cracked block

[twinty]

just pulled my 4.3 from my 85 awd blazer and found a 2 inch crack in the cylinder wall on number 4. at least i know why it had a misfire and a milkshake in the oilpan.....lol...
my question for all of you 4.3 guru's is , does this happen all the time? i mean when you run lots of boost to a 4.3.. I did some reading and cant find any info to support this, and i was worried about my rods....lol..
i run propane and 20 lbs boost and its an otherwise stock 91 4.3 , my only real mods are my kb118 22cc dish pistons and proted lb4 heads with vortec exhaust valves (the ones with the skinny shafts). oh ya and arp's throughout.
i was thinking about eagle rods and splayed caps but now im thinking about a vortec 350 with trickflows that I have laying around and a big single turbo.....seeings as i already have a full 4" exhaust on it ...

just looking for the light at the end of the tunnel
thanks in advance

 

[jwaller]

yes with stock blocks it's a problem boost and bore size. of +0.040. I have personally busted 2 stock blocks in the #4 clyinder.

 

[twinty]

ok so after further inspection of the crappy stock block i have also discovered that the cylinder walls of all six holes were deforming under load so bad that the rings were only touching on about 50% of the walls!! The block is only bored .030 and I only had about 5000km on this block since the rebuild..... so my plan now is to either get this block punched out and sleeved or get a gm performance block. Is there any stock 4.3 blocks that are better than others? casting number on mine is 10105867.

 

[jwaller]

yes the "T" block is stronger but hard to find. it came in the cargo astro vans and "work" series full size trucks.

I know some builders also claim that they fill the lower 30% or so of the block with block filler and this helps the bottom end.

 

[Crazy J]

what are the identifying marks or casting #'s of a "T" block?

 

[twinty]

My search continued for a stronger block and i came across a couple of marine blocks that seem to have thicker cylinder walls at a local machine shop layin around, so i might pick up one of these, also one is already bored 0.030 so my pistons will fit. Im gonna try to find some info on a T series block as i found with some research that the 8600gvw trucks had a different block, probably one of these? i will try to find some casting numbers.

 

[93ty475]

also one is already bored 0.030 so my pistons will fit

i'd plan for at least .040 or so on the one that is already bored .030 over...from what i understand...even better if the marine block has thicker cylinder walls...

 

[jwaller]

the T block will have the front and rear freeze plugs cast over one can bee seen in my site under jamie hacking rebuild. they also have larger cam bearings and thicker castings all the way around. the blocks have a large T cast in them.

 

[canadian]

where is the "T" located on the block. couldn't seem to see it in the gallery.

 

[jwaller]

if I remember correct it's on the bellhousing. I'll have to go look. the dead giveaway is no front and rear freezeplugs.

 

[twinty]

So on some further research the last week and a bit i have come up with some casting numbers of the thicker , higher nickel content 4.3 blocks.
these blocks are from the 92,93 era and the last three digits of the casting numbers are 073, and as in the pictures on jwallers website under jamie hacking rebuild, 756. The 756 blocks appear to have came with or without front and rear frost plug holes.

 

[Crazy J]

do the 073 blocks have freeze plugs front/rear?

 

[sean]

Re: cracked block

i know it is an old post but twinty did you find out anymore info. on this?

 

[jwaller]

Re: cracked block

I used another one on the buck spruill rebuild. you can check his block for those casting numbers as well.