How to tell what motor is in a 1972 CMC - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Pat leary · 06-20-2015, 02:27 PM

I just bought a 1972 GMC 2500 from northern California; it was part of an estate sale. It was an old ranch truck with 31,000 original miles that the son had been using for the last ten years or so, AC, power steering and power front disc brakes. The truck has not yet been shipped home to Massachusetts but the question I have is how do you tell what engine is in it. I know it is a big block the seller said last time he had it serviced that the mechanic looked up the numbers and told him it was a 454. My gut feeling is it is a 402, I looked up the VIN on the web and just identified as an eight cylinder. The truck looks like it has never had anything done to it, original paint etc. and with only 31,00 I would think it is matching numbers. If anyone could give me some guidance I would appreciate it.

Thanks, Pat

**Already Gone** · 06-20-2015, 02:41 PM

Hi Pat and welcome to the site. It makes sense that the BB in the truck should be a 402. Its possible the 402 blew up and a 454 was installed as replacement. By the way, you must have pictures of your truck and we love pictures on this site.

davepl · 06-20-2015, 05:31 PM

Need the three casting code off the block as a start. For example mine is

TO42TTBG

..which decodes to 1970 truck w/ TH400, L-47 310hp 402

So you can narrow it down to "is this a motor that could have come with it?" but never to matching numbers as trucks didn't get serialized engines.

Pat leary · 06-21-2015, 12:39 PM

Thanks for the information, it looks like I will have to wait for the truck get home and look at the numbers cast into the block. Are the numbers somewhere that can be accessed with the motor still in the truck?
I only have one picture of the truck, I will try and post the one that I have.

Thanks again, Pat

geezer#99 · 06-21-2015, 12:46 PM

Look here for where to look.
http://www.mortec.com/

Pat leary · 06-21-2015, 01:05 PM

Thanks,
I will check them out.

67 chevelle · 06-21-2015, 02:37 PM

if the number is on the block in front of the passenger head thats an easy one to get to and read ,, otherwise taking a valve cover off and checking the number cast in the middle of the head is also a good indication ,, as long as you have decent heads any big block will run well ,, peanut port heads run alright but lose it at higher rpm

here is a direct link to moretecs sight
http://www.mortec.com/location.htm

on moretecs sight you are hoping to see number 4 , blocks that have been surfaced lose the nomenclature
then onto numer 1 , they will be there
an example would be 3999241 ,, that is an 402 truck head number
nasty z28s site is better imo for casting numbers

Pat leary · 09-03-2015, 10:05 PM

I finally got the truck home, it took almost two month. It has a 402 in it, there is a foil tag on the valve cover with build date and displacement. There is also a sticker on the radiator support with the emission information that is marked 402.
I went to buy new tiers and was told the 16.5” tiers are getting hard to find. Is there a later year truck with ether 16” or 17” rims that will have the same 8 lug bolt pattern, center hole and offset so I can look for a used set.
Thanks, Pat

**68350** · 09-03-2015, 10:39 PM

Look for a set of rims off of a 73 and up. They are 16" rims and should be easy to find. Tires are easy too

Pat leary · 09-04-2015, 05:18 AM

Thanks,
That was what I was hoping.
Pat

06-20-2015, 02:27 PM	#1
Pat leary Registered User Join Date: Jun 2015 Location: Whitman Ma. Posts: 5	How to tell what motor is in a 1972 CMC I just bought a 1972 GMC 2500 from northern California; it was part of an estate sale. It was an old ranch truck with 31,000 original miles that the son had been using for the last ten years or so, AC, power steering and power front disc brakes. The truck has not yet been shipped home to Massachusetts but the question I have is how do you tell what engine is in it. I know it is a big block the seller said last time he had it serviced that the mechanic looked up the numbers and told him it was a 454. My gut feeling is it is a 402, I looked up the VIN on the web and just identified as an eight cylinder. The truck looks like it has never had anything done to it, original paint etc. and with only 31,00 I would think it is matching numbers. If anyone could give me some guidance I would appreciate it. Thanks, Pat

06-20-2015, 02:41 PM	#2
Already Gone 70+ ( Old Skool Club ) Join Date: Nov 2003 Location: Saskatoon, Saskatchewan ,Canada Posts: 9,108	Re: How to tell what motor is in a 1972 CMC Hi Pat and welcome to the site. It makes sense that the BB in the truck should be a 402. Its possible the 402 blew up and a 454 was installed as replacement. By the way, you must have pictures of your truck and we love pictures on this site. __________________ 1972 C10 Custom/Deluxe 613 Highlander 406/700R4 1999 White Tahoe LS 4x2 with Z56 Police Package 1992 K1500 GMC Suburban Members I have personally met: MusicMan70 - HeavyD - ChewyChevy67 - StingRay -71SWB4x4 - 67 Burb - DeadheadNM - too much stuff - bc65 - das601 " Circumsatances Do Not Change Responsibility " " The Sky is not the Limit, Your Mind is." Marilyn Monroe .. RIP Charlie Watts 1941 - 2021

06-20-2015, 05:31 PM	#3
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Re: How to tell what motor is in a 1972 CMC Need the three casting code off the block as a start. For example mine is TO42TTBG ..which decodes to 1970 truck w/ TH400, L-47 310hp 402 So you can narrow it down to "is this a motor that could have come with it?" but never to matching numbers as trucks didn't get serialized engines. __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible

06-21-2015, 12:39 PM	#4
Pat leary Registered User Join Date: Jun 2015 Location: Whitman Ma. Posts: 5	Re: How to tell what motor is in a 1972 CMC Thanks for the information, it looks like I will have to wait for the truck get home and look at the numbers cast into the block. Are the numbers somewhere that can be accessed with the motor still in the truck? I only have one picture of the truck, I will try and post the one that I have. Thanks again, Pat Attached Images

06-21-2015, 12:46 PM	#5
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,546	Re: How to tell what motor is in a 1972 CMC Look here for where to look. http://www.mortec.com/

06-21-2015, 01:05 PM	#6
Pat leary Registered User Join Date: Jun 2015 Location: Whitman Ma. Posts: 5	Re: How to tell what motor is in a 1972 CMC Thanks, I will check them out.

06-21-2015, 02:37 PM	#7
67 chevelle Registered User Join Date: May 2013 Location: WEST PALM FLORIDA Posts: 1,174	Re: How to tell what motor is in a 1972 CMC if the number is on the block in front of the passenger head thats an easy one to get to and read ,, otherwise taking a valve cover off and checking the number cast in the middle of the head is also a good indication ,, as long as you have decent heads any big block will run well ,, peanut port heads run alright but lose it at higher rpm here is a direct link to moretecs sight http://www.mortec.com/location.htm on moretecs sight you are hoping to see number 4 , blocks that have been surfaced lose the nomenclature then onto numer 1 , they will be there an example would be 3999241 ,, that is an 402 truck head number nasty z28s site is better imo for casting numbers __________________ 68 Long Fleet , ly6 , turbo 350 , 3-5 drop , original paint , front discs 67 Small window , 7 foot bed , tweaked 6.0 LSX 2004R Medium Olive 58 Apache fleet , 235 , offy intake , dual exhaust , 4 on the floor , red/white 69 Long Fleet , Custom , 6.0, 4l60 , AC , Medium Olive Last edited by 67 chevelle; 06-21-2015 at 02:48 PM.

09-03-2015, 10:05 PM	#8
Pat leary Registered User Join Date: Jun 2015 Location: Whitman Ma. Posts: 5	Re: How to tell what motor is in a 1972 CMC I finally got the truck home, it took almost two month. It has a 402 in it, there is a foil tag on the valve cover with build date and displacement. There is also a sticker on the radiator support with the emission information that is marked 402. I went to buy new tiers and was told the 16.5” tiers are getting hard to find. Is there a later year truck with ether 16” or 17” rims that will have the same 8 lug bolt pattern, center hole and offset so I can look for a used set. Thanks, Pat

09-03-2015, 10:39 PM	#9
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: How to tell what motor is in a 1972 CMC Look for a set of rims off of a 73 and up. They are 16" rims and should be easy to find. Tires are easy too __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

09-04-2015, 05:18 AM	#10
Pat leary Registered User Join Date: Jun 2015 Location: Whitman Ma. Posts: 5	Re: How to tell what motor is in a 1972 CMC Thanks, That was what I was hoping. Pat



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