Home » Public Forums » GMCnet » spark plugs & timing
| spark plugs & timing [message #150153] |
Sat, 19 November 2011 18:19  |
jayrabe
Messages: 509
Registered: June 2009
Location: Portland, OR
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455 in my 76 PB has been running a bit rough, so decided to check/replace the spark plugs. Last time was 3000mi ago, but I didn't check or adjust the timing at that time, being clueless about how to do that. Also, I gapped the plugs to .040 that time, but this time I read the manual more completely, and see that when you have an HEI distributor (which a year ago frankly I didn't know I had - did I mention I'm not a mechanic?), plugs should be at .080.
Also have Howell TBI.
Bought a timing light and before replacing plugs, at idle it was about +16 BTDC (w/ vac disconnected). Way too far advanced per manual that specs +8 at 1100rpm. Also, when I pulled the plugs, they were all black and unhealthy looking. So first question is, could the poor condition of the plugs be due to the timing so far off and/or the gap being 1/2 what it should be?
Second question: Napa didn't have the R46SZ so gave me RapidFire #7. Will they work for me? assuming I gap them to .080?
Any other advice to help this non-mechanic will be Greatly appreciated.
Thanks.
Jay Rabe
76 PB
Portland, OR
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| Re: [GMCnet] spark plugs & timing [message #150155 is a reply to message #150153] |
Sat, 19 November 2011 18:32  |
emerystora
Messages: 4442
Registered: January 2004
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On Nov 19, 2011, at 5:19 PM, Jay Rabe wrote:
>
>
>
> 455 in my 76 PB has been running a bit rough, so decided to check/replace the spark plugs. Last time was 3000mi ago, but I didn't check or adjust the timing at that time, being clueless about how to do that. Also, I gapped the plugs to .040 that time, but this time I read the manual more completely, and see that when you have an HEI distributor (which a year ago frankly I didn't know I had - did I mention I'm not a mechanic?), plugs should be at .080.
>
> Also have Howell TBI.
>
> Bought a timing light and before replacing plugs, at idle it was about +16 BTDC (w/ vac disconnected). Way too far advanced per manual that specs +8 at 1100rpm. Also, when I pulled the plugs, they were all black and unhealthy looking. So first question is, could the poor condition of the plugs be due to the timing so far off and/or the gap being 1/2 what it should be?
>
> Second question: Napa didn't have the R46SZ so gave me RapidFire #7. Will they work for me? assuming I gap them to .080?
>
> Any other advice to help this non-mechanic will be Greatly appreciated.
>
> Thanks.
>
> Jay Rabe
> 76 PB
> Portland, OR
>
DO NOT USE .080.
This has been found to be too hard on the coil and other ignition parts.
The current accepted wisdom is .045. That is what Dick Paterson recommends for the AC/Delco #7 plugs.
However Dick Paterson doesn't recommend the #7 anymore.
Here is what he said about a year ago:
> The spark plug issue was that AC DELCO changed suppliers for their spark plugs and the Rapidfire #7 'platinum ' plug was still made but was no longer a 'needle point' style similar to a Bosch -it now comes as a regular plug configuration in the electrodes .
> I like the features offered in the bosch style so I crossed to NGK (who used to make plugs for AC Delco) .
> I have been using NGK for several years on my oval track 355 chev customers ---tune and set-ups and they are a first class plug.
> There are 2 levels for the OLDS/GMC heat range application----first is an NGK "V" groove XR5 or the premium series NGK # XR51X (7355).
> I would check the gap and look for .038-.040----- if not avail locally ----both available from Summit on line .
> regards dick
I purchased the XR51X at O'Rielly's. They ordered them and had them in one day. The same price as Summit but without the high handling charge.
They have an electrode that looks like a needle. Very fine wire.
Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: [GMCnet] spark plugs & timing [message #150156 is a reply to message #150153] |
Sat, 19 November 2011 18:38 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Jay,
Plugs gapped at 0.040 are just fine. You DO NOT want to use the 0.080
gap as it can cause the HEI to fail. Here is a chart on spark plugs
that can be used in the coach. It is fairly current but I need to
update it again. You do not want to use the current Rapid Fire#7 plug
as it is NOT the same as the Old AC Rapid Fire #7 See bottom of plug
chart. As for timing 8 to 10 should be just fine
http://www.gmcmhphotos.com/photos/data/5237/Spark_Plug_Application_Gu.pdf
JR Wright
GMC Great Laker MHC
GMC Eastern States
GMCMHI
78 Buskirk 30' Stretch
1975 Avion (Under Reconstruction)
Michigan
>
>
>
> 455 in my 76 PB has been running a bit rough, so decided to check/
> replace the spark plugs. Last time was 3000mi ago, but I didn't
> check or adjust the timing at that time, being clueless about how to
> do that. Also, I gapped the plugs to .040 that time, but this time I
> read the manual more completely, and see that when you have an HEI
> distributor (which a year ago frankly I didn't know I had - did I
> mention I'm not a mechanic?), plugs should be at .080.
>
> Also have Howell TBI.
>
> Bought a timing light and before replacing plugs, at idle it was
> about +16 BTDC (w/ vac disconnected). Way too far advanced per
> manual that specs +8 at 1100rpm. Also, when I pulled the plugs, they
> were all black and unhealthy looking. So first question is, could
> the poor condition of the plugs be due to the timing so far off and/
> or the gap being 1/2 what it should be?
>
> Second question: Napa didn't have the R46SZ so gave me RapidFire #7.
> Will they work for me? assuming I gap them to .080?
>
> Any other advice to help this non-mechanic will be Greatly
> appreciated.
>
> Thanks.
>
> Jay Rabe
> 76 PB
> Portland, OR
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GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: spark plugs & timing [message #150157 is a reply to message #150153] |
Sat, 19 November 2011 18:43 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| jayrabe wrote on Sat, 19 November 2011 19:19 |
455 in my 76 PB has been running a bit rough, so decided to check/replace the spark plugs. Last time was 3000mi ago, but I didn't check or adjust the timing at that time, being clueless about how to do that. Also, I gapped the plugs to .040 that time, but this time I read the manual more completely, and see that when you have an HEI distributor (which a year ago frankly I didn't know I had - did I mention I'm not a mechanic?), plugs should be at .080.
Also have Howell TBI.
Bought a timing light and before replacing plugs, at idle it was about +16 BTDC (w/ vac disconnected). Way too far advanced per manual that specs +8 at 1100rpm. Also, when I pulled the plugs, they were all black and unhealthy looking. So first question is, could the poor condition of the plugs be due to the timing so far off and/or the gap being 1/2 what it should be?
Second question: Napa didn't have the R46SZ so gave me RapidFire #7. Will they work for me? assuming I gap them to .080?
Any other advice to help this non-mechanic will be Greatly appreciated.
Thanks.
Jay Rabe
76 PB
Portland, OR
|
Jay,
There have been a great number of HEI module failures attributed to trying to run with the old specification of 0.080. The consensus seems to be that 0.036 ~0.040 is good and will keep the coach from dying on the road. GM revised the recommended spark plug gap some years after the manuals were printed.
Black plugs are not a symptom of timing too far advanced. They can be a symptom of an engine running too rich or too cold (maybe being started and not run to temperature and nominal load). They can also indicate that too cold a heat range plug was installed.
Yes, that timing should be too far advanced, but if there is no aluminum spattered on the plugs, you are probably OK. You should have heard it knocking. If you did hear it, check the harmonic balancer as the rubber joint may have slipped. Checking this is a little bit involved, but there are often marks across the balancer face that may make that unnecessary.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] spark plugs & timing [message #150159 is a reply to message #150157] |
Sat, 19 November 2011 18:52 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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check your plug wire also.
On Sat, Nov 19, 2011 at 4:43 PM, Matt Colie <matt7323tze@gmail.com> wrote:
>
>
> jayrabe wrote on Sat, 19 November 2011 19:19
>> 455 in my 76 PB has been running a bit rough, so decided to check/replace the spark plugs. Last time was 3000mi ago, but I didn't check or adjust the timing at that time, being clueless about how to do that. Also, I gapped the plugs to .040 that time, but this time I read the manual more completely, and see that when you have an HEI distributor (which a year ago frankly I didn't know I had - did I mention I'm not a mechanic?), plugs should be at .080.
>>
>> Also have Howell TBI.
>>
>> Bought a timing light and before replacing plugs, at idle it was about +16 BTDC (w/ vac disconnected). Way too far advanced per manual that specs +8 at 1100rpm. Also, when I pulled the plugs, they were all black and unhealthy looking. So first question is, could the poor condition of the plugs be due to the timing so far off and/or the gap being 1/2 what it should be?
>>
>> Second question: Napa didn't have the R46SZ so gave me RapidFire #7. Will they work for me? assuming I gap them to .080?
>>
>> Any other advice to help this non-mechanic will be Greatly appreciated.
>>
>> Thanks.
>>
>> Jay Rabe
>> 76 PB
>> Portland, OR
>
> Jay,
>
> There have been a great number of HEI module failures attributed to trying to run with the old specification of 0.080. Â The consensus seems to be that 0.036 ~0.040 is good and will keep the coach from dying on the road. Â GM revised the recommended spark plug gap some years after the manuals were printed.
>
> Black plugs are not a symptom of timing too far advanced.  They can be a symptom of an engine running too rich or too cold  (maybe being started and not run to temperature and nominal load).  They can also indicate that too cold a heat range plug was installed.
>
> Yes, that timing should be too far advanced, but if there is no aluminum spattered on the plugs, you are probably OK. Â You should have heard it knocking. Â If you did hear it, check the harmonic balancer as the rubber joint may have slipped. Â Checking this is a little bit involved, but there are often marks across the balancer face that may make that unnecessary.
>
> Matt
> --
> Matt & Mary Colie
> '73 Glacier 23 Chaumière (say show-me-air) Just about as stock as you will find
> SE Michigan - Twixt A2 and Detroit
> _______________________________________________
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--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] spark plugs & timing [message #150163 is a reply to message #150157] |
Sat, 19 November 2011 19:28 |
jayrabe
Messages: 509
Registered: June 2009
Location: Portland, OR
Karma: 0
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OK, so I hear from several people that .080 is not necessary and .040 or so will work as good with less stress on coil etc.
Also hear that current RapidFire-7 are not recommended, but since they're already bought and installed, what might I expect as a downside if I use them?
Still concerned about the black plugs. If most common cause would be too rich, does that mean my Howell is out of adjustment or something has failed?
I'll be setting the timing back to +8 or so, but have never heard any knock/ping with current +12. Any idea what that might suggest?
Thanks again,
Jay
76 PB
Portland, OR
> To: gmclist@temp.gmcnet.org
> From: matt7323tze@gmail.com
> Date: Sat, 19 Nov 2011 18:43:28 -0600
> Subject: Re: [GMCnet] spark plugs & timing
>
>
>
> jayrabe wrote on Sat, 19 November 2011 19:19
> > 455 in my 76 PB has been running a bit rough, so decided to check/replace the spark plugs. Last time was 3000mi ago, but I didn't check or adjust the timing at that time, being clueless about how to do that. Also, I gapped the plugs to .040 that time, but this time I read the manual more completely, and see that when you have an HEI distributor (which a year ago frankly I didn't know I had - did I mention I'm not a mechanic?), plugs should be at .080.
> >
> > Also have Howell TBI.
> >
> > Bought a timing light and before replacing plugs, at idle it was about +16 BTDC (w/ vac disconnected). Way too far advanced per manual that specs +8 at 1100rpm. Also, when I pulled the plugs, they were all black and unhealthy looking. So first question is, could the poor condition of the plugs be due to the timing so far off and/or the gap being 1/2 what it should be?
> >
> > Second question: Napa didn't have the R46SZ so gave me RapidFire #7. Will they work for me? assuming I gap them to .080?
> >
> > Any other advice to help this non-mechanic will be Greatly appreciated.
> >
> > Thanks.
> >
> > Jay Rabe
> > 76 PB
> > Portland, OR
>
> Jay,
>
> There have been a great number of HEI module failures attributed to trying to run with the old specification of 0.080. The consensus seems to be that 0.036 ~0.040 is good and will keep the coach from dying on the road. GM revised the recommended spark plug gap some years after the manuals were printed.
>
> Black plugs are not a symptom of timing too far advanced. They can be a symptom of an engine running too rich or too cold (maybe being started and not run to temperature and nominal load). They can also indicate that too cold a heat range plug was installed.
>
> Yes, that timing should be too far advanced, but if there is no aluminum spattered on the plugs, you are probably OK. You should have heard it knocking. If you did hear it, check the harmonic balancer as the rubber joint may have slipped. Checking this is a little bit involved, but there are often marks across the balancer face that may make that unnecessary.
>
> Matt
> --
> Matt & Mary Colie
> '73 Glacier 23 Chaumière (say show-me-air) Just about as stock as you will find
> SE Michigan - Twixt A2 and Detroit
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] spark plugs & timing [message #150166 is a reply to message #150163] |
Sat, 19 November 2011 19:39 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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If it is not pinging, leave it a 12 degrees BTDC. Mine is at 13 BTDC. If it is pinging, reduce it by 2 degrees.
.040" is fine on the plugs.
Current AC #7 will also work fine. It is just the fine tip plugs will last longer and will fire under fouling conditions.
If all of the plugs look the same (black). I would run the coach down the road at 40 to 70 mph for a few miles, then bring it back, and shut it down immediately. Pull the plugs again and see if they are still black. If they are, then go looking for why you are running rich.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: spark plugs & timing [message #150187 is a reply to message #150153] |
Sat, 19 November 2011 21:41 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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When GM came out with the HEI it was a great system and was supposed to do wonders with a big fat spark. It did if everything was perfect. The idea of the big gap was it took more voltage to jump that gap, so longer coil rise time and higher voltage before discharge. This was all fine at first, but as wires, caps and rotors and plugs aged (lost the sharp square edges on the electrodes) it became a cumulative problem and put a lot of stress on the system with the spark "looking' for an easier ground than that big wide plug gap. The second problem was all the 'no starts' (1975 and still carbs no EFI) with poor driver starting habits and flooding. Once the plugs were wet, it was very hard to start them at .080 especially with people not knowing how to hold to the floor and crank to unload, they would pump more and make it worse. My friend was a mechanic at a Pontiac dealer at the time and in severe cold snaps lots of nice GP's and TAs would come in on the hook. GM then did a TSB on the revised gap as far as I know.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] spark plugs & timing [message #150550 is a reply to message #150545] |
Wed, 23 November 2011 16:50 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Pete,
Go to the junk yard, get a used HEI module, and install it. Keep the one
you remove as a spare. Cheap & you'll know you've got a functional spare.
Even if you buy a new one, install it so you know it works.
Don't forget the heat sink compound.
JWID,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Wed, Nov 23, 2011 at 4:52 PM, Pete wrote:
>
>
> Speaking of HEI modules, what would be a good source for a spare to carry
> with me?
> --
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Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] spark plugs & timing [message #150592 is a reply to message #150550] |
Thu, 24 November 2011 11:14 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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If you go to a GMCMI rally Dick Paterson always has a bunch of used ones that he took out of the distributors he rebuilds. He gives them away for free.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] spark plugs & timing [message #150595 is a reply to message #150550] |
Thu, 24 November 2011 11:20 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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[quote title=Ken Henderson wrote on Wed, 23 November 2011 14:50]Pete,
Go to the junk yard, get a used HEI module, and install it. Keep the one
you remove as a spare. Cheap & you'll know you've got a functional spare.
would that qualify for a five finger discount ?
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: spark plugs & timing [message #150659 is a reply to message #150545] |
Fri, 25 November 2011 22:58 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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| PETEinLongBeach wrote on Wed, 23 November 2011 13:52 |
Speaking of HEI modules, what would be a good source for a spare to carry with me?
|
There is no reason you cannot get a module at a junk yard. If you are tempted to get a coil while you are at it, make sure you get one with Red-Yellow-Black wires. Our Olds (front wheel drive Tornado)had a different coil than most of the GM cars/engines to match the pickup under the module. Our pickup has a reversed polarity when compared to other GM pickups.
That being said, I drove for 30,000 miles with the coil and the distributor pickup being mismatched and lived to tell about it. Ha.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: [GMCnet] spark plugs & timing [message #150663 is a reply to message #150661] |
Sat, 26 November 2011 02:38 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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| WD0AFQ wrote on Fri, 25 November 2011 23:20 |
| Ken Burton wrote on Thu, 24 November 2011 11:14 |
If you go to a GMCMI rally Dick Paterson always has a bunch of used ones that he took out of the distributors he rebuilds. He gives them away for free.
|
And, some of those are bad. Ask me how I know. I say, we get what we pay for.
Dan
|
It is just like buying a new one. You have to try it out first to make sure it is good.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
[Updated on: Sat, 26 November 2011 02:38] Report message to a moderator |
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| Re: spark plugs & timing [message #150667 is a reply to message #150153] |
Sat, 26 November 2011 07:33 |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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Senior Member |
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IMO, it really hardly matters what brand of spark plug you use. Neither you or your motor will notice the difference. You are not running a High performance motor at high RPM. Most any major brand will do....AC, Champion, Autolite, Bosch,,,etc. The key is not running a wide gap, as explained in the previous responses. You may want to get a Platinum tipped plug in any of the major brands to run. Changing plugs can be a real hassle, and the Platinum plugs don't need to be changed as often.
Again...JMHO
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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| Re: [GMCnet] spark plugs & timing [message #150671 is a reply to message #150663] |
Sat, 26 November 2011 07:51 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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| Ken Burton wrote on Sat, 26 November 2011 00:38 |
| WD0AFQ wrote on Fri, 25 November 2011 23:20 |
| Ken Burton wrote on Thu, 24 November 2011 11:14 |
... He gives them away for free.
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And, some of those are bad. Ask me how I know. I say, we get what we pay for.
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It is just like buying a new one. You have to try it out first to make sure it is good.
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That reason for the recommendation to get a replacement BEFORE you need it and install it. KEEP the current, WORKING, module as the spare.
Swapping the module at home lets you "test" if you have the correct tools for the job. See if you can do it with only the "carry aboard" tools. (Rob M doesn't need to worry about this... his carry aboard toolboxes are more complete than my home/shop tool boxes!)
Note that you'll need to keep some of the "heat transfer grease/paste" for any "on the road" reinstalls of your spare module.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] spark plugs & timing [message #150680 is a reply to message #150667] |
Sat, 26 November 2011 10:28 |
jayrabe
Messages: 509
Registered: June 2009
Location: Portland, OR
Karma: 0
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Just did first test drive after changing plugs to AC Delco RapidFire #7 Platinum. Didn't get up to highway speeds, but cruising through the neighborhood things were much smoother than before. Happy camper.
Didn't take it out onto fwy because alt/gen light came on again, solid this time, not just flickering. Guess the loose belt wasn't the problem. Found an alternator check procedure from Matt Collie in my archives and will investigate things today.
Jay Rabe
76 PB
Portland, OR
> To: gmclist@temp.gmcnet.org
> From: weidnerl@wwt.net
> Date: Sat, 26 Nov 2011 07:34:00 -0600
> Subject: Re: [GMCnet] spark plugs & timing
>
>
>
> IMO, it really hardly matters what brand of spark plug you use. Neither you or your motor will notice the difference. You are not running a High performance motor at high RPM. Most any major brand will do....AC, Champion, Autolite, Bosch,,,etc. The key is not running a wide gap, as explained in the previous responses. You may want to get a Platinum tipped plug in any of the major brands to run. Changing plugs can be a real hassle, and the Platinum plugs don't need to be changed as often.
> Again...JMHO
> --
> Larry :)
> 78 Royale w/500 Caddy
> Menomonie, WI.
> _______________________________________________
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| Re: spark plugs & timing [message #150723 is a reply to message #150153] |
Sun, 27 November 2011 01:29 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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| jayrabe wrote on Sat, 19 November 2011 18:19 |
Bought a timing light and before replacing plugs, at idle it was about +16 BTDC (w/ vac disconnected). Way too far advanced per manual that specs +8 at 1100rpm.
Jay Rabe
76 PB
Portland, OR
|
You also should check your distributor centrifugal advance to see if it is working correctly. They have a tendency, after this many years, to stick. This could be why yours was so far advanced but did not have a pinging problem.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: spark plugs & timing [message #150739 is a reply to message #150667] |
Sun, 27 November 2011 10:18 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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| Larry wrote on Sat, 26 November 2011 06:33 |
IMO, it really hardly matters what brand of spark plug you use. Neither you or your motor will notice the difference. You are not running a High performance motor at high RPM. Most any major brand will do....AC, Champion, Autolite, Bosch,,,etc. The key is not running a wide gap, as explained in the previous responses. You may want to get a Platinum tipped plug in any of the major brands to run. Changing plugs can be a real hassle, and the Platinum plugs don't need to be changed as often.
Again...JMHO
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Larry--I totally agree. Many times folks fall in love with a certain type of plug because they replaced a bad one and noticed an improvement. I have replaced some sorry looking plugs in my days and have never even remorely noticed a difference unless the plug wasn't firing at all.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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