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Air Cooled VW question...

General engine tech -- Drag Racing to Circle Track

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Krooser
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Air Cooled VW question...

Post by Krooser »

OK... I sorta entered the old school VW world recently after buying a '73 Beetle project for a DD for my bride.

It's been 50+ years since I laid a wrench on one of these while employed as a mechanic at a few car dealerships. I have done the usual maintenance and repairs before... tuneup, brakes, etc.

Now my question... stock Weiner Wagons like mine use an aluminum pushrod...valve clearance set at .006 cold. The fanboys on these online forums tell me that when using a chrome moly pushrod you set the cold clearance to ZERO.

Now I am not going to mod this engine at all... doing just what's needed to get it running good. But what's with the zero cold valve clearance especially on an air cooled engine?

VW experts chime in please...
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mag2555
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Re: Air Cooled VW question...

Post by mag2555 »

Aluminium heads on a water cooled motor expand at least .004” when up to temp, air cooled ones even more.
Running zero lash with steel push rods when cold will get you the needed .006” or so when all is hot.

When setting the cold lash on a water cooled race motor or even a street motor with Aluminum heads and a solid lifter Cam it’s typical to, for instance set the lash .006” to .008” tighter then the Cam card calls for, in this way when the everything is fully up to temp the proper lash is achieved,

In short Aluminium heads and Aluminium push rods expand a lot, and steel push rods do not.
Last edited by mag2555 on Wed Jul 21, 2021 7:48 am, edited 1 time in total.
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Re: Air Cooled VW question...

Post by BillK »

Dont really feel like an expert but have built about 20 of those engines years ago when my Wife was drag racing her 70. To be honest with you I never remember having to replace a pushrod ? What is wrong with the ones in yours ? If they do indeed need replacing are the stock ones no longer available ? Its been so long I honestly dont remember them being aluminum.
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Krooser
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Re: Air Cooled VW question...

Post by Krooser »

Nothing wrong with my stock pushrods and they will stay put.

Just wondering how you get away with zero lash on a solid lifter cam in an air cooled engine.
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David Redszus
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Re: Air Cooled VW question...

Post by David Redszus »

Krooser wrote: Wed Jul 21, 2021 5:45 pm Nothing wrong with my stock pushrods and they will stay put.

Just wondering how you get away with zero lash on a solid lifter cam in an air cooled engine.
Compare the thermal growth of the head to that of the air-cooled cylinders.

The only time I ever replaced a push rod in a VW (or Porsche 356,) is when I over-reved the snot out of
it being a stupid little show off.
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Re: Air Cooled VW question...

Post by Krooser »

David Redszus wrote: Wed Jul 21, 2021 9:07 pm
Krooser wrote: Wed Jul 21, 2021 5:45 pm Nothing wrong with my stock pushrods and they will stay put.

Just wondering how you get away with zero lash on a solid lifter cam in an air cooled engine.
Compare the thermal growth of the head to that of the air-cooled cylinders.

The only time I ever replaced a push rod in a VW (or Porsche 356,) is when I over-reved the snot out of
it being a stupid little show off.
You are saying the lash comes in when the engine is hot?
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modok
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Re: Air Cooled VW question...

Post by modok »

With a magnesium engine case and aluminum head.....the lash expands approx + .010 or more at running temp.
if you are using a camshaft with very short lash ramps and steel pushrods then you nearly have to set the lash at zero cold to avoid excessive lash when hot.

Why use a cam with only .010 of lash ramp? don't ask me, makes no sense.

the effect of less lash ramp can be had by just running looser, but how to do the opposite? you will be needing to take a file to your cam base circle..... :wink:
And a few times, i have, and it worked just fine.
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