Pros And Cons Of 402bb? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

soala70 · 11-29-2002, 12:51 AM

I am planning to buy a 72 gmc sierra Swb loaded w/402bb. 2nd owner doesnt use oil smokes a little when first cranked but thats all.owner not for sure if original owner had been into motor being he pasted.Anything I should look for and IF it turns out to need a rebuild being (if Im correct) a 396 bored .030over from the factory what are my best options? Also being in good condition no dents or rust whats a fair offer hes wanting $5500?

Hooter · 11-29-2002, 01:00 AM

the 402 was bored out for company reasons. Chevy cmae out with the 400 sb and they didnt want their smal block to out displace the 396. Voila 402. I have no problems wit 402's torquy and fun. But of course being a big block they are hard on gas. The smoke thing is just valve guides. Maybe just a head job. dont run under 91 octane unless necessary. Ive found big blocks like higher octane gas

littlebubba · 11-29-2002, 01:32 AM

Sounds like the price is high, seeing it needs work. How many miles on it? Whats the rest of it like? Driveable as is? What else does it need? The thing it has going for it is: SWB and Big Block. They say there is an a$$ for every seat, sounds like about worth half of what hes asking IMO.

mikep · 11-29-2002, 11:45 AM

I paid $500 for a loaded 68 anniversary special CST with the 396 that needed paint and interior work. 6 months later the engine is rebuilt ( not the same engine . I went with a small block although it would have been cheaper to rebuild the big block ) , the paint is new and it has a new interior and new trim. Drives like a new truck. I dont have close to $5500 total in it.

IMHO his price is too high.

Bill72BB · 11-29-2002, 11:50 AM

soala70

Out here that would be a good price for a SWB ,BB .With ps,Pdb air ,tilt , auto .

Longhorn Man · 11-29-2002, 12:03 PM

Up in these parts, a short/fleet big block with no rust would get that even if it didn't run.
Depressing huh?

Bill72BB · 11-29-2002, 12:11 PM

Quote:

Originally posted by longhornmail
Up in these parts, a short/fleet big block with no rust would get that even if it didn't run.
Depressing huh?

Andy there was a 67 swb in the next town restored for 16,000 ,they are just getting out of sight.

Terry'sToy · 11-29-2002, 02:40 PM

I think the 402's are just fine. I've had two. You can safely bore the 402 another .030 and if you have to go .060 get it sonic checked for cylinder wall thickness. They make tons of torque and tow like a beast. I had a 69 camper special 402/th400 dana 3.54 and towed a 68 3/4 4x4 with the box full of stuff. Total weight was 13,700 lbs when we crossed the ( closed for the night ) scale. We hauled this over a small mountain pass and it maintained 50 mph no problem. It averaged 9 mpg. Unloaded it gets 15 mpg. I'm considering building another for my truck now and putting the Throttle body injection unit on it.
The price seems good to me considering you said it had no rust or dents and it's a short box with a BB.

mikep · 11-29-2002, 03:17 PM

Terry... Let me get this straight. Your 3.54 geared big block 1969 truck gets 15 mpg unloaded. Is that downhill with a good back wind? I'm not saying your full of it but mine got 9.6 mpg when I was REALLY trying to see what kind of mileage I could get out of it. same rig . Long bed 1968 C20 396 with 3.54 gears 4 speed tranny , stock q jet in excellent condition , excellent compression etc. weighed in at 4550

Terry'sToy · 11-29-2002, 04:34 PM

mikep, I'm not kidding. I drove this thing back and forth to work for a long time. approx. 40 miles per day, and I checked the gas mileage often. I also had a 8' camper I used to haul it and I got 12-13 mpg all the time.
Actually my buddy just bought the truck from me and he is here right now. He did two trips lately. One with a camper,trailer and race car and got 9mpg with a scaled weight of 12100 lbs. The last trip was unloaded and he went 14.5 mpg driving at 60-65 mph. Maybe the difference is this engine has a 600 holley with 64 primary jets. Also our gallon is 4.54 litres and your is 3.78 litres. This will make a bit of difference.
Terry.

mikep · 11-29-2002, 06:21 PM

Hahaha .... I guess using imperial gallons would make a wee bit of a difference.

soala70 · 11-29-2002, 10:45 PM

Everything works cold ac,auto trans,wipers,etc. He still drives it about three time a week to work has approx. 80k on it bed is in good shape as far as rust but used alot. Im going to offer 4k it doesnt hurt to try heh?
On the engine a 402 is already bored .030 over .030 more is all you can go isnt it?Im asking cause I have no idea just what Ive read.Are there .040 over slugs for a 396 or would you say .010 slugs for a 402?If needed at all

mikep · 11-29-2002, 11:23 PM

.040" is possible on a 402 but not real likely . Sonic testing is the best way to go. Different area have different expectations of what a sonic test will cost but in this area its about $150 for a mapped test. Ive had a few done and its saved me from boring at least one block to the point it was unusable. Its difficult to go from .030" to .040" without problem on an engine thats been run for a while. Sometimes it wont get cleaned up all the way. It might not even be necessary to rebore anyway. If the cylinder walls are within spec you might just be looking at a hone and re-ring. Still sounds like too much money. Good 396 blocks are getting harder to find although you might find a standard bore block in the $400 range if your'e lucky. Desert rat seems to have some good pricing on 396 blocks if you dont mind paying the shipping.

Johns70 · 11-30-2002, 12:43 AM

mikep i had purchased a 396, when i went to rebuilt it i was suprised it was still origanal bore.calling around for machine work,britco in chehalis wanted it pretty bad because it hadn't been touched yet, offered $200 cash for bare block or a 454 block aready done for 550 fully prepped.i stuck with it though now i have 396 .030 overbore{402} now it runs pretty strong now with the forged pistons and tradeing the truck heads that were on it for a set of $200 rebuilt swap meet 4290 heads that i pocket ported and polished.

mikep · 11-30-2002, 02:31 AM

Good old Brittco. Back in the day when I lived in Longview I used to be good drinking buddies with half the guys who worked there. Remember when their shop was under 8 feet of water during the flood of '96 ? I had a brand new siamesed bow tie block submerged with it. Had to have it overbored after that as the cylinders got all pitted. Pissed me off as I had to get different pistons. Some jerkoff swapped my nodular caps out for standard 4 bolt caps too. Last work I ever had them do.

11-29-2002, 12:51 AM	#1
soala70 Registered User Join Date: Mar 2002 Location: geneva al usa Posts: 343	Pros And Cons Of 402bb? I am planning to buy a 72 gmc sierra Swb loaded w/402bb. 2nd owner doesnt use oil smokes a little when first cranked but thats all.owner not for sure if original owner had been into motor being he pasted.Anything I should look for and IF it turns out to need a rebuild being (if Im correct) a 396 bored .030over from the factory what are my best options? Also being in good condition no dents or rust whats a fair offer hes wanting $5500? __________________ bogey5

11-29-2002, 01:00 AM	#2
Hooter My other Love Join Date: Aug 2001 Location: Castlegar B.C. Canada Posts: 4,085	the 402 was bored out for company reasons. Chevy cmae out with the 400 sb and they didnt want their smal block to out displace the 396. Voila 402. I have no problems wit 402's torquy and fun. But of course being a big block they are hard on gas. The smoke thing is just valve guides. Maybe just a head job. dont run under 91 octane unless necessary. Ive found big blocks like higher octane gas __________________ Castlegar B.C.The great white North (Canada Eh!) Hooter_5@hotmail.com First generation Monte Carlo club pictures of my life

11-29-2002, 01:32 AM	#3
littlebubba Registered User Join Date: Jun 2002 Location: Clinton Twp., Michigan Posts: 321	If it needs work Sounds like the price is high, seeing it needs work. How many miles on it? Whats the rest of it like? Driveable as is? What else does it need? The thing it has going for it is: SWB and Big Block. They say there is an a$$ for every seat, sounds like about worth half of what hes asking IMO.

11-29-2002, 11:45 AM	#4
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	I paid $500 for a loaded 68 anniversary special CST with the 396 that needed paint and interior work. 6 months later the engine is rebuilt ( not the same engine . I went with a small block although it would have been cheaper to rebuild the big block ) , the paint is new and it has a new interior and new trim. Drives like a new truck. I dont have close to $5500 total in it. IMHO his price is too high. __________________ No truck :-(

11-29-2002, 11:50 AM	#5
Bill72BB Thats the Hillbilly way Join Date: Jul 2001 Location: Torrance,Ca Posts: 5,979	soala70 Out here that would be a good price for a SWB ,BB .With ps,Pdb air ,tilt , auto . __________________ BILL Torrance Calif 90504 Member DUF Club Member Old Farts Club 72 3/4ton Custom Camper BB402/400 trans Dynomax Cerama-coat headers , Hei distributor ,Edelbrock 1411 air,ps,pb,leafsprings ,98 chevy 60/40 seat,S10 shoulder belts tilt,3.54 Dana 60 rear. 16" Eagle wheels with LT265/75 16 tires,Gaylord Lid,H4 headlights with 100W relay conversion. " If I knew I was going to live this long I would have taken better care of myself " Marriage changes passion...suddenly you're in bed with a relative. A GUY'S PRAYER.... Lord, I pray for a nympho with huge boobs who owns a liquor store and likes to fish and hunt and has a Harley .Amen , Last edited by Bill72BB; 11-29-2002 at 11:53 AM.

11-29-2002, 12:03 PM	#6
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Up in these parts, a short/fleet big block with no rust would get that even if it didn't run. Depressing huh?

11-29-2002, 02:40 PM	#8
Terry'sToy Registered User Join Date: Oct 2002 Location: Victoria B.C Posts: 109	I think the 402's are just fine. I've had two. You can safely bore the 402 another .030 and if you have to go .060 get it sonic checked for cylinder wall thickness. They make tons of torque and tow like a beast. I had a 69 camper special 402/th400 dana 3.54 and towed a 68 3/4 4x4 with the box full of stuff. Total weight was 13,700 lbs when we crossed the ( closed for the night ) scale. We hauled this over a small mountain pass and it maintained 50 mph no problem. It averaged 9 mpg. Unloaded it gets 15 mpg. I'm considering building another for my truck now and putting the Throttle body injection unit on it. The price seems good to me considering you said it had no rust or dents and it's a short box with a BB. __________________ 69 GMC 1/2 ton lwb, LS1, headers X-pipe 4L60E Yank 3500 stall 3.73 w/eaton brute force. moroso trick front springs,jeep rear springs, QA1's

11-29-2002, 03:17 PM	#9
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	Terry... Let me get this straight. Your 3.54 geared big block 1969 truck gets 15 mpg unloaded. Is that downhill with a good back wind? I'm not saying your full of it but mine got 9.6 mpg when I was REALLY trying to see what kind of mileage I could get out of it. same rig . Long bed 1968 C20 396 with 3.54 gears 4 speed tranny , stock q jet in excellent condition , excellent compression etc. weighed in at 4550 __________________ No truck :-(

11-29-2002, 04:34 PM	#10
Terry'sToy Registered User Join Date: Oct 2002 Location: Victoria B.C Posts: 109	mikep, I'm not kidding. I drove this thing back and forth to work for a long time. approx. 40 miles per day, and I checked the gas mileage often. I also had a 8' camper I used to haul it and I got 12-13 mpg all the time. Actually my buddy just bought the truck from me and he is here right now. He did two trips lately. One with a camper,trailer and race car and got 9mpg with a scaled weight of 12100 lbs. The last trip was unloaded and he went 14.5 mpg driving at 60-65 mph. Maybe the difference is this engine has a 600 holley with 64 primary jets. Also our gallon is 4.54 litres and your is 3.78 litres. This will make a bit of difference. Terry. __________________ 69 GMC 1/2 ton lwb, LS1, headers X-pipe 4L60E Yank 3500 stall 3.73 w/eaton brute force. moroso trick front springs,jeep rear springs, QA1's

11-29-2002, 06:21 PM	#11
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	Hahaha .... I guess using imperial gallons would make a wee bit of a difference. __________________ No truck :-(

11-29-2002, 10:45 PM	#12
soala70 Registered User Join Date: Mar 2002 Location: geneva al usa Posts: 343	Everything works cold ac,auto trans,wipers,etc. He still drives it about three time a week to work has approx. 80k on it bed is in good shape as far as rust but used alot. Im going to offer 4k it doesnt hurt to try heh? On the engine a 402 is already bored .030 over .030 more is all you can go isnt it?Im asking cause I have no idea just what Ive read.Are there .040 over slugs for a 396 or would you say .010 slugs for a 402?If needed at all __________________ bogey5

11-29-2002, 11:23 PM	#13
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	.040" is possible on a 402 but not real likely . Sonic testing is the best way to go. Different area have different expectations of what a sonic test will cost but in this area its about $150 for a mapped test. Ive had a few done and its saved me from boring at least one block to the point it was unusable. Its difficult to go from .030" to .040" without problem on an engine thats been run for a while. Sometimes it wont get cleaned up all the way. It might not even be necessary to rebore anyway. If the cylinder walls are within spec you might just be looking at a hone and re-ring. Still sounds like too much money. Good 396 blocks are getting harder to find although you might find a standard bore block in the $400 range if your'e lucky. Desert rat seems to have some good pricing on 396 blocks if you dont mind paying the shipping. __________________ No truck :-(

11-30-2002, 12:43 AM	#14
Johns70 Registered User Join Date: Dec 2001 Location: Spring Creek, nevada. U.S.A. Posts: 456	mikep i had purchased a 396, when i went to rebuilt it i was suprised it was still origanal bore.calling around for machine work,britco in chehalis wanted it pretty bad because it hadn't been touched yet, offered $200 cash for bare block or a 454 block aready done for 550 fully prepped.i stuck with it though now i have 396 .030 overbore{402} now it runs pretty strong now with the forged pistons and tradeing the truck heads that were on it for a set of $200 rebuilt swap meet 4290 heads that i pocket ported and polished. Attached Images __________________ 69 chevy short wide box project 70 GMC jimmy project

11-30-2002, 02:31 AM	#15
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	Good old Brittco. Back in the day when I lived in Longview I used to be good drinking buddies with half the guys who worked there. Remember when their shop was under 8 feet of water during the flood of '96 ? I had a brand new siamesed bow tie block submerged with it. Had to have it overbored after that as the cylinders got all pitted. Pissed me off as I had to get different pistons. Some jerkoff swapped my nodular caps out for standard 4 bolt caps too. Last work I ever had them do. __________________ No truck :-(

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