idea of this is that regardless of where the valve actually touches down, the velocity (and thus energy/impact) will be the same (at a given engine speed).

I'd expect a manual system like the NC to have constant vely ramps both ends, so providing the clearances are such that the contact points are on the ramps, it will work OK. The heights of the ramps take account of thermal expansions and deflections due to dynamic effects, plus some allowances for wear/setting tolerance.

The accel curve gives the requirement for the valve spring loads, which must be able to accelerate the valve system to maintain contact at all times, plus provide sufficient seating load for heat transfer and gas sealing, keeping the seats clean etc. but without resulting in too high loads for lubrication and friction or unnecessary wear on the other components. Spring design is a lot more complex than simply matching the accel curve, they are a very dynamic item with potentially high internal vibration/surge etc, and tricks like dual rate designs can be used to change the natural frequency between lift and closed periods which will very effectively damp out internal vibration.

There is another 3rd derivative (vely is first derivative, accel is second) called "jerk", which equates to impulse if you like, this indicates how rapidly the accel and thus forces change and can be significant for noise/vibration.

Cam profiles were once upon a time based on "three arcs" etc, basically sections of curves joined together, but these can result in very high jerk at the joins so to speak, where the lifts and velocities match but the accels don't, so a theoretical infinite jerk. Modern profiles are polynomials where the functions are at least continuous so avoiding infinite jerk.

Edited June 29, 2017 by embee

[matt28 401]

Just done valve clearance adjustment on my NC.

Mileage is 7600, bike is 3 years old.

All 8 needed adjustment. 

In were loose, outs tight.

Adjustment was out - 0.28, in 0.18 mm.

[CFB 4,601]

That worries me!

Not telling you how to suck eggs, but that sounds like the crank was slightly off the marks and cam wasn't quite at the correct timing.

It might be a good idea to double check. Ball ache, I know but better safe than sorry.

[SteveThackery 3,090]

19 hours ago, matt28 said:

Just done valve clearance adjustment on my NC.

Mileage is 7600, bike is 3 years old.

All 8 needed adjustment. 

In were loose, outs tight.

Adjustment was out - 0.28, in 0.18 mm.

 

Could you tell us how loose and tight they were?  And exactly how you checked them?  This is interesting.