Friday, November 24, 2006

VW - Flaming Distributors, Batman!

Distributors normally don't run hot.

Even when the engine over-heats, the location of the distributor, up on a relatively cool corner of the crankcase, combines with the heat-flow path and the ratio between the neck of the distributor and its body to cause the distributor to run significantly cooler than the crankcase.

So if you have a hot distributor it's a pretty good sign that something is wrong ...and that 'something' is usually that your engine has been improperly assembled.

Have you got a distributor handy? If you'll examine the neck of the distributor you'll see a hole drilled into the neck just below the groove for the O-ring. A machined trough runs from the hole to the bottom edge of the neck. As you may have guessed, the hole and the trough are there for a purpose, which is to lubricate the shaft of the distributor.

Grab a crankcase and peek down inside the hole where the distributor goes. On the uphill side of the hole -- the side nearest the center-line of the crankcase -- you'll see a small window cast into the side of the hole. When the distributor is properly installed, the trough on the side of the neck of the distributor connects with that window. Of course, that only happens when the engine is properly assembled, since the orientation of the distributor's pinion gear dictates the installed orientation of the distributor. (On the Type I engine, on the pinion gear the slot for the dog-gear on the distributor must be perpendicular to the center-line of the crankcase when the #1 cylinder is at 7.5 degrees before TDC. The smaller segment must be toward the pulley. Note that the alignment is for the static firing point and not TDC.)

Notice that the window opens onto the cast 'shelf' that serves to align the thermal insulator that isolates the fuel pump from the crankcase. The angle at which the distributor is installed and the location of the shelf combine to provide a constant supply of oil for the distributor shaft. Install the distributor incorrectly and you've just shut off the oil to the distributor-shaft bushings. And while the distributor shaft only rotates at half the speed of the crankshaft, it still needs a drop of oil now & then.


Back in the Good Ol' Days -- whenever that was -- it was pretty rare to run into an improperly installed distributor. Nowadays it's become pretty common. Why? Mostly because incompetent mechanics install the distributor's pinion gear incorrectly. Which leads to plugging in the distributor so that no oil can get to the oiling trough.


Gotta hot distributor? Then there's a high probability it's been running without adequate lubrication. So fix it. Bring the engine to the firing point on #1, pull the pinion gear (you'll need the special puller) and re-install it correctly, making sure to provide the proper number of shims.

How common is this problem? I wish I could say it was rare but about half of the engines I see have the distributor drive-pinion off by one or more teeth. Which is a good reason to send the fellow on his way, at least here in the Peoples Republic of California. Because as soon as you lay hands on the thing you can be held liable for any future problems. Neat, eh? And you wondered why it's so hard to find a good VW mechanic :-)

Fortunately (for me) you don't have to pull the distributor to see that it is mis-aligned. Installing the distributor's drive-pinion incorrectly is good evidence that whoever assembled the engine doesn't know their ass from their elbow, meaning there's liable to be other, less visible problems, such as mis-aligned bearing shells, wonky valve train geometry and even a mis-aligned cam gear -- all of which they will lay on your doorstep since you were the last person to work on the vehicle.

So you smile, praise their paint job, tell them you're too busy right now and wave them on their way.

> Is it always the same set-up? > I have a '59 with the leads different plugged than my '73...


I assume the main purpose of the window is to provide lubrication for the upper end of the pinion gear, which uses the parent metal of the casting as a bearing and must be a nice fit in the bore because of that, something you check prior to assembly when blueprinting the crankcase. (A lot of used crankcases fail this test.) It is the orientation of the drilled hole and machined trough on the neck of the distributor that makes it clear they are meant to align with the window.

I've never measured the width of the window in the wall of the distributor bore (it will vary slightly from one casting to the next) but it's an oval which I think is about 5/8" wide on its major axis. The trough on the distributor comes only to the top of the window, meaning it has to be nicely centered to keep from being obstructed due to the oval shape.

Given that the bore is about 27mm in diameter, and that the pinion gear has 12 teeth, I suppose you could be off by a tooth on either side without obstructing the oil channel... assuming a wide and relatively square window. But any greater mis-alignment will drastically reduce the amount of oil getting to the distributor bushings -- or shut it off entirely.

Fortunately, the alignment of the pinion gear is easy to check: First, find a picture of the correct orientation in the factory service manual. (I wouldn't trust Muir; a lot of the drawings are inaccurate.) Bring the engine to the firing point for #1 and simply pull the distributor. On a bug you can look directly down the bore (on a bus you'll probably need an inspection mirror).

-Bob Hoover

PS -- I've received a couple of interesting messages from folks eager to argue about the orientation of the pinion gear. I'm not.


>>But this point that Bob brings up is more serious: if the erstwhile type IV > owner installs a spankin'-new SVDA distributor, figures out the wire > re-mapping and congratulates himself on doing right by his ride, he could be > in for a nasty surprise.

I don't consider myself qualified on Type IV's (ie, the '1700,' '1800,' and '2000' engines, to use VW's terminolgy ['Type' actually refers to the chassis.] My post was specific to the '1600' & earlier crankcases (and I'm too lazy to go dig a T4 our from under the bench :-)

But it should be easy enough to check, assuming you're up to your eyeballs in T4 parts. One method is to compare a stock distributor from a T4 to the same thing from a T1. If the groove is in a different location relative to the vacuum can then you may have a problem. Method #2 is examine a T4 crankcase to see if it has a similar window and if it is in the same relative location as on the T1. If the answer(s) is yes, then you've got a problem, since as you've pointed out, the location of the canister on the beetle distributor forces you to install the distributor in a position that will block or reduce the flow of oil to the bushings.


As a point of interest, the earliest VW distributors were made of cast iron, fitted with replaceable bronze bushings having a spiral oil channel. I don't recall them having an external oiling groove.

> Isn't the timing for cylinder #3 slightly retarded normally, so that one > would run cooler? Is that not accomplished with the distributor? >

Yes. At least, for all carburetted engines starting with the 1965 model year and continuing until the introduction of the external 'dog-house' oil cooler. The #3 lobe of the distributor was ground with 2 degrees of retardation. Because of the 2:1 ratio between the cam and crank that means #3 will be retarded by 4 degrees. (There's a VW Service Bulletin covering the beginning dates & serial numbers. I assume another was issued when they went back to the unmodified cam but I've never seen it.)

If you're unsure of the provenance of your distributor you should have it checked on distributor testing machine. Or you may check it using a stroboscopic timing light and accurate degree-wheel. Simply transfer the timing light's pick-up to the other three spark plug leads, noting the firing point for each.

The main hazard is that if an early distributor is installed incorrectly the fellow is liable to time the engine using the #3 lobe (ie, directly opposite #1 in the firing order). Which means the other three jugs will now be advanced by four degrees. During hot weather, with the engine under a heavy load, 4 degrees of unwanted advance can result in detonation. And has.

> is there a way i can get the distributor drive gear out without having the > special puller?

(First things first: Start by pulling the fuel pump and removing its push-rod. Now you're good to go.)

On an old (ie, worn) engine you can sometimes extract the pinion gear by driving a hardwood dowel into the recess for the compression spring. Of course, if the dowel breaks off in the hole you're pretty well screwed.

I've used a pair of 'reverse-pliers' (ie, squeezing them causes the jaws to open rather than close) which were designed to extract the broken-off pipe from pop-up lawn-sprinklers. They have hardened jaws which grip the pinion gear in a manner similar to the special tool.

However, I've done it a time or two and this is one of those cases where experience counts. Because the pinion's driver-gear is a spiral (ie, the 'brass gear' on the nose of the crankshaft) the pinion and the crankshaft must be rotated as the pinion gear is extracted. Not a bunch... just a tad. There is a certain feel that tells you when it's coming out okay. Plus, the circular inclined plane that drives the fuel pump often builds up a layer of varnish on its outer edge, making it a tight fit in the upper bore. Here again, there's a certain feel that tells you if all is going well or if you should back off, rotate the thing and try again.

Like riding a bicycle, touch-typing or hitting a fast-ball, once you've done it a few times -- once you know you can do it -- it's really pretty simple. And once you know you can do it you will see other ways to get a grip on the pinion gear.

But the main reason for using the regular tool is that once you've removed the pinion gear you are expected to replace it, and that is one hell of a lot harder to do without the proper tools.

-Bob Hoover

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