Weird ignition timing issue

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Weird ignition timing issue

Post by Who.Me? » Mon Sep 23, 2019 12:49 pm

Sorry for the long post..

As above, I have a weird ignition timing issue. I'm running a 1600 dual port engine in my Single Cab and it has not run right since I got the truck. The main symptom has been sluggish starting.

Having been through all the various systems, I think I've isolated the problem to the distributor. I've always struggled to time it with a light using the factory timing marks and have basically had to time it to where it seems happy, but I'm not sure if it's actualy too far advanced or retarded.

The distributor is a Bosch SVDA unit, correct for the engine and carb combination. I bought this distributor a couple of years ago to replace a 009 because the engine suffered from the 'flat spot'

My timing light has a variable advance on it and I spent a few hours over the last couple of weekends going through a back-to-basics tune up routine. At 7.5º BTDC, the engine barely runs and has almost zero power. By adjusting the distributor, then varying the advance setting on my timing light and watching the marks come in to view, I've worked out that it only starts to run smoothly the idle advance set at 25-26º BTDC (vac advance disconnected and vacuum fitting capped at the carb). It actually seems to prefer even more advance than that, but I'm concerned about over-advancing.

This has had me stumped, so I pulled the distributor to investigate.

I think there are two issues.

1/.Someone seems to have reversed the drive dog on the end of the distributor. I'd unknowingly compensated for that by installing the plug leads based on where the rotor was pointing at TDC on #1 and working round the cap 1-4-3-2

2/. I think the distributor drive has been installed in to the block one tooth out of position. From the pictures below you can see that, with the engine at TDC on #1, the slot in the distributor drive is skewed over rather than perpedicular to the crank. I think it's one cog/spline over.

I need some advice on whether either or both issues are causing my apparent issue with timing (am I actually close to correct, but the timing marks on the pulley are no longer relevant because of the out of sync distributor drive?)

This is my distributor drive...

Image

...and this is how the Haynes manual says it should be installed...

Image

I think there are 12 teeth on the drive gear, so if it's one tooth out, the drive will be 360º/12 = 30º out.
The crank rotates twice for each rotation of the distributor drive, so I think that would equate to 30º/2 = 15º degrees at the pulley

That would tally with what I'm seeing in terms of advance at idle (7.5º + 15º 'position error'= 22.5º). I've currently got the timing set at 25º, according to the TDC mark on the pulley.

If the distributor drive is out of position, does that make the timing marks invalid for timing purposes?

Or am I barking up the wrong tree?
Last edited by Who.Me? on Mon Sep 23, 2019 7:07 pm, edited 1 time in total.

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8 8US
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Re: Wierd ignition timing issue

Post by 8 8US » Mon Sep 23, 2019 2:00 pm

The marks on the pulley wheel relate to the position of the pistons and valves, so TDC of the piston with valves closed.

The distributor drive has no effect on where the pistons or valves sit, so won't affect it at all. Timing is still referenced to TDC.

The drive being out of line will only give you an issue where someone attempts to cross reference the position of the rotor arm against their distributor, for setup purposes it doesn't matter, unless it puts the vacuum advance pot against the fuel pump and stopping you adjust the timing.

Set No1 at TDC, check the piston is at TDC and both valves are closed with rocker arms loose and do as you have done previously and set the the rotor to point to No 1 lead and follow the sequence.

At 3,000 RPM or above with the vac advance disconnected and plugged you should be between 28-32 degrees. The issue could be your mechanical advance is stuck or there is another problem with the distributor.
Richard

1960 Single Cab Pickup “Barny” (resto thread - https://www.ssvc.org.uk/phpbb/viewtopic ... 8&t=122082)
1966 Devon “Hetty”

1980 Brasilia gone :(

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Re: Wierd ignition timing issue

Post by BJ1 » Mon Sep 23, 2019 4:43 pm

Agree with Richard. Looks like the advance mech is stuck so you are trying to compensate for that by advancing the timing on the dizzy. Check that someone has not put a long screw in the vac can mounting that is jamming the top plate. Check the vac can by sucking the vac tube and seeing if the top plate moves. If the top plate is free then the weights below it are jammed. There is only one way to time a VW engine properly - NOT the static timing method that VW manuals and people like Muir recommend. As Richard says, time it with a gun at 28-32 degrees at 3000 rpm and above. The timing at idle is not 7.5 degrees - it can be anything from 5 - 10 degrees but it doesn't matter because your engine is working hard at 3000 rpm +, and that is where the timing is critical. If you time it at 3000rpm and it won't idle either the dizzy is screwed and/or the idle jet on the carb is blocked. Good luck!
1966 Westy in Velvet Green - being restored
1967 Devon from Devon still in Devon
1967 Sundial from Idaho
1971 Westfalia from LA
1971 patina Delux from Montana now living in Germany
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Re: Wierd ignition timing issue

Post by Who.Me? » Mon Sep 23, 2019 5:44 pm

Thanks both. I pulled the distributor last week, removed the top late, cleaned, lubricated and reassembled. The vac advance moves smoothly and the can holds pressure (confirmed with a pump and guage).

While I had the top plate out, I used a screwdriver to move the mech advance weights. They moved freely. How much force should it take to move the weights?

I have an identical distributor that I know is bad (the fibre washers have disintegrated). I've just pulled the top plate off both of them to compare. It's hard to tell whether the weights are stiffer on one of them than the other. The one I've been using *might* be a bit stiffer, but if so, it's marginally so.

The springs are different though.

The one I've been using is the one on the left with too much grease in it (my fault, a little sprays a long way it seems)...
DSC_0107-002.JPG

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Re: Weird ignition timing issue

Post by Who.Me? » Wed Sep 25, 2019 7:13 pm

I've been doing some reading and I have another theory - I think the timing issue is a result of poor compression.

From reading around, it's not uncommon for engines with low compression to need the timing advanced to run.

I haven't done a compression test in a while, but I did one a few years ago and it was 110, 115, 110, 115 warm and 97, 100 ,97 ,100 cold, which is pretty low.

I know it's due a top end rebuild. Maybe this winter I should finally bite the bullet and do it.

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Re: Weird ignition timing issue

Post by vwJim » Wed Sep 25, 2019 7:29 pm

I've got a bus in that made me want to set fire to the bloody thing!

It arrived with the timing set at 30 degrees idle / 48 degrees at full advance. The compression results were pathetic, (80-90 range). Also the oil pressure light bulb had been left as a 6v bulb so blown. So the owner didn't know the oil light comes on at idle. Really bad scatter when trying to get the timing set too. Basically needs a new engine!

Which type of pulley wheel is fitted to your engine? Have you confirmed TDC is actually at TDC?
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Re: Weird ignition timing issue

Post by Who.Me? » Wed Sep 25, 2019 8:10 pm

vwJim wrote:
Wed Sep 25, 2019 7:29 pm
I've got a bus in that made me want to set fire to the bloody thing!

It arrived with the timing set at 30 degrees idle / 48 degrees at full advance. The compression results were pathetic, (80-90 range). Also the oil pressure light bulb had been left as a 6v bulb so blown. So the owner didn't know the oil light comes on at idle. Really bad scatter when trying to get the timing set too. Basically needs a new engine!

Which type of pulley wheel is fitted to your engine? Have you confirmed TDC is actually at TDC?
Thanks Jim. Yes, I fitted a VW 'D' stamped pulley. I've confirmed the TDC mark with a piston stop tool and measured to verify that the 7.5 degree mark is correct.

A VW air cooled garage in California had this as a shop truck for several years before it came to Europe. It was pretty shocking to see what they thought was safe to drive. The brakes and steering were a horror story. The engine had so many vacuum leaks it only ran because the carb was set as rich as it could go.

I'm assuming the engine is stock inside because it looked like whoever built it couldn't be arsed to spend any money on it. But who knows what lurks beneath :roll:

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Re: Weird ignition timing issue

Post by vwJim » Wed Sep 25, 2019 11:26 pm

Yeah, it is surprising what some people pass as acceptable.
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Re: Weird ignition timing issue

Post by Who.Me? » Sat Sep 28, 2019 3:55 pm

I figured that if I'm going to have to do a top end rebuild, I might as well know where the problems are, so I bought a leak down tester. It's a Sealy unit, so not the best, but not the cheapest. It took a couple of goes to get the hang of it and I got some odd one-off readings, but by re-calibrating and repeating the tests until I got three within a reasonable range of each other I came away with these readings...

Cylinder 1
10-17% leakage. Air leakage through the rings (loudest) and inlet valve (less noisy). No detectable sound of exhaust valve leakage

Cylinder 2
15-25% leakage. Air leakage through the inlet valve (loudest) and rings (less noisy). Faint sound of exhaust valve leakage.

Cylinder 3
7-10% leakage. Air leakage through the rings (loudest) and inlet valve (less noisy). No detectable sound of exhaust valve leakage

Cylinder 4
18-22% leakage. Air leakage through the inlet valve (loudest) and rings (less noisy). No detectable sound of exhaust valve leakage

I expected leakage through the rings and I'd anticipated that I'd find exhaust valve issues as they seem to be an achillies heal of these engines, but I was surprised that the exhaust valves seem good (with the exception of #2), but all the inlet valves are leaking quite a bit.

I've set the timing it by ear to get through the next month or so before I lay it up for the winter, but I did notice that the #3 & #4 felt hotter than #1 & #2.

I double-checked the crank and I can't feel any play at the pulley, so I'll start reading up on top end rebuilds.

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Re: Weird ignition timing issue

Post by vwJim » Sun Sep 29, 2019 3:20 pm

Was the engine warm?

I solved my problem with a second set of new plugs.
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Re: Weird ignition timing issue

Post by Who.Me? » Sun Sep 29, 2019 6:49 pm

vwJim wrote:
Sun Sep 29, 2019 3:20 pm
Was the engine warm?

I solved my problem with a second set of new plugs.
Yes that was with a hot engine.

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Re: Weird ignition timing issue

Post by vwJim » Mon Sep 30, 2019 7:53 am

That's pretty poor results.

Do you have a part number for the tool? I tried a Berger brand one and it rubbish so I returned it.
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Re: Weird ignition timing issue

Post by Who.Me? » Mon Sep 30, 2019 12:35 pm

Sealey VSE2020

I'd heard bad things about the £20 quid ebay jobs, so I went with that one. It also meant I could get it through Amazon Prime in time for the weekend. It's not great, but it does the job and it told me what I need to know (the rings are leaking and most of the inlet valves).

It doesn't help that the instructions for the regulator are stamped on the bottom of it, rather than written in the manual. You're supposed to pull the regulator 'handle' down, then turn to adjust and push it back up to lock. There's nothing in the manual to say that, so I couldn't work out why I couldn't turn it to calibrate. I was about to put it back in the box and refund it, when I turned it upside down and noticed the writing on bottom of the regulator handle (black text embossed on a black background).

I found that it was most accurate if I recalibrated before every test (dialled the regulator back before disconnecting from the cylinder, then calibrated before reconnecting). Even then I got one or two 'outlier' readings like 90% leakage. It seemed to give those if the air line connector between the unit and the hose that screws in to the spark plug holes didn't engage smartly so air leaked out through the connector before it sealed. If I got it in smartly it gave sensible readings.

I used some old aquarium air line as a stethoscope. Worked fine in a quiet garage. So quiet I nearly cr&pped myself when the compressor kicked in to re-fill the tank. :lol:

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Re: Weird ignition timing issue

Post by vwJim » Wed Oct 02, 2019 8:51 am

Lol...

Interesting to see what you find / eventually resolve the issue.
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