Valve clearances - argh!

[speedy231278]

So, after lots of piddling about, I managed to eventually remove the carbs. Cam covers came off with a little gentle persuasion, and I set about the contorsionist's trick of getting as the flaming shims. I swear they were invented by a masochist!

I've never measure shims before, so I enlisted the help of a friend who has been a mechanic for longer than the 34 years I have existed to make sure I was doing it right. His opinion on measuring the clearance is that if there's a little drag on the gauge, but you can still slide it through fairly easily, then you've not quite found the gap and you need to increase the thickness by another thou, and when it just barely slides through and the next size up refuses to go in is when you have found the right figure. I can't comment on this as I'm utterly inexperienced about this, however I'm assuming that this is the correct way to do it, surely you couldn't end up pushing a valve down with something as flimsy as a feeler gauge?

Anyway, aside from the technique, there are a couple of things that are nagging at my mind. Firstly, I noticed that the rockers have a little play in them. When set at the appropriate point for measuring, I noticed that you could lift the rockers ever so slightly, and then push them back down again. ie, the first time I put a gauge in that was thick enough to almost fill the gap, the rocker lifted by a few thou. Is this normal? If so, would the clearance be measured with it at the higher position? If it's wrong, does it mean the camshaft was in the wrong place? There's no difference betwen my NC35 and the NC30 when doing this, is there? If the indicator on the camshaft was just a tiny fraction to the side of the top/bottom position, would that affect the rockers? I'll very happily go back and do them again just in case, however, I did actually cycle the whole lot round and measure a second time. And I measured again after I replaced the shims when checking the sizes. Same results each time.

I'm a bit concerned because it appears that all bar one of rear valves I measured were on the generous side (the other was right on the tight limit), and one of the two fronts I did was a fag paper wide too. Given that I've always had the bike's valves done by a local shop with a very good reputation, within literally a few hundred kms of the schedule, I find it a little surprising that it seems they're almost exclusively coming up loose! As I haven't finished front, here's what I found on the rear with clearance in mm and (shim number):

In .12 (220) .20 (220) ......... .18 (220) .19 (215)
............cyl 1 .............................. cyl 3
Ex .31 (200) .32 (200) ........ .30 (205) .30 (205)

Assuming I've not fouled up, I would assume that most people would adjust the .12 by putting a 215 in to widen the clearance to .17? Question is, would you drop the .19 for the sake of a hundredth of a mm that's going to close up over time anyway, especially as aftermarket shims only seem to come in 0.05 increments, so it would mean buying or finding a Honda 2.125? Are the exhaust valves too far outside the wide spec? I was told if that wider means more valvetrain noise, and the bike certainly has a reasonable amount. I wouldn't say it's unhealthy sounding, but if it did quieten down a bit I wouldn't object! Clearly the .32 could lose a whole 0.05 increment, and that would also take the .31 to .26, doing the same for those at .30 would leave them almost bang in the middle. Or would you take out .025 and leave them a fag paper over the wide end of the limit?

Sorry, so many questions! It's not rocket science, and it's something that I should be able to do with time and experience. However, with my complete lack of experience and the obvious and very expensive consequences of getting it wrong, I want to be absolutely sure that what I'm doing is right before relying on it to make any changes and ending up with what Martin Brundle often describes as the valves having a chat with the pistons!

[Neosophist]

wow big post.


1. Measure between the shim and the rocker as per 3-8 of the Honda workshop manual, the rocker arm will move and have a little play as this is the clearance, shoving a feeler gauge under it will move it up a small amount until it hits the cam lobe, if theres a huge gap then either the shim is way to small or the timing isnt set right (again refer to 3-8) or your measuring it wrong somehow.

2. Yes drop 0.05 on the shim to change 0.12 into 0.17.

3. Valve clearances seem excessivly loose

[CMSMJ1]

I'd guess you've measured between cam and rocker or that is a slack old engine!

[speedy231278]

Nope, definitely definitely between shim and rocker! Would the fact that it was absolutely bloody freezing yesterday have any effect whatsoever on the clearance? If I was measuring a few thou tight, I would be less uneasy as I would expect everything to have tightened up very slightly assuming it was done correctly in the past. Being slack makes me slightly nervous that I may have got something wrong. I'm definitely going to measure the ones I've done so far yet again just to be sure after making absolutely sure that everything is spot on alignment wise.

There's no difference between the NC30 and NC35 when setting the engine up, is there? T1 mark, camshaft markers facing away for #1 (rear left) and facing towards for #3 rear right?

[CMSMJ1]

Clearances would be expected to go tight with age and the repeated smashing into the valve seat of the valve..

No difference in the process - and as long as the cam lobe is not touching the rocker at all and then you slide the gauge between rocker fingertip and the top face of the shim then all good.

Your method of getting it to drag a lot might account for a couple of nths.. I would tighten it up if the gauge slipped in easy..but if it had to be actually pushed through then I would say a touch tight. A slight drag for me.
Reading your example - I would also note that my experience of these would see far mroe higher numebrs shims

I have loads and loads of 235s and 230s - it was rare to see 200s and 205s.

So..do you know if these have ever been done before?

[speedy231278]

Yes, it's been done before. I got the bike with about 40000kms on it, and have had the shims done as per the Honda schedule. The first time I had it done at 48k, the workshop who did it claimed to have had to change 11 shims (and charged about a fiver plus VAT each for them!). It was last done by my regular (now retired) bike mechanic who did them at 72k and 96k. The bike is not quite at 120k yet, but it's only about 1k off, and as I'm doing the carbs it seemed like a sensible idea to save a bit of faffing and do them at the same time. Quite honestly, I wish I had never started. I now understand why it always used to cost so much even at mate's rates!

I'll go back and measure again next Saturday and see what I get if I stop increasing the gauge thickness with slight drag rather than the absolute limit of what I can squeeze through. I'd rather not tighten anything up if there's a chance I might be adding a thou or two extra to the measurement due to my lack of experience, only means they'll end up and the tight end of the scale more quickly... I can't imagine that someone as thorough and highly recommended as my old mechanic would have set them so wide that they're several thou wide 24k later. Still, I suppose anyone can make a mistake, but it's much more likely to be me!

[speedy231278]

Right, here we go again. Wish me luck... lol Having trawled many different forums, I've decided that if the gauge fits but has to be slid through with lots of pressure then it's probably slightly large, however define lots of pressue.... In all honesty I'm probably just going to measure everything up, and put the bike back together. I need it next weekend, and depending on what I find today, I may well want a second opinion before I start replacing shims. The bike runs fairly well right now, a few hundred more miles isn't going to make any difference, but the wrong shims very well might!

[CMSMJ1]

It should slide in nicely... Think of that special first time with the young lass from school....

[speedy231278]

Right, I've done the lot. I think I've got a bit more of a feel for it now. There were a few where I cuold go an extra thou or possibly two, but it felt like I was maybe having to work too hard to get there. I also found if you put a finger on the blades so that they slide through level with the shim rather than just stick them in you get a different feel although it doesn't appear to affect what actually fits. Anyway, I'm a lot happier with this morning's work. The really tight inlet valve has measure fine, the very slack exhausts have coeme up a little tighter. I've found three exhaust valves to be a thou wide, and one of the inlets to be three thou wide. Given that I've measured some today at a substantially different clearance to last weekend, I am inclined to leave the lot as they are. The three thou wide valve was one of the first ones I did, so I would suspect I may have gone a touch heavy on the gauges. Anyway, here are the results:

Ex .24 (212) .27 (210) ........ .24 (210) .28 (210)
.......... cyl 2 ............................... cyl 4
In .17 (2??) .21 (220) ......... .17 (220) .15 (220)

In .15 (220) .18 (220) ......... .18 (220) .17 (215)
............cyl 1 .............................. cyl 3
Ex .27 (200) .28 (200) ........ .27 (205) .28 (205)

Somewhat iritatingly, cylinder 2's left inlet valve shim has the number partly worn away. It's definitely a 2 to start, and the last figure is either 0 or 8, but the rest is a lost cause. Given the number of 220s elsewhere it would be easy to form a dangerous assumption, and only a micrometer or sticking another known 220 in that location and measuring would give the answer.

Right, now to get the bloody thing back together!

[lukemillar]

It should slide in nicely... Think of that special first time with the young lass from school....

So I should be able to do the valve clearances in about 30 secs then!?