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I set valve clearances at the 10° timing mark. Bug is not happy.
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the_8th_dwarf
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PostPosted: Sun Jan 10, 2021 10:16 am    Post subject: Re: I set valve clearances at the 10° timing mark. Bug is not happy. Reply with quote

bugbyte wrote:
One of the most wrong things I've ever read on the samba since I joined.


That is a label I will choose to wear with honor. Thank you
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jarmchairpilot
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PostPosted: Sun Jan 10, 2021 10:22 am    Post subject: Re: I set valve clearances at the 10° timing mark. Bug is not happy. Reply with quote

Do you run points, if so that's the first thing to check is the condition and set the gap correctly.
If electric ignition then you check the ignition timing with a strobe light After you have adjusted the valve gaps according to spec. nearly always 0.15mm..for most bugs.
A service including oil change is always a good idea
I replace distributor cap,rotor,spark plugs and ignition leads every 5 years because my bug is my daily driver.Buy the best Bosch quality where possible,German,Mexican,Brazilian in order of quality.
Change fuel filter every year too,it's crucial to keep carb clean.
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joemama
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PostPosted: Sun Jan 10, 2021 10:34 am    Post subject: Re: I set valve clearances at the 10° timing mark. Bug is not happy. Reply with quote

Did you by chance disconnect the plug wires? If so, check the firing order.
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ashman40
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PostPosted: Sun Jan 10, 2021 4:28 pm    Post subject: Re: I set valve clearances at the 10° timing mark. Bug is not happy. Reply with quote

Short answer, it does not make a difference in the adjustment if you are a few degrees off from TDC when you set the valve gap. +/- 10deg makes no difference.

Ignition timing and valve timing are two different things. The crank pulley timing marks are primarily for ignition timing.
The TDC mark is used when setting the valve gap, but only as a means of making sure the specific cylinder you are adjusting is near TDC at the end of the compression stroke. You want to be near the TDC mark for cylinders 1 & 3. You want to be near the BDC mark (or about 180 crank deg off from TDC) for cylinders 2 & 4. Each cylinder must have both valves closed when making adjustments. The range of cam degrees when both are closed is rather large and the corresponding crank degrees is twice as large. You do not need the crank to be exactly at TDC when making the adjustments. You can actually be quite a bit off from TDC and still be fine.

61SNRF’s pics illustrate this...
61SNRF wrote:
For reference here is a cam lobe profile chart...
Image may have been reduced in size. Click image to view fullscreen.

In the above pic, TDC at the end of the compression stroke is somewhere close to the bottom of the cam lobe pictured inside the base circle. Also realize that the crank rotates twice (720deg) for each single (360deg) rotation of the cam, and the timing marks on the crank pulley are in crank degrees. This means the more than 180deg of base circle is more than 360deg of crank rotation!

61SNRF wrote:
Here's a pic with both lobes...
Image may have been reduced in size. Click image to view fullscreen.

In this diagram you see both intake and exhaust lobes mapped against crank degrees. The two lobes are offset (lobe offset). The base circles of both lobes are near the top. The degree marks are from 0 to 720 because it takes two crank rotations (720deg) to rotate the cam once. Crank pulley TDC is zero (0) at the top of the diagram (and also at 360deg at the bottom.. again two rotations). Notice that both lobes have zero lift between around 630deg and 90deg. That is 90deg of crank rotation on either side of TDC where the valve gap is the same. So +/- 10deg on either side of the crank pulley TDC mark will make no difference in the valve gap adjustment. Even on a radical race cam you could go with 45deg off from TDC and there should still be no difference.

Your problem is not with using the 10BTDC timing mark as your reference.


The factory documented method for adjusting valves is to rotate the crank pulley CW 180deg between adjustments and set the valves in the order 1-4-3-2. This is the firing order stamped into the base of the generator stand.
You mentioned above setting valves in the order 1-2-3-4. This only works if you rotated the crank pulley CCW instead of CW. Did you rotate the crank CCW when you were making your adjustments?
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'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
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Last edited by ashman40 on Sun Jan 10, 2021 4:33 pm; edited 1 time in total
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the_8th_dwarf
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PostPosted: Sun Jan 10, 2021 4:33 pm    Post subject: Re: I set valve clearances at the 10° timing mark. Bug is not happy. Reply with quote

ashman40 wrote:


The factory documented method for adjusting valves is to rotate the crank pulley CW 180deg between adjustments and set the valves in the order 1-4-3-2. This is the firing order stamped into the base of the generator stand.
You mentioned above setting valves in the order 1-2-3-4. This only works if you rotated the crank pulley CCW instead of CW. Did you rotate the crank CCW when you were making your adjustments?


I did generally rotate CCW, but it's possible that I did some CW movement while adjusting the pulley to line up correctly with the crack in the case. But I did continually check that my rotor was pointed to the correct position for the valve I was adjusting. So that should not be a problem, right? Unfortunately I did not get the chance to reset the valve lash today so I might be next weekend before I can take another stab at this
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PostPosted: Mon Jan 11, 2021 9:41 am    Post subject: Re: I set valve clearances at the 10° timing mark. Bug is not happy. Reply with quote

the_8th_dwarf wrote:
I did generally rotate CCW, but it's possible that I did some CW movement while adjusting the pulley to line up correctly with the crack in the case. But I did continually check that my rotor was pointed to the correct position for the valve I was adjusting. So that should not be a problem, right? Unfortunately I did not get the chance to reset the valve lash today so I might be next weekend before I can take another stab at this

If your engine was running well, you can trust the rotor as an indicator of which cylinder is at the end of the compression stroke where the valve lash/gap is set.

If you really want to make sure... watch the intake rocker arm/valve. While rotating the crank CW, watch the intake rocker for the cylinder you are adjusting. Watch the valve open then close. Rotate the crank another 180deg until the TDC mark (1 & 3) or BDC mark (2 & 4) lines up with the case split. Rock the crank pulley back and forth a bit and confirm the intake and exhaust valves for the cylinder you are working on do not move (valves closed). You have now confirmed the cylinder you are looking at is at the end of the compression stroke. Adjust the valve lash/gap (engine cold). Look at the rotor position and confirm the spark plug wire for the cylinder is over the rotor tip.
This method is never wrong because you are seeing the effect of the crank and cam on valve movement to confirm which stroke the cylinder is in. Then you make sure the valve gap is correct when both valves are closed AND that the distributor is delivering a spark to the correct spark plug when that cylinder needs a spark. Even if your distributor is indexed incorrectly and the plug wires are installed incorrectly the above method confirms identifies this and corrects for it. The only thing the above cannot accommodate is if the cam+crank are not indexed correctly. This would require the case be opened to fix so is a major problem which should have been caught when the engine was built. It can be assumed the cam+crank are indexed correctly if the engine is/was running.
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PostPosted: Tue Jan 12, 2021 10:07 pm    Post subject: Re: I set valve clearances at the 10° timing mark. Bug is not happy. Reply with quote

owdlvr wrote:

You need to wait for your engine to be stone cold (ideally overnight) to adjust the valves. So read up, ask your questions, and re-adjust on Sunday.


While this is how I've done it. Reading thru VW manuals (vw 1200 workshop manual pg 19) and dealer instructions, the directions were for the engine to be cool (less than 50C). So, draining the oil, filling in fresh oil were amongst the ways to cool the engine down faster.

So it does not really need to be stone cold - it needs to be cool -> less than 50C (122F).

I did some rough math (i've not double checked it) and at 50C vs 20C, the change in valve gap turned out to be about 0.0002".
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PostPosted: Wed Jan 13, 2021 1:15 am    Post subject: Re: I set valve clearances at the 10° timing mark. Bug is not happy. Reply with quote

Back in ye olden daze, the Germans set the valve lash to .004" because that is exactly what was required for the engine. In the late sixties, VW couldn't figure out why American engines (their largest market) were burning #3 exhaust valves at an alarming rate, so they sent inspectors across the pond to investigate.

As it turns out, when American mechanics finished their daily shifts, they put their tools down and hit the bars. The next morning, they pulled that day's cars in for tune-ups, and adjusted valves on "cold" (not really) engines. Those .004" valve lash specs on "cold" engines shrank down to .002" when the engines were actually allowed to sit overnight, (heat expansion is a bitch.) Meanwhile, the Germans, (a more fastidious group of mechanics,) put their tools down at 4:50pm, and pulled the next day's cars into the shop. By adjusting those valves truly cold, their cars didn't have the problem of dropped valves.

VW gave the American dealerships two choices: prep your work before visiting the pubs, or set the valves to .006" the following morning.

The sticker on our fan shrouds tells us which path the American mechanics chose.

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modok
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PostPosted: Wed Jan 13, 2021 1:57 am    Post subject: Re: I set valve clearances at the 10° timing mark. Bug is not happy. Reply with quote

bnam wrote:
owdlvr wrote:

You need to wait for your engine to be stone cold (ideally overnight) to adjust the valves. So read up, ask your questions, and re-adjust on Sunday.


While this is how I've done it. Reading thru VW manuals (vw 1200 workshop manual pg 19) and dealer instructions, the directions were for the engine to be cool (less than 50C). So, draining the oil, filling in fresh oil were amongst the ways to cool the engine down faster.

So it does not really need to be stone cold - it needs to be cool -> less than 50C (122F).

I did some rough math (i've not double checked it) and at 50C vs 20C, the change in valve gap turned out to be about 0.0002".

It's not that simple.
Due to the design of the engine the heads and pushrods and case may all be different temperatures, so the simplest thing to do is just wait long enough they all equalize down to ambient.
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PostPosted: Mon Jan 25, 2021 2:33 am    Post subject: Re: I set valve clearances at the 10° timing mark. Bug is not happy. Reply with quote

@modok,
Even if the they are all at different temperatures, as long as the warmest is less than 50C, it would seem to me that setting gap would be ok as the most variance between the different valves which are presumably at different temperatures (but all below 50C) - would be much less than 0.0002" (which is how much the gap would vary if set at 50C and later measured at ambient - IFF my calc is roughly correct).

Again - just trying to rationalize why the factory manual says it's ok to do timing as long as temp is below 50C. Not recommending it. And I prefer to do it cold.
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PostPosted: Mon Jan 25, 2021 3:45 am    Post subject: Re: I set valve clearances at the 10° timing mark. Bug is not happy. Reply with quote

I'm not sure if you are calculating that right.
Roughly the difference in expansion between iron and aluminium is .001" per 1 per 100degrees f

four inches of cylinder, 50f, that's a difference of .002"

Then again the valves are ALSO about 4", so that would cancel out the cylinder, if we assume the heads and cylinders and pushrods are all at the same temp, which is plausible.

But the CASE, would probably be last to cool, and magnesium has 2.5 times more expansion than iron. if the case was 50F hotter than the rest it would have you adjusting your valves ABOUT .002" too tight.
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