[DeTomaso] Why would an engine idle faster after valve adjustment?
Pantdino
pantdino at aol.com
Sun Dec 11 02:30:47 EST 2016
My Fiat Abarth has an Autobianchi A112 A2 1050cc pushrod 4 cylinder engine, 10.5:1 CR, fairly aggressive aftermarket cam per previous owner, who used the car in vintage racing in Germany.
I checked the tappet clearances set by the previous owner and found them to be 6-8 thou, which is what a stock Fiat 4 cylinder engine of similar type called for, and the engine idled at about 1000 rpm
I found the correct specs for this engine with stock cam, which are 10 intake, 12 exhaust
But I looked up the specs for CatCams cams for the A112 A2 motor on their website and even their most mild “sport” cam calls for 0.35mm (0.014”) “lash ramp”. So I adjusted the tappets to 14 thou.
Now the car idles at 2000 rpm with the idle screw completely out, even after I downsized the idle jet one size.
Compression testing shows 195 – 198 - 198 – 190 psi with a cold engine, which is higher than the 175-195-190-175 with a warm engine I had gotten with the 6-8 thou clearances.
Power is very subjective, but I would say the car runs better now.
How can adjusting the valves make a car idle so much faster, and can too much lash cause a problem other than loss of power?
Thanks,
Jim Oddie
Sent from AOL Mobile Mail
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My Fiat Abarth has an Autobianchi A112 A2 1050cc pushrod 4 cylinder
engine, 10.5:1 CR, fairly aggressive aftermarket cam per previous
owner, who used the car in vintage racing in Germany.
I checked the tappet clearances set by the previous owner and found
them to be 6-8 thou, which is what a stock Fiat 4 cylinder engine of
similar type called for, and the engine idled at about 1000 rpm
I found the correct specs for this engine with stock cam, which are 10
intake, 12 exhaust
But I looked up the specs for CatCams cams for the A112 A2 motor on
their website and even their most mild asporta cam calls for 0.35mm
(0.014a) alash rampa. So I adjusted the tappets to 14 thou.
Now the car idles at 2000 rpm with the idle screw completely out, even
after I downsized the idle jet one size.
Compression testing shows [1]195 a 198 - 198 a 190 psi with
a cold engine, which is higher than the [2]175-195-190-175 with
a warm engine I had gotten with the 6-8 thou clearances.
Power is very subjective, but I would say the car runs better now.
How can adjusting the valves make a car idle so much faster, and can
too much lash cause a problem other than loss of power?
Thanks,
Jim Oddie
Sent from AOL Mobile Mail
References
1. tel:195%20-%20198%20-%20198%20-%20190
2. tel:175-195-190-175
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