924Board.org

[coup85]

Doing a rebuild on my '79 924 2.0L. The head is at the machine shop right now and the machinist says everything looks mostly fine, but he wants to do a standard valve lapping.

My worry is the weird valve clearance adjustment on these engines. If they lap the valves, the valves will sit deeper in the head, which shrinks the clearance. I'm afraid I'll bottom out my stock adjusting screws when I try to set the valve lash later –does anyone know the adjustment margin the original ones have?

Has anyone gotten away with just lapping the original valves without needing to buy the thicker oversized screws?
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924 - 79'

[Cedric]

There are several classes of screws(indicated by the marking on the end), it might work, might bottom one out(be aware not to screw them to far, you could get around by swapping them around if you are lucky because often several of the types are present normally.

I have machined seats on two heads (one got new echaust valves though) and it mostly worked out, i think i swapped one or maybe two screws out. I think they can be bought new from porsche these days, but if you stumble over some cheap head its a good way to get spares like these screws.
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1980 924 Turbo
www.instagram.com/garagecedric/

[coup85]

Thanks, the truth is I never did the valve clearance adjustment, and I'm a little unsure about how to get it right, I have the Haynes –and some videos, but I suppose there is nothing like just trying

I'll get the head back in a few days. I hope I can make it work. Someone just told me to just switch to shimmed cam followers. Seeing the price of those screws, if I need to change more than a couple of them, I might think about it.
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924 - 79'

[924RACR]

The shimmed followers are great for racing - the stock followers are a liability at high revs thanks to the holes in the sides for the adjusters. But for street use, the stock ones are so much easier to adjust...

Doing the stock adjustment isn't such a big deal; I just redid them on my '82 931 the other day. Just measure and re-measure, and spin the motor over and measure again if you are worried...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Fifty50Plus]

As Vaughan says, using shims in a race engine is a good thing. It saves weight (lifters are empty, without the heave standard adjuster screw) but requires removing the cam to change shims. Plus the 9mm shim kit (Alfa's use them) is expensive.
As Cedric says, there are 4 ranges of the factory adjustable screws. Lapping existing valves probably won't make much of a change in your engine. If you need to replace an adjustment screw, you will need to remove the cam from the head to, pull out the lifter, unscrew the adjuster from the side of the lifter and replace with another. Measure and adjust all eight several times before you decide whether you need to change one. That way, you might or might not have to remove the cam only once to change the adjustment screw range.
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1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA