Mike and Jessica, GMCMI has a really good chart for plugs online that =
I created, but I have added a text version today. If you need to have ques=
tions please call Jim K or you can call me at nine8nine eight5nine-zero 7on=
e5. The GMC community is large and very knowledgeable. The 78Z parts book=
is a 1970=E2=80=99s snapshot in time as Ken has said. The part interchang=
e list on GMCMI is probably the most current listing of part number for the=
GMC coach. As for you request on PCV valves you can use any of the fo=
llowing: Fram FV-112 Motorcraft EV-10 AcDelco CV-679-C NAPA C=
BR-29281 Typically if you have a 455 motor then use the 1975 Toronado =
as a base and a 77 Toronado for the 403 and chances of you have a Californi=
a version are very slim. Anything other that the engine use the 1975 Toron=
ado as a search item. J.R. Wright GMC Great Laker MHC GMCGL Tech E=
ditor GMC Eastern States Charter Member GMCMI 78 GMC Buskirk 29.5=
=E2=80=99 Stretch 75 GMC Avion (Under Reconstruction) Michigan Midland=
Spark Plug Application Guide (09/28/13)Reviewed 5/8/17 Brand=
Type 455 403 =
Gap ACDelco Platinum 41818 4=
1818 .038 ACDelco Standard R46SZ =
R46SZ .060 ACDelco Platinum AC=
41833 (Napa) AC41833 (Napa) .038 Autolite Standard =
847 847 .060 Autolit=
e Platinum AP847 AP847 =
.038 Bosch Standard 7921(WR10FCZ) 7920(WR10FCY) =
.060 Bosch Platinum 4023(WR9FPZ) 4022(WR9FPY) =
.038 Champion Standard 66(RJ18YC6) 66(RJ18YC6) =
.060 E3 Premium
E3.52 E3.=
52 As from Box NGK Standard 4536 =
4536 .038 NGK Iridi=
um XR45IX (7293) XR45IX (7293) .038 NGK =
Iridium XR5IX (7355) XR5IX ( 7355) .038 =
Plug Gap Settings: Gap setting is gap out of the box; plug gaps out of =
the box vary by manufacture and application and should always be checked be=
fore installation. Dick Paterson several years ago conducted Dyno testing o=
n several different plug gaps and found that there was little difference be=
tween the large and small gap settings for power output. My personal setup =
was a Paterson HEI, running original ACDelco #7 Rapidfire gapped @ .038 as =
per DP, yours may vary. The smaller gap reduces the load on the HEI coil. F=
actory specified gaps have varied over the years for the coach. The 73/74 p=
oint distributor called for a .040 gap. The 455 with the HEI distributor (7=
5 thru 77) called for a .080 gap. The 403 with HEI distributor (77 thru 78)=
had 2 gaps listed. The gap for the Federal motor was .060 and the Californ=
ia motor was .080. It has been seen that the .080 gap was hard on the coil =
and module and had seen a higher failure rate. An article in GMCMHI newslet=
ter V 4, I 3, P 3 stated that GM dealers both in California and east were r=
ecommending a .045 for the 403 HEI giving the best performance. Now a=
personal comment and again yours may vary. I had run our 77 403 with the .=
060 gap (R46SZ) (98 thru 03) and saw that the plug gap was pounded out to b=
etter than .075 in less than 4K miles. I was changing plugs every year. I a=
lso had several modules failures during that time. I switched to the DP HEI=
and #7 plug in 2004 I did not had any failures. Same #7 plugs, 32K miles, =
Cleaned and regapped in 2008, still looked good, ACDelco listed these as a =
100K-mile plug. Another personal comment, is I would run one of the platinu=
m or Iridium plugs and close the gap down to the .036 to .040 range or the =
E3 plug as it comes out of he box. NOTE: The original ACDelco #7 i=
s no longer available in original plug tip. New ACDelco #7 is not the same =
construction and should be avoided. In 2010 Dick Paterson recommended the N=
GK XR5IX plug as a replacement. I now run the E3 Brand
E3.52 plug and have =
about 10000 miles. Onan Spark Plugs: Both the 4K & 6K use the same=
heat range spark plug. Plug gap for both is .020=E2=80=9D Cummins On=
an spark plugs are part# 167-0262-99 On=
Sep 29, 2019, at 11:07 PM, Mike via Gmclist wrot=
e: > > So...now that I know what engine I have (see thread
http://gmc.b=
ackyardwildlife.com/GMCforum/index.php?t msg&th 42989&start 0&rid 5=
830) I'm making a > list of AC Delco part numbers for a tune up. I want =
to replace the PCV valve. They are cheap and I don't know when it was last=
done. However, I > cannot find the PCV valve listed in my parts manual.=
Everything listed is for the 455 not the 403. I looked up a 78 Toranado =
and found one, but I'm > not sure yet which engine parts cross over and w=
hich do not. > > Also on the breather side, I have a breather in goo=
d shape, but the two rubber elbows that connect it to the air horn are shot=
. Are those available? > > -- > Mike and Jessica > West Michiga=
n (Just north of Grand Rapids) > 1978 Royale Twin bed, Dry Bath
