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Old April 13th, 2012, 09:54 AM   #1
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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?
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Old April 13th, 2012, 12:56 PM   #2
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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.
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Old April 14th, 2012, 11:59 AM   #3
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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?
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Old April 14th, 2012, 01:01 PM   #4
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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.
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Last edited by russell-t; April 14th, 2012 at 01:10 PM. Reason: adding question
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Old April 14th, 2012, 02:26 PM   #5
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I'd double the gasket in this case!!
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Old April 14th, 2012, 05:11 PM   #6
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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.
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Old May 2nd, 2012, 06:41 PM   #7
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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.
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Old May 10th, 2012, 05:38 AM   #8
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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.
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Old May 10th, 2012, 05:38 AM
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