How do you indentify a 400SB - The 1947 - Present Chevrolet & GMC Truck Message Board Network

beaterC10 · 08-15-2003, 09:09 AM

I posted the same question on the drivetrain board. Hoping someone has the answer.

Is there a quick a dirty way to identify a SB400 that is still in the truck without the gymnastics involved trying to read the casting numbers on the back of the block.

I was hoping the balancer might be the tipoff like it is on a 305. I thought some of the early 400's had 3 freeze plugs per side instead of the normal 2.

The engine is supposed to be a '75 vintage that runs but has a miss. The guy thinks it is bad valves, but I guess it could also be a sloppy timing chain, worn out cam, vacuum leak etc.

Any idea what a complete 400 is worth. Probably more than a 305 and less than a 454.

Tx Firefighter · 08-15-2003, 09:18 AM

You're on the right track, with the balancer and freeze plugs.

I read in Hot Rod awhile back that there had only been a very few 400 SB found that didn't have 3 freeze plugs on the side of the block. That's the safest bet is to count the plugs.

beaterC10 · 08-15-2003, 10:53 AM

Thanks

Do you know what the difference is between a 350 and 400 balancer? I know the 305 is smaller in diameter and thicker than a 350, but I dont' know the differences between the 350 and 400.

Blazer1970 · 08-15-2003, 11:11 AM

Since the 400 is externally balanced, the balancer has a notch missing out of the OD. It is an 8 inch balancer, but you will see (or feel if it is on the bottom at the time), the notch that is cut out for balance.

Personally, I would go by the block ID number and/or casting number. A '75 400 should be CHS, CSH, CSM, CSR, CSS, CST, CTB, CTL, CTM, CTR, CTU, CTW, TLD, TLH, TLR, TLS, TLT, or TLU (Cs are car engines, Ts are truck engines). The casting number should be 3951509, 3030817 or 330817.

If you know what to look for, the 400 block casting can be quickly recognized because the outside of the block has bulges around each cylinder bore that are not present on any other small block casting.

*1FaastC10* · 08-15-2003, 12:09 PM

Quote:

Originally posted by beaterC10
Thanks

Do you know what the difference is between a 350 and 400 balancer? I know the 305 is smaller in diameter and thicker than a 350, but I dont' know the differences between the 350 and 400.

both the 305 and 350 bablancers are zero balanced, so in reality someone could've put a 350 balancer on a 305, or a 305 balancer on a 350. should always go by the casting numbers to tell you for sure. they're not that hard to get to.

beaterC10 · 08-15-2003, 12:32 PM

Thaks for the help. The casting numbers are on the rear near the bellhousing and ID number is on the front passneger side near the intake, correct?

Blazer1970 · 08-15-2003, 12:38 PM

Quote:

Originally posted by beaterC10
Thaks for the help. The casting numbers are on the rear near the bellhousing and ID number is on the front passneger side near the intake, correct?

Yup

jimfulco · 08-15-2003, 04:18 PM

Don't the 400's have 3 freeze plug bosses on each side?

82 Silverado 4X · 08-15-2003, 04:48 PM

The 400 in my 77 Blazer Chalet only has 2 freeze plugs 1 on each side.

jimfulco · 08-15-2003, 06:01 PM

But is the boss there for a third one?

82 Silverado 4X · 08-15-2003, 08:10 PM

There is no boss for the 3rd freeze plug on my block. It's casting number is 3951509 and the stamping suffix is TLS. I had the oil pan off to change the oil pan gasket in 94 and it's only a 2 bolt main. My neighbor bought it new in 77 and it has only 54,000 original miles.

*mike reeh* · 08-15-2003, 08:54 PM

the best and easiest way is to start the engine, and crawl under the engine and look up at the backside of the harmonic balancer.. it will look really wobbly and/or out of balance due to the huge counterweight void.. then you can kill the engine and see it a little easier if you didnt know what to look for.

mike

08-15-2003, 09:09 AM	#1
beaterC10 Senior Member Join Date: Jul 2003 Location: Indianapolis, IN Posts: 1,277	How do you indentify a 400SB I posted the same question on the drivetrain board. Hoping someone has the answer. Is there a quick a dirty way to identify a SB400 that is still in the truck without the gymnastics involved trying to read the casting numbers on the back of the block. I was hoping the balancer might be the tipoff like it is on a 305. I thought some of the early 400's had 3 freeze plugs per side instead of the normal 2. The engine is supposed to be a '75 vintage that runs but has a miss. The guy thinks it is bad valves, but I guess it could also be a sloppy timing chain, worn out cam, vacuum leak etc. Any idea what a complete 400 is worth. Probably more than a 305 and less than a 454.

08-15-2003, 09:18 AM	#2
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	You're on the right track, with the balancer and freeze plugs. I read in Hot Rod awhile back that there had only been a very few 400 SB found that didn't have 3 freeze plugs on the side of the block. That's the safest bet is to count the plugs. __________________ I'm on the Instagram- @Gearhead_Kevin

08-15-2003, 11:11 AM	#4
Blazer1970 Registered User Join Date: Dec 1999 Location: Old Mission, MI, USA Posts: 2,507	Since the 400 is externally balanced, the balancer has a notch missing out of the OD. It is an 8 inch balancer, but you will see (or feel if it is on the bottom at the time), the notch that is cut out for balance. Personally, I would go by the block ID number and/or casting number. A '75 400 should be CHS, CSH, CSM, CSR, CSS, CST, CTB, CTL, CTM, CTR, CTU, CTW, TLD, TLH, TLR, TLS, TLT, or TLU (Cs are car engines, Ts are truck engines). The casting number should be 3951509, 3030817 or 330817. If you know what to look for, the 400 block casting can be quickly recognized because the outside of the block has bulges around each cylinder bore that are not present on any other small block casting. __________________ Tim

08-15-2003, 04:48 PM	#9
82 Silverado 4X Genuine Chevrolet Join Date: Feb 2003 Location: South West Pennsylvania. Posts: 582	The 400 in my 77 Blazer Chalet only has 2 freeze plugs 1 on each side. __________________ George 82 Silverado LWB 4x4 350 SM465 NP208 77 Chevrolet Blazer Chalet 400 TH350 NP203 Last edited by 82 Silverado 4X; 08-15-2003 at 08:12 PM.

08-15-2003, 08:10 PM	#11
82 Silverado 4X Genuine Chevrolet Join Date: Feb 2003 Location: South West Pennsylvania. Posts: 582	There is no boss for the 3rd freeze plug on my block. It's casting number is 3951509 and the stamping suffix is TLS. I had the oil pan off to change the oil pan gasket in 94 and it's only a 2 bolt main. My neighbor bought it new in 77 and it has only 54,000 original miles. __________________ George 82 Silverado LWB 4x4 350 SM465 NP208 77 Chevrolet Blazer Chalet 400 TH350 NP203

08-15-2003, 10:53 AM	#3
beaterC10 Senior Member Join Date: Jul 2003 Location: Indianapolis, IN Posts: 1,277	Thanks Do you know what the difference is between a 350 and 400 balancer? I know the 305 is smaller in diameter and thicker than a 350, but I dont' know the differences between the 350 and 400.

08-15-2003, 12:32 PM	#6
beaterC10 Senior Member Join Date: Jul 2003 Location: Indianapolis, IN Posts: 1,277	Thaks for the help. The casting numbers are on the rear near the bellhousing and ID number is on the front passneger side near the intake, correct?

08-15-2003, 04:18 PM	#8
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	Don't the 400's have 3 freeze plug bosses on each side?

08-15-2003, 06:01 PM	#10
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	But is the boss there for a third one?

08-15-2003, 08:54 PM	#12
mike reeh 5 day ban, learn to behave. Join Date: Nov 2002 Location: san diego, ca Posts: 683	the best and easiest way is to start the engine, and crawl under the engine and look up at the backside of the harmonic balancer.. it will look really wobbly and/or out of balance due to the huge counterweight void.. then you can kill the engine and see it a little easier if you didnt know what to look for. mike



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