Post by dpeters81westy on Oct 22, 2007 19:27:17 GMT -5
I received this in my inbox from the Karmann Ghia Club of North America and though I'd share it...
My purpose for this is to open up a discussion on motor maintenance and build-up topics..
So, The original poster asked about Valve Clearances on his 1776cc engine...
The replies are as follows...
> Subject: Re: [KG] 1776 tappet clearances
>
> I usually split the difference and set mine at 5mm. Even if we all used
> the same feeler gauge there would probably be a lot of variation because some
> set it so the feeler gauge slides tight and some do it loose. And then
> there's the school of thought that if you have ratio rockers and steel
> push rods you should set them tighter. When I heard about that I started
> setting my Berg engines at a tight 4mm and that seems to be good for them.
>
>>...VW changed the spec from 0.1mm (0.004") to 0.15mm (0.006") in order to
>>provide an increased measure of safety due to (mostly U.S.) customers not
>>adhering strictly to the adjustment schedule. It was _not_ due to any
>>change in engineering. VW as much as says this in their literature as the
>>specification changed at a time when there was no corresponding change in
>>the parts involved.
>>
>>Note that the valve clearance increases when the engine warms. Too large a
>>gap wastes performance (both power and ecconomy) while too small a gap
>>doesn't give the (exhaust) valves time to cool (while closed and in
>>contact with the seat).
>>
>>So long as you check the valves very regularly, there is no data I'm aware
>>of to support a larger valve clearance than the earlier value. If you went
>>to aluminum cylinders, you would get an even greater increase as the
>>engine warms so you might then alter the composition of the pushrods to
>>try and keep the ratio of coefficients of expansion about the same. To
>>really get this right, take a stock engine with perfectly set valves (one
>>valve will do!), get it properly warm (say 160 to 180F) and measure the
>>gap as quickly as possible. Whatever that value is should be maintained,
>>as a warm/warm comparison, after altering the engine's construction
>>materials.
>>
>>BTW, I've been meaning to make just exactly this measure on several
>>engines I have for comparison's sake but have never gotten 'round to it.
>>If anyone does, please share with me your raw data!
>>
>>Regards,
>>Richard
Now....
DISCUSS...
- DP
My purpose for this is to open up a discussion on motor maintenance and build-up topics..
So, The original poster asked about Valve Clearances on his 1776cc engine...
The replies are as follows...
> Subject: Re: [KG] 1776 tappet clearances
>
> I usually split the difference and set mine at 5mm. Even if we all used
> the same feeler gauge there would probably be a lot of variation because some
> set it so the feeler gauge slides tight and some do it loose. And then
> there's the school of thought that if you have ratio rockers and steel
> push rods you should set them tighter. When I heard about that I started
> setting my Berg engines at a tight 4mm and that seems to be good for them.
>
>>...VW changed the spec from 0.1mm (0.004") to 0.15mm (0.006") in order to
>>provide an increased measure of safety due to (mostly U.S.) customers not
>>adhering strictly to the adjustment schedule. It was _not_ due to any
>>change in engineering. VW as much as says this in their literature as the
>>specification changed at a time when there was no corresponding change in
>>the parts involved.
>>
>>Note that the valve clearance increases when the engine warms. Too large a
>>gap wastes performance (both power and ecconomy) while too small a gap
>>doesn't give the (exhaust) valves time to cool (while closed and in
>>contact with the seat).
>>
>>So long as you check the valves very regularly, there is no data I'm aware
>>of to support a larger valve clearance than the earlier value. If you went
>>to aluminum cylinders, you would get an even greater increase as the
>>engine warms so you might then alter the composition of the pushrods to
>>try and keep the ratio of coefficients of expansion about the same. To
>>really get this right, take a stock engine with perfectly set valves (one
>>valve will do!), get it properly warm (say 160 to 180F) and measure the
>>gap as quickly as possible. Whatever that value is should be maintained,
>>as a warm/warm comparison, after altering the engine's construction
>>materials.
>>
>>BTW, I've been meaning to make just exactly this measure on several
>>engines I have for comparison's sake but have never gotten 'round to it.
>>If anyone does, please share with me your raw data!
>>
>>Regards,
>>Richard
Now....
DISCUSS...
- DP
