Shim Under Bucket -- WHY????

[nhchris]

It seems to me absurd that you need to remove an entire camshaft to simply adjust a valve that is marginally out of spec.  Who decided this?

After wrenching on cars and other engines all my life I really want hydraulic lifters that NEVER need adjustment.  Is that too much to ask in 2021?

We long ago sent men to the moon. Why can't we come up with a better and more practical valve mechanism than shim under bucket?  It is a positively medieval way to make a motorcycle valve train!

(Maybe air lifters like in F1?)

Edited February 14, 2021 by nhchris

[peteinpa]

my first bike, 83 650 Nighthawk. 10k redline, automatic hydraulic valve adjustment.

Nuff said.

[koth442]

Well.. it's REAAAAAALLY simple to install, at the factory. After that it's our problem. Kidding, sort of.

I'm not sure why hydraulic valves aren't more wide spread. 

[Lone Wolf]

I still have a 750 Nighthawk with hydraulic valve adjustment.

1 hour ago, peteinpa said:

my first bike, 83 650 Nighthawk. 10k redline, automatic hydraulic valve adjustment.

This article mentions "The Nighthawk gave up some performance in favor of reduced maintenance."

Why do so many bikes use shim-under-bucket valve adjusters? - RevZilla

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Why do modern motorcycles have shim-over-bucket valves...

[Ride365]

Get a Harley perhaps?  

[knyte]

My '83 Nighthawk 550C seems to have torque for dayyysss in all gears...not sure what they mean by loss of performance in favour of reduced maintenance?

EDIT: ahh, slightly reduced redline.  "Slightly".  IIRC the redline on my 550 is 12k.  Still pretty good!

[johnmark101]

I retired from QC with Toyota Motor Manufacturing.  At the time I was working in powertrain, our four cylinder engines had a shim on top of the bucket arrangement.  The top of the "bucket" surface was recessed, with a raised rim around the top.  The shim sat in this recess beneath the cam lobe and was the exact thickness to fill the recess so that it was flush with the rim.  We had a specialized tool that pushed down on the bucket at the rim, creating enough clearance that allowed you to pry the shim out and replace it with a different sized shim.  Made valve adjustment a simple and quick operation that could be done with the cams in place.

I often wondered why we never saw anything like this attempted with motorcycle engines.  I can thing of a couple of reasons why this might not work on a higher revving, high compression engine, but imagine there might be a brilliant design engineering solution that could make this feasible.  

[peteinpa]

I know there have been several shim over bucket bikes through the years. They were worried the shim could spit out at high RPM.

My 650 Nighthawk had great power and tourqe. The press raved about it having 750 power.

[Junkie]

Hydraulic lifters are bulkier, heavier, and don't allow as much force to be applied to the valve. By going shim under bucket, weight is minimized, the engine can be more compact, and you can run more aggressive cam profiles. 

I think most of it is most likely space issues rather than the others on these bikes. 

 

Some bikes have been shim over bucket - I believe the GS500E was that way. The downside is that the shim could theoretically come out if your profiles are too aggressive. 

 

I'm not sure I've seen hydraulic valves on an OHC engine. I know my old Integra used rocker arms and called for fairly frequent manual adjustment. I know my old Subaru Outback used shims, although I don't recall if they were under or over bucket. Using a hydraulic adjuster an an OHC engine would make it dramatically larger I imagine. In comparison, on a pushrod engine, a hydraulic lifter (hydraulic roller lifter at that) takes up what's otherwise wasted space, so the downsides are minimal. 

[nhchris]

14 hours ago, Lone Wolf said:

I still have a 750 Nighthawk with hydraulic valve adjustment.

This article mentions "The Nighthawk gave up some performance in favor of reduced maintenance."

Why do so many bikes use shim-under-bucket valve adjusters? - RevZilla

---

Why do modern motorcycles have shim-over-bucket valves...

Great article.  Thanks!!

[pilninggas]

5 hours ago, johnmark101 said:

I retired from QC with Toyota Motor Manufacturing.  At the time I was working in powertrain, our four cylinder engines had a shim on top of the bucket arrangement.  The top of the "bucket" surface was recessed, with a raised rim around the top.  The shim sat in this recess beneath the cam lobe and was the exact thickness to fill the recess so that it was flush with the rim.  We had a specialized tool that pushed down on the bucket at the rim, creating enough clearance that allowed you to pry the shim out and replace it with a different sized shim.  Made valve adjustment a simple and quick operation that could be done with the cams in place.

I often wondered why we never saw anything like this attempted with motorcycle engines.  I can thing of a couple of reasons why this might not work on a higher revving, high compression engine, but imagine there might be a brilliant design engineering solution that could make this feasible.  

Lots of 80s jap bikes had this sort of set-up. I have an XJ600 with this exact system of shim 'on top'.

The trouble with this arrangement is the size of shim needed (it has to be bigger so that it will never come out in normal operation), bigger shim and follower assembly means more mass means less revs.

The japs use bucket with shim underneath as it cheap to assemble (as has been said) and allows high revs. I think they dont do hydraulic lifters is due to the fact a loss of oil pressure at high rpms, not only being catastrophic for the engine, would also be extremely dangerous as it could result in the valves not opening and the drive train locking up.

[Lone Wolf]

On 2/15/2021 at 4:07 AM, johnmark101 said:

Toyota ...our four cylinder engines had a shim on top of the bucket arrangement.  The top of the "bucket" surface was recessed, with a raised rim around the top.  

I often wondered why we never saw anything like this attempted with motorcycle engines.  I can thing of a couple of reasons why this might not work on a higher revving, high compression engine, but imagine there might be a brilliant design engineering solution that could make this feasible. 

Read the article posted previously - they explain why.

It was attempted, I still have the tools to hold the "bucket" down to enable access to the shim on top.

On 2/15/2021 at 5:22 AM, Junkie said:

I'm not sure I've seen hydraulic valves on an OHC engine.

... Using a hydraulic adjuster an an OHC engine would make it dramatically larger I imagine.

Here's a diagram of how the hydraulic valve lifter is placed (part #7) on the Honda 750 Nighthawk that was made from 1991 to 2003. The "rocker arm" is part #5.

Although the cam isn't directly on top of the valve stem (has rocker) it is still OHC. 

The article describes Harley, which has the cam down low (not Overhead) and other examples are old flathead V-8, old Briggs and Stratton lawnmower engines where you pull the head and see the top of piston and valves that are "below" the head.

Most modern American V8 engines have valves above pistons, but still not "OHC" because the cam is lower in the engine, below the head. 

 

There is a performance hit for using hydraulic adjustment, as described in that article. Totally acceptable for a grocery getter minivan, but when the motorcycle magazines were throwing this Nighthawk under the bus for being "boring" the manufacturers had to keep doing more to keep up.

It's one of the reasons an R6 can smoke this 750 despite having less displacement.

Edited February 16, 2021 by Lone Wolf

[bwringer]

Over in the vintage Suzuki and Kawasaki world, where shims are huge and sitting on top of the buckets, over-revving by a significant amount back in the racing days was know to spit out a shim occasionally and cause all sorts of expensive havoc. And it can still happen these days if a rider misses a shift badly enough. No rev limiters on these olde analog bikes, ya know...

Redline on those engines was 9,000, and you were taking a big chance if it zinged over 10,000. The shims are basically only glued into place via the surface tension of the oil. This works perfectly well, but only to a point.

So yeah, shim under bucket is light, durable, works great at high RPM and with steep cam profiles, but... yeah, it's kind of a pain in the ass to check and adjust.

Although there are plenty of bikes that make this a LOT more difficult than the Yamaha triples. And most require checking more often.

Go fight with the cam chain tensioner on an ABS V-Strom 650 for a few hours, and you'll adore the straightforward stone-axe simplicity of the Yamaha triple.

 

As noted above, there were some Toyotas that used shim over bucket. I had a couple with well over 250,000 miles, and never once saw a valve clearance out of spec. The manuals told of an exotic tool for compressing the bucket and swapping the shim, but it may have been only a legend...

Later on, Toyota started skipping the shim entirely and using buckets with tops of different thicknesses. I never saw one out of spec, and I don't think anyone ever has. Obviously, low-revving grocery-getter engines are a whooooole different world and are apparently quite gentle on their valvetrains.

Edited February 16, 2021 by bwringer

[Buggy Nate]

19 hours ago, johnmark101 said:

I retired from QC with Toyota Motor Manufacturing.  At the time I was working in powertrain, our four cylinder engines had a shim on top of the bucket arrangement.  The top of the "bucket" surface was recessed, with a raised rim around the top.  The shim sat in this recess beneath the cam lobe and was the exact thickness to fill the recess so that it was flush with the rim.  We had a specialized tool that pushed down on the bucket at the rim, creating enough clearance that allowed you to pry the shim out and replace it with a different sized shim.  Made valve adjustment a simple and quick operation that could be done with the cams in place.

I often wondered why we never saw anything like this attempted with motorcycle engines.  I can thing of a couple of reasons why this might not work on a higher revving, high compression engine, but imagine there might be a brilliant design engineering solution that could make this feasible.  

There are quite a few motorcycle engines that use this design. Their motors aren’t quite as compact and light though. One of the best designs as far as maintenance goes is the Kawasaki Zrx engines. Rocker arm under the cam shaft that is spring loaded and simply slides out of the way to remove the valve shim nestled on top of the valve. But again it is quite a large motor. Can’t have it all unfortunately!

[keithu]

On 2/15/2021 at 5:22 AM, Junkie said:

Using a hydraulic adjuster an an OHC engine would make it dramatically larger I imagine. 

No, not really. Most modern cars are OHC with hydraulic valve adjusters. See the diagram posted by @Lone Wolf, which shows the system on an OHC Honda motorcycle from the 1980s. The hydraulic lifter is pretty small. 

BTW, hydraulic lifters are one of the reasons it's so much more critical to follow the engine manufacturer's recommendations for oil viscosity. Remember when you could just run 10w-40 in everything and you were fine? With hydraulic valves, if the oil's viscosity is too high it can cause excess pressure inside the valve lifter. Valves get held open a little bit and eventually burn. The 3-cylinder motor used in the Suzuki Swift and Geo Metro was famous for this.