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February 27, 2021, 05:57:37 PM

Valve adjustment

This is a discussion for the topic Valve adjustment on the board Beach Buggy Engine and Exhaust Help.

Author Topic: Valve adjustment  (Read 913 times)

this user is offline Zip Buggy

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on: April 19, 2020, 01:25:05 PM
I'm sure everyone has their way of doing their tappets but this one grabbed my attention.
https://youtu.be/lfkxlHWZmxM
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this user is offline Manxdavid

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Reply #1 on: April 20, 2020, 08:45:27 AM
Interesting he's using standard gap for inlet and standard + gap for exhaust on what looks to be a 'built' engine, that's going to be noisy!
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this user is offline Peter

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Reply #2 on: April 20, 2020, 10:10:07 AM
Well well,

I have always tried to set my exhaust valves slightly wider than the inlets...

The only reason and typical me, is that I have always felt that though the heads
are warming fast everywhere, the exhaust valves at full lift are getting a 'heat boost' along
their exposed stems due to the very very hot exhaust gas running up, past and all around them
whilst exiting the heads, causing the stems to expand slightly more length wise and thus closing the gap.

May be wrong but I have never noticed any extra clatter, that said, when the engines
running my exhaust drowns out other sounds so I probably can't hear it anyway!  ;D

Peter  :)
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this user is offline Manxdavid

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Reply #3 on: April 20, 2020, 10:39:05 AM
Well well,

I have always tried to set my exhaust valves slightly wider than the inlets...

The only reason and typical me, is that I have always felt that though the heads
are warming fast everywhere, the exhaust valves at full lift are getting a 'heat boost' along
their exposed stems due to the very very hot exhaust gas running up, past and all around them
whilst exiting the heads, causing the stems to expand slightly more length wise and thus closing the gap.

May be wrong but I have never noticed any extra clatter, that said, when the engines
running my exhaust drowns out other sounds so I probably can't hear it anyway!  ;D

Peter  :)

I was thinking that a high spec engine would at least have a hotter cam and hence steel or chrom moly pushrods that'd need a smaller, if any, gap.
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"Ah, Beach Buggies, sure, just a quick cheap way of getting a few more years out of a rusty Beetle. You can throw one together in a weekend." anon.


this user is offline snoopy

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Reply #4 on: April 20, 2020, 11:00:08 AM
would it work on longer duration cams where the ramps are longer.


this user is offline Peter

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Reply #5 on: April 20, 2020, 12:51:26 PM
Any use of push rods that dont expand would be useful I would have thought, if
only to stabilise things, my thoughts were that valve stems will expand a small amount lengthwise
due to the severe heat of the gas flowing all over them whilst on its way out, whereas the inlet port will be
cooling the stems due to the inrush of cool vaporised fuel, some of that fuel will be flowing over the
valve head itself too, cooling it from the back.


Don't know, but the two environments are very very different in terms of the world a valve has to live in.

I have always given my exhaust valve a tiny bit more gap and so far all's been fine, I think this point is
fundamental to any engine really, with the exhaust port being a hotter world than the inlet...

Peter  :)
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this user is offline Manxdavid

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Reply #6 on: April 20, 2020, 03:33:27 PM
VW used to state 4 thou clearance but changed their recommendation to 6 thou in an attempt to stop the spate of dropped valves (usually #3 exhaust) that occurred in the 1960s before they developed the dog house oil cooler that took the cooler out of the fan shroud increasing airflow to #3 cylinder. With stock alloy pushrods I'd say the ideal clearances would be inlet 4 thou exhaust 6 thou.
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"Ah, Beach Buggies, sure, just a quick cheap way of getting a few more years out of a rusty Beetle. You can throw one together in a weekend." anon.


this user is offline Paul1953

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Reply #7 on: April 20, 2020, 06:39:15 PM
spate of dropped valves (usually #3 exhaust) that occurred in the 1960s

Saw this many times way back when I was a lad... All my Beetles were single port, pre doghouse motors. Always No 3. VW agency quoted this as being resultant from air flow restriction to no 3 because of position of oil cooler.


this user is offline IDA

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Reply #8 on: April 21, 2020, 01:46:12 AM
I been doing it for years like that..  It will have £150! set of 7075 alloy push rods in that engine
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