Timing? Am I dwelling on this too much

[CamB]

And the award for the worst ever thread title goes to..... Cam!

I promise this has Porsche content - earlier Porsches have points too.

I have what I consider to be weird timing in the BMW 2002. It has a pretty standard Bosch distributor (0 231 149 008 I think), and is running an MSD.

When I check the dwell, it might be:

- 54 deg at 1000rpm
- 60 deg by 3000rpm
- nearly 70 deg by 6000rpm

And hence I appear to get points bounce and an early trigger on the MSD rev limiter.

What is worn to cause this? Or is this normal?

I feel clueless! I had the car on (effectively) a hill climb (see my other post) and during those runs the dwell was waaaaay out (I had set it to specification of 62 deg at 1000rpm, so they were probably never closed (open? can't remember) at 5000-5500rpm.

And 5000rpm was it. Top speed of about 145kph. I fixed it for the drive home (but couldn't use it).

[RoninLB]

I would check the dizzy shaft play in the housing first..........Ron

[CamB]

Thanks Ron.

How much wiggle (if any) is ok? I have wiggled it and it doesn't seem to have much play. Is any play bad?

Cam

[Early_S_Man]

Cam,

If the distriutor has a vacuum module ... perhaps the point plate tensioning spring/ball bearing retainer is loose or has inadequate tension, allowing the plate and points to 'bounce' around!

See if this generic Bosch diagram which applies to both 4 and 6-cylinder distributor models is any help ...

[CamB]

Thanks Warren.

It has no vacuum anything - just mechanical advance which (seems) to work, although it is pretty short (I believe it is a "performance" distributor). Timing an '02 isn't as easy as timing a 911 unfortunately - there is a TDC mark on the crank pulley but no other timing marks and you are expected to look at an inaccessible hole in the bellhousing.

Can I take it that a dwell reading which changes with RPM is a definite no-no! It certainly doesn't make sense.

I seem to remember reading somewhere that the breaker plate can wear and move around.

[Early_S_Man]

On centrifugal-advance-only Bosch distributors ... the point plate is fixed to the body of the distributor with 2 or 3 screws!

With fixed point plates, the only sources of dwell variation are:

1. Bushing wear causing radial play of central shaft

2. Uneven cam lobe wear on cam shaft -- #10 in diagram

3. Loose rubbing block on points

4. Worn or missing fiber washers or shims along central shaft causing excess end float (axial play) ... causing points' rubbing block to 'ride' up and down on the cam lobes

5. Bent central shaft

Or, some combination of the above ...

My suggestion is to remove, disassemble, and clean the distributor parts ... then reassemble dry and check for play in any of the above! Surely, something will be obvious with the amount of variation you are experiencing!

Be sure to lubricate central shaft with engine oil, and cam lobes with Bosch grease before reinstalling distributor in engine!