rebuild or retire?

[lawdog49]

ok, I am the proud owner (about 3rd I think) of a 91 GMC Suburban- 5.7/700r4/4WD.  This beauty has 313 000 on the clock, yes you read correctly.  The original owner was meticulous- I have notebooks where he documented every oil change or maintenance work for the life of this truck all the way til just a year or so before I got it(oil/filter every 5K).  I think he died, and it sat for awhile before the grandson sold it off.  He even had a notebook for every fuel fill p with mileage/date/gallons/etc.  This thing is cleaner underneath than my 99 Chevy.

Anyway, in looking through the records- I don't believe the 350 has ever been replaced or gotten into- replaced rear main (which is leaking) around 250K, intake gasket has been replaced.  Although the water pump has been replaced about 5 times, along with a few new radiators, and of course various other maintenance items- the engine itself does appear to be original.  I can't find a spot to look for numbers on heads or block to confirm this, any ideas?  Would this be a 2 or 4 bolt main?  I'm guessing 2.  I would like to build a 383 to pull this heavy beast around, but not sure if I should use this block or not.  I know Capt is gonna tell me to get an LS engine, but I'm not sure I can muster enough help to do that swap without it costing me lots of labor.  Should a 2 bolt block be built into a 383?  Should I rebuild this engine, or could it be so worn that I would have to bore more than .30 over?  It smokes a little upon cranking, but only like valve seals may leak a little and then it stops.  Uses about a half quart every 3000.  I don't think the converter has been replaced either, which I'm surprised it isn't completely clogged up.  The truck runs well, but I haul the family around on out of town trips, and I don't want to continue to risk this 300K SBC finally giving out during a trip out of town.  I think 300K is a great lifespan on this engine.  The trans was rebuilt at about 265000, will the 700r4 live behind a 383- not trying to hotrod it, just want the torque to haul this heavy truck loaded down.

Thanks for the help guys.

[eventhorizon66]

There is absolutely nothing wrong with a 2-bolt main block, especially for a street build.  I'd say find a good machine shop and go for it.

[zieg85]

300K is broke in, I wouldn't touch a good running engine if it were me.  1/2 quart in 3K miles, not bad at all.

[joesgarage71]

 I would find another engine to build while still running the truck, when its ready take a weekend and do the swap. Engine rebuilds always take more time than we all figure, that minimizes the down time of the Sub.
Nothing wrong with a 2 bolt 383.

[eventhorizon66]

I would find another engine to build while still running the truck, when its ready take a weekend and do the swap. Engine rebuilds always take more time than we all figure, that minimizes the down time of the Sub.
Nothing wrong with a 2 bolt 383.

Good point.  If this is your driver then a swap is the way to go.

[low budget]

I had a friend that had 350,000 on a 350 in his company truck.  Tore it down over the winter when it was his slow time and he said it really didn't need it...

[Captkaos]

I would find a 383 replacement and keep it on standby until this one croaks.  I have heard from dealerships of TBI trucks running for 450K and above.

[VileZambonie]

The most wear on your engine is probably the valve guides. I agree, keep it going and find a donor and build your 383

PS 2 bolts have proven to be stronger than 4 bolts time and time again

[Captkaos]

I agree on the 2 bolt thing also.  I have broken a 4bolts and I broke a 4bolt with a steel crank
I have yet to break a 2bolt, and several of us have tried.

[SUX2BU99]

^ Crazy. Any theories or reasons why that would be?

[Captkaos]

The 4 bolt setup reduces the amount of the lower webbing and therefore makes it weaker. 
If you want a strong 4bolt main for racing purposes, most hard core race shops start with a 2 bolt block and machine it for a splayed 4 bolt main..

[VileZambonie]

Exactly. I have a 4 bolt block with broken mains sitting in my trailer. Never beaten too hard plow truck... I have a 2 bolt block in the sk

[lawdog49]

thanks guys, i knew i'd get some good answers.  Capt, know of any good 350 blocks around town?  i guess i will just start the search for a good block, find some vortec heads, keep the tbi with a new intake and start building a 383.

[joesgarage71]

 Late 60's early 70's GMC trucks had good 350's. Every one I tore down had 4-bolts mains and pink rods. Might find a wore out truck for the motor. the last three numbers on the better castings is "010" Stay clear of any .060 over blocks.
 Steve

[Captkaos]

I actually have 2 torn down in my parents garage that will be liquidating, and one complete motor.