Valve Clearances...how can you tell they're out?

[alhendo1 3,043]

Morning folks...as per the title...(I tried googling this for my cb500x and all I could find was how to's etc)...how would you know if your clearances were too tight or too loose....is it an audible thing or would you lose power accelerating or something similar...or would this only be noticeable when disaster struck and the valve receeded or whatever they do....there's lots of info re 500s valve clearances that found most in spec but one, two or sometimes more out of spec.....what would the symptoms or warning signs be....thanks in advance. Alan........and so to bed....off nightshift😅

[Slowboy 20,408]

The easy answer is to get in there and measure them, if they are far enough out to lose performance, then the chances are, all be it small, the damage could already have been done. You might hear a rattle if they are very loose, and I do remember Tex saying a tight one rattles to. If they are slightly out it's unlikely you'd notice anything.

 

Please feel free to correct me if I'm wrong anyone.

[Tex 36,817]

The ‘tight rattle’ was the old OHV (pushrods) motors. Brian is quite right, the only way to establish whether your valve clearances are correct is to measure them. Too small a gap will risk valve/seat damage and too large will result in reduced performance excess noise and faster wear. 

[Trev 18,613]

Rocker cover gaskets arrived yesterday for my Guzzi V7 so will be checking valve clearances this weekend, to me it sounds a little noisy but that may just be how they sound.

 

Looks like a pretty straightforward job but then so did removing the rear wheel of a CBF125 last night until it became clear that the wheel spindle had seized in. An hour later I was carefully trying to recapture the thread on the end of the spindle after having to resort to hammer and punch. A patch of rust had developed on the part inside the brake shoe hub which wouldn't let the spindle through the bearing. I also now need to replace the rear wheel bearing as well as the tyre which was the original reason for taking the wheel out 

[SteveThackery 3,090]

Totally agree with what's been said already.  The only symptoms of loose valve clearances are excessive noise*, and if the clearances are too tight you won't know until you get a loss of compression.**

 

* Let's be honest, if the clearances are so loose as to cause a noticeable loss of performance, then the din will be unmissable.  The higher accelerations in the valve gear arising from excessive clearances may (probably will) lead to excessive wear.

 

** If a valve is held slightly open during combustion the hot gases pass through the tiny gap between the valve and the seat and "burn" it, causing a runaway effect until the valve is "burnt out" and that cylinder will no longer due to loss of compression.

 

So, the only reliable way to know if they're OK or not is to measure them.

 

 

Edited July 26, 2018 by SteveThackery

[embee 7,288]

The cam profiles have "ramps" at each end with what is termed a "constant velocity" (for non-hydraulic systems anyway, see red line in picture). What this means is a constant rate of lift versus angle, clearly the actual velocity depends on engine speed but cam details are in terms of angle. As long as the contacts are made (opening and closing) on the ramps then in theory the noise will be more or less the same at idle. Valve train noise at speed is more complex than this, but at idle this aspect is a large part of it.

The clearances would have to be a long way out to really hear all that much difference usually, the bigger risk is with tight clearances which in extreme circumstances can prevent exhaust valves from seating fully, resulting in gas leakage and overheating. Not something you want.

 

As others say, simply check them at sensible intervals, the NC750 is at 16k miles. The 700 recommended 8k but I see no reason why this could not also se the 750 intervals, there was no significant technical change that I'm aware of, and experiences of folk have suggested this would be absolutely fine.

 

 

[Tex 36,817]

Didn’t Andy M say the shims could be done on a CB500 without removing the cam? 

[trisaki 2,029]

I have checked valve clearance on a few ncs now at either 8000 intervals  (700) or 16000 (750)  some have not needed to be done others needed all 8 to be adjusted (tight ) customer had been quite happy the way it was running  but even happier  afterwards  because  it was smoother and revved better  -have them checked at the correct mileage 

[Slowboy 20,408]

3 hours ago, Tex said:

Didn’t Andy M say the shims could be done on a CB500 without removing the cam? 

He did, I think it's a bit like my CRF where you can slide the actuators over to access the shim.

[Tex 36,817]

28 minutes ago, slowboy said:

He did, I think it's a bit like my CRF where you can slide the actuators over to access the shim.

 

Thanks, I thought so. Similar to the later Triumph twins, then. Got to be easier (and cheaper) to service that way.  

[Dunnster 1,650]

On checking mine, 700, @16,000 miles, all bar one needed adjusting.  Checking again at 24,000 miles all were in spec and didn't need adjusting. When I reach 32,000 I'm expecting to adjust a few. 

 I imagine that's why Honda increased the service intervals on the 750, to every 16,000 miles. 

[alhendo1 3,043]

Thanks for the replies folks...that clears that up....the reason I'm asking is the CB500 is giving me problems...lots of vibration through the bars....I just wondered if out of spec clearances could cause engine vibes....at idle the bars are vibrating and this is now translating into vibration when underway....I was up at the dealer last week and they loosened off and retorqued the four forward engine mounting bolts but it's made no difference. ...I spoke to them today and I'm dropping it off on Monday for them to look at Tuesday. ...we'll see what happens....my gut feeling is I think I know the answer already..."they all do that sir..it's a twin...." ...if they admit theres a problem they'll have to fix it....if they deny it exists its easy...I'll give them a shot at it....the thing is the bike was so smooth before hand and it just seemed to change suddenly....weird.

[embee 7,288]

First thing to check is that both spark plugs are correctly gapped, clean and tight, and the caps are fitted properly. Sparks will jump quite a big gap if the cap isn't fully home, but it won't run "properly". I failed to fit one cap fully home on the NC once and it ran on both cyls but something was definitely not right.

I've found plugs in engines with very small gaps before now, usually someone drops a plug and doesn't bother to look at it.

Sometimes it's simple things .......................

Edited July 26, 2018 by embee

[Trev 18,613]

2 minutes ago, alhendo1 said:

Thanks for the replies folks...that clears that up....the reason I'm asking is the CB500 is giving me problems...lots of vibration through the bars....I just wondered if out of spec clearances could cause engine vibes....at idle the bars are vibrating and this is now translating into vibration when underway....I was up at the dealer last week and they loosened off and retorqued the four forward engine mounting bolts but it's made no difference. ...I spoke to them today and I'm dropping it off on Monday for them to look at Tuesday. ...we'll see what happens....my gut feeling is I think I know the answer already..."they all do that sir..it's a twin...." ...if they admit theres a problem they'll have to fix it....if they deny it exists its easy...I'll give them a shot at it....the thing is the bike was so smooth before hand and it just seemed to change suddenly....weird.

 

My Fantic Caballero used to do that just before the flywheel came off 

 

Probably won't be that on the CB 

[Andy m 23,502]

The Haynes book of many lies and over simplifications says you slide the cams aside having taken off the end caps.

 

It also says assembly is the reverse of disassembly etc.

 

Andy

[Tex 36,817]

1 hour ago, alhendo1 said:

Thanks for the replies folks...that clears that up....the reason I'm asking is the CB500 is giving me problems...lots of vibration through the bars....I just wondered if out of spec clearances could cause engine vibes....

 

No, it’s most unlikely.

 

1 hour ago, alhendo1 said:

 

I was up at the dealer last week and they loosened off and retorqued the four forward engine mounting bolts but it's made no difference. ...I spoke to them today and I'm dropping it off on Monday for them to look at Tuesday. ...we'll see what happens....my gut feeling is I think I know the answer already..."they all do that sir..it's a twin...." 

 

That’s easy to prove (or not) ask for a ride on their demo model. 

 

1 hour ago, alhendo1 said:

 

The thing is the bike was so smooth before hand and it just seemed to change suddenly....weird.

 

That is strange. And disappointing. I effing hate vibration! The traditional British twins used to vibrate like a bast**d. I never got over it. 

 

 

[Iron horse 121]

6 hours ago, trisaki said:

I have checked valve clearance on a few ncs now at either 8000 intervals  (700) or 16000 (750)  some have not needed to be done others needed all 8 to be adjusted (tight ) customer had been quite happy the way it was running  but even happier  afterwards  because  it was smoother and revved better  -have them checked at the correct mileage 

Did mine at 8000 and found both no.2 exhausts tight. Always thought the engine was quite lumpy before that but thought all NCs were like that! Well worth doing and easier the second time on the NC with screw adjusters. Never bothered with the valves on the cb500 years ago and as didn't fancy messing with shims

[alhendo1 3,043]

6 hours ago, Tex said:

 

No, it’s most unlikely.

 

 

That’s easy to prove (or not) ask for a ride on their demo model. 

 

 

That is strange. And disappointing. I effing hate vibration! The traditional British twins used to vibrate like a bast**d. I never got over it. 

 

 

I don't think they have a demo...the one I tried to get a feel for the bike was a 2 year old used one...felt absolutely fine apart from a slightly poor gearshift....I was happy enough to purchase on the strength of that....problem I have is if my local dealer don't play ball then I only have a couple of other options....one of which tightened my chain like a bow string on my nc 600 mile service so they're out of the running....I'd need to go further afield for a second opinion...

[SteveThackery 3,090]

13 hours ago, trisaki said:

 customer had been quite happy the way it was running  but even happier  afterwards  because  it was smoother and revved better  -have them checked at the correct mileage 

 

Sorry, but I just don't believe it.  Placebo effect.  "Smoother" means less vibration.  Think about it - tweaking valve clearances by a few thou isn't gonna make a jot of difference to the inertia of the rotating and reciprocating parts and the efficacy of the balance shafts.  "Revved better"??  What does that even mean?  More power?  Naah - you wouldn't detect it on a dyno, never mind by the seat of your pants.

 

I've heard loads of people say how much "smoother" an engine runs, or "revs better", or "is happier".  Subjective stuff like that is totally unreliable, as I know from personal experience.  Show me some objective data and I'll believe it.

 

9 hours ago, alhendo1 said:

I just wondered if out of spec clearances could cause engine vibes...

 

No, they can't.

 

Edited July 26, 2018 by SteveThackery

[DaveM59 1,603]

I know the Integra bars vibrate badly, you can visibly see them vibrate like aircraft wing in turbulence but I found dropping the front tyre pressure 2 or 3 psi cured it to a point I can live with. The bars seem like they could use a cross brace but the plastic covers prevent this. They were bad before I fitted the risers but are worse with them on which is odd as they are clamped in exactly the same place, distance apart etc.

Doing the valves made no difference to anything although IIRC only one was a bit out of tolerance, most of the vibration comes from the road surface.

[makman 975]

I'd check them.  I was not sures if mine had been done on the NC700 at the 16k service as there was no record of the check.  Got them done at 19k and one inlet and one exhaust were out.

 

Going to have them checked at the 24k service as it is silly not to.

[embee 7,288]

8 hours ago, SteveThackery said:

 

………….. 

I've heard loads of people say how much "smoother" an engine runs, or ………………………..

 

Small changes to clearance settings can certainly make quite significant effects on things like exhaust emissions and combustion stability (coefficient of variation of IMEP) etc. One engine family I worked on had shims under bucket valve train, and I recall the exercise an engineer did plotting CO/HC vs clearance to determine sensitivity in order to specify production tolerances. It's going back a long time but that was a speed/density fuelling system like many bikes use, mass flow systems are less sensitive to such things.

Clearance (or more specifically lift area and effective timing) can certainly affect the residual exhaust gas at overlap ("gas exchange"), which at idle and very low loads can certainly affect the measured stability. Because the ramps are quite slow velocity, a small difference in clearance setting changes the point at which the valve leaves the seat quite a lot, although the effect on the overall lift area is minimal. At higher speed/loads the effect is minimal but at idle it can be significant. Say the ramp is 0.01mm/deg cam (typical), a change in clearance setting of 0.05mm changes the lift point by 5deg cam, or 10deg crank. At idle the inlet port is at pretty low pressure (0.5Bar abs typically) so exhaust gas is drawn back into the inlet briefly during overlap. The resultant EGR can affect the combustion stability significantly. This internal EGR (for NOx emissions) is what is behind much of the cam phasing strategy of modern engines.

Bear in mind there's a big difference between what you can measure and what you can feel.

[Trev 18,613]

42 minutes ago, embee said:

 

Bear in mind there's a big difference between what you can measure and what you can feel.

 

 

Never a truer word spoken, ooer    

[Rocker66 34,411]

21 hours ago, alhendo1 said:

I don't think they have a demo...the one I tried to get a feel for the bike was a 2 year old used one...felt absolutely fine apart from a slightly poor gearshift....I was happy enough to purchase on the strength of that....problem I have is if my local dealer don't play ball then I only have a couple of other options....one of which tightened my chain like a bow string on my nc 600 mile service so they're out of the running....I'd need to go further afield for a second opinion...

Where are you located?

[rjp996 1,091]

I'm pondering if to check my values as it's due a service as turned 57k, or leave until the next as I've been doing the past 3 years. 

Last time I adjusted valves was on my lawn tractor, it having no TDC mark I used a chopstick (as you do) down the plug hole, snapped it off and ended up having to take the head off to retrieve the bits....

 

... maybe leave it again till the next service. ;-)