shims in points type distributor 1970 350 c.i.

On Dec 28, 8:43 am, Von wrote:
> On Dec 28, 6:39 am, George wrote:
>
> > Does anyone know what shims should be used above the gear drive on my
> > distributor shaft?  I am having a lot of peculiar problems with
> > erratic running and difficulty in timing the ignition.  I noticed when
> > I took the distributor right out that the gear at the bottom of the
> > shaft could move up and down about 1/4 of an inch.  This does not seem
> > correct, but could have been like this for years as I have always had
> > problems like this, - and for years I changed the distributor to a HEI
> > type, but - of course I lost the Tachometer.  I want to go back to the
> > old distributor.
>
> > If I shim it to give only a few thou clearance is this likely to cause
> > any problems?
>
> > Thanks.  George.
>
> George,
>
> The travel that is spoken about on the up and down should have no
> effect on the timing of the vehicle.  If the timing is erratic I would
> be looking at a bent distributor shaft or loose bushings at the top of
> the distributor shaft. The distributor is pretty easy to rebuild and
> it is just a matter of taking it a part and replacing the bushings.
> The up and down travel should have some movement and not be
> preloaded.  Understand that the distributor timing does vary due to
> the Chevrolet design of having the distributor at the back so you will
> never eliminate the torsion of the cam shaft from front to back.  Now,
> with the vacuum plugged the timing should be steady.  That is, unless
> your carburetor is adjusted up and out of the idle circuit.  If it
> were me I would rebuild the distributor and put in a Petronix
> breakerless system in.  It is under the cap so no one will know and
> you can always convert it back to points to sell the car.  The nice
> part is you do not have to set points again.  I did a conversion on a
> 62 Chevy 409 Impala and it works great.

George,

Also, if you have a cable drive tach the cable could be dry or
corroded and causing drag. Thus, causing your points to bounce. For
every degree of dwell you get a degree of timing so this is a
possibility.
 >> Stay informed about: shims in points type distributor 1970 350 c.i. 

George wrote:
> Does anyone know what shims should be used above the gear drive on my
> distributor shaft? I am having a lot of peculiar problems with
> erratic running and difficulty in timing the ignition. I noticed when
> I took the distributor right out that the gear at the bottom of the
> shaft could move up and down about 1/4 of an inch. This does not seem
> correct, but could have been like this for years as I have always had
> problems like this, - and for years I changed the distributor to a HEI
> type, but - of course I lost the Tachometer. I want to go back to the
> old distributor.
>
> If I shim it to give only a few thou clearance is this likely to cause
> any problems?
>
> Thanks. George.

I think the clearance would be about .060 in a new distributor.
Why not play it safe and have it rebuilt?
 >> Stay informed about: shims in points type distributor 1970 350 c.i. 

George wrote:
> Does anyone know what shims should be used above the gear drive on my
> distributor shaft? I am having a lot of peculiar problems with
> erratic running and difficulty in timing the ignition. I noticed when
> I took the distributor right out that the gear at the bottom of the
> shaft could move up and down about 1/4 of an inch. This does not seem
> correct, but could have been like this for years as I have always had
> problems like this, - and for years I changed the distributor to a HEI
> type, but - of course I lost the Tachometer. I want to go back to the
> old distributor.
>
> If I shim it to give only a few thou clearance is this likely to cause
> any problems?
>
> Thanks. George.

Ok, here's a different, off-the-wall thought
which might be less costly than a rebuild on the
old distributor.

If the HEI is doing the job it might be
worthwhile to keep it and convert to an
electronic tach. (The HEI module should have a
tach terminal.)

Don't know what's available in the U.K. but you
might find a spedo/tach/clock gent who could fit
the guts from a 78-79 GM V-8 tach into the case
of your mechanical tach. Note, you'll also need
a low cost 'tach filter' to keep the ignition
hash out of the tach circuit.

While you have the distributor off, check to
make sure the lube spiral is clean and the
shaft/sleeve is getting oil. As the shaft
wears, lube gets less efficient and it tends to
accelerate wear.

--
pj
 >> Stay informed about: shims in points type distributor 1970 350 c.i. 

On 28 Dec, 19:24, pj wrote:
> George wrote:
> > Does anyone know what shims should be used above the gear drive on my
> > distributor shaft?  I am having a lot of peculiar problems with
> > erratic running and difficulty in timing the ignition.  I noticed when
> > I took the distributor right out that the gear at the bottom of the
> > shaft could move up and down about 1/4 of an inch.  This does not seem
> > correct, but could have been like this for years as I have always had
> > problems like this, - and for years I changed the distributor to a HEI
> > type, but - of course I lost the Tachometer.  I want to go back to the
> > old distributor.
>
> > If I shim it to give only a few thou clearance is this likely to cause
> > any problems?
>
> > Thanks.  George.
>
> Ok, here's a different, off-the-wall thought
> which might be less costly than a rebuild on the
> old distributor.
>
> If the HEI is doing the job it might be
> worthwhile to keep it and convert to an
> electronic tach.  (The HEI module should have a
> tach terminal.)
>
> Don't know what's available in the U.K. but you
> might find a spedo/tach/clock gent who could fit
> the guts from a 78-79 GM V-8 tach into the case
> of your mechanical tach. Note, you'll also need
> a low cost 'tach filter' to keep the ignition
> hash out of the tach circuit.
>
> While you have the distributor off, check to
> make sure the lube spiral is clean and the
> shaft/sleeve is getting oil.  As the shaft
> wears, lube gets less efficient and it tends to
> accelerate wear.
>
> --
> pj

Thanks for all the usefull comments. The history of this car is
rather unique and it is very low mileage. It belonged to the Oil
Minister in Abu Dhabi first and he had it flown to a lot of meetings
round the world. When it got a bit old, he gave it to one of his
aquaintances who sold it to me in the early 80s. it is a 350 c.i. /
350 hp. and is a convertible with a hardtop. I roared about in it for
a few years putting a lot of black lines all over Abu Dhabi's roads
and collected a lot of speeding tickets.

I shipped it to UK a few years later and it has hardly been used
since. Petrol prices have deterred me a bit. I have
a bit of spare time at present and thought that it would be nice to
get it going again. I have a big workshop with everything I might
need and I did box up a lot of spares to be sent home with it, - like
6 various small block engines! of various models and years. I can
remember having a lot of trouble with this distributor and it may be
that I had it all apart and did not put it back correctly. I have 3
or 4 HEI distributors too.

I never thought of it as any sort of collectors car and when I
realised that aircon would be more of a problem than a benefit I
dumped it. I will take the advice on board and see what seems to be
the best plan. Today I have established that the TDC mark is correct
but I am not sure how many degrees there are to a division. Also,
however I adjust the gap my dwell meter always reads off scale. It
has got so difficult to start and keep running that I have ordered the
contact, condensor, and some new plugs and leads and I shall start
from scratch when these arrive. It has a brand new Rochester
Quadrajet which seems OK and I don't suspect much to be wrong with
that. I connected the vac advance to a thin pipe coming out of the
side of the carb on the right side looking forward. It has vacuum, but
I am not sure that this is where it should go. I can easily connect it
directly to the manifold.

It's an interesting exercise that keeps me in the dry so I will plod
on and see how it goes.

Thanks again.
 >> Stay informed about: shims in points type distributor 1970 350 c.i. 

George:

It's not a shim, it's a thrust washer (tanged), and there's only one.

If the shaft, as you say, is able to raise a whole quarter of an inch out of
the camshaft gear, then you have some excessive wear either at the cam gear
or the distributor gear, or both. Typically, there is a small amount of
run-out, maybe a sixteenth of an inch to the eye.

If your shaft is able to raise a quarter of an inch the rotor could come too
close to the electrodes on the cap. This could cause a variance of the air
gap between the rotor electrode and the cap electrodes. It can also cause
excessive wear on rotor contact, and will wreak havoc with the points
follower and alignment in relationship to the distributor shaft cam.

Yes this will alter your dwell as well as your timing. Sound like the
distributor is worn out.
 >> Stay informed about: shims in points type distributor 1970 350 c.i. 

I agree with Billy, about 1/16" end play is normal and will not affect idle
quality.

Some Qs:
Is this a base engine (300hp?) or 350hp/350 ?
Is the vacuum can source ported or direct?

Joe
72 coupe
 >> Stay informed about: shims in points type distributor 1970 350 c.i. 

On 28 Dec 2007, 21:32, George wrote:
> On 28 Dec, 19:24, pj wrote:
>
>
>
>
>
> > George wrote:
> > > Does anyone know what shims should be used above the gear drive on my
> > > distributor shaft?  I am having a lot of peculiar problems with
> > > erratic running and difficulty in timing the ignition.  I noticed when
> > > I took the distributor right out that the gear at the bottom of the
> > > shaft could move up and down about 1/4 of an inch.  This does not seem
> > > correct, but could have been like this for years as I have always had
> > > problems like this, - and for years I changed the distributor to a HEI
> > > type, but - of course I lost the Tachometer.  I want to go back to the
> > > old distributor.
>
> > > If I shim it to give only a few thou clearance is this likely to cause
> > > any problems?
>
> > > Thanks.  George.
>
> > Ok, here's a different, off-the-wall thought
> > which might be less costly than a rebuild on the
> > old distributor.
>
> > If the HEI is doing the job it might be
> > worthwhile to keep it and convert to an
> > electronic tach.  (The HEI module should have a
> > tach terminal.)
>
> > Don't know what's available in the U.K. but you
> > might find a spedo/tach/clock gent who could fit
> > the guts from a 78-79 GM V-8 tach into the case
> > of your mechanical tach. Note, you'll also need
> > a low cost 'tach filter' to keep the ignition
> > hash out of the tach circuit.
>
> > While you have the distributor off, check to
> > make sure the lube spiral is clean and the
> > shaft/sleeve is getting oil.  As the shaft
> > wears, lube gets less efficient and it tends to
> > accelerate wear.
>
> > --
> > pj
>
> Thanks for all the usefull comments.  The history of this car is
> rather unique and it is very low mileage.  It belonged to the Oil
> Minister in Abu Dhabi first and he had it flown to a lot of meetings
> round the world.  When it got a bit old, he gave it to one of his
> aquaintances who sold it to me in the early 80s.  it is a 350 c.i. /
> 350 hp. and is a convertible with a hardtop.  I roared about in it for
> a few years putting a lot of black lines all over Abu Dhabi's roads
> and collected a lot of speeding tickets.
>
> I shipped it to UK a few years later and it has hardly been used
> since.  Petrol prices have deterred me a bit.  I have
> a bit of spare time at present and thought that it would be nice to
> get it going again.   I have a big workshop with everything I might
> need and I did box up a lot of spares to be sent home with it, - like
> 6 various small block engines! of various models and years.  I can
> remember having a lot of trouble with this distributor and it may be
> that I had it all apart and did not put it back correctly.  I have 3
> or 4 HEI distributors too.
>
> I never thought of it as any sort of collectors car and when I
> realised that aircon would be more of a problem than a benefit I
> dumped it.  I will take the advice on board and see what seems to be
> the best plan.  Today I have established that the TDC mark is correct
> but I am not sure how many degrees there are to a division.  Also,
> however I adjust the gap my dwell meter always reads off scale.  It
> has got so difficult to start and keep running that I have ordered the
> contact, condensor, and some new plugs and leads and I shall start
> from scratch when these arrive.  It has a brand new Rochester
> Quadrajet which seems OK and I don't suspect much to be wrong with
> that.  I connected the vac advance to a thin pipe coming out of the
> side of the carb on the right side looking forward. It has vacuum, but
> I am not sure that this is where it should go. I can easily connect it
> directly to the manifold.
>
> It's an interesting exercise that keeps me in the dry so I will plod
> on and see how it goes.
>
> Thanks again.- Hide quoted text -
>
> - Show quoted text -

New Query, the bits I ordered for the distibutor have not come yet so
I am a bit stuck. What can I do about a few gouges and scratches in
the paintwork. I was thinking of cleaning them out and the filling
with epoxy resin mix and the touching up and grinding down the surface
using etching primer and trying to get this smooth before applying the
top coat. Will this work or is there another technique for fibreglass?

By the way it has done 35,411 miles, - hardly run in. The distributor
does not seem to be worn at all and the play I wrote about is less
than 1/4 inch. (but more than 1/8th. The coil has 6 V written on it
so there must be a dropper resistor in the circuit somewhere. Anyone
know where this is?
 >> Stay informed about: shims in points type distributor 1970 350 c.i. 

"George" wrote in message

On 28 Dec 2007, 21:32, George wrote:
> On 28 Dec, 19:24, pj wrote:

By the way it has done 35,411 miles, - hardly run in. The distributor
does not seem to be worn at all and the play I wrote about is less
than 1/4 inch. (but more than 1/8th. The coil has 6 V written on it
so there must be a dropper resistor in the circuit somewhere. Anyone
know where this is?


GM did not use the so-called "ballast resistor" on their V8's with points
and an internal alternator voltage regulator. Instead they use a resistor
wire to drop the voltage down around 9 volts, and a by-pass wire off of the
R terminal on the starter to the coil +. This allowed for 12 volts in the
crank position, then would revert to the resistor wire in the run position.
 >> Stay informed about: shims in points type distributor 1970 350 c.i. 

On 2 Jan, 22:45, "Billy Ryman" wrote:
> "George" wrote in message
>
>
> On 28 Dec 2007, 21:32, George wrote:
>
> > On 28 Dec, 19:24, pj wrote:
>
> By the way it has done 35,411 miles, - hardly run in.  The distributor
> does not seem to be worn at all and the play I wrote about is less
> than 1/4 inch.  (but more than 1/8th.   The coil has 6 V written on it
> so there must be a dropper resistor in the circuit somewhere. Anyone
> know where this is?
>
> GM did not use the so-called "ballast resistor" on their V8's with points
> and an internal alternator voltage regulator. Instead they use a resistor
> wire to drop the voltage down around 9 volts, and a by-pass wire off of the
> R terminal on the starter to the coil +. This allowed for 12 volts in the
> crank position, then would revert to the resistor wire in the run position..

Thanks Billy,

I should be able to test that this is working OK. Maybe I shall get a
9 volt coil. I expect that the one labelled 6v is an incorrect one. I
am still waiting for the spares I ordered. (Christmas/New Year
delays, I expect). There is not much experience of Corvettes in this
rural area of UK. It's getting really cold in my workshop now, so I
may have to stop and organise a bit of heating!

Regards George.
 >> Stay informed about: shims in points type distributor 1970 350 c.i. 

I should be able to test that this is working OK. Maybe I shall get a
9 volt coil. I expect that the one labelled 6v is an incorrect one. I
am still waiting for the spares I ordered. (Christmas/New Year
delays, I expect). There is not much experience of Corvettes in this
rural area of UK. It's getting really cold in my workshop now, so I
may have to stop and organise a bit of heating!

Regards George.


George:

I'd stay with a 12V coil and verify that the resistance wire is in-fact
there. If you have a 6V coil with this resistance wire then your primary
voltage will be diminished causing your secondary to be less. Your spark may
not be as hot as the plugs are designed for. The original coil was a GM#
1115238 (or AC-Delco# D512). The AC-Delco D512 coil has been replaced by a
"universal" coil part numbered as U505, or E552C. Both replacements
accomodate the conventional high-performance ignition systems on the 350,
and the 454. Also, these replacements cover models with the old resistor
configuration as well as the newer resistance wire set-up. Hope this helps
you out.
 >> Stay informed about: shims in points type distributor 1970 350 c.i. 

Billy Ryman wrote:
> I should be able to test that this is working OK. Maybe I shall get a
> 9 volt coil. I expect that the one labelled 6v is an incorrect one. I
> am still waiting for the spares I ordered. (Christmas/New Year
> delays, I expect). There is not much experience of Corvettes in this
> rural area of UK. It's getting really cold in my workshop now, so I
> may have to stop and organise a bit of heating!
>
> Regards George.
>
>
> George:
>
> I'd stay with a 12V coil and verify that the resistance wire is in-fact
> there. If you have a 6V coil with this resistance wire then your primary
> voltage will be diminished causing your secondary to be less. Your spark may
> not be as hot as the plugs are designed for. The original coil was a GM#
> 1115238 (or AC-Delco# D512). The AC-Delco D512 coil has been replaced by a
> "universal" coil part numbered as U505, or E552C. Both replacements
> accomodate the conventional high-performance ignition systems on the 350,
> and the 454. Also, these replacements cover models with the old resistor
> configuration as well as the newer resistance wire set-up. Hope this helps
> you out.
>
>
>
Whoa, other way around. The 6v or 9v coil will
pull more current and produce a hotter spark
with 12v applied.

The 12v transition in 1953-55 was made to
provide both improved cranking and a hotter
spark to match up with higher compression
ratios. Stayed pretty much that way with either
a ballast resistor or resistive link until we
got HEI.

The objective was to run the 6v coil at 6-8v
during cruise but apply about 9 volts to it for
cold weather starting.
--
pj
 >> Stay informed about: shims in points type distributor 1970 350 c.i.