Valve shim gaps -All equal or not?

Oh brother.... I just talked to a buddy who is a big shot Mazda mechanic at the dealership and he said many DOHC and SOHC engines, with direct cam over valve, will see an increase of lash with a hot engine over cold... man have I been doing this wrong for the last 43 years?
Or, just following the FSM and using 0.05mm to .010mm "COLD" ....takes all this into consideration and screw the rest of this chatter?
CRAP!!

missionkz wrote:

will see an increase of lash with a hot engine over cold...

Must say that, that rocks my world, but I am open for new views.

So running an engine with less than 0,05 is no big deal, the thermal expansion of Al (22) will save my day and exhaust valves.

Nissan lists both the cold and hot valve clearance specs for the Altima 2.5 L engine. The hot spec is larger than the cold spec by .004 in.
Tight valves make for hard starting and poor idle so running with less than .05 is a big deal. Set your valves tight and let us know how it works.

Every engine design is different depending on specification and the materials used .
You cannot use the old OHC vs pushrod valve train expansion rate comparison pulled off some automotive engineering website as a blanket statement.
It may be typical but it is NOT applicable to every OHC design.
On these particular KZ engines the valve clearance reduces with heat.
I have measured this many times in my 35 years of KZ riding, tuning and racing .
The thermal expansion of the exhaust valves exceeds that of the head greatly and the intakes less so due to intake charge cooling but it's still slightly more than the head material.
The intakes expand almost in line with the head whilst the exhausts close up dramatically.
You are all welcome to go thrash your KZ's with 0.05mm valve clearances if you like but don't come back moaning when you have burnt exhaust valves and a large mechanics bill to pay.

on the Megacycle cam website this is what they list for valve lash for 650/750 engines
NUMBER LIFT AT .040" CENTERS DESCRIPTION AND APPLICATION EXHAUST OPEN/CLOSE CLEARANCE
471-00 .354" 254° 110° OK with stock pistons and springs. Mild increase 17 btc/57 abc .004"
.354" 254° 110° in power from 3800 to 7500. Good mid-range. 57 bbc/17 atc .004"
471-70 .380" 256° 105° All around street/road performance cam. Wide 23 btc/53 abc .004"
.380" 261° 108.5° smooth power band. GPZ-750 OK with stock 59 bbc/22 atc .004"
pistons and springs. All other models require
modified pistons and springs.
471-10 .410" 250° 105° Use racing pistons & springs. Road race/drag race. 20 btc/50 abc .006"
.410" 250° 105° Great throttle control. Mid-range and top-end. 50 bbc/20 atc .006"
Great for ¼ and ½ mile mini sprint

for the 900/1000 it is even more at .006-.007 thous.the higher the horsepower, the more heat is created, the more the valve expands.

Aluminum expands more than steel, but the valve is hotter than the overall head. It could theoretically go either way depending on the details of construction and materials.

On the 550's the gap gets smaller as it heats up. Several 650 guys reported that their gaps got bigger as it heats up.

If I had under bucket shims and a radical cam set up, I might go .006-7. With shim on top, I'll stick with .002-4. :whistle:
Steve