Dwell Angle - Help!

[jaymanek]

Hi All,

Ive got myself a new condensor and points from mercedes.. glad some things are still a decent price!

Anyway, my haynes manual states a dwell angle of 38-39 degrees.

Reading on here, many are saying 30 degrees?

What should I go for.

p.s. mercedes werent sure whether to get me parts for a cast iron distributor or a light alloy... i went for light alloy!

My car is a 1969 280 - originally an Italian car.

Thanks

[Naj ✝︎]

Hello, Jay,

AFAIK, all Euro cars were fitted with cast iron distributors until the end of production.
Replacement distributors were aluminum bodied, so, you really need to check what one is on your car.
The points and condenser are not interchangeable between the two.

The dwell setting should be 38* +3*/-1*
Timing should be set at 30* BTDC @3000 rpm (vacuum line disconnected)

Hope this helps.

naj

[jaymanek]

ok so it looks like i guessed wrong.. Ill order the cast ones too as they are so cheap so that im prepared...

So from what has been said, aluminium housing then 30 degrees, cast iron then 38-40 degrees.

[Naj ✝︎]

Hi, Jay,

I think you are confusing dwell angle (related to points gap) to timing (when the spark is fired)

Both distributors have the same setting values unless you have a 70/71 US spec with emissions gear.

Best to check what distributor you have first.
The cast iron ones have the points wire fixed thru a bolt + nut thru the distributor body.
On aluminum bodied ones, the points have a push-on connector under the cap.

naj

[jacovdw]

Just to add to what Naj has mentioned, 38° +3/-1 = 37° - 41° and is applicable to non transistorized ignition distributors.

From the above 38° dwell would be the optimum setting.

[dseretakis]

So should the dwell for a 70/71 model with emissions gear and transistorized ignition be around 30 degrees?

[jaymanek]

Hi Naj,

Ok thanks for that... I know the timing is 30 deg but i was told the dwell should also be 30...

anyway, I will figure it out.. Ill need to look at my distributor tonight to see what ive got..

[Naj ✝︎]

So should the dwell for a 70/71 model with emissions gear and transistorized ignition be around 30 degrees?

Hi,

I don't know.

I have a book about details when the /8 models came out and it says it can be measured from one of the terminals on the transistorised ign. box but not what the reading should be.

Maybe someone here who owns one can throw some light (?) on the subject?

naj

[jacovdw]

Dimitri and Naj,

The dwell value for US spec 280SL's with the transistorized ignition should be 30° - 36°.
The minimum point gap should be 0.4mm.

Also it is recommended to use the minimum value in the dwell range, ie. 30°.

[jaymanek]

my dizzie is definately cast, it is a Bosch item with a black coating. There is a nut and bolt holding the points connection.

[dseretakis]

Dimitri and Naj,

The dwell value for US spec 280SL's with the transistorized ignition should be 30° - 36°.
The minimum point gap should be 0.4mm.

Also it is recommended to use the minimum value in the dwell range, ie. 30°.

Thanks Jaco. I have my dwell at 30 degrees and the car runs pretty well.

[Naj ✝︎]

my dizzie is definately cast, it is a Bosch item with a black coating. There is a nut and bolt holding the points connection.

Now check the Bosch # on the tag: 0 231 116 xxx  

Thanks Jaco for the info on US distributor settings.

naj

[jacovdw]

It's a pleasure Naj and Dimitri...

[jaymanek]

guys what a day... i set out to change the points and condensor and all seemed well.
luckily a very knoweldgable friend turned up and he spent the whole day on my car.

We got the points perfectly at 38 but after a whille of running this seemed to jump into the mid 40's..

So we set them to 32/33 and then after a while it settled to around 38/40..

So with that ok we thought we would look at my occasional misfires and bad idle.
We set the timing which was out... we set it at 3000 rpm to 30 degrees without vac... this seemed a lot better. We checked the timing figures at idle etc and all seemed on spec.
so then we looked at fuel air mixture..  We set all the throttle positions against their respective stop points and then adjusted idle mixture with the screw on the side of the injection pump, once running and starting ok, we tweaked the idle air screw....
We would get it perfect but then after a while the car would misfire and run lumpy again! We spent most of the day trying to perfect this..
We checked ignition side and my leads seemed to be pretty bad, so i swapped them temporarily for a good set from an engine i had lying around.
This didnt make that much difference really.

My next port of call is brand new caps, leads, plugs etc.

Anyone else had trouble tuning their car?


p.s. we checked compresions and all were ok, varying between 10.5-12.5 bar.  

[jacovdw]

Jay,

Those dwell readings should not fluctuate that much within such a short space of time. You are allowed a change in the dwell angle of ±3° between idle speed and 3000rpm.

Did you guys lube the rubbing block of the point set before installation (very easy to forget - been there myself once)?

Other possibilities (applicable to the distributor only) that spring to my mind would be:

1) point rubbing block not greased as mentioned above
2) worn lobes on the rotor shaft
3) sticking base plate (the plate the point unit is mounted on)
4) wobble in the rotor shaft
5) rotor shaft not moving smoothly due to lack of lubrication (neglect to lube the felt on top of shaft during annual service)

The above problems can introduce a wide variety of idle/running problems and can be fixed (if present on your distributor) by means of a rebuild.

 

[jaymanek]

Hi,

Well im going to have to own up.. i never knew that I had to lube the shaft and rubbing block... im not sure the haynes workshop manual mentions it either!

So what should i use, normal grease?

I will do this next week as im going to get some new parts from SLS... leads, cap, plugs etc. 

[jacovdw]

Jay,

There is a special high temperature Bosch grease that is used for the point rubbing block.
Normal grease is a little too thin to provide adequate lubrication and longevity.

Part number 5 700 002 025 (Ft1v4) and comes in a tube. You should be able to get a tube from your nearest Bosch agent.

It is quite thick and almost like soft beeswax.

Failure to apply grease results in premature wear of the rubbing block (change in dwell angle) and also the lobes on the rotor shaft eventually.
See attached picture for where to apply the grease.

[dseretakis]

Yes I bought that Bosch grease online. It comes in a tube. And someone correct me if I'm wrong but the distributor shaft felt just takes a few drops of engine oil.

[jacovdw]

That's correct Dimitri.

I wonder how many owners fail to lube that felt during their annual service routine.

Just as a side note, according to the Service Manual, the felt should not be lubricated in vehicles manufactured after January 1970.
No specific reason is given as to why it shouldn't be done, but for all vehicles manufactured before that date 2 drops of engine oil should be used.

[dseretakis]

Well then I should stop lubricating my felt! My car was built in September 1970.

[Cees Klumper]

I would put in new leads and caps (after checking resistance of current ones) and a fresh set of spark plugs; these two items can make a big difference in how the engine will run. And check to make sure your linkages are nice and tight, no sloppiness or loose connections / support brackets (don't ask ...).

Good luck, the good news is that once sorted out, usually these cars hold on for a very long time.

[stickandrudderman]

Or just fit a 123 distributor.........

[wd]

Whoops.

[wd]

JACOVDW said:
Just as a side note, according to the Service Manual, the felt should not be lubricated in vehicles manufactured after January 1970.
No specific reason is given as to why it shouldn't be done, but for all vehicles manufactured before that date 2 drops of engine oil should be used.
[/quote]


ok, that is two drops if made before Jan 1970 and none if made after Jan 1970.  My car was made Jan, 1970 so....split the difference?   One drop!

[ja17]

Yes, the special ignition contact grease is best, however, in a pinch, any lube is better than none at all.  Use a ohm meter to diagnose igintion wire or resistor end problems.