Valve shim gaps -All equal or not?

Interestingly, the Suzuki GS engines, which were heavily influenced by the big KZ engines (if not a copy in some ways), run valve clearances between .03-.08 mm, and these engines are supremely durable. No concern with burning valves or seats at these crazy tight clearances. Not sure what's so different between a big GS and KZ?

I guess I'm a bit dense on this one, so help me see if I understand the theory.

If the valve clearances are greater the valves close earlier in the cam rotation. Is the idea that because of the shape of the cam lobes this then permits the valves to close a bit more gently than if they were closing later in the cam rotation, and this would reduce the slamming effect? Thanks for your patience. Ed

If the clearance is too tight, no oil will be allowed in between the cam and lifter, plus there will be no cushioning effect of the oil. With shim on top lifters, the gap can't exceed a certain point or "spitting" can occur. That's why in the day, KZ650 lifters were used with radical cams. I understand the clearance was to be larger for this reason. Lubrication and cooling. They or that style are used in HP mods today.
Steve

swest wrote: If the clearance is too tight, no oil will be allowed in between the cam and lifter, plus there will be no cushioning effect of the oil.

Steve that statement is wrong irregardless of clearance the pound's per square inch load is still the same.
As the cam rotates the lobe will draw a micro thin layer of oil in between the lobe and sim/bucket
and the only thing that will change that is spring pressure.

Nessism wrote: Interestingly, the Suzuki GS engines, which were heavily influenced by the big KZ engines (if not a copy in some ways), run valve clearances between .03-.08 mm, and these engines are supremely durable. No concern with burning valves or seats at these crazy tight clearances. Not sure what's so different between a big GS and KZ?

It's all to do with heat expansion.
On the KZ, at around 0.5mm the valve stem can expand so much that it no longer shuts fully which exposes the seats to excessive heat which then erodes the seats and burns valve heads , especially the exhausts and the hotter the motor gets the more clearance you need .
Just ask Yoshimura why they specify 0.20mm clearance for their performance cams ).
The Suzuki heads were designed to run cooler than the KZ hence being able to run tighter clearances before problems arise.
The GS engine was not so much influenced by the KZ engine but actually designed by the SAME designer (starting with the GS750) hence the strong similarity with improvements in some areas although it was weaker in others.
It is actually a reworked KZ with enough differences not to cause copyright issues and the GS actually shares the same combustion chamber and cylinder stud spacings which means that the GS head will bolt straight on the KZ block with some idler modifications .
This is exactly what a lot of racers did back in the day to take advantage of the GS's larger valves and increased gas flow before the Kawasaki 'J' head came out with even bigger valves than the GS and this overtook the GS conversion due to it needing less modification ( idler tower conversion) to fit.

zed1015 wrote:

Nessism wrote: Interestingly, the Suzuki GS engines, which were heavily influenced by the big KZ engines (if not a copy in some ways), run valve clearances between .03-.08 mm, and these engines are supremely durable. No concern with burning valves or seats at these crazy tight clearances. Not sure what's so different between a big GS and KZ?

It's all to do with heat expansion.
On the KZ, at around 0.5mm the valve stem can expand so much that it no longer shuts fully which exposes the seats to excessive heat which then erodes the seats and burns valve heads , especially the exhausts and the hotter the motor gets the more clearance you need .
Just ask Yoshimura why they specify 0.20mm clearance for their performance cams ).
The Suzuki heads were designed to run cooler than the KZ hence being able to run tighter clearances before problems arise.
The GS engine was not so much influenced by the KZ engine but actually designed by the SAME designer (starting with the GS750) hence the strong similarity with improvements in some areas although it was weaker in others.
It is actually a reworked KZ with enough differences not to cause copyright issues and the GS actually shares the same combustion chamber and cylinder stud spacings which means that the GS head will bolt straight on the KZ block with some idler modifications .
This is exactly what a lot of racers did back in the day to take advantage of the GS's larger valves and increased gas flow before the Kawasaki 'J' head came out with even bigger valves than the GS and this overtook the GS conversion due to it needing less modification ( idler tower conversion) to fit.

Very interesting and informative post.

zed1015 wrote:

Nessism wrote: Interestingly, the Suzuki GS engines, which were heavily influenced by the big KZ engines (if not a copy in some ways), run valve clearances between .03-.08 mm, and these engines are supremely durable. No concern with burning valves or seats at these crazy tight clearances. Not sure what's so different between a big GS and KZ?

It's all to do with heat expansion.
On the KZ, at around 0.5mm the valve stem can expand so much that it no longer shuts fully which exposes the seats to excessive heat which then erodes the seats and burns valve heads , especially the exhausts and the hotter the motor gets the more clearance you need .
Just ask Yoshimura why they specify 0.20mm clearance for their performance cams ).
The Suzuki heads were designed to run cooler than the KZ hence being able to run tighter clearances before problems arise.
The GS engine was not so much influenced by the KZ engine but actually designed by the SAME designer (starting with the GS750) hence the strong similarity with improvements in some areas although it was weaker in others.
It is actually a reworked KZ with enough differences not to cause copyright issues and the GS actually shares the same combustion chamber and cylinder stud spacings which means that the GS head will bolt straight on the KZ block with some idler modifications .
This is exactly what a lot of racers did back in the day to take advantage of the GS's larger valves and increased gas flow before the Kawasaki 'J' head came out with even bigger valves than the GS and this overtook the GS conversion due to it needing less modification ( idler tower conversion) to fit.

Zed that's neat little bit of history. I had heard about Suzuki heads being used, so there was some truth to that. Very cool.

My 1300 is a water cooled 2 valve, and they actually run larger clearance on the exhaust valves compared to 1000's. You'd think it would be the other way since the heads should running much cooler than an air cooled 4. .15-.25MM is the spec.

At what point do you risk spitting shim? That's really the danger in running the valves too loose.

Tyler wrote: At what point do you risk spitting shim? That's really the danger in running the valves too loose.

No!
Spitting shims is really nothing to do with loose clearances.
It's a combination of camshaft profile and the groove around the perimeter of the shim on top valve bucket .
Most spit shims arise from using performance cams and high rpm.
The higher profile of the performance cam sweeps a greater distance across the shim and rocks the edge of the shim into the groove in the bucket which lifts the opposite side of the shim .
This then sets up a constant rocking motion which can eventually lead to the shim being spat out like tiddlywinks.
Before shim under racers used to fill the groove with hard solder to prevent this.
Later on, performance buckets were available from the likes of RC engineering etc without the groove and with tighter tolerances for the shim. these were then made redundant with the advent of the shim under set up as it was easy just to convert the early engines to shim under using Z650 valve train components.

650ed wrote: I guess I'm a bit dense on this one, so help me see if I understand the theory.

If the valve clearances are greater the valves close earlier in the cam rotation. Is the idea that because of the shape of the cam lobes this then permits the valves to close a bit more gently than if they were closing later in the cam rotation, and this would reduce the slamming effect? Thanks for your patience. Ed

I realize, Ed, you already suspect this. But to confirm...

Less lash clearance yields less "slamming". It should be obvious when you think of how the cam profile transitions to base circle. The rate at which the cam radius changes is indicative of the valve velocity. The rate at which the cam radius decreases is not constant. As the radius decreases near closing, the rate at which it decreases also decreases (decelerating). This means as the valve gets closer to being closed, the valve is moving slower. If there is a larger lash gap, that means the valve hits the seat at a higher velocity. (And on the opening side, the cam hits the bucket (or shim) at a higher velocity.) If the closing rate of the valve was constant, we would see a distinct line on the cam where the closing ramp transitioned to base circle (because the transition from decreasing radius to constant radius would be abrupt).

But we don't even need to think about all that. We also can simply try it and listen. You don't get loud ticky valvetrain because the valves and seats are meeting more gently, they are loud because there is more "slamming", which is louder when the lash gap is bigger.

I think the idea of early valve seat demise when the lash gap is too small (ie below spec), comes from what happens when the valve fails to close all the way (which will unfortunately happen when going hard throttle on the expressway, when the valve heats and expands). I would assume that will cause the burned valve and seat.

Thanks; that all makes sense to me. Ed

I think what Loudhvx and ZED said go's along with what I said about oiling the lobe
it's the shape of the closing ramp on the lobe that control's valve seating.

With more clearance you're seating the valve at a higher lift point on the lobe and coming off the closing ramp to soon
causing a harder seating.of the valve instead of setting the valve on the seat softly .
Granted we're talking millisecond's here..

In a perfect world .001 clearance would work

...Also performance cams have harsher acceleration ramps to increase the duration and add extra lift - they whack them open and slam them shut a lot harder.

I think the need for the clearance is to allow the exhaust valve to temporarily heat sink into the head, hence tight clearances risks burning out the exhaust valves.