cmp retard question
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Joined: Mar 2009
Posts: 8,453
From: Belleville, Michigan
The outside diameter of the distributor housing is ~3/16" smaller than the inside diameter of the hole in the intake manifold. This allows for slight rotation of the distributor, in an arc, which provides ~15 degrees total adjustment of camshaft retard. See post #3 in this thread for more info.
Junior Member
Joined: Mar 2007
Posts: 401
From: Shreveport, LA
Distributor drive gear wear will cause CMP to change. If it's worn, replace it. CMP retard is checked at idle, immediately after snapping throttle above 2K rpm. 18 degrees is not enough to set P1345, but it is enough to cause some serious crossfire inside the cap. Crossfire in the cap will cause P0300 series DTC's to set. Spec is zero degrees, plus or minus 2 degrees. Adjustment is done by turning the distributor. The factory distributor hold down bracket will only allow a maximum of ~15 degrees total, (from one extreme to the other of the adjustment). If you need more than that, the bracket needs to be modified or replaced with an old style SBC, (small block chevy) hold down bracket, (Mr Gasket #1009). This will make the distributor fully adjustable.
And where is this 15* of play? Are you just leaning the shaft closer to one edge of the hole and tightening? I've tried to see where your finding this adjustability at but I'm not finding anything? Thanks.
Moderator
Joined: Mar 2009
Posts: 8,453
From: Belleville, Michigan
Good questions! The distributor base, where the hold down bracket makes contact, is round, hence the round gasket. The bracket that you posted is the correct kit. You can actually modify the original hold down bracket, but you end up removing most of the "ears" from it.
The hole in the intake manifold that the distributor goes through is larger than the outside diameter of the distributor. This "slop" is what provides the adjustment. The distributor moves on an arc as the adjustment is made. By replacing the original hold down bracket with the new one, the distributor becomes fully adjustable. The only limitation is when the distributor housing stops against the intake manifold. Each tooth on the distributor drive gear accounts for ~13.69 degrees of shaft rotation. The total adjustment is slightly less than that, typically only about 11 degrees. When camshaft retard is adjusted correctly, the distributor housing, (and the gears) are nearly perfectly aligned, (plumb) which keeps gear wear to a minimum.
The hole in the intake manifold that the distributor goes through is larger than the outside diameter of the distributor. This "slop" is what provides the adjustment. The distributor moves on an arc as the adjustment is made. By replacing the original hold down bracket with the new one, the distributor becomes fully adjustable. The only limitation is when the distributor housing stops against the intake manifold. Each tooth on the distributor drive gear accounts for ~13.69 degrees of shaft rotation. The total adjustment is slightly less than that, typically only about 11 degrees. When camshaft retard is adjusted correctly, the distributor housing, (and the gears) are nearly perfectly aligned, (plumb) which keeps gear wear to a minimum.
Last edited by Captain Hook; Feb 3, 2016 at 03:11 PM.
Junior Member
Joined: Mar 2007
Posts: 401
From: Shreveport, LA
Good questions! The distributor base, where the hold down bracket makes contact, is round, hence the round gasket. The bracket that you posted is the correct kit. You can actually modify the original hold down bracket, but you end up removing most of the "ears" from it.
The hole in the intake manifold that the distributor goes through is larger than the outside diameter of the distributor. This "slop" is what provides the adjustment. The distributor moves on an arc as the adjustment is made. By replacing the original hold down bracket with the new one, the distributor becomes fully adjustable. The only limitation is when the distributor housing stops against the intake manifold. Each tooth on the distributor drive gear accounts for ~13.69 degrees of shaft rotation. The total adjustment is slightly less than that, typically only about 11 degrees. When camshaft retard is adjusted correctly, the distributor housing, (and the gears) are nearly perfectly aligned, (plumb) which keeps gear wear to a minimum.
The hole in the intake manifold that the distributor goes through is larger than the outside diameter of the distributor. This "slop" is what provides the adjustment. The distributor moves on an arc as the adjustment is made. By replacing the original hold down bracket with the new one, the distributor becomes fully adjustable. The only limitation is when the distributor housing stops against the intake manifold. Each tooth on the distributor drive gear accounts for ~13.69 degrees of shaft rotation. The total adjustment is slightly less than that, typically only about 11 degrees. When camshaft retard is adjusted correctly, the distributor housing, (and the gears) are nearly perfectly aligned, (plumb) which keeps gear wear to a minimum.
Moderator
Joined: Oct 2014
Posts: 4,334
From: North Central Indiana
Cool. Thanks. I got my new aluminum RichPorter Technology #GM02 distributor installed and it still needs to be finished up, so I'm just preparing for worst case scenario. Haha. Hopefully there won't be an issue. I got the new one lined up exactly where the old one was so as long as there's nothing unusual going on with the cap/rotor phasing, I should be ok I think.
Probably same distributor as this one? Both offshore manufacturing. https://blazerforum.com/forum/2nd-ge...-review-90827/
Last edited by LesMyer; Feb 4, 2016 at 02:36 PM.
Starting Member
Joined: Feb 2025
Posts: 1
From: Bethpage, TN
Camshaft Retard angle is not correctly readable at idle. You should check the camshaft retard angle at an engine speed 1200 RPM or higher. This is straght from the engine repair manual for all vehicles equipped with this ignition system,
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