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Bore size in my 402

 
allbbcchevy
V-6 Camaros rule!
Posts: 42
Joined: 07/11
Posted: 09/04/11 05:15 AM

My 402 has a standard bore of 4.125 and has been bored in the past .040 over to 4.165. Getting it ready to send to the machine shop. I honed the bored to just break the glaze to measure and look at the wear pattern. I measured 4.170 with about 0.001 - .002 taper.

I didn't want to bore over the 4.185. Pistons seem to very difficult to find any larger until you get to 4.250. In my research I believe I can go to that but 0.100 over would be the max and I really don't want to take it to that extreme. Worried about wall thinkness. I want to know if this small amount of bore would be possible or should I punt and go with another block.

Thanks  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 09/04/11 08:12 AM

as a start..  one might want to check out this article..

http://www.circletrack.com/techarticles/ctrp_0701_engine_block_prep/index.html


about sonic testing and core shifts..

i would really worry about trying to bore a 396 or 402 block that to the next bigger size.. i had a 402..  bored +.030 was 4.155..    

thats  +.060 over a 396 stock bore..   i have not personally bored these until i got air..    i am sure that  you will get an answer..

you might want to post a block casting number and julian date..  

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allbbcchevy
V-6 Camaros rule!
Posts: 42
Joined: 07/11
Posted: 09/04/11 08:52 AM

Thanks Wayne. Interesting article.

Here is what I know.

Block:
Engine ID - T0406TBG
Casting - 3969854
2 bolt

1970 Truck block Hi Perf Pass. Not sure what julian date you are refering to.

Read more: http://forums.chevyhiperformance.com/70/8786188/car-engine/402-bbc-build/index.html#ixzz1X00NzBcN

My understanding is that is a true 402 block casting. Not a 396 bored over to a 402. At least my machinist said they actually cast 402 blocks. The engine ID reflects this.

I was going to get the main bore alignment but I don't believe I have enough meat to do a cylinder bore alignment.  

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Pontiacman2
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Posts: 8956
Joined: 09/08
Posted: 09/04/11 08:56 AM

3969854 396/402/454 69-72 2 & 4-Bolt  
Pontiacman2
Pontiacman2

Professional Hi-performance engine builder

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allbbcchevy
V-6 Camaros rule!
Posts: 42
Joined: 07/11
Posted: 09/04/11 09:07 AM

Thanks Pontiacman.

Could someone explain this to me this? I have seen this everywhere where the casting numbers as mentioned reference several engine sizes. As with mine, 396/402/454. To me this would mean that these blocks were cast from the same mold then machined to a specific engine CID. If it came from the same mold then why couldn't the bore for a 396 or 402 accomadate a much larger size as with a 454 bored over .060 for instance. Again if you want to uses a 454 crank in a 396 or 402 you have to remove material for clearance for the counterweights on the 454 crank? It would seem that the bore size would be the only difference in the block but obviously isn't.  

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skyeking
I mow my lawn and find Chevys
Posts: 2738
Joined: 08/09
Posted: 09/04/11 05:22 PM

Hi there,
I would be looking for a 427/454 original block..
When in doubt...DON'T...  
skyeking

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allbbcchevy
V-6 Camaros rule!
Posts: 42
Joined: 07/11
Posted: 09/04/11 06:10 PM

Thanks Sky. Spent the day looking for just that block. Just not going to take the chance. Still don't completley understand this same casting number designation over several engine sizes.  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 09/04/11 08:58 PM

the julian date is the somewhere on the block... give the exact date of the casting of the block..  look kinda like this (\)B149(\)  this would be B  as feb  14 1969


about the multiple engines possible.. i am not sure..  i am away from home on a repair job..

google your casting number. there will be more info..  

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tuffnuff
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Posts: 7841
Joined: 12/09
Posted: 09/04/11 09:07 PM

396 has a 4.094" bore and 3.760" stroke
402 has a 4.126" bore and 3.760" stroke
both blocks are similar except for bore

427 has a 4.250" bore and 3.760" stroke
454 has a 4.251" bore and 4.000" stroke
both blocks are similar except for stroke

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 09/04/11 09:43 PM

ahh.. but what he is asking.. is there enough meat in the cylinder bores to bore it out to a 4.250+ since it is is beyond stock sized 402 pistons...

he really needs to get it sonic tested..  at least...  

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Pontiacman2
Moderator
Posts: 8956
Joined: 09/08
Posted: 09/05/11 05:29 AM

Sonic testing is the only way to know for sure.
I have seen many bbc with thin cylinder walls.  
Pontiacman2
Pontiacman2

Professional Hi-performance engine builder

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allbbcchevy
V-6 Camaros rule!
Posts: 42
Joined: 07/11
Posted: 09/05/11 07:06 AM

Thanks guys for your responses. Always appreciated. I have the freeze plugs out and just using my fingers it seems the cylinder walls seem to be .250 thick or less. I would guess less. Extremely accurate measurement right. Smile

The julian date looks like K289.

Since I am putting about $3700 in the motor I have decided that the safest course of action is to just replace the block. 40+ years of service just put it to bed. There are many good blocks available and I can actually get 427 forged pistons cheaper than cast hypereutectic for the 402. If I can't find a block for $500 or less I'll just get a Dart block for $1500 and call it a day. Piece of mind.

Again thanks everyone for your input.  

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waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 09/05/11 08:07 AM

november 28 1969 is the translation of the julian date.  so it was for a late 69 (1970 model)assembly date..  or an early 70 production ..


there is one last thing that is possible to save the block.. and i forgot to mention it..

sleeve the block..  but use HIGH strenth thinwall steel sleeves..  this prevents the #7 cylinder wall from breaking out on these oem blocks as i recall they did..  

properly boring the block so the sleeves sit against a step to lock their height in the block..    yes i know that is the way it is usually done..  i am just restating it..

i discussed that a LONG time ago with a friend who ran C streamliner..  then i see it done on other race motors.. i am almost sure a call over to LA sleeve company here in the los angeles area would get you some proper info on just what the current thinking is and available products..

i just thought of it.. but i should have on the many trips to la sleeve.. as them what kind of tricks they had up their sleeve..

i would bet that there is one or two articles on this at the link site  i posted above..  

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skyeking
I mow my lawn and find Chevys
Posts: 2738
Joined: 08/09
Posted: 09/05/11 04:50 PM

Laugh Hi there Agent 402,
Go for the Dart heads and Forged pistons if the bank/book says O.K. Confused
Sleeving is an each way bet which solely depends on the ENGINEER who does the work.
If you pay the freight on a 427 you will never look back..Heads are up to you. I
will let the Egsperts advise you on that one. Have the peace og mind and success.  
skyeking

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allbbcchevy
V-6 Camaros rule!
Posts: 42
Joined: 07/11
Posted: 09/05/11 07:10 PM

Thanks Wayne and Sky,

I don't think I will sleeve it just get a 427 block. That way I can use my crank and rods. Save some cash anyway. I would really like the Dart heads. WOW expensive. I think money well spent though. Maybe I just get the bottom end done and save for the top. It will be a while before she is back on the road anyway.

Cheers sky Smile  

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