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Pinging - distributor problem?
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thomas.
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PostPosted: Tue Feb 02, 2016 5:39 am    Post subject: Re: Pinging - distributor problem? Reply with quote

You shouldn't have to run premium. Your car will ping if it runs hot. Are all your cooling tins in place. Have you checked for obstructions at the fan area ? I had a paper towel get sucked in there once and it didn't take long before the pinging started. You can cause big damage in a vw motor if it's pinging. Newer cars are more forgiving in the same situation. Wouldn't hurt to post a photo. good luck.
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61SNRF
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PostPosted: Tue Feb 02, 2016 8:26 pm    Post subject: Re: Pinging - distributor problem? Reply with quote

What is pre-ignition? In a spark controlled IC engine, that's when the mixture is ignited before the spark is optimally set to occur.
Basically the engine wants to run like a diesel without the need for a spark plug.

What is main cause? High combustion chamber temperatures, or second to that a small chunk of carbon that glows red when under pressure (=heat).

Can idle mixture affect conditions pulling up a hill?
Yes, but only to a lesser degree. True the idle circuit is active from idle to max RPM, it's your main jet circuit that should take over with most of the fuel needed at higher cruise speeds.
Either way, since an overall lean fuel mixture can negatively effect engine cooling, it's conceivable it might be felt worse pulling up a hill.

Other than ignition timing the real main factor is compression ratio.
Next question, do you know what yours is?
Higher compression ratios bring higher combustion chamber temperatures which bring the resultant pinging.
Even VW modified the engines with low compression pistons for some markets, perhaps your market is one that was(is) applicable?
Perhaps whoever built the engine flycut the heads a little extra for more CR/cheap HP?
Something basic to consider before pulling all your hair out.

As far as the vacuum port in your carb, stop probing it with metal objects Razz

Your vacuum advance distributor uses that ported vacuum signal from the carb that is relatively low at idle and increases quickly as the throttle blade exposes the orifice upon opening. Look up the carb cross section in your manual.
On that note, to say if your vacuum signal at idle is relatively too high or not means you will need to quantify how much vacuum you have there by measuring it with a gauge then report back.
Next, someone here has to go out and measure their car for a relative comparison.

To advance lets now say your carburetor vacuum signal is found to be relatively normal. After that it comes to distributor calibration. Notice inside the distributor there is a return spring for the movable points plate.
That spring is carefully calibrated for different engine/market applications.
It can conceivably weaken or loose tension.
It also has an adjustable eccentric mounting post in the distributor base that when turned can increase or decrease spring tension, but I don't suggest you F with that unless you have a Sun distributor bench tester.

It should also be brought up and mentioned that pinging can be caused by poor driving habits.
If you are lugging the engine, the pinging might be a warning sign to simply change down a gear.
BTW do you down shift to third when this occurs?
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andk5591
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PostPosted: Wed Feb 03, 2016 5:36 am    Post subject: Re: Pinging - distributor problem? Reply with quote

Part of your problem IMHO is that you pissed several people off by not listening. At least you did me - good luck and hopefully you wont insist on being told the same thing 6 times before you pay attention to it.
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HippyTom
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PostPosted: Wed Feb 03, 2016 6:01 am    Post subject: Re: Pinging - distributor problem? Reply with quote

I have a 62 Bug and a 63 Bug with 1600 cc single port engines, one with a 009 centrifugal advance distributor and the other with a SVDA distributor.

1) Ignore the 40hp manual. You don't have that engine.
2) Print the degree wheel mentioned earlier in the thread. Cut it out, cut a circle in the middle, then remove your pulley nut and washer and apply the paper wheel over your pulley. Put the nut back on finger tight without the washer. Feel to make sure the square notch for the Woodruff key is 90* from the case split on the left side and the engine is at TDC (check rotor and pull #1 plug and use a drinking straw to double check TDC on cylinder 1 is true).
3) Paint the TDC mark, 7.5* BTDC, and 30* BTDC, BDC.
4) Static time the engine at 7.5* TDC (youtube videos galore on this).
5) Use a strobe to double check the advance at 3500 rpms (get a strobe light that will tell you how many rpms it is). You should be at 7.5* idling at 900 rpms. 30* at 3500 rpms. If you have a vacuum advance distributor, you have to check timing with the vacuum hose disconnected and plugged. vw-resource.com has detailed instructions and explanations on this.
6) If you think it is a vacuum issue, buy a 009 type distributor and properly gap the points and plug the vacuum ports and see if that makes a difference. It's simple and easy to do and having an extra in your tool bag in the car is not a bad idea anyway. Simple to swap on the side of the road. Get an extra coil too. Can't hurt.
7) Are you running points or electronic ignition? If points, use an emory file to clean your points the adjust the gap to .016"

If doing all of that doesn't change anything, then it's not the ignition.
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tomfreo
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PostPosted: Fri Feb 05, 2016 3:26 am    Post subject: Re: Pinging - distributor problem? Reply with quote

Thanks for all your interest.

Thomas: You're right, I shouldn't need to run premium. Yes, from what I understand, the ability of fuel to withstand knock is reduced with greater heat. All colling tins in place, nothing obstructing fan. What would you like me to post a photo of?


61SNRF: I don't think I've got pre-ignition. I think I've got detonation. I understand spark timing has nothing to do with pre-ignition. I've read that one of the reasons pre-ignition is so insidious is there's no pressure spike to resonate the block so you don't hear it. My problem, I hear it.

I don't know the compression ratio of the engine but in the years I've had the bug I've never had such a problem with pinging so i reckon it's going to be something else.

I'm guessing perhaps that at low-ish rpm going up hills, the idle circuit will be contributing most (?). I cracked open the idle screw another half turn (more in line with specs given in manual to tell the truth), had to bump up the idle rpm, the bug seems more responsive, but no real discernible difference in occasional light pinging going up hills after extended run. The engine is still hotter after an extended run than I remember it being in the past before I dragged the bug out of storage after a year-long trip away up north. BTW, daytime summer temps here between 35-42*C (95-108).

About vacuum advance at idle. I was told that I should have no vacuum advance at idle. At 650rpm the timing jumps c.2.5* and at 850rpm it jumps c.5* with vacuum line put back on.

You may be right about driving habits. I know "lugging the engine is bad", but why would this cause pinging? On reflection maybe I am just luggin the engine. At what speeds should I change down in third and fourth?

(o\ ! /o): I'm the first to admit I don't really know sh*t about motors. My bug is the only car I drive, I can't afford to send it to the mechanix to fix everything that goes wrong, and I'm learning as time goes by, probably not in any rational order.

"Ignore the 40HP manual" - For timing stock distributor with stock carb I would've thought I should follow directions specific to those bits, regardless of the motor I have (assuming normal cylinder compression).

"Paint TDC [etc]" - I've got 7.5* and 10* marks on the crank. I've measured the crank at 17cm diameter and worked out that each 5mm on the circumference is 3.37*. From that I can work out max advance with a strobe. (It's 30* at the kerb. But this is a question I'd really like to hear people's opinions on: with a vacuum-only advance distributor, does checking max advance at the kerb really tell me what the advance will be under driving conditions?)

"Static time the engine at 7.5*" - are you sure about this? I believe I should be timing it at 10* for my distributor. Having said that, currently I'm static timing the engine at 7.5* because of the pinging.

"Running points or electronic (points replacement?) ignition" - difficult to find 6V points replacement, but yes, points clean, dwell correct. I have thought about buying another distributor to check issue, but I'm not exactly flush with cash right now. Maybe poor people should drive civics. Coil was replaced a few hundred miles ago.

Thanks again for all your input. I guess my questions at this point are:

    Is it a problem I'm seeing such vacuum advance as mentioned above at idle? Can anyone with the same setup (dizzie-carb) check to see whether they've got vacuum advance at idle? If vacuum advance at idle is a problem, how can I remedy it?

    When should I change down gear going up hills?

    Does checking max advance at kerb with vacuum-only advance distributor tell me anything useful?


Thanks again
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Slow 1200
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PostPosted: Fri Feb 05, 2016 3:58 am    Post subject: Re: Pinging - distributor problem? Reply with quote

doesn't the 28 PICT have the high speed enrichment tube? if that got clogged the engine will run lean and overheat
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tomfreo
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PostPosted: Fri Feb 05, 2016 5:01 am    Post subject: Re: Pinging - distributor problem? Reply with quote

Is the power fuel jet in the picture the tube you mention? If I rev the engine at the kerb, should I see fuel flowing out? How much is usual?

Image may have been reduced in size. Click image to view fullscreen.

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glutamodo Premium Member
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PostPosted: Fri Feb 05, 2016 7:00 am    Post subject: Re: Pinging - distributor problem? Reply with quote

The power fuel (high speed enrichment) system only functions at high engine vacuum. You won't see anything at the curb. If it gets blocked off though, it has a definite effect on the top speed - the last time I experienced it, 1st-3rd gears were "ok" but 4th gear was horrible. The 28 series has a check ball inside the body of the carburetor that prevent flows through the system except at higher engine speeds (that carb that I had issues with, the check ball was stuck)

Image may have been reduced in size. Click image to view fullscreen.


VW did experience some carbs that had issues with the power fuel system - but I suspect these were all caught and replaced back in the 60s. However it does echo my experience by mentioning a lower top speed if it's not working:

Image may have been reduced in size. Click image to view fullscreen.
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61SNRF
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PostPosted: Fri Feb 05, 2016 9:06 pm    Post subject: Re: Pinging - distributor problem? Reply with quote

tomfreo wrote:
...I don't think I've got pre-ignition. I think I've got detonation. I understand spark timing has nothing to do with pre-ignition. I've read that one of the reasons pre-ignition is so insidious is there's no pressure spike to resonate the block so you don't hear it. My problem, I hear it

Call it what you want to, your intake charge is igniting before it is planned to.


tomfreo wrote:

I don't know the compression ratio of the engine but in the years I've had the bug I've never had such a problem with pinging so i reckon it's going to be something else

Simply stated, you can't say what it is though, can you?
Been fine for years?
Factoid: Nothing stays the same and nothing lasts forever.
Over time, fuel and carbon deposits can build up on the piston crowns and cylinder head combustion chambers conceivably increasing the CR even if only slightly. You've got the car in your hands grasping for straws, all we have is your descriptions. Like I said, a very basic element to rule out given your woes.


tomfreo wrote:
About vacuum advance at idle. I was told that I should have no vacuum advance at idle. At 650rpm the timing jumps c.2.5* and at 850rpm it jumps c.5* with vacuum line put back on.

For your reference, here is a cross section of a Solex 30 PICT2 that I found on a quick Google search.
Best I could find, but it shows the same ported vacuum circuit for distributor advance that the 28PICT has...
Image may have been reduced in size. Click image to view fullscreen.

#35 is the fitting for the vacuum advance.
-Look closely at the tip of the fitting and what you see is a metered restriction pressed into the vacuum fitting, Andy would probably know more about applications and version numbers. Your carb may or may not have this feature.
-In any case, follow that cicuit down to where it exits just at the edge of the throttle blade, and please note in particular that the port is barely covered by the leading edge of the throttle blade. That opening in the carb is subject to the strong vacuum created by the air being drawn into the engine at idle and is closely calibrated. If the port itself is damaged or altered in any way, or if your idle speed is set a little too high, or your throttle blade is loose or mis-adjusted on the shaft, warped or twisted, it may un-cover the port more than ordinary and induce a small vacuum signal to the distributor at "idle" speeds.
That is also why I added relative vacuum at idle, as there could be a tiny amount of vacuum there even under normal circumstances. Some distributor versions have stronger return springs for the points plate to overcome this. Again, if you want any accurate answers you must quantify your vacuum reading at idle so we can make relative comparisons to known good examples.

tomfreo wrote:
You may be right about driving habits. I know "lugging the engine is bad", but why would this cause pinging? On reflection maybe I am just luggin the engine. At what speeds should I change down in third and fourth?

Don't ask why*, just know unequivocally that it does!
If it "pings" under a heavy load with low RPM and high throttle opening, shifting down, and slowing down in some instances, is the best thing to do.
As to when, you might refer to the shift points on the speedo or as advised in the Owner's manual, but again that is only for basic starting points.
*I'm no engineer Laughing , just a well experienced auto mechanic/long time VW nut with tons of practical knowledge.
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tomfreo
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PostPosted: Fri Feb 05, 2016 9:54 pm    Post subject: Re: Pinging - distributor problem? Reply with quote

Glutamodo: "The power fuel (high speed enrichment) system only functions at high engine vacuum. You won't see anything at the curb."

Ok. I read the second excerpt with interest. I've got a 28PICT so I don't think it applies to me, but I was curious about the "speed is considerably lower than the specified 115kph (72mph)". I kinda baby the beetle a bit, old car and all. Don't like to take it (haven't taken it?) past about 80kph (48mph). You mention having a "horrible" fourth gear when the check ball stuck in your power fuel system. At what speed did you notice that? What sort of speeds should I be seeing in fourth to gauge whether the power fuel system is functioning well?

61SNRF: "Call it what you want to, your intake charge is igniting before it is planned to."

But I think I can rule out pre-ignition which is good, right?

Re. compression ratio: "Simply stated, you can't say what it is though, can you? "

Well, I did say, "I don't know the compression ratio". Am I wrong thinking you have to pull a head and measure the cc's, deck-height, etc to get compression ratio? Maybe you're talking about measuring compression?

The diagram I have of a 28PICT doesn't have the restriction in the vacuum port. I take your point there could be a number of factors that induce unusual vacuum signal at idle. Unfortunately I don't have a vacuum gauge. Would comparing jump in timing advance at idle between different cars with same setup be another way to gauge vacuum?

Re. lugging and ping: "Don't ask why*, just know unequivocally that it does! "

I've heard that before! Private knowledge perhaps? Laughing

"you might refer to the shift points on the speedo or as advised in the Owner's manual". yeah, sorry about that, probably would've taken less time looking in the manual than typing out the question!

So I guess I'm still hoping someone with the same setup as me might be able to tell me if they get a jump in advance at idle.

Thanks
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PostPosted: Fri Feb 05, 2016 10:28 pm    Post subject: Re: Pinging - distributor problem? Reply with quote

When did I notice? Pretty much as soon as I got into 4th. I was testing out a 28PICT-2 I had bought cheap at a swap meet and as soon as I got out of town and tried to accelerate in 4th gear I knew something was wrong. I got up to 55, which was the speed limit where I was driving, but it took a lot longer than usual, and then that was it. After a while I found an empty shopping center parking lot and stopped there and swapped my other carb back on there. Later I took out the brass insert to look at the check ball and found it stuck.

The restriction in the fitting for the vacuum advance serves only to slow down the response time of the advance - eventually the same amount of vacuum will reach the canister but it takes longer to get there. This does alter the advance curve a bit but it won't affect total advance nor the idle vacuum either. The restriction began "around May 1963" according to the Bentley, which was about 5 months before the 28PICT was replaced by the 28PICT-1.

Others have reported that they get a fair amount of vacuum at idle out of the 28PICT and I've seen it too. One thing to remember is that most people set the idle speed these days to 900-1000 RPM. The original spec was 550RPM, and VW later revised that to 750-900 and you'll see less vacuum at those speeds.
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blue65
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PostPosted: Mon Nov 20, 2017 2:13 am    Post subject: Re: Pinging - distributor problem? Reply with quote

Would using a light weight oil 15W/40 in Summer cause the engine to run hotter and cause pinging?
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herbie1200
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PostPosted: Tue Nov 21, 2017 12:46 am    Post subject: Re: Pinging - distributor problem? Reply with quote

VW reccomandation, to avoid use of stroboscopic lamp, is related to perfectly matched carburetor-distributor-air filter-engine set.

A change in one of those 4 parts make vw reccomandation no more valid.
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PostPosted: Tue Nov 21, 2017 6:45 am    Post subject: Re: Pinging - distributor problem? Reply with quote

blue65 wrote:
Would using a light weight oil 15W/40 in Summer cause the engine to run hotter and cause pinging?

I would not characterize "40" as "light".

Max
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PostPosted: Tue Nov 21, 2017 9:15 am    Post subject: Re: Pinging - distributor problem? Reply with quote

The higher the number, the heavier the oil. Back in the day, you would run 30 weight in the summer and like a 20 weight or so in the winter. Some folks run a heavy mutigrade, like a 20-50. I run 10-30.
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