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Pinging - distributor problem?
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tomfreo
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PostPosted: Sun Dec 13, 2015 1:52 am    Post subject: Pinging - distributor problem? Reply with quote

Since I got the bug (1600sp, 28PICT, ZV/PAU 4R5) out of storage where it sat for over a year, and after protracted faffing about it now runs OK. It starts and idles great. It appears to have good power (tho I never take it above c. 45-50mph). After running for 8+ miles, however, there's a persistent pinging accelerating in 3rd and 4th and going up hills. I've never had this problem before to such an extent. It used to ping lightly when I was living up in the hills returning home after a 25 mile drive. But otherwise no problem.

I started putting 95RON petrol into the tank and the problem went away. But it bothers me that it used to run fine on 91RON - something must be off.

The tappets, points and timing are spot on. That is, the vacuum-only advance distributor is statically timed fractionally to the left of the 10*BTDC mark. And the dwell is set statically with a mark 80* left of TDC. The tappets, I have to admit, are gapped at 0.008" in/out because for some reason the PO gapped them this way; he used to drive a lot outback, and the engine has quite a few miles on it now. I didn't think to second-guess his reasoning (and it was in the original manual albeit for a 40HP engine) tho I do read that "all engines are gapped at 0.006""??

The engine seems to be **slightly** hotter than usual after a prolonged run (the dipstick is pretty hot immediately after shutdown, but I can hang onto it no problem).

I suspect the distributor. Prolly only because I had a persistent pinging problem with my other car, a '77 bus, that was fixed by rebuilding the dizzie.

Last time I checked the distributor with an analog (no power source) dwell meter it was giving me wierd readings - like 65-70* odd. Since it was running ok I tried not to worry about it. Someone showed me the base plate was moving about.

I started the bug an hour ago, let it warm up a bit, and checked the timing with a timing light. With the vacuum port detached the light showed idle at specified 10*BTDC, and no change (unsurprisingly) increasing RPM. Plugged the vacuum line back, and the timing jumped about 7mm left of 10* mark, which by my reckoning is about 4*+10*=14* advanced. Revving the engine, the 10* mark moved about 2.5cm left of the crankcase crack - about 17*+10*=27.5* advance. I realise the advance revving a stationery bug is probably meaningless. But I was wondering if anyone might interpret these figures? The timing is otherwise very steady.

My manual suggests timing at the leftmost notch in the crank (7.5*) if the engine starts pinging. Maybe I should just time it there and see if there's any difference?

Maybe petrol here is, really, "just crap" says a local mechanic suggesting I run premium fuel (95+RON) in my bug? Maybe it's something else? Would a large valve gap induce pinging? Would low fuel pressure induce pinging? Should I start checking for vacuum leaks?

Any help?
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PostPosted: Sun Dec 13, 2015 2:36 am    Post subject: Re: Pinging - distributor problem? Reply with quote

Well, the .008" valve adjustment was for original "long stud" 1200s. You have a 1600 with should have "short studs" - VW's original specification for such engines was actually .004" - around the start of model year 1972 they "retconned" that spec to .006" for those.

This should have nothing to do with pre-detonation (pinging) though. Pinging comes down down to compression ratio, timing and fuel.. both the type of fuel used and the mixture.

With a vacuum-only distributor like that, you can get a fairly good read on total advance "at the curb", so to speak. Yes it will vary under load some but as for total advance you should able to read and yours seems fine. Are you just guessing those numbers or do you have a timing light with an advance wheel on it? Or did you make some full-advance marks on your pulley for a standard timing light?

Low fuel pressure - if it was too low you'd probably be starving for fuel and having the engine cut out and die. If you suspected such a thing, the final test is to kill the engine immediately when this happens, declutch and coast to a stop, get out and remove the air cleaner and carburetor top and check the fuel level in the carb bowl.

If you have a vacuum leak you're usually going to know it because it won't idle very well. But it doesn't hurt to do the "spray carb cleaner at the intake flanges" at idle test.

Excessive carbon buildup in the combustion chamber and top of the piston can effectively raise the compression ratio, of course...

I used to get pinging from a big-bore 40HP I had in my 62, and had to use mid-grade or premium fuel, especially in the summertime, to eliminate it. But that was due to the compression ratio being fairly high from the non-stock pistons/cylinders. If everything else seems good here I would likely do the same in this instance.

-Andy
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PostPosted: Sun Dec 13, 2015 5:40 am    Post subject: Re: Pinging - distributor problem? Reply with quote

Something I had with a 28PICT1 on my 65 bug sounded similar. The vacuum advance circuit has 2 passages into the carb throat and you have to bear with me, its been quite a few years since I fixed this and Andy will have a better handle on this.

BUT the vac port I think went straight into the carb throat with an internal T going down to a hole below butterfly. When I hooked up the vacuum port at idle, the timing jumped. What had happened is the port straight into the carb throat was plugged, so it was pulling vacuum all the time. I ran a small piece of wire straight in the vacuum port and kept working it until I cleaned out the crud and them blasted it with carb cleaned. Problem fixed.

I am not sure that this is your problem, but it will take you maybe 5 minutes to do and might fix your problem.
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PostPosted: Sun Dec 13, 2015 9:28 am    Post subject: Re: Pinging - distributor problem? Reply with quote

Quote:
The engine seems to be **slightly** hotter than usual after a prolonged run (the dipstick is pretty hot immediately after shutdown, but I can hang onto it no problem).

Well it is summer there. So that can be a factor.
Have you checked for mouse nests? If you have mice there that is. We have them up here in the northern hemisphere. Little bastards can really get into some real tight places. Look at your cooling fan for foreign matter that does not belong there. Pull a plug boot off and see if there is a nest under your cooling tin.
Good luck
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PostPosted: Sun Dec 13, 2015 9:48 pm    Post subject: Re: Pinging - distributor problem? Reply with quote

"And the dwell is set statically with a mark 80* left of TDC."

? What does this mean in 'merican?
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PostPosted: Mon Dec 14, 2015 1:04 am    Post subject: Re: Pinging - distributor problem? Reply with quote

Thanks for the replies.

Quote:
You have a 1600 which should have "short studs"


Might there be any reason why I shouldn't gap at 0.006"? Is it possible there's something peculiar about my 1600 that would require gapping at 0.008"?

Quote:
With a vacuum-only distributor like that, you can get a fairly good read on total advance "at the curb"


I've been eyeballing the distance the timing mark advances with RPM and calculating degree advance with some basic math and a crankwheel diameter of 17cm (ie 1cm is 6.8*). I would consider painting a max advance mark on the crank but I've read elsewhere that "at the curb" measurement is meaningless. Is this not true?

Quote:
When I hooked up the vacuum port at idle, the timing jumped. What had happened is the port straight into the carb throat was plugged, so it was pulling vacuum all the time


My idle slows without the vacuum line attached. Is there not supposed to be vacuum advance at idle? I've had a quick look in my manual and it says, "the spark advance is controlled over the whole range of engine speed by means of vacuum".

Quote:
"And the dwell is set statically with a mark 80* left of TDC."

? What does this mean in 'merican?


There was a post in this forum by KTPhil which described how you can set the dwell with the engine off, a test light, and a measured mark on the crank. And I should have said the mark is 80* left of the timing mark, not TDC!

It's quite ingenious and indispensable when your distributor gives dodgy readings with a dwell meter (like mine!). I recommend you search for the post. Basically you measure the number of degrees the points stay open (test light on) and you know how many degrees the points will be closed (ie dwell).
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PostPosted: Mon Dec 14, 2015 4:44 am    Post subject: Re: Pinging - distributor problem? Reply with quote

Read my post - you should NOT have vac at idle unless you have something like a DVDA which has 2 hoses going to the vacuum canister on the distributor. Of course if you choose to ignore the advice, keep plugging away. Its an easy test and possible fix.

The studs for the heads can be dependent on the heads you are using....

And no reason to set valves to .008. I use .006" on all of ours with stock pushrods. The cars with chromoly pishrodsget set to loose 0.
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PostPosted: Mon Dec 14, 2015 6:50 am    Post subject: Re: Pinging - distributor problem? Reply with quote

tomfreo wrote:
I've been eyeballing the distance the timing mark advances with RPM and calculating degree advance with some basic math and a crankwheel diameter of 17cm (ie 1cm is 6.8*). I would consider painting a max advance mark on the crank


I painted such 30 BTDC maximum advance mark on my stock pulley. PM with your E-mail address if you want a correct-size PDF of a degreed pulley that you could print and use to mark yours.
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PostPosted: Mon Dec 14, 2015 7:03 am    Post subject: Re: Pinging - distributor problem? Reply with quote

tomfreo wrote:

Might there be any reason why I shouldn't gap at 0.006"? Is it possible there's something peculiar about my 1600 that would require gapping at 0.008


No, there should be no reason at all. If the engine was built with chromoly pushrods instead of the light alloy stock ones, you would want to decrease the valve adjustment to around zero. But I don't know of any reason on square-boss short-stud heads to go larger, unless you like the noise I guess.

-Andy
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PostPosted: Mon Dec 14, 2015 4:50 pm    Post subject: Re: Pinging - distributor problem? Reply with quote

Quote:
Read my post - you should NOT have vac at idle


I did read your post, thanks, I just wanted to make sure I hadn't misread it, or maybe I just wanted to waste your time by getting you to confirm that's what you actually meant Smile Maybe I should've also asked whether you were getting pinging with your carb always pulling vacuum and this was fixed by unplugging it? In any case, I think I should check I was actually at idle when I checked the vacuum advance with a strobe - it's quite possible I had the accel lever hanging a few teeth on the linkage? The choke's been disabled on the carb and until the engine's warm that's how I get it started. Thanks for the tip though about the vacuum port.

Quote:
I painted such 30 BTDC maximum advance mark


Thanks for the offer. I think I've that covered measuring the diameter of the crank and figuring out what distance is how many degrees along the circumference.

Quote:
No, there should be no reason at all [...] unless you like the noise I guess


I gotta admit the only bug I've ever driven or heard is my own and the occasional one I see and hear from a distance. Maybe I should make the effort and find someone local with a bug? I've heard people say they can gauge the valve gap just listening to the engine, but that's not me. I'll regap the valves to 0.006" tho and have a go.

Quote:
With a vacuum-only distributor like that, you can get a fairly good read on total advance "at the curb"


I'm not doubting you here but I have read in various places including my manual that you don't/can't set the timing with a strobe:

40HP manual
Quote:
The adjustment of ignition firing point on a cold engine must always be done with a 6V test lamp. A stroboscopic lamp should not be used as it will alter the entire setting range


I understand you're not talking about adjusting the timing with a strobe, and that what we're doing is checking the advance after setting the timing statically; but, could you explain a little more to a dumbass like me what I'm seeing when I advance the RPMs with a strobe? vs what the advance might be like driving under load?

Quote:
Have you checked for mouse nests?


I'll have a peer under the tin when I next look at the plugs. Thx. Smile And yes, we've got mice here but it's more likely I think to be infested with these horrible plagues of caterpillars we get for a short spell each year that cocoon themselves en masse in a tight mess of wool-like silk after defoliating the trees in the area.

BTW, I'm a little surprised no ones mentioned the carb is maybe too small for the engine and might contribute to the engine running lean and hot. But then, I drive quite sedately so perhaps it's not an issue?
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PostPosted: Mon Dec 14, 2015 5:24 pm    Post subject: Re: Pinging - distributor problem? Reply with quote

Quote:
I did read your post, thanks, I just wanted to make sure I hadn't misread it, or maybe I just wanted to waste your time by getting you to confirm that's what you actually meant Smile Maybe I should've also asked whether you were getting pinging with your carb always pulling vacuum and this was fixed by unplugging it? In any case, I think I should check I was actually at idle when I checked the vacuum advance with a strobe - it's quite possible I had the accel lever hanging a few teeth on the linkage? The choke's been disabled on the carb and until the engine's warm that's how I get it started. Thanks for the tip though about the vacuum port.


I don't run my cars when they ping. Anytime I install a distributor, I check to make sure the timing is advancing properly. In this case, I had been using an 009 mechanical advance distributor and switched over to the correct vacuum only distributor. Since the car immediately ran like crap, I checked the idle speed with and without the vacuum line connected. That is when I saw the issue. I researched on here and learned about the vacuum passages and fixed the problem.

What you may be trying to do is run the car with a very limited range of spark advance. Either the max advance is too high or its too high at idle. BUT you are 100% correct. If your throttle was partially open, you would have some advance.

Take your time when you test and make sure you are using the same conditions when you make changes....and only change one thing at a time.

As far as timing marks - I run degreed pulleys on most of my cars, but on the couple with stock ones, I make 4 marks. TDC, BDC 28 and 32 degrees. There is a template on the hotspark.com site you can download and print once you know where TDC is.
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PostPosted: Mon Dec 14, 2015 6:35 pm    Post subject: Re: Pinging - distributor problem? Reply with quote

Quote:
you may be trying to [...] run the car with a very limited range of spark advance. Either the max advance is too high or its too high at idle


I can understand if I'm getting too much advance the engine might ping, but how might a limited range of advance, or an advance too high at idle effect pinging?

Thanks for your help Smile
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PostPosted: Tue Dec 15, 2015 6:41 am    Post subject: Re: Pinging - distributor problem? Reply with quote

The point I am making is to get it to run half decent is that you may have the initial advance set too high, which may result in pinging. Just be careful because detonation can break things....

Something else that I dont think was mentioned was checking for vacuum leaks. Just a good general practice. Lean conditions can cause pinging. What I do is use starter fluid with a straw and with the car idling, give it little blasts at any junctions (carb/manifold, manifiold/cylinder head, carb itself). You will always get a little leakage around the throttle shaft and if you are too close to the air cleaner. And not a bad idea to spray along the intake itself. I have a beautiful, freshly painted intake that I got at a swap meet that is now wall art because of a crack in the tubing.
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PostPosted: Tue Dec 15, 2015 7:37 am    Post subject: Re: Pinging - distributor problem? Reply with quote

vacuum only distributors are notorious for developing slop and/or weak springs that let the advance kick in at idle (i.e when it shouldn't)

advance should not change at idle when the vacuum canister is connected and disconnected from the carb

of course as has recommended above make sure that the carb passages are clear, as that can provoje unexpected vacuum signals that will mess up your advance curve
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PostPosted: Wed Dec 16, 2015 12:17 am    Post subject: Re: Pinging - distributor problem? Reply with quote

I regapped the valve tappets to 0.006", reset dwell/timing and went for a drive. A little quieter I guess, though not markedly so. No appreciable increase in power.

As for the pinging, I have to admit that between starting the post and today, I was getting low on fuel and filled up with premium 95RON. The pinging has not reappeared. Stupid of me if I was hoping to get to the bottom of the pinging. Rolling Eyes

There's still a very slight vacuum from the port on the carbie. I'm not entirely sure where I should be setting the idle speed. A 40HP manual I have says to set the speed 550-600RPM. The Idiot book says 850RPM or enough to make the generator light go out.

550-600RPM seems pretty low, and at 850RPM the generator light is on bright. I set the idle at 900RPM. I've heard it also helps cooling in stop-go traffic (?).

Any advice on idle speed?

BTW, the RHS cylinder head has the number 040 101 373 2 stamped on it under the rocker cover. A quick google says this is a 1600sp VW head made in Brazil 35.5mm intake 32mm exhaust.

Does this in any way confirm that I should be gapping the tappets at 0.006" given I doubt I've chromalloy valves?

Sorry for being so persistent about this - I just find it hard to believe the PO would've been gapping them at 0.008" unless told to do so by the people who put the engine in or for other reasons only known to himself. I do know he took the beetle across the Gibson Desert 20-30 years ago - and if you want to have a look at an atlas that's about as remote as you can get in the world - and wonder if he wasn't gapping the valves for the conditions he often drove the beetle? Not that I'm likely to do such driving.
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PostPosted: Wed Dec 16, 2015 2:57 am    Post subject: Re: Pinging - distributor problem? Reply with quote

tomfreo wrote:
Does this in any way confirm that I should be gapping the tappets at 0.006" given I doubt I've chromalloy valves?

Stop questioning this. All 1500s and 1600s are meant to have .006" of lash. Originally, these engines were spec'd at .004" of lash. You can quite safely set your lash to .004". The reason VW changed the spec to .006 was to accommodate neglecting owners who refused to take their cars in for a valve adjustment at the proper interval. Adding that .002" of lash gave more room for neglect.
Chances are that you are much more diligent today at checking your lash than the general public was 40 years ago, so you don't need that extra safety margin that .006 gives you.
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PostPosted: Wed Dec 16, 2015 3:21 am    Post subject: Re: Pinging - distributor problem? Reply with quote

ok ok Laughing I guess I'm the kind of person who has to hear something more than several times before he's willing to admit something contrary to what otherwise previously believed. Excess serotonin or something.

Re-reading your post, are you saying I should set my valves at 0.004"? Shocked
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PostPosted: Wed Dec 16, 2015 5:35 am    Post subject: Re: Pinging - distributor problem? Reply with quote

Set them at .006.....wanting to hear things a couple times is one thing, but what is it now? 5 or 6? Using the PO as a reference doesnt mean squat. I have worked on a shitload of cars that the owner or their mechanic was doing things wrong.

I am pulling out of this thread at this point....You can lead a man to water.......
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PostPosted: Wed Dec 16, 2015 9:20 am    Post subject: Re: Pinging - distributor problem? Reply with quote

tomfreo wrote:
A 40HP manual I have says to set the speed 550-600RPM. The Idiot book says 850RPM or enough to make the generator light go out.

550-600RPM seems pretty low, and at 850RPM the generator light is on bright. I set the idle at 900RPM. I've heard it also helps cooling in stop-go traffic (?).

Any advice on idle speed?



Again, you've got a 1600 engine masquerading as a 1200 40HP, right? It's not the same engine, and the 1600SP had a different distributor and carburetor than what you have. And you can't just go blindly by "old 40HP manuals" on this - as evidenced by the talk I had about long-stud heads.

And I also mentioned the .004" specification that VW used up to around 1972 earlier in this thread.

Now, Idle speed was another area that VW later revised the specification. Up to around 1966 or so, 550RPM was the specification, but they retroactively raised that later on. Here's a small excerpt (the translations, I added) from a Dec 1972 VW Technical Bulletin listing of carburetor specifications for the 1960s 1200 engines... it says 750-900 RPM. I tend to go towards the upper end of that range myself.

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PostPosted: Tue Feb 02, 2016 3:22 am    Post subject: Re: Pinging - distributor problem? Reply with quote

Still occasional pinging going up hills after a long run. I'm running 98RON (highest octane fuel here in Oz) and have retarded the timing to 7.5* from 10*BTDC.

I can't find vacuum leaks. The idle mix has been adjusted following instructions (would this even affect conditions pulling up a hill?)

I checked timing advance with a strobe: max advance is 3cm to the right of the 10* mark. I measured my crank at 17cm which would give 3.37*/0.5cm - so 3cm to the right of the 10* mark would give a total advance of 30.44*. Too much?

But ... there's vacuum at the port going to the (single vacuum-only) distributor at idle (650-850RPM). The timing jumps from 7.5* to about 12.5* at 850RPM (less at 650RPM) when I connect the vacuum line to the distributor.

I tried broddling a wire into the port, spraying with carb cleaner, etc but no change. There doesn't seem to be any block from the vacuum port straight into the carb body.

I don't know about the lower pipe from the vacuum port into the bottom of the carb, where it tee's off. Don't know whether it's blocked or whether this would cause problems?

If what others have said is any guide, I shouldn't see any vacuum at idle. Does anyone have any advice or recommendations?
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