Tightening down distributor causes engine miss and idle speed drop.
April 13th, 2012, 09:54 AM
#1
Registered User
Thread Starter
Join Date: Nov 2010
Posts: 99
Tightening down distributor causes engine miss and idle speed drop.
Olds 215 4bbl...Checked timing and adjusted to spec.,7 1/2 degrees.
Vacuum line disconnected and plugged.
After tightening down the dist. clamp,restarted engine and it ran noticably
slower and rougher. Timing lite also had no light from #1 wire..induction clamp
style. Loosened dist. clamp while engine was running and idle speed picked
up and timing light worked from #1 wire.
Tightened clamp very slowly, noticed gradual drop in rpm and began to
develop a miss and rough idle. Timing lite did not work.
What could be causing this problem when tightening the dist. clamp
down? Engine was rebuilt with all new internal parts,distributor has new
points (uniset),plugs and wires,cap and rotor.
Tightening the clamp also changes the timing setting to one that is
advanced from my initial setting.
I can understand a small change when clamping down the distributor,
but I've never seen the amount of change in idle speed and missing
that comes with just tightening a clamp. This is the first time since the
rebuild I've done a timing check. Was not running quite right before check
and discovered timing was too advanced. Reset back to spec, and here I
am. Has anyone seen this before?
Vacuum line disconnected and plugged.
After tightening down the dist. clamp,restarted engine and it ran noticably
slower and rougher. Timing lite also had no light from #1 wire..induction clamp
style. Loosened dist. clamp while engine was running and idle speed picked
up and timing light worked from #1 wire.
Tightened clamp very slowly, noticed gradual drop in rpm and began to
develop a miss and rough idle. Timing lite did not work.
What could be causing this problem when tightening the dist. clamp
down? Engine was rebuilt with all new internal parts,distributor has new
points (uniset),plugs and wires,cap and rotor.
Tightening the clamp also changes the timing setting to one that is
advanced from my initial setting.
I can understand a small change when clamping down the distributor,
but I've never seen the amount of change in idle speed and missing
that comes with just tightening a clamp. This is the first time since the
rebuild I've done a timing check. Was not running quite right before check
and discovered timing was too advanced. Reset back to spec, and here I
am. Has anyone seen this before?
April 13th, 2012, 12:56 PM
#2
Old(s) Fart
Join Date: Mar 2007
Location: Northern VA
Posts: 47,255
Sounds like the bushings inside the distributor are worn. As you tighten the clamp, the distributor body moves. With the bushings worn, the shaft (and point cam) moves relative to the body, changing the timing. Pull the distributor and wiggle the shaft side-to-side. You can replace the bushings.
April 14th, 2012, 11:59 AM
#3
Registered User
Thread Starter
Join Date: Nov 2010
Posts: 99
Removed distributor and found no movement at all from side to side.
However there is .036 of movement up and down of the shaft in the housing,
measured with a feeler gauge. A generic book I have from Peterson Publish-
ing says that end play should be no more than .012 to .016. Is there any
difference regarding GM distributors (Oldsmobile),or is this an accurate
measurement to work for?
However there is .036 of movement up and down of the shaft in the housing,
measured with a feeler gauge. A generic book I have from Peterson Publish-
ing says that end play should be no more than .012 to .016. Is there any
difference regarding GM distributors (Oldsmobile),or is this an accurate
measurement to work for?
April 14th, 2012, 01:01 PM
#4
Registered User
Thread Starter
Join Date: Nov 2010
Posts: 99
I have taken pictures of the distributor as it appears in the shop manual,
and as mine appears. Left one in the shop manual picture is showing NO
gap between the thrust washer next to the gear and the distributor body.
Right one is my distributor showing a significant gap(almost .036) between
the thrust washer and the body. Is this where my problem is? Do I put
another washer at the bottom or at the top?
There is no gasket between the distributor and the engine when installed.
Do I need a gasket on the distributor? Common sense tells me that I
should replace the thrust washer between the gear and the body with a
thicker one to take up the end play. Am I right about this? Is it possible
to overtighten the distributor clamp. Book calls for 25-30 ft.lbs.
and as mine appears. Left one in the shop manual picture is showing NO
gap between the thrust washer next to the gear and the distributor body.
Right one is my distributor showing a significant gap(almost .036) between
the thrust washer and the body. Is this where my problem is? Do I put
another washer at the bottom or at the top?
There is no gasket between the distributor and the engine when installed.
Do I need a gasket on the distributor? Common sense tells me that I
should replace the thrust washer between the gear and the body with a
thicker one to take up the end play. Am I right about this? Is it possible
to overtighten the distributor clamp. Book calls for 25-30 ft.lbs.
Last edited by russell-t; April 14th, 2012 at 01:10 PM. Reason: adding question
April 14th, 2012, 05:11 PM
#6
Old(s) Fart
Join Date: Mar 2007
Location: Northern VA
Posts: 47,255
There is no gasket. The O-ring is the seal. The excessive end play you have found is unfortunately common in Delco distributors and it will cause the timing to change as the distributor is tightened down. You can buy thrust washers from Mr. Gasket and other sources. Drive out the split pin to remove the distributor gear, shim to fit, and reinstall the gear and pin.
May 2nd, 2012, 06:41 PM
#7
Registered User
Thread Starter
Join Date: Nov 2010
Posts: 99
Got distributor back from local electrical shop after long search for someone
to even look at it. Shims were placed in the space between the gear and
the body and new points and condenser put in.This cured the weird behavior
when the clamp was tightened down. The down-force of the clamp made
the breaker plate ground out, causing the miss and stumbling idle.
to even look at it. Shims were placed in the space between the gear and
the body and new points and condenser put in.This cured the weird behavior
when the clamp was tightened down. The down-force of the clamp made
the breaker plate ground out, causing the miss and stumbling idle.
May 10th, 2012, 05:38 AM
#8
Registered User
Thread Starter
Join Date: Nov 2010
Posts: 99
Found the other reason for my stumbling idle problem. When doing timing
check I was not getting a light from no.1 and engine was running rough.
Thought timing light had gone bad,then decided to try the other cylinders
to check it. The light worked on all other cylinders except no. 1 and an
intermittent light on no. 4.Pulled plug on no.1 and found it was carbon
fouled. Running the engine for the 3 or 4 days at idle while checking all
my settings had packed all the plugs with carbon. A rich choke setting
contributed to this too.
Cleaned plugs with a wire brush and reinstalled them. Idles nice now.
The simplest things can cause big problems,you just have to know where
to look.
Many thanks to all who have responded to this post,you've helped me
learn a lot about my Oldsmobile 215.
check I was not getting a light from no.1 and engine was running rough.
Thought timing light had gone bad,then decided to try the other cylinders
to check it. The light worked on all other cylinders except no. 1 and an
intermittent light on no. 4.Pulled plug on no.1 and found it was carbon
fouled. Running the engine for the 3 or 4 days at idle while checking all
my settings had packed all the plugs with carbon. A rich choke setting
contributed to this too.
Cleaned plugs with a wire brush and reinstalled them. Idles nice now.
The simplest things can cause big problems,you just have to know where
to look.
Many thanks to all who have responded to this post,you've helped me
learn a lot about my Oldsmobile 215.
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