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164 carb ignition timing

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Old Mar 19th, 2021, 10:57   #1
TonyCy
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Default 164 carb ignition timing

A strange one - or is to me. Perhaps someone has experienced similar and hence has ideas. I’ve rebuilt the 164 engine, refitted, statically timed at 10d btdc. So far, so good. Distributor was put in with drive aligned as per book, at cyl1 TDC rotor pointed to 1 plug on distributor cap. Engine starts and runs well, so this morning set up to check dynamic timing on cyl 1 by strobe and 10d btdc mark on crank pulley. What did I find? Way, way out according to this? And ok way to bring in line without engine running rough. In fact, runs smoothly exactly where it was statically timed and falls off either side when I move distributor. Vacuum advances both off. Idling at 800. Dwell low and I need to correct but I don’t think that’s likely to cause perhaps a 10-20 deg deviation I’m seeing. Puzzled.....

One thing to add. When I opened engine initially I found that the timing gear was one tooth out which I corrected. I’m starting to wonder if there was a reason for that! But that would also mess up valve timing if out by one.

Anyone any thoughts?

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Old Mar 19th, 2021, 10:59   #2
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“Ok way” above should read “no way”.
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Old Mar 19th, 2021, 17:18   #3
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First off, you never specified how far "way, way out" is. You also never specified whether way way out is advanced or retarded.

Second, what type of timing light do you have? Is it a fixed inductive pick up style or does it have the feature which allows you to enter an advance setting? If it is the latter, is there a chance that a timing offset has been entered into the timing light (I like the simple fixed style)? Finally, the inductive pick up should have an arrow on it indicating the correct direction for clamping on to the spark plug wire. Getting the arrow backwards can result in a timing offset or intermittent operation which will make accurate timing impossible.

I don't have a service manual for what is presumably a non USA B30A so I don't know the advance curves. How much mechanical advance is the advance mechanism supposed to provide at 800 RPM? I am not sure what "both" means when you say "Vacuum advances both off." ; but, I presume that means that you have clamped off the vacuum line to the distributor so that the vacuum servo on the distributor has no effect when using the timing light?

The points gap (which is the only thing that can affect dwell) should be set before you set the static ignition timing. If you set the static timing first then adjust the gap it will alter the static timing.

Finally, if the timing is showing up as retarded, it is possible that your timing light has / is failing and is triggering late. That is a separate issue from incorrect offset in the timing light (if it has that feature) or incorrect orientation of the inductive pick up. That is why guidance on whether the timing is way out advanced versus retarded along with the amount is important.
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Old Mar 20th, 2021, 00:27   #4
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You need to remove the vacuum advance at the dizzy capsule and plug it, not just pull it off from the carb stubs (i'm guessing twin carb from everything else you've said) as that will introduce air leaks into the inlet manifold making the mixture leaner and hence needing a bit more retard to run correctly.

As has been nicely pointed out above by 142 Guy, you need to set the dwell angle first and then static time it or the timing could be a long way out and you won't be able to pull it in from there without problems. If memory serves, the dwell is 50 deg and the timing is 15 BTDC at idle (without vacuum) but i may be wrong on that - fairly certain the dwell is correct but the exact figure for the timing eludes me. You may well find that by setting the dwell correctly, the dynamic timing moves to where it should be.
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Old Mar 22nd, 2021, 09:40   #5
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Thanks gents, appreciated.

I have vacuum advance and retard on my distributor- I think in US you have one or none depending upon model. I blanked by a pipe between the two spigots on the carb so net nil effect and no intake to lean mixture.

My light is a (very) old in line type ie no inductance and no dial up advance. I’ve asked my kids to club together for a new one for my birthday next month but that’s another story - I’ve had this one 40y! Better than another pair of socks.

I estimate it’s firing about 20-25 btdc. But runs smoothly and doesn’t like it when I move distributor either side.

Agree re dwell - I set initially just to get engine started and it’s only about 20 on meter so yes, need correct that first and go from there. Thanks again.
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Old Mar 22nd, 2021, 18:32   #6
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I am guessing that your timing light is the type that requires a little adapter to be inserted between the spark plug and the spark plug cap and then you connect the light's trigger lead to that adapter? If so, it is pretty much impossible for that type of light to consistently falsely trigger early.

Your comment about having both advance and retard on the distributor was ..... confusing. To fix this I was motivated to find an internet copy of the service manual (in case you are ever looking for one):

http://www.240.se/litteratur/tp10868.pdf

Sure enough, the 164 does manage to 'suck and blow' at the same time. The specifications indicate that with the vacuum lines blocked the timing should be 10 deg BTDC with an idle speed of 600 - 800 RPM. The specification indicates that centrifugal advance does not start until 850 - 1050 RPM.

The specification for the centrifugal advance mechanism indicates a total advance of about 22 deg (at the crankshaft). At your idle speed of 800 RPM you should be getting no centrifugal advance. However, I am wondering if something has happened to your centrifugal advance mechanism, specifically I am wondering if one or both of the springs has broken which would allow centrifugal advance to commence much sooner than desired. The service manual is a little thin on details when it comes to checking the advance mechanism - lubricate and make sure the springs are attached is about the limit before you have to use a testing machine.

With the contact breaker plate in place, you can't even see the advance mechanism; but, by twisting the breaker cam on its shaft you might be able to get a subjective feel as to whether it twists too easily which might be an indication of a broken spring. The reality is that to check the mechanism you pretty much have to remove the distributor from the engine and disassemble. If a spring is broken or the advance mechanism otherwise mucked up I don't know what you will do (other than 123 distributors) since I don't know whether replacement parts are available for the advance mechanism.

Before removing the distributor, it should be possible to do a running test on the car. With the engine idling at 800 RPM and the vacuum servos blocked off, increase the engine speed up to about 2500 RPM. At 2500 RPM the centrifugal advance should be providing about 20 degrees of crankshaft advance so you should see the timing marks move about 20 deg. The specs for the centrifugal advance are exceedingly loose. The manual says that 20 deg occurs somewhere between 2300 and 3300 RPM so you may have to go slightly higher than 2500 RPM if your advance mechanism is arthritic. If you get no significant increase in advance as you increase the engine speed from 800 to 2500 RPM then I expect that your advance is coming in way too early indicating a problem with the advance mechanism. If your advance increases from your current 20 - 25 BTDC at 800 RPM to 40 - 45 BTDC at 2500 RPM, then your centrifugal advance mechanism appears to be working and I really don't have a clue as to what is going on.

Assuming I am correct, lets address why the engine operation deteriorates when you try to correct the running advance to where 'it should be'. At idle, the effect of increasing ignition advance (within limits) is to increase engine speed. Anybody who has a B20E with the vacuum retard function will observe that when you clamp the vacuum servo line the engine speed will increase by about 200 - 300 RPM. This is because the idle speed advance is changing from about 3-5 deg BTDC to something over 10 BTDC (depending on how much the RPM goes up). If, after you rebuilt your engine and set you static ignition timing to 10 deg BTDC, you set up your idle speed using a distributor which was actually providing 20 - 25 deg of advance, as you tried to correct the advance back to 10 deg BTDC you were effectively causing the idle speed to drop, likely to the point where the engine cannot operate. The set static advance, start engine and set idle speed then check actual advance and do fine adjustment on advance and idle is the correct procedure when everything is working.

So, you need to check the distributor and confirm that the advance mechanisms are functioning correctly. Assuming I am correct, when you reinstall the corrected distributor and set static advance, you will have to reset the idle speed. At that point you can do the check of timing which should be around 10 deg at 800 RPM.

If you don't have it, I have attached a screen grab of the ignition setting spec for the B30A
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File Type: jpg B30A distributor.jpg (109.6 KB, 5 views)

Last edited by 142 Guy; Mar 22nd, 2021 at 18:38.
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Old Mar 22nd, 2021, 19:17   #7
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That’s a very comprehensive response and much appreciated.

I actually have three other 164’s sitting here so you could say I have a few spares to dig into also. I think starting point will be to get dwell spot on - I know it’s not right and for sure needs to be, although I didn’t think it would cause such a deviation. Re centrifugal advance yes, good point, will see if any “resistance” to turning. That would also explain static being ok but dynamic not. So, dwell first, check again, then centrifugal. If no joy, “spare” distributor next.

Will follow up.
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Old Mar 22nd, 2021, 20:03   #8
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Quote:
Originally Posted by 142 Guy View Post
I am guessing that your timing light is the type that requires a little adapter to be inserted between the spark plug and the spark plug cap and then you connect the light's trigger lead to that adapter? If so, it is pretty much impossible for that type of light to consistently falsely trigger early.

Your comment about having both advance and retard on the distributor was ..... confusing. To fix this I was motivated to find an internet copy of the service manual (in case you are ever looking for one):

http://www.240.se/litteratur/tp10868.pdf

Sure enough, the 164 does manage to 'suck and blow' at the same time. The specifications indicate that with the vacuum lines blocked the timing should be 10 deg BTDC with an idle speed of 600 - 800 RPM. The specification indicates that centrifugal advance does not start until 850 - 1050 RPM.

The specification for the centrifugal advance mechanism indicates a total advance of about 22 deg (at the crankshaft). At your idle speed of 800 RPM you should be getting no centrifugal advance. However, I am wondering if something has happened to your centrifugal advance mechanism, specifically I am wondering if one or both of the springs has broken which would allow centrifugal advance to commence much sooner than desired. The service manual is a little thin on details when it comes to checking the advance mechanism - lubricate and make sure the springs are attached is about the limit before you have to use a testing machine.

With the contact breaker plate in place, you can't even see the advance mechanism; but, by twisting the breaker cam on its shaft you might be able to get a subjective feel as to whether it twists too easily which might be an indication of a broken spring. The reality is that to check the mechanism you pretty much have to remove the distributor from the engine and disassemble. If a spring is broken or the advance mechanism otherwise mucked up I don't know what you will do (other than 123 distributors) since I don't know whether replacement parts are available for the advance mechanism.

Before removing the distributor, it should be possible to do a running test on the car. With the engine idling at 800 RPM and the vacuum servos blocked off, increase the engine speed up to about 2500 RPM. At 2500 RPM the centrifugal advance should be providing about 20 degrees of crankshaft advance so you should see the timing marks move about 20 deg. The specs for the centrifugal advance are exceedingly loose. The manual says that 20 deg occurs somewhere between 2300 and 3300 RPM so you may have to go slightly higher than 2500 RPM if your advance mechanism is arthritic. If you get no significant increase in advance as you increase the engine speed from 800 to 2500 RPM then I expect that your advance is coming in way too early indicating a problem with the advance mechanism. If your advance increases from your current 20 - 25 BTDC at 800 RPM to 40 - 45 BTDC at 2500 RPM, then your centrifugal advance mechanism appears to be working and I really don't have a clue as to what is going on.

Assuming I am correct, lets address why the engine operation deteriorates when you try to correct the running advance to where 'it should be'. At idle, the effect of increasing ignition advance (within limits) is to increase engine speed. Anybody who has a B20E with the vacuum retard function will observe that when you clamp the vacuum servo line the engine speed will increase by about 200 - 300 RPM. This is because the idle speed advance is changing from about 3-5 deg BTDC to something over 10 BTDC (depending on how much the RPM goes up). If, after you rebuilt your engine and set you static ignition timing to 10 deg BTDC, you set up your idle speed using a distributor which was actually providing 20 - 25 deg of advance, as you tried to correct the advance back to 10 deg BTDC you were effectively causing the idle speed to drop, likely to the point where the engine cannot operate. The set static advance, start engine and set idle speed then check actual advance and do fine adjustment on advance and idle is the correct procedure when everything is working.

So, you need to check the distributor and confirm that the advance mechanisms are functioning correctly. Assuming I am correct, when you reinstall the corrected distributor and set static advance, you will have to reset the idle speed. At that point you can do the check of timing which should be around 10 deg at 800 RPM.

If you don't have it, I have attached a screen grab of the ignition setting spec for the B30A
Useful info there! I forgot completely when i suggested the dwell would be 50deg that this is a 6 cylinder, i was thinking of the 4-pot and that may not even be right for the 4-pot either.

However, if the OP has only 20deg dwell on the points, they're opening ~20deg too early (dizzy shaft degrees) which translates to 20deg too early at the crank.

That means, if the OPs suspicion that it's firing at 20deg BTDC, the dizzy is in the right place and once the dwell has been corrected to 40 +/-3deg, the timing should "move itself" to 10deg +/- 1.5deg.

The timing light sounds as if it's the variety where you remove the plug lead and fit it to one of the timing light leads and the other timing light lead goes on the spark plug. This fires a neon tube which illuminates the timing mark at the correct time.
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Old Mar 27th, 2021, 13:09   #9
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Default The answer!

Hi, thought would follow up here with the issue re static timing spot on but dynamic not. I pulled the distributor and stripped fully. Reason became immediately apparent - counterweights and actuating pins heavily worn to the extent that the weights not only slop before coming onto spring tension - thereby immediately the distributor runs that it takes up this «*slack*» and throws timing out as experienced - but the pins are binding on the worn part of the weights and not then releasing the advance. In short, the advance stays on. Photo says it all I think. I have taken a complete distributor off one of my other three and will overhaul/check that one out - it cannot be much worse. As an aside, any source known for spares for these? Weights etc?
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Old Mar 27th, 2021, 15:12   #10
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To close the story - took off a distributor from the spares car, stripped that down, general overhaul, no wear at all on the centrifugal weight mechanism. Swapped it back into the problem car, static timed 10 deg, fired up and checked dynamically - spot on 10 deg at 800 rpm. Job done.
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