8000 mile valve check

[670cc]

I am new to the sport, but my vintage biker friends tell me one sure sign the valves are off is the spark plugs are black instead of a light brown colour or one of the pipe is more BLUE than the other(S)

Pipe comparison will not be possible with the NC since the exhausts join inside the cylinder head and exit to one header pipe.

I expect valve adjustments to be a rare concern/event with the NC700 engine.

 

[michaelks]

Could someone explain why this nut and bolt valve adjustment system is still used when shims seem to be so much more reliable, maintenance-free and exact, or also hydraulic tappets ?

 

[soggybottom]

Could someone explain why this nut and bolt valve adjustment system is still used when shims seem to be so much more reliable, maintenance-free and exact, or also hydraulic tappets ?

I like the old style of screw and locknut, Its a simple and fast method, shims are a PITA, I could see shims for a High Performance bike but not a utility bike. Hydraulic will not work with overhead cams me thinks.

 

[michaelks]

My very basic XR250 has shims, and i was told by the Honda mechanic not to think about it before 30000 km at least. And the DOHC CBX 750 had hydraulic. I think adjusting with this screw system is very error-prone, especially if there already is some wear, because then when you tighten, the gap changes.

 

[bamamate]

Same design that is in the Fit from which the engine is based.

 

[Beemerphile]

I like it like they built it. You don't have to buy a box of shims. Once you get the feel of it, it is quite satisfying getting just the right amount of drag on the feeler gauge. Of course, 35 years of riding BMW boxers has settled me with the process. Compared to taking camshafts out and putting them back in, it is pretty sweet. As far as "reliable, maintenance-free, and exact"... Reliable? Well, the clearances don't change because the adjusters slipped, they change because of valve train wear, valve recession and so on. "Maintenance-free" was not the thought in my head after adjusting the shim valves on my Honda ST1100. Admittedly only a couple were out a couple of thousandths, but so it has been with my BMW's. Exact? Digital vs. analog. Numbers vs. feel. I bet I can get it to half a thousandth by feeler gauge resistance. Compare that with shuffling through a box of shims. Considering that you'd have to remove the cams again if you weren't satisfied, you'd likely just go with it.

Here is the Maintenance-free valve adjustment procedure for the stone age and highly agricultural KLR650 with shimmed valves...

Mark's KLR650 Website - Valve Clearance Check & Adjustment

 

[Bamo]

As a "former" certified Honda Service manager and tech, I think the valve set up in the NC's is perfect. I did a lot with shims, on the dirt side especially. The people who do not know how to clean an air filter or how to take it out and replace it without getting a bunch of dirt in the intake, always had valve issues. We were shimming CRF250 valves on a daily basis. The adjusters we have go right along with a HUGE factor for me when I bought this bike. Cost of ownership. Not only is it more expensive to shim a valve, but that is more stuff to take apart and potentially mess up putting back together. I will do my own valves, but for those of you who do not, a tech having a bad day or one who is inexperienced could really mess your bike up messing with shims. Honda did this bike right IMO.

 

[michaelks]

Most of the hassle Mark describes would be the same whatever the valve clearance system, i guess. Anyway my (very limited) experience is that it's very hard to be confident with screw adjustment, because upon tightening the clearance changes, so it's very frustrating. I really like the idea of a precise machined shim providing the correct setup.

Very funny btw, the "abyss, men go crazy, women faint and children cry", lol.

An interesting point, however, is that what causes the valve gap to be off spec is more the "valve train wear, valve recession and so on" than the actual adjusting method. I don't know where that leaves me with the 30000 km advice from the Honda mechanic.

And what about hydraulic, any ideas ?

 

[Beemerphile]

Most of the hassle Mark describes would be the same whatever the valve clearance system, i guess.

Steps 20-29 would go away. As would the statement that if it isn't right you have to go back to 20 and start over.

Anyway my (very limited) experience is that it's very hard to be confident with screw adjustment, because upon tightening the clearance changes, so it's very frustrating. I really like the idea of a precise machined shim providing the correct setup.

Very limited experience is only cured by additional experience. The key is to hold the adjusting nut firmly fixed while tightening the lock nut. You develop a feel for pushing them against each other but only allowing the lock nut to move.

Very funny btw, the "abyss, men go crazy, women faint and children cry", lol.

Every KLR mechanic knows the abyss. I always stuffed mine well with torn T-shirts.

An interesting point, however, is that what causes the valve gap to be off spec is more the "valve train wear, valve recession and so on" than the actual adjusting method. I don't know where that leaves me with the 30000 km advice from the Honda mechanic.

The manual for the XR250 calls for valve inspection every 1,000 miles...

Honda XR250 R XR 250 Owners Maintenance Manual

The possibility exists that your mechanic is wrong. I just had one incorrectly install a drive chain on mine. A simple task. The XR250 is an off-road motorcycle and generally the maintenance intervals are much shorter than road bikes. It may take twice as many operating hours to reach the same mileage. At any rate, 30,000 km (18,000 miles) without a valve check on any kind of bike, much less an off-road bike, is beyond reason or common sense. Be careful there.

And what about hydraulic, any ideas ?

That is a better question. Honda had them on the Nighthawks as early as 1983 so they know how to do it. Certainly the rev range would allow it. Might have to ask Honda that one. Economics possibly.

 

[Hitandrun]

My experience has been that the screw and locknut system is a lot easier to adjust, and a lot more likely to need adjusting. I have had numerous shim-under-bucket bikes and never had a single valve go out of adjustment. The screw type engines I've owned were not that way. Kind of a Catch 22.

 

[duk2n]

My XT350 has valve shims, pretty similar setup to the KLR, including the abyss

I agree is more difficult than adjusters, but it is a very reliable setup. It needs more than 10,000 km of rude use to have one or two of the four shims out of speec

 

[michaelks]

Well, there you have it. Anyway, i'm going to check the XR's valves, but i guess no surprises, the engine runs like clockwork, very good mileage, no strange noises.

Lee, when you tighten the adjusting screw, doesn't it get forced upwards by the locknut ? I mean, there's always some play on the screw, all the more so if the machine is older and this adjustment has been done a number of times. You then have to allow for this, setting the gap a little less so that in the end you get it right...not the easiest thing to do, i'd guess.

 

[soggybottom]

The screw and locknut was common on older cars and muscal cars of the 60' & 70's, so my old timer friends have told me anyway. They are also common on big diesel engines even in todays Cummins, Cat, Detroit Diesel. Even the little Cummins found in Dodge P/U trucks have screw and locknut adjuster.

 

[MZ5]

The screw adjuster & lock nut setup is like my old Z-car (Datsun 240Z), and also a Honda CRX I used to have. The shim-under-bucket is like an Alfa Romeo I used to have. I decided to let the Alfa's valve clearance just be whatever it was. I HATE shims. HATE THEM.

You all who say that the clearance will change slightly when you tighten the lock nuts are correct; it _will_ change slightly. It's not that tough to learn about how much change there will be, though, and set the screw adjuster correctly. Or, just loosen the lock nut, move the adjuster a 64th of a turn (or whatever it takes you), and tighten it back up.

I'm glad Honda has implemented the system they have, though honestly I'd most prefer hydraulics.

I also believe, though of course I have no way to know, that the dealer saying the valve check is 'optional' is basing that on experience with Honda street bikes. Much more often than not, they are right on spec for _several_ of those valve clearance checks. That doesn't mean _your_ bike will be on-spec, though.

 

[L.B.S.]

Unless it would have had a Yamaha-like 26,000 mile interval for valve checking, I would not have bought the 700 if it had been shimmed valves. I specifically did buy it so I could do the valves myself, with minimal tools and fuss. I can't stand shim valvetrains. I was so happy to discover the NCX was good 'ol screw and locknut!

 

[fedtech]

OK, so, i will not do mine ever. i will let you know if i have any problems.