Pic 1. Distributor drive pinion at ignition point
around 16 degrees BTDC (No. 1).
Volvo Ignition from Scratch 12/01 R. Kwas
Jump to
Detailed Centrifugal Advance Servicing.
added 1/03
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Vintage Volvo
Ignition system and the Armored Cable. added 8/07
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So you've been lucky enough to get a great deal on that vintage Volvo...the way you tell it that is, (not your wife or even maybe your friends)...because there's just a slight problem...the ignition system is kind of apart...more like an ignition system do-it-yourself-kit really. This page, in addition to just about any of the available shop manuals, should allow you to keep some, if not all of your hair!
Reassembling a B18/20 Ignition System in Disassembled or Unknown Condition including Static Timing:
For reference: Firing order for B18/20 motors is 1-3-4-2, cylinder closest to radiator is NO.1, a quality beer smells and tastes good even at room temperature and, distributor rotation is counter-clockwise (CCW).
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Note: The procedures following have been prepared with the utmost care, are however strictly guides, to be used in conjunction with normal cautious shop practice. I cannot be responsible for your actions. Work safely!
Checking Distributor Installation and Setting Motor to Ignition Point:
1. With ignition OFF and no gear selected. Use a wrench at crankshaft nut holding pulley on front of motor, to turn motor, in normal running direction, to desired timing (16 degrees BTC is a good start), as seen by looking at timing marks on crankpulley and timing cover pointer on front of motor. BOTH valves for NO.1 cylinder should be up and closed (visible by looking into removed oil filler cap hole). If valves are not up and closed, rotate engine one more rotation in normal running direction, to timing marks, when this condition is achieved (reminder, this is a 4 stroke - Otto cycle motor, where TDC of cylinder No. 1 occurs once for every TWO times the timing marks come around on the pulley). Leave engine at this ignition point for rest of this procedure.
Note: If distributor is not installed, continue with Step No. 2., if distributor is installed proceed to Step 3.
2. Verify angle of drive slot position in distributor drive pinion as approximately 300 degrees when looking from distributor side of engine (see Pic 1). If repositioning is necessary, lift pinion to remove, turn appropriately, and reinstall pinion to achieve correct position (it will be necessary to turn motor to engage drive pinion with cam, so Step No.1 must be repeated). Install distributor, which has been checked over and has had points gap set at .016" (turn rotor to turn shaft until engaging pinion drive slot), then lock distributor holding collar to engine block.
3. Remove distributor cap. Determine to which plug wire the distributor rotor points when cap is in place. Starting with this wire, verify and/or correct wiring of firing order as 1-3-4-2.
Pic 1. Distributor drive pinion at ignition point
around 16 degrees BTDC (No. 1).
4. Assemble rest of the distributor and ignition system and proceed to Static Timing.
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This procedure is to be performed AFTER: engine has been set to ignition point, distributor drive pinion and distributor have been correctly installed, cylinder No. 1 ignition wire has been determined, all ignition wires have been installed in the correct firing order, setting the points gap to .016", checking for free Centrifugal Advance, smooth return, and lubing CA mechanism with a few drops of engine oil (felt pad located in shaft center under distributor rotor).
1. With all ignition components in place and assembled, set motor to ignition point (see preceding procedure), remove plug wire from Cylinder No1. spark plug, and lay onto valve cover with a gap to cover so that a spark will be visible when it occurs.
2. Turn ignition ON with key.
3. Loosen timing adjustment locking nut on distributor collar.
4. Turn distributor housing CCW about 45 degrees to assure points are closed, and it is therefore positioned BEFORE ignition point (point at which lobe on distributor shaft opens ignition points and causes high voltage spark). Note: This procedure can still be used, even if ignition has been upgraded with electronics which eliminate the points, and replaces them with a Hall-effect, or an Optical sensor.
5. With ignition rotor, cap, wires in place, slowly turn housing CW (simulating a normal CCW distributor shaft rotation) until spark occurs at test gap. Repeat steps 4 and 5 as many times as is required to get a feeling for when the spark occurs, and to be able to IMMEDIATELY STOP turning the housing after the spark does occur.
6. Turn ignition power OFF with key, lock timing adjustment by snugging timing adjustment locking nut on distributor collar, restore No. 1 plug wire to No. 1 cylinder, assure ALL IS SAFE and engine is clear to run.
7. Ignition system is now timed and presuming all else is in order (fuel), engine can be started and run. After applying choke, handbrake, placing gearbox in neutral, engine may be started using ignition key and (preferred) Start push button (or better yet, Service Switch under hood!).
8. It may be necessary to reset the idle after timing. This should be done after choke has been disengaged, engine has come to normal operating temperature as indicated by thermostat opening (as can be seen on temperature gauge).
Note: I have used this this Static Timing method for years, and found it to be absolutely fine, and perfectly adequate for the B18/20 engines...after timing in this manner and checking with a timing light (NOT mine - I don't own one!...what for?), I have found that my adjustments, performed according to these procedures, have put the timing within one degree of the 16 degrees specified...can't argue with that!...plus, since minimal tools are required, this procedure can be performed - if necessary - on the side of the road, although the garage or driveway, with a well stocked fridge not too far away is clearly preferred! Cheers!
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Automatic Adjustment of the Spark Timing
General: In addition to the fixed distributor timing adjustment, the precise timing of the spark during engine running is further influenced by the Centrifugal Advance, a mechanical system controlled by rotational speed (RPM) of the distributor itself, and also a Vacuum Advance/Retard (if installed, this is year and model dependent). Both of these systems function by further varying position of the top of distributor (where lobeshaft control the points), from the bottom of the distributor (mainshaft is driven by the camshaft). In the case of the vacuum system, it is possible to generally verify its operation by disconnecting vacuum tube at distributor, connecting a test vacuum tube, providing some test suction, while watching for movement at movable points plate (any leaking-down or outright failure to operate is a sign of a jammed points plate or damaged diaphragm). Here's a cute little animated graphic which I couldn't help stealing from a very informative automotive site: [http://www.kfz-tech.de]
Vacuum dependent timing adjustment (Retard) in action
Centrifugal Advance In the case of the centrifugal system, it is a bit more subtle...centrifugal weights below the points plate, their rpm dependent force working against springs vary the relative position of the stacked concentric shafts of the distributor. Clearly, it is not possible to accurately check this action when motor is not running, but by turning an installed rotor, CW about 20 degrees, one can get a pretty good general idea of the state of the CA mechanism. A smooth action against the springs should be felt, returning to the non-advanced position when released (any step or non-smooth action is a sign of problems which can cause erratic engine surging while driving). I have seen wear of the centrifugal weight assembly (on a number of different distributors), which resulted in the centrifugal weights not moving smoothly, but this will take another specific section to cover. See: Detailed CA Servicing. The springs are arranged for a rising rate action, that is, initially one light spring acts against the turning force, and approaching the end of the travel, another stronger spring. In this manner, the springs set the shape of the advance curve.
Theoretical Advance Curve
The info presented here is in addition to distributor tune-up information found in just about any decent shop manual. The intent here is not to copy what they already cover (and every vintage Volvo owner should have at least one as a reference...preferably slightly soiled by oily hands... to show use, but also that a certain amount of respect was showed to the book!), but to augment their basic coverage with more detailed handling of what can occur due to high mileage, or what I call "excessive maintenance", etc.
Indication that there may be a problem with the CA mechanism. Poor Starting. High idle when it was previously fine (but otherwise decent running) is possibly a sign that the CA mechanism may be bound up, and not returning to the non-advanced position.
Checking the CA mechanism is simple! Remove Dist cap, rotor should be against the CW stop and not be able to be turned further in that direction. If it is possible to turn it CW, it means it's time for a CA mech inspection. On the other hand, it should be possible to turn the rotor in a CCW direction for about 20 degrees, against an increasing return spring force. The movement should be smooth and return fully to the unadvanced position. If distributor is not installed on engine, distributor mainshaft must be held in place before the same checks cam be performed.
Bosch xxx078 distributor
with Vacuum advance. The plate on which the once-piece points assembly
mounts is also movable by vacuum, in this manner, vacuum also adjusts the
timing. This distributor has the vacuum diaphragm pulling the plate CCW,
therefore it is arranged for vacuum retard. Some models were set
up as vacuum advance distributors. CA mechanism is
under the points plate.
View of the CA
mechanism of an xxx003 distributor, once points plate has been removed. Note the differing springs,
and that one
end of the heavier spring has an extended end-loop, which allows the loop to
slide, and not contribute any return force until the higher revs are reached.
To check action, use a small screwdriver placed in the depressions of the
weights. They should freely move through their arc against the force of
the return springs.
Disassembly of dist Carefully remove CA springs. Remove circlip. See following:
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After "C" clips retaining CA weights are removed, weights, fibre washers, and height bearing (three arrows) may be removed for inspection and cleaning.
CA
weights can jam up when supporting fibre washers are damaged or worn below minimum
thickness, it is important also to remove, inspect, and clean the (center)
plastic (height) bearing.
Off-center wear is evident
on centrifugal weight. This can occur with worn fibre washer, height
bearing, or bent contact cam on lobeshaft.
Polishing the lobeshaft to perfection! A polished lobeshaft and just a bit
of lube on reassembly makes for a happy, long-lived, points-rubbing-block!
Visible are washer and circlip used for securing lobeshaft.
Polishing the mainshaft to an equal perfection! Note discoloration on
shaft, probably caused by inadequate or overheated, and oxidized lubricant.
A polished, well lubed mainshaft makes for a smooth, repeatable CA curve. The fibre washers
seen here
look to be in very good shape.
After careful disassembly, inspection and cleaning, reassemble with a film of engine oil...I now use synthetic motor oil for its consistent viscosity over a wide temperature range, and to possibly prevent gumming due to cooking which may have contributed to the jamming of the Snow Weasels CA mechanism. See: A Tune-up out of Guilt, Update II
Reassembly is, as they say, "the reverse of disassembly".
Don't forget a couple of drops into the recess on the top lobeshaft, and to soak and replace the felt, and to fill the little (turn cover) oil reservoir at the outside beltline of the distributor with (normal) engine oil (this lubes the mainshaft in the housing, eventually draining into the sump, and it's not right to mix wine and beer)...better yet, since it wasn't included in many manuals, here is the official exploded distributor lubrication diagram, showing how important, and extensive the recommended distributor lubrication really is. Source: intereurope Workshop Manual 162 ISBN 0-85666-066-3
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The Bosch xxx003 distributor...reassembled with a new tune-up kit, gapped to
.016", checked with an Ohmmeter and ready
for installation in the Snow Weasel, static timing, and another 50k miles of
trouble free service!...nah, I promise to do more regular tune-ups and
maintenance!
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Vintage Volvo Ignition system and the Armored Cable
The vintage Volvo IGNition system is a classic, simple, points and coil design. It does feature two notable differences which set it apart from ignition system found on American Vehicles of the era, which a mechanic may be familiar with.
1. No Ballast Resistor. In IGN systems which employ a ballast resistor, the trick of running the coil at part voltage under normal operating condition (with the ballast resistor dropping part of the voltage), while applying full battery voltage during cranking, is employed (by shorting across the resistor with the IGN switch while in the Start Position). This improves the chances of starting by working the coil harder and increasing the spark voltage during starting, while letting the coil work at a less stressful and cooler operating point normally...but apparently designers at Bosch figured this was unnecessary, figuring out a way to reliably start and also eliminate this component and the complexity that switching it into and out of the circuit brings.
2. The Armored Cable and Internal-only Coil + Terminal. It is also not possible to “Hot-Wire” a vintage Volvo! [“Hot Wiring” is defined as bypassing the IGN Switch, and applying battery power with a “Hot Wire”, to the positive terminal of IGN coil]. In Vintage Volvos, there is simply no access to this node (see diagram), so there is just no way to get the IGN system to function. Only the IGN Switch can apply power, and it requires the key to turn. The connection between IGN Switch and coil is further protected by the Armored Cable of fame and lore. This is a pretty effective anti-theft measure...and we vintage Volvo owners like it that way!
Standard Sixties IGNition
System with Ballast Resistor, and Volvo’s version
without Ballast Resistor, but with the “Armored Cable”.
Further details of the internal switching of the IGN Switch can be seen in the diagram.
Position 1. “Radio” or Accessory Position: ONLY the IGN power terminal (54) is powered.
Position 2. “Neutral” or Off Position: No terminals are powered. (This is the only position the key can be removed in.)
Position 3. “Driving” or Ignition On Position: In addition to the IGN power terminal being energized, power is also applied to the coil positive node (not otherwise accessible, see text).
Positon 4. “Starting” or Momentary Start Position: Power is removed from IGN power terminal (to shed additional loads and eliminate the resulting voltage drop during starting attempts), and power is applied to the Starting terminal (50)...power continues to be applied to the coil positive (see IGN Switch internal diagram). This is a momentary position against the force of a (gorilla) return spring. Turning the key against this spring repeatedly is what causes metal fatigue in keys and results in them breaking...this why you can also call this IGN Switch position the “Torsional Key Test Position”, and why you should NEVER have just one key, and might seriously also want to consider installing a Sw-Em Start Switch Upgrade!
Modifications: The internal connections and workings of the vintage Volvo IGN switch must be carefully considered when making modifications like the Sw-Em Start Switch Upgrade (and rest assured, I have!), or upgrading to an electronic IGN module to eliminate the points....because of the disconnection of power to the IGN power terminal (54) during cranking (see above), it is not enough to simply power an electronic IGN module from this terminal...it doesn’t get power during cranking!...so wouldn't work so good! An ORing cable consisting of two diodes connected in a power ORing circuit (power is routed from one OR the other input) must be used.
"OR"ing power connection.
Note: When used in combination with a Sw-Em Start Switch Upgrade, the ORing cable is not required since the IGN switch is no longer switched to the no. 4 position (Start) which would normally remove power to terminal 54.
Comments are welcome. Ron
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The contents of this article are Copyright © 2007 by Ronald Kwas. You are welcome to use this article and its contents in good health and at your own risk for non-commercial purposes. But if you copy and republish it, whole or in part, without giving credit to the author, or linking back to the Sw-Em site as the source, you’re just a lazy, scum sucking plagiarist! Go work for the Boston Globe or something!
