Bosch Distributor Shims and Washers

[John76]

I've noticed a lot of posts about the axial play in Bosch distributors.

I checked the "slop" on mine, and found 0.032" of play....far exceeding the 0.004" - 0.005" recommendation.

Upon disassembly, I found the upper fiber washer (between the two metal shims) missing. The broken remains were at the bottom of the distributor.

Does anyone know what the thickness of the upper fiber washer should be? I measured the broken pieces, and they appear to be about 0.025".

Attached photo shows the shims and fiber washer found in my distributor (all original).

Also, does anyone know of a source for shims and fiber washers?  I know a complete distributor rebuild kit is available for about $50....a bit pricey if you only need 1 washer.

Thanks,

John

['76mintgrün'02]

I ordered a shim kit from Blunttech several years ago.  IIRC, it was around $15... but even if I am correct, the price has likely gone up.

My friend Andy ordered that kit recently and like me, he had to wait for it to come from Germany.  He would know the current price : )

Anyway, it comes with a variety of washers, many of which do not go to our distributors.

I believe it comes with one or two of the fiber washers... hopefully two.  I think it does... but I am forgetful.

 

I just measured the two fiber washers on the bench in my shop.  One is .032 thick and the other is .035.  The second one is new, I believe.

 

I am not sure what causes these washers to die, but I believe they are the most common cause of axial play.

The amount of play people find is usually very close to their thickness.

 

Perhaps your fiber washer blew up because someone put it together with too little clearance?

(although I believe you are the original owner, so , no offense intended)

Aluminum expands more with heat than steel, hence the need for play.

 

Vintage VWs use similar distributors, with the same size shim washers; so I have robbed a few of mine.  I have not looked yet, but it would be nice to find a link to Bosch bits through VW guys.

 

It is good that you measured before disassembly, since it helps you predict the shims you will need to put it in spec..

If I want to shim .005" of play out, I may pull out one that is .005 and install one that is .010" thick.  

 

There are a few other wear points I have noticed when taking these apart.

The two plastic sleeves on the pins at the bottom of the center post can wear flats where they make contact.

I believe rotating them so new meat makes contact will correct that wear.

The weights are top heavy by design, with the bottom half having the pivot hole.

I think this causes them to want to tilt and over time the pivot hole becomes elongated.

You can inspect this, by trying to lift the outer bit of the weights and observe the slop/tilt.

This tilt affects how the 'cam end' of the weight aligns with the mating surface of the center post.

Look for flat spots here as well.  

 

I had one of mine apart and partially put back together when I was fiddling with it on the bench, I noticed that one weight would swing out farther than the other.  I tried swapping the weights, pin for pin, but got the same thing.  Then I pulled off the center post and rotated it 180 degrees.  Now the weights swing the same amount, no matter which pin they are on.  I would suggest checking this, because it wants to be balanced when you are done.  Funny little puzzle.  Four ways to install the center post/weights.  In a perfect world, they would all work, but in reality there are right and wrong ways to reassemble; at least after many years of wear and tear.

 

I like this topic.

Tom

EDIT: I just noticed the roll pin for the drive gear.  Unless you just bought this to replace the tapered original, it implies that someone has been in this unit before...

I found that the roll pin works much better if you stretch one end open with a small nail set, or a similarly tapered punch. prior to installation.  There is a wider side to the hole through the gear and it wants to be snug.

Edited January 11, 2017 by '76Mintgrun'02

['76mintgrün'02]

Have you removed the center post from the shaft?  

That area needs to be cleaned and lubed as well.  

I have found gummy messes in there.  

That will give you access to the plastic sleeves mentioned above.

 

Sometimes they put a screw in the center, under the felt plug, but usually they have little keeper rings.  

I dug at that ring for a long time, trying to take my first one apart and finally got it, with a homemade pick.  

 

Then I learned that it is meant to be pried up and will overcome that ring.  

To put it back, I found a piece of tubing with the correct ID/OD and pushed down on it.

 

Nice photos, btw!

Tom

[John76]

Thanks Tom for the "heads-up".  I noticed the advance springs are different...one has a long hook while the other has round eyes on both ends.

I haven't removed the cam lobe and weights to check for the items you referenced. Just cleaned and lubed everything and it appears to function smoothly.

As for the roll pin...I did remove the drive gear way back in 1978 when I experimented with a Mallory Dual-Point distributor. I fell victim to thinking I could improve the advance curves (hence performance).

All I achieved was a lot of ignition noise in the radio and no noticeable driving improvement. It is amazing to see what the stock factory parts can do when they are properly used.

John

[halboyles]

If it helps, this is what currently comes in the Bosch rebuild kit.  The four top center washers are all some kind of fiberboard.  The rest of the spacers are metal.  You only need about 1/4 of the parts to rebuild the average '02 distributor.

 

W&N has them for around $15 bucks:  https://www.wallothnesch.com/en/repair-kit-12-03-15.html

[halboyles]

I forgot that the kit also holds the shaft oil o-ring.  I had to steal the one from this kit for another dizzy.

[Jam3422]

Tom is right, I recently got the kit from Blunt for <$19.  Any BMW dealer can get them too.

[John76]

I went to my local BMW dealer today and inquired about the distributor rebuild kit 12-11-8-630-239.

List price:  $37.....my price $26...with a three-day delivery.

BTW, according to the parts manager, there are only 3 of these kits in the USA, and a total of 221 world-wide.

[Buckeye]

if it helps

 

 

[John76]

Thank you for your help.

Your '76 looks just like mine...except a different part number (49-state version?).

Does the felt pad come with the shim kit? Mine was missing also, and I wonder if this lead to the disintegration of the upper fiber washer? The mechanical thrust on the distributor shaft is downward, so any lack of lubricant to the upper fiber washer would explain why it fell apart.

I could not remove the advance cam from the shaft assembly. Pulled the felt puck out of the top, hoping to see a retaining screw. Nope....only the small "c" clip that I could not get to, even with a small dental pick.

Tom ('76 Mintgrun'02) mentioned this could be pried up to overcome the hold of the "c" clip. I gave it a go, but it wouldn't  budge. I just cleaned the whole thing with carb cleaner and let light oil drip through it overnight.

Does it matter where you put the shims to achieve the < .005" axial play? Above or below the fiber washer? Is it critical to keep the oil spirals on the shaft centered in the bearings?

One other note, the OEM parts diagram shows 1 part number for the advance weight springs...but our distributors have two very different springs. The one with the long hook is the weakling. The short thick one with eyes on both ends is the stronger spring that does all the work. This is seems odd....is the advance rate progressive?

 

['76mintgrün'02]

I am using the same #164 distributor that Buckeye has.  I believe it is the 49 state stock unit for the '76, with the manual transmission.  The #164 only has vacuum advance, unlike yours which also has the retard function... which I believe most people disconnect.

 

The shim kit comes with several felt plugs, but the felt piece that wraps the shaft is sold separately.  I bought one, but have not installed it, despite having it apart several times.  I have taken half a dozen or so apart and have never found one inside.

 

A lack of lubrication may have led to the demise of that washer.  I am still wondering whether there was sufficient play, if the gap you measured  before disassembly is essentially the same as the fiber washer's thickness.  Hard tellin', not knowin'.

 

It is a pretty tight squeeze, trying to get something in there to pry that piece up.  Digging for the clip is not the way to do it.  I think I want to make a little puller to do that job.

 

I don't think the shim placement matters much.  I put the large washers (2) against the aluminum body (one above and one below) and then a fiber washer next to each, followed by the smaller washers.  The fiber washer wants to be contained between shim washers, one large and one small.  After that, the final shimming could be done above the gear, so you don't have to pull the shaft to change them out.  It does not typically take many washers, in total and the total thickness of the washers does not affect the spirals cut into the shafts much at all, that I can see.  Valid question though.  I had not considered it....

 

The spring with two round ends does all the work, until the weights spin out enough to engage the looped end spring, then it adds resistance, to flatten out the advance curve.  I have noticed flat spots on the cam portion of the center post and the weights, which I believe correspond to the place that the loop spring comes into action.  Just a theory though.  I think the flat spot then makes a spike in the curve, when it tips past it.  I would like to be able to touch up those profiles, but doing it symmetrically seems a little tricky.  They are hardened steel and would need to be very smooth.  Elongated pivot holes in the weights are a common problem too.

 

Essentially, the two springs do work together to form 'progressive' resistance.  The length of travel before the looped one engages can be changed, by bending the tab it attaches to.  The differences were subtle, when I messed around with that detail.  I am not sure about your particular distributor, but on the #164 there is a little oval window (with a plug) that you can reach through, to bend those tabs, without having to disassemble it again.  It is a simple bending tool to make.  I posted photos in this thread here

  https://www.bmw2002faq.com/forums/topic/178062-distributor-mechanical-advance-limiting-screws/?do=findComment&comment=1099851

(I will warn you, that thread takes a few tangents... the amphibians are on page three)

Tom

 

 

 

[Buckeye]

4 hours ago, John76 said:

Your '76 looks just like mine...except a different part number (49-state version?).

Does the felt pad come with the shim kit? 

Does it matter where you put the shims to achieve the < .005" axial play? Above or below the fiber washer? Is it critical to keep the oil spirals on the shaft centered in the bearings?

One other note, the OEM parts diagram shows 1 part number for the advance weight springs...but our distributors have two very different springs. The one with the long hook is the weakling. The short thick one with eyes on both ends is the stronger spring that does all the work. This is seems odd....is the advance rate progressive?

 

That is correct.

No, sold separately, part # 12111350261

Fitting instruction in Service manual shown insulating washers (fiber washers) contacting distributor housing, then shims. I maintained number of shims above bevel gears the same as it was prior to dis-assembly. I included following in my write-up

 

 

Noticed spring eyes differences. Kept track of their relative location to each cam during entire rehab

['76mintgrün'02]

I assume the fiber washer is the 'insulating washer' in that illustration.  

 

My washer sequence advise was simply based on what I found when taking mine apart, but it seems to jive with the order you laid the pieces out for your photo.  I also used a felt wheel/rouge on a dremel, to polish the washers, as well as the cam portion of the shaft.  I have seen the rubbing block wear quickly, due to a slightly rusty cam post.

 

I have also found fine powdered aluminum in the oil where the washers meet the housing, suggesting wear to the body.  This would add to axial play over time.

 

Do the weights swing out an even amount?  The one I mentioned above had almost a 1/16" difference at the outer limit of the swing, which would make it quite unbalanced.  

 

Do your weights contact the stop tabs at full swing?  On some I have seen, the little pins on the bottom of the center post make contact with the ends of their slots, before the weights reach the stop.  

 

Either way, this is what determines the all-in advance limit.  The same tool shown above can reach in and bend the stop tabs, to change the limit; if needed.

 

How did you get your parts so clean John?  They look really nice!

Tom

Edited January 14, 2017 by '76Mintgrun'02

[John76]

Three of my favorite chemicals:  Simple Green, Wenol metal polish, WD-40.

[John76]

OK guys....way too much information!

Tom, I read your thread on the experiments you did. Mind boggling to say the least.

How much improvement can be made to a decades-old mechanical/ vacuum advance distributor?

I was trying to understand why the heavier advance spring acts FIRST, and the weaker spring chimes in to flatten the advance curve.

This is not intuitive....I would think it would be the other way. Soft spring first, and the heavy spring stops the action at the end.

Anyway, start throwing in the vacuum curves (ported vacuum has No vacuum at idle, and then dies off as revs increase, except when the throttle is closed while coasting). Then tying all this together with when you want/need advance, at what RPM, and what speed (depending on your diff ratio)........ this can make you crazy...but very fun if you have a Sun machine and the patience of a Saint.

With all the modern precision ignition systems and direct injection, all controlled hundreds of times per revolution, it's no wonder our beloved carburetors and distributors are considered obsolete.

John