Shims vs. Threaded tappets

[Guest]

So I was down to my local Suz. dealer looking for a tappet adjuster tool and they told me that nobody uses threaded tappets anymore because they are not as reliable as shims and require adjustment about every 10k miles. And no, they didn't have the tool I needed.

So I went home and adjusted my valves with a homemade tool. Found that 3 of 16 valves needed very slight adjustment. After 36k miles, previous mantenance records/procedures unknown. This was all last spring (March or April, IIRC).

My question is this: Is my Suzuki dealer correct or is he just trying to discourage me from bringing my old dinosaur into his shop?
And are shimmed valves any more reliable (i.e., requiring less frequent adjustment) than threaded tappets?
Are they (shims) easier or more difficult to replace/adjust than tappets?
Seems like it was a pretty easy valve adjust to me. I have never seen valves that are shimmed.

[rphillips]

I'd rather have the tappets & rockers, but I'm sure others have differeng ideas. Too much figuring with the shims, then you have got to go find shims. Adjust the tappets & go.

[trippivot]

opinions are like elbows.

Why ask an mechanical engineering question to a person who is not one???

if your local shop is like the ones around here well let me say this:


if an employer only pays peanuts he'll only get monkeys to work for him.


consider the source of the information

threaded tappets do have a bigger chance to vibrate out of adjustment before a shimmed valve sinks into the head


however they both are effective and reliable just different

2008 ninja bikes(500 650) still have split rockers and threaded tappets

[jpaul]

Shims don't need adjusting as frequently as tappets, but it does take a little longer to do. With the shim over bucket arrangement used on the 8 valve GS's, there is a chance that you can spit a shim out if you overrev the engine far enough. The newer bikes use shim under bucket that eliminates that issue, but require that the cams be removed to change shims.
All mechanical systems are a balance of comprimises. Tappets are the easiest to adjust, and allow higher revving than shim over bucket, but won't allow revving as high as shim under bucket, due to higher mass to move. Since most of today's bikes (at least those with inline fours) are street-going versions of racebikes, ease of maintenance isn't a high priority.

[Steve]

From my experiences and other opions I have heard, both are good systems. The threaded adjusters are easier, and you don't have to chase down shims. The shims are a bit harder to adjust, but tend to hold their adjustment longer. Some racing teams prefer shims to minimize the possibility of the threaded adjusters coming unthreaded during a race.


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[Mark whiz]

I have to agree that the screw adjusters are WAY more convienent to have.

The shims aren't any more reliable, what they are is LIGHTER, they tend to wear less and so need adjustment less often, and there is less slop in valve actuation. Lighter valve trains are essential to engine health as the rpms rise and the controllability (less slop in the action) helps prevent or at least delay the possibility of valve float - which is the limiting factor in today's higher revving engines.

[tkent02]

I have to agree that the screw adjusters are WAY more convienent to have.

The shims aren't any more reliable, what they are is LIGHTER, they tend to wear less and so need adjustment less often, and there is less slop in valve actuation. Lighter valve trains are essential to engine health as the rpms rise and the controllability (less slop in the action) helps prevent or at least delay the possibility of valve float - which is the limiting factor in today's higher revving engines.

Agree with all this, one more thing is that the valves and guides wear quicker with the screw type adjusters, the head will need work sooner. This because the forces in that area are all in a straight line with the shim and bucket arrangement, there are other angles and twisting forces at work in the screw adjuster type engine. There are also more parts in there to wear out, rockers and shafts, etc. With four valves per cylinder there are more parts to fix when it gets worn out.

Although the screw type valves can be adjusted very quickly, I believe it pays to get the clearances as even as possible between two valves on any one cylinder, take the extra time.

That said, I have no preference, don't keep bikes long enough to wear this stuff out anyway.
Usually get bored and sell them down the river before too long.
Kind of like the older engines, but they are both OK with me.
I like both chains and shafts too, I'm just cool like that.

[Mark M]

Although the screw type valves can be adjusted very quickly, I believe it pays to get the clearances as even as possible between two valves on any one cylinder, take the extra time.

The best way to do this is to use a pair of feeler gauges together, with one under each adjuster on the fork. Eliminates twisting the rocker while setting clearances.

As noted, screw & locknut adjusters are more convenient, but heavier and require more frequent adjustment. Shim under bucket is lighter and has longer maintenance intervals but require pulling cams if shims need changing. For high RPM engines, the shims are simply superior.

My 97 ZX-9 had the best system I have seen. It used shims on top of the valve retainers, with little finger followers on the shims that the cams worked on. To change shims you simply pushed the follower to the side and pulled the shim with a magnet. Simple, light and easy to work with. Too bad they gave up on it...

Mark

[Nessism]

Agree with all this, one more thing is that the valves and guides wear quicker with the screw type adjusters, the head will need work sooner. This because the forces in that area are all in a straight line with the shim and bucket arrangement, there are other angles and twisting forces at work in the screw adjuster type engine. There are also more parts in there to wear out, rockers and shafts, etc. With four valves per cylinder there are more parts to fix when it gets worn out.

Although the screw type valves can be adjusted very quickly, I believe it pays to get the clearances as even as possible between two valves on any one cylinder, take the extra time.

That said, I have no preference, don't keep bikes long enough to wear this stuff out anyway.

Good post!

Shim and bucket valve trains are very stable and durable. Rockers wear faster and cause valve guide wear.

Forked rockers need to be set equal for each valve or the rocker will twist - not good for wear on the cam and follower. Setting the clearances just right takes more time than swaping a GS shim, assuming you have the proper shims on-hand.

Regarding the poster that mentioned Kawasaki twins using rockers - have you ever seen an EX500 with the rocker cover off? I've worked on three different EX's and all have suffered rocker and cam wear. Very poor durability in my experience.

[Steve]

Now, for your next adventure in valve adjusting...

How about a Honda CBX? Maybe cbxchris can confirm some of this, but there are 24 valves to adjust. Fortunately, the shims over the buckets, but I seem to remember that you had to drop the engine to get enough room to remove the valve cover. :shock:
Fortunately it was relatively easy, as there were no downtubes to contend with.


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[robertbarr]

With all this chatter about valve clearance adjustment, it occurs to me that I've NEVER checked or adjusted the valve clearances on my current bike. Ever! Should I worry, or just ride the s*&#$## out of it?

[Mark whiz]

robertbarr,
if that 1985 Nighthawk is your current bike, you don't have to worry about valve adjustments - it has hydralic valve adjusters just like most all car engines.

[Smokinapankake]

Wow, thanks for all the input. I'd never considered the idea of a forked rocker twisting on the camshaft because both valves were not set at the same clearance. Makes me think I should go back and readjust....

[bwringer]

Just to correct something...

On a GS with shim valve adjustments, valve clearance checks are specified every 4,000 miles. I don't know where the 10,000 mile figure came from, but that's waaaaaaaaay too long to let a GS go.

Too many people neglect this, and then wonder why the bike is slowly running worse and worse...

Personally, I sorta prefer shim valve adjustments. It's more definite, I think. Once you learn the procedure, it's easier to make sure the clearances are in spec. With the screws and locknuts, there's an element of the mechanic's skill to it.

But then again, until you build up a nice collection of shims, it can be rather inconvenient, especially if you have to order shims. I live 20 minutes from CRC2, so that's nice. At least with the screw-and-locknut type, you're never going to be stuck waiting for a shim.

For my VX, which uses screw and locknut adjusters, I bought two of the tiny two-blade feeler gauges -- there's very little room to work in there, and these make the project a bit easier.

6 of one, half dozen of the other -- any way you slice it, valve clearance checks are a royal pain in the rear. I think modern Yamahas can go something like 26,000 miles between valve checks. I like that.

Many Toyotas also use shim adjustments (currently, just valve buckets of different thicknesses -- no separate shims). However, I've never found one of these out of spec, even at 200,000 miles. They have super-hard valves, seats, and cams, and/or the pace of wear is in perfect balance.

[Nessism]

Many Toyotas also use shim adjustments (currently, just valve buckets of different thicknesses -- no separate shims). However, I've never found one of these out of spec, even at 200,000 miles. They have super-hard valves, seats, and cams, and/or the pace of wear is in perfect balance.

My little Nissan car engine is similar. There is no service interval to check the valve clearances but they mention something about checking them if the engine gets noisy. Apparently they are not worried about the valves sinking into the head, something that occurs on our GS engines. Two valve engines have larger, and heavier, valves than a 4 valve engine, and said valves are more difficult to manage. For that reason I think 4 valve engines have a theoretical durability advantage assuming everything else equal.