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Which is better, shims or screw and locknut valve adjustment?

670cc

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I just did a valve clearance check on my car’s 1600cc in line four engine. It is built somewhat like a motorcycle engine. If I remember right, Yamaha was partly involved in the early version of this engine design. Anyway, the double overhead cams actuate tappets directly. There are no rockers, roller rockers, or hydraulic lifters. Adjustment requires removal of the camshaft and replacement of the tappet with one of different thickness.

This was the first valve clearance check I did, at about 137,000 miles. I found all 8 exhaust valve to be still within the spec range, and only one of the 8 intake valves was outside of spec by one thousandth of an inch. I left it as is and buttoned it up. Maybe when the engine is past 200,000 miles, I‘ll check to see which way that one intake valve is trending.

There is often debate about screw adjustment vs shims. The NC may be easy to adjust but the check intervals are way too frequent at 16,000 miles (my 2012 actually called for 8,000 mile valve checks). Granted, changing shims is a lot more work than turning screws, but I’ll take an engine that can go 100,000 or 200,000 miles between adjustments over one that needs checking every 8,000 or 16,000 miles. Likewise, my Goldwing is closing on 90,000 miles and no valve adjustment has ever been needed. If shims mean far less frequent checks and adjustments, I’m all for it.
 
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MZ5

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My Honda pickup’s V6 uses screw adjusters just like the NCX, and it calls for a valve check at 100k miles (or is it 105k?), but only if the valves are noisy.

Check interval isn’t, or needn’t be, particularly related to adjustment method.

BTW, I feel like that Honda V6 check interval is too long, and telling customers to only check if the valves are noisy is also a mistake, IMO. Those engines’ valves wear tight rather more than they wear loose, and that burns valves.
 
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It's very clever design to make a valve train that becomes noisy with wear - my Toyota echo has solid shimbuckets that only need to be checked if they are noisy. It's an excellent engineering technique which is done by making the valve train relatively softer than the valve seats, so wear opens the tolerances at a faster rate than valve recession closes them.

OTOH my Suzuki Alto had solid shimbuckets that needed check/adjustment every 35k miles. It was a total nightmare to adjust and a 3 month wait for parts.

Generally screw and locknut designs are more independent of the dealership/supply chain. The NC is ideal for it with its low revving engine, but if you have this valve train on a high revving engine, the adjustment intervals become rather short. For example,
-Suzuki v Strom 250 = 11k redline = 3k check intervals
-Honda cb125e = 10k redline = 2.5k check intervals

I prefer easy, frequent maintenance compared to nothing-nothing-nothing-okaytimetosellthebike... Looking at you, desmo ducatis.
 

670cc

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My Honda pickup’s V6 uses screw adjusters just like the NCX, and it calls for a valve check at 100k miles (or is it 105k?), but only if the valves are noisy.

Check interval isn’t, or needn’t be, particularly related to adjustment method.

BTW, I feel like that Honda V6 check interval is too long, and telling customers to only check if the valves are noisy is also a mistake, IMO. Those engines’ valves wear tight rather more than they wear loose, and that burns valves.
I agree that the adjustment method itself should not necessarily determine check intervals. Now that my NC is well broken in, I’m going to stretch the valve check to 24,000 miles, then based on that, maybe out to 32,000 miles. Has anyone on the forum extended their NC valve checks to run out longer than the maintenance schedule says? 8,000 or 16,000 mile intervals just seem a little silly.
 
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dduelin

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Yes, but Honda cars with screw and locknut valve trains don’t burn valves. Just not an issue. I’ve owned a handful of them that neared or passed a quarter million miles each with never a valve adjustment or valve problem.

The NC engine valve adjustment is ridiculously easy to do. What possible benefit is it to extend it - to save an hour or two of time every two or three years of riding?
 

670cc

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Yes, but Honda cars with screw and locknut valve trains don’t burn valves. Just not an issue. I’ve owned a handful of them that neared or passed a quarter million miles each with never a valve adjustment or valve problem.

The NC engine valve adjustment is ridiculously easy to do. What possible benefit is it to extend it - to save an hour or two of time every two or three years of riding?
I agree it takes a relatively small amount of time to adjust NC valves. But add that to changing drive chains and serpentine belts and air filters and brake fluid and engine oil and filters and tires and batteries and timing belts and transmission oil and coolant and rear AWD drive fluid and brake pads and mower blades and winterizing RVs and pressure washer pumps and draining carbs for off season and sharpening chain saws and everything else that needs maintenance (and repair) in the garage. It all adds up. If I can reduce maintenance needs or intervals anywhere in the fleet, it’s more time to enjoy the toys and less time working on them.
 

670cc

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My Honda pickup’s V6 uses screw adjusters just like the NCX, and it calls for a valve check at 100k miles (or is it 105k?), but only if the valves are noisy.

Check interval isn’t, or needn’t be, particularly related to adjustment method.

BTW, I feel like that Honda V6 check interval is too long, and telling customers to only check if the valves are noisy is also a mistake, IMO. Those engines’ valves wear tight rather more than they wear loose, and that burns valves.
I couldn’t make a determination of whether valves are normal or noisy. I would need some way to measure or quantify that. That would be like telling someone to just tighten bolts rather than providing a torque spec. Engines sound different from one another, and I’d have no way of knowing what it should normally sound like.
 
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davidc83

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I agree that the adjustment method itself should not necessarily determine check intervals. Now that my NC is well broken in, I’m going to stretch the valve check to 24,000 miles, then based on that, maybe out to 32,000 miles. Has anyone on the forum extended their NC valve checks to run out longer than the maintenance schedule says? 8,000 or 16,000 mile intervals just seem a little silly.
Not on the Honda, but I did on my 2007 Suzuki C50 Boulevard....it had 3,000 mile check intervals (sucks the royal big one)...which I paid to do because that thing is a bear up till 27,000 miles...at the 27,000 miles I was told checked, still within specs (all previous stated same thing-those were at the dealership, last one was at my mom-pop neighbor shop and trust him and his staff).....so I decided not to do them anymore....at 100,000 miles, I decided to check them again....this time I broke down and did it myself (by the way, never again) and the valves were still in specs....not perfect, but within specs....so 102,000 miles, valves never have needed an adjustment, and those are screw/nut....not shims....
 

davidc83

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In my experience valve lash adjustment necessity is directly proportion to how much time I spend near the redline.
The C50 Boulevard doesnt have a tach...only speedo/odo....so never know when it is at a redline, but 90% of the time I ride it laid back, only had it over 90mph a hand full of times and even less in the 80mph range....It is my commute bike in the spring/summer/fall and mostly Interstate speed riding 65-70 mph....
 

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I agree with post #10 100%. When checking every other year,9K. my valves were so close to the .17/.28 +-.02 that i could of left them alone. I did adjust to the .17/.28 spec (.007/.011in). These engines are so low revving and light weight,has anyone pushed down on the spring by hand while doing inspection besides me? The valve train is so matched for this application, small valves, light springs low friction rockers and the rev limiter of 6500 that checking at the 8K is a little bit of overkill. When I was redlining my CB900F all those years ago and checking the valves every 5K I could not understand why the clearance was always tight (.006~.013 range). After tear down to build it up(1000cc 10.5 comp) I discovered that the valves were"hammered" into the seats. They were not flat anymore but had a recessed ring on there face from the valve seat in the head. Following any MFG maintenance is always good, they spend a lot to come up with that. But how we use and sometimes abuse the product is on us. A standard I learned years ago still holds true, tight valves will burn and can have a rough idle while "happy" valves make noise.
 

dduelin

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I agree it takes a relatively small amount of time to adjust NC valves. But add that to changing drive chains and serpentine belts and air filters and brake fluid and engine oil and filters and tires and batteries and timing belts and transmission oil and coolant and rear AWD drive fluid and brake pads and mower blades and winterizing RVs and pressure washer pumps and draining carbs for off season and sharpening chain saws and everything else that needs maintenance (and repair) in the garage. It all adds up. If I can reduce maintenance needs or intervals anywhere in the fleet, it’s more time to enjoy the toys and less time working on them.
Thin the herd and save lots of time.
 
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yojimg

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FWIW, my 2015 CB500X uses shims and it has the same 16,000 mile valve-check interval as my 2018 NC750X. One of the reasons I bought the NC is that I don't want to have to deal with replacing shims, I prefer the screw/locknut method.
 

the Ferret

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This NC is my first modern bike with screw & lock nut adjusters. I think my last was my 1981 XS 650 Yamaha, so I'm not sure how it will stack up against the shim bikes I have had with regards to needing adjustment. The shim bikes have been very reliable. I don't think I've had to replace a shim in 8 or 9 different motorcycle and probably 250,000 miles.

There is a difference in effort between a clearance check as recommended by the manufacturer and an adjustment depending on what the check reveals. However, if an adjustment IS NEEDED, it's simpler with the screw & locknut as you don't have to pull cams or get different thicknesses of shims.

I also think some guys just like to make extra work for themselves, as when a shim valve is still in spec, but they insist on taking it to the middle of the spec, instead of waiting until the next check to see if it is still in spec or actually OUT of spec. To me, in spec is IN SPEC. It's good. Especially on a shim bike.

I do know that almost all the mfgs went to shim valve adjustments because they were less apt to go out of adjustment in the first place.

I also BELIEVE how you ride your bike matters, as to whether the valves will need frequent adjustments, whether it's shim or screw & locknut.
 

lootzyan

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The use of shims (or buckets) allows them to be made of special wear-resistant alloy steel. Moreover, the contact surface between the cam and the shim is much larger so the wear resistance is thereby increased. So the answer to the question which is better is rather obvious. In many cases, by using shims, it is not necessary to adjust the valves clearance.
 

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Interestingly no one mentioned hydraulic tappets as an alternative to valve calibration. Most American car engines from the 60's had them and they never required adjustment. Motorcycles were not as quick to jump in that wagon, apparently due issues at high RPMs, at least that was the standard reply. Yet, I had a Nighthawk 750 in 91-93 with a 10,000 RPM redline and hydraulic lifters. I rode it for ~50,000 miles and never had a problem.

So, why they were not more popular? No sure but probably cost and revenues had something to do with it. Certainly the slow NC engine would be perfect for them.

Most DIY bike owners are ok with changing oil/filters, adjusting chains, changing brake pads and other small maintenance chores. But opening up the engine head to adjust valve clearance is not one of them. I suspect many shops would lose a good chunk in revenues if not valve adjustment was in the cards.
 
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lootzyan

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Interestingly no one mentioned hydraulic tappets as an alternative to valve calibration ...
I have no experience with hydraulic tappets so I can only quote from Wikipedia:
"There are a number of potential problems with hydraulic lifters ... Hydraulic tappets require more complex and more expensive cylinder head design. A number of subcompact car manufacturers prefer solid valve lifters ... Generally, hydraulic tappets are more sensitive to engine oil quality and frequency of oil changes ... " etc.
 

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The Honda Nighthawk and Shadow models of past used a hydraulic fulcrum for the valve train as opposed to a lifter design. They differ by not moving with the cam but by the pivot point of the rocker. By using that design it makes the valve train lighter and lower in friction losses. Kawasaki did use a design like that in there ZR1200s that had a shim adjustment under a "finger" rockers on top of the valve that without any special tools or cam removal could be moved to the side against spring pressure and changed very easy. Mazda has used hydraulic buckets for some of there car engines, you always new that the oil needed changing when you heard valve clatter. It seems that some engineers do not consider the cost or time it takes for maintenance no matter who is doing the work but leave that to the cost cutters to insure profit margins. With all this development done by many MFGs there is still not a "Keep It Simple Stupid" design that would decrease costs, lighten up valve train weight, lower time and money for maintenance. At least they all agree (Automotive,Motorcycle)with 2 things Fuel Injection & Radial tires. God Bless them for that.
 
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670cc

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Regarding different valve actuation and adjustment schemes, the Honda NSS250 has an interesting system. You can adjust the valves in a few minutes without removing the valve cover. The adjustment levers are external to the cylinder head. To adjust the valve lash, you move an external lever until resistance is felt, then back it off one increment on the scale.

I’m not one to like videos for explaining things, but this video is an example I quickly found that shows part of the process.
 
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