Cracked 350 Crank, build 383?

[teeteeplz]

Hey hoping to get some suggestions as to an economical yet fun solution to my recent dilemma.
Ive got a 1972 C-10 with a jasper reman 350SBC (quadrajet, stock manifolds, stock build i believe) installed in 2014 and ive put about 20k miles on it since the install.

Last week or so I noticed a knocking of a two tones (hi,lo) near the motor and noticed the harmonic balancer was hitting the timing tab, and had more wobble to it than normal. I bent the tab up a bit hoping for a quick fix, until i got the time and $ to replace the original harmonic balancer. it took care of the pinging of hitting that timing tab, but a deep knocking remained, faint at idle until hot, and noticeable with the vehicle at 0mph and the truck in gear (auto th350 trans). oil pressures seem normal

I dropped the truck off at my local repair shop for further investigation, and possible harmonic balancer replacement. when they popped it off, they noticed (and I later verified) a large amount of play on the snout? of the crankshaft. They claim that it is cracked, and others have told me that it has broken in a way that is allowing the motor to run but is on very borrowed time. The motor has never been overheated to my knowledge, but was installed by a rather inept mechanic prior to my ownership.

Is it safe to assume the Crankshaft is toast at this point and requires engine removal from the truck, crank replacement, and Main bearings done while in there? How much would this cost for a minimal fix with new parts? Is this a smart solution?
Would I be better off Building a 383 stroker out of this lightly used 350 core,reman 350SB? As the Crank sounds like its in need of a replacement anyhow. Or should I buy a crate of some sort and dump this 350?

I believe the rear end gear ratio on this truck is a 3.08(3.07?) as my tach is just about 3k if im doing 85mph with 265/75/15. I dont have known any issues with the TH350.

-true dual exhaust flowmaster 40's

The truck has been in my family since around 94 and has a lot of sentimental value. I appreciate any recommendations on what I can do to add some fun with out a second mortgage

the only other modification I really want for this "rebuild/repair/replacement etc" Is switching to Posi-trac. One wheel burn-outs just arent cutting it!

[teeteeplz]

I noticed my last post on this truck was from 2007, as I was anticipating driving this truck at age 16 (over a decade ago). I did end up having to pay for it to get it from my pops a couple years ago, but I'm glad they made they decided to hold off on me. I prolly would have wrecked it in my youth. Anyhow, here are some updated photos, mostly the same, just a few minor changes thankfully!

[Warrens69GMC]

nice!

[Boog]

Very nice looking truck. As for the engine you could remove the flywheel cover to watch the fore and aft movement of the crankshaft on both ends of the engine. Wobble of the damper is not good. Or it's yank the engine to pull the pan and give it a good look over. Lower end noise is never good. A fella used to be able to buy a stock reman'd crank kit for less than 200 for an affordable repair. A stroker crank kit runs the cost up. How deep is your pocket?

Loose torque converter bolts make a knocking noise too.

[Mike C]

If the rest of the motor is in good shape, I would disassemble and get the bore size. I would then buy an Eagle internally balanced 383 kit from someone like Competition Products.

Complete rotating assembly, balanced for about $800.

[teeteeplz]

Thanks for the reply’s! I think the motor is in good shape besides the alleged broken crankshaft. I like the idea of the 383 kit plus some supporting mods (intake heads cam headers carb(if required, haven’t had any Quadrajet issues yet, but hear they can be tough to tune to the un-acquainted). I’d like to make more than 400hp/tq or so with the motor. Budget is flexible, I’d rather wait and save and do it right than to skimp out and wish I had done it differently in the future. I’m hoping to get it done with 5k or less including positrac upgrade.!
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[sick472]

Nice set up! sorry about the noise...

Old saying..."there is not replacement for displacement".

Stroke it! so long as you make sure the crank is junk, or stroke it anyway.

I can't help with costs as I have only stroked a F@rd, and P@ntiacs are born stroked. Both are expensives motors to build, but the Tried & True 350 ought to be budget friendly.

Think about a rear gear change since you're swapping guts out. Next thing you know, you'll need wider wheels and stickier tires...It's fun spending your money.

[crazyjeenyus]

My two cents:

Its virtually impossible to know the extent of the damage without opening it up. I wouldn't consider anything short of a full tear down. Take the block to get checked for cracks in the webbing. Irregular vibrations at high rpms can cause all sorts of problems.

If the block gets an OK from a reputable shop, you've got a clean slate. At that point, if you're looking for 400hp/400tq you may as well go with a longer stroke rotating assembly. You could even get a 3.875" crank and build a 390 (std bore) or a 395 (@ 4.030" bore).

You'll likely want new heads and valve train to provide better flow. Personally I like Holley carbs, but they're are several good options out there. You may even consider an EFI system. My brother put a Holley Sniper kit on his '68 Firebird and he loves it. It's self-tuning and the car runs much better in the cold weather.

I'd have a hard time sleeping if I rebuilt a motor without having it checked for cracks first.

[truckster]

Originally Posted by crazyjeenyus

My two cents:

Its virtually impossible to know the extent of the damage without opening it up. I wouldn't consider anything short of a full tear down. Take the block to get checked for cracks in the webbing. Irregular vibrations at high rpms can cause all sorts of problems.

If the block gets an OK from a reputable shop, you've got a clean slate. At that point, if you're looking for 400hp/400tq you may as well go with a longer stroke rotating assembly. You could even get a 3.875" crank and build a 390 (std bore) or a 395 (@ 4.030" bore).

You'll likely want new heads and valve train to provide better flow. Personally I like Holley carbs, but they're are several good options out there. You may even consider an EFI system. My brother put a Holley Sniper kit on his '68 Firebird and he loves it. It's self-tuning and the car runs much better in the cold weather.

I'd have a hard time sleeping if I rebuilt a motor without having it checked for cracks first.

I agree in principle, but if you're going that far, I'd consider an L31 crate. The roller cam and Vortec heads will make a huge difference in how it makes power.

[57taskforce]

Makes me kinda wonder if the thrust bearing isn’t out of it. I guess it’s possible to be cracked and flexing but I would expect it would only flex once or twice before it broke all the way thru and the balancer wouldnt be turning if it even ran at all. Thrust bearings seem a lot more likely in my mind. They can and will make all kinds of noise with the crank walking back and forth. I guess that internet diagnoses also depends on the direction of the play, if it’s in and out thrust bearing is my bet, up and down... not as likely to be the thrust...

[crazyjeenyus]

Originally Posted by truckster

I agree in principle, but if you're going that far, I'd consider an L31 crate. The roller cam and Vortec heads will make a huge difference in how it makes power.

L31 is a far cry from 400/400. Getting the block machined, purchasing a good rotating assembly and some decent heads shouldn't put you much higher than L31 would cost. And this way you'll end up with a lot more than 250hp.

Going custom allows you to choose all your engine parts. Use your desired horsepower/torque output as the basis for your design and go from there.

[truckster]

The L31 with a HT 383 cam in it will put out 330 HP and 400 ft-lbs. I didn't read the part where he said he wanted 400/400. Torque is what you want in a heavy truck anyway.

[tim_mc]

I might agree with the L31 advice, or if you have time yank it out and have a shop check it out. I went with a 4-bolt main 350 195-249hp crate motor (hp rating varies depending on the web site) but am adding a Comp Cams roller cam & lifter set with Brodix IK-180 alumimum heads. Had I took more time to investigate, I may have gone with a Vortec L31 and maybe a different cam. Or had the timing worked out, my cousin just gave my dad a later 350 with a 1-piece rear seal and provisions for a factory roller cam ('95-'99, casting 10243880), which would be a great block to build on.

[Richard2112]

Originally Posted by 57taskforce

Makes me kinda wonder if the thrust bearing isn’t out of it. I guess it’s possible to be cracked and flexing but I would expect it would only flex once or twice before it broke all the way thru and the balancer wouldnt be turning if it even ran at all. Thrust bearings seem a lot more likely in my mind. They can and will make all kinds of noise with the crank walking back and forth. I guess that internet diagnoses also depends on the direction of the play, if it’s in and out thrust bearing is my bet, up and down... not as likely to be the thrust...

This was my first thoughts. It kinda hard to imagine that a crank which is cracked all the way through, enough to allow wobble at the dampener is going to get very far without some serious problems. Thrust bearing seems more likely. Still, building a 383 is fun work if you're not pressed for the motor.

[1971 GMC SHORTY]

Best Bet Pull It And Check Crank end Play Might Need To Be Line Board Seeing Crankshaft Is Wobbling in a block< Then All The Metal Shavings And Maybe Thurst And Bearing Shavings! might Be Cheaper To buy A GM 383 3 Year 50k Miles Unless You Know a Great Machine Shop My 2 Cents

[teeteeplz]

Originally Posted by 57taskforce

Makes me kinda wonder if the thrust bearing isn’t out of it. I guess it’s possible to be cracked and flexing but I would expect it would only flex once or twice before it broke all the way thru and the balancer wouldnt be turning if it even ran at all. Thrust bearings seem a lot more likely in my mind. They can and will make all kinds of noise with the crank walking back and forth. I guess that internet diagnoses also depends on the direction of the play, if it’s in and out thrust bearing is my bet, up and down... not as likely to be the thrust...

it definitely is easily movable up and down sadly

[teeteeplz]

any suggestions for a crate motor? https://blueprintengines.com/product...ock-bp38318ct1 4,550$ after rebate+tax. vs https://blueprintengines.com/product...or-bp38318ctc1 5300$ +tax

I like that these are new cast blocks vs "seasoned" blocks. is this an important factor?

I am tempted to find a motor with a forged crank after this one took such an early crap out on me. I imagine supplemental modifications would need to be made to the TH350 to make it survive awhile.

https://blueprintengines.com/product...etor-bp3961ctc 5,500$+tax

The 396 is more power than I currently am planning for, but its so close in price to the fully dressed 383, I dont want to kick myself in the pants later wishing i would have done this project differently.

I dont have any intentions of drag racing with the truck, just want tire smoking adrenaline goosebumps and the classic lopey idle.

also, project cost creep is definitely going to be difficult to manage on this, but hey when things are done right, and properly taken care of, they tend to last a long time. thanks everyone for their insight.

[57taskforce]

Originally Posted by teeteeplz

it definitely is easily movable up and down sadly

It’ll be interesting to see what you find.

[teeteeplz]

Well I've been saving my $ this past year, Truck is still parked in the garage waiting for a powertrain replacement. Just got off the phone today with Blueprint engines, I think I want to drop the 396ci Stroker into it, 500hp/500tq approx.

After speaking with a local engine builder, re doing my 350 into a 383, with cast and not forged parts, didnt even include roller setup vs flat tappet, and price near 5,000$ I'll be better off with a crate replacement.

The motor I'm interested in claims to be fully forged, roller setup, and a brand new block, so it hasn't been shaved down to handle the increased CI.

My questions now, are accommodating the system to be able to match the engine suggesting a stall converter rpm of 2000-2400. I could strengthen the current TH350 to handle more power, and add a transmission cooler. Or should swap to 700r4 at this time if I will be getting into the transmission anyway? Still interested in the eaton true trac system for the rear end. currently equipped with an open rear 3.08's, approx 2700rpm at 80mph. tire size currently is 265/75/r15

I would like to still be able to pull a 3-4k lb. trailer occasionally with the truck, if at all possible.

Any suggestions as for transmission coolers, transmissions, gear ratios, torque converters, rear gears etc would be greatly appreciated!

Or just general input on if I'm a fool for going this deep on a truck that could use a paint job!

[57taskforce]

A 700r4 is the last thing you want behind a 500ftlb engine. Just my .02... it won’t last long even in “built” form.

[LT7A]

When looking at crate engines I stare hard at the torque dyno sheets. I don't often spin a motor over 4000 RPM anyway, but I'm not a big burnout guy. Some of the less expensive, less built engines have a nicer torque curve where I use the power. Just my two cents, but I got to thinking about 500 horsepower in a pickup truck, even with posi. Definitely not a wet weather vehicle, and no winter driving. That said, it sure sounds fun. I think your initial 400 / 400 is a good balance of power to driveability.

[MARKDTN]

Do you really need 500HP? What do you want to do with the truck? Go fast, drag race, haul heavy, car show, spin tires? Sitting at a car show, nobody knows it that small block is a 262 or a 400. Sitting there it could have 100 HP or 500 and still look the same. If you just want a good sounding engine, you don't have to have 500HP. Anything over 350HP is a different ballgame to me.

I like a 700R4 but it won't last long at 500HP. I would go 4L80E with your new engine. But in fact, if it was me I would have some kind of fuel injection. If it was me, I would build a Vortec head 350 with Tuned Port fuel injection and a 700R4. You can get 350HP/425 ft-lb with a very streetable engine. It will tow fine, it will be less likely to overheat. Tune Port looks awesome.

Whatever you decide, enjoy your truck-it looks great.

[Davidf]

LS swap! dime a dozen 5.3L truck engine makes what 300hp (or close to it). My (not original) 350 fouls the #7 spark plug...all the excuse I needed to pull th trigger on a LS swap. Bought my neighbors '01 Tahoe for $600 (185k miles) and going through the engine now.

Good thing I decided to go through the engine as I found traces of coolant in the oil. Asked the neighbor and he said mystery coolant lose for past year. Good thing COVID caused him to work from home and rarely drove the truck since the issue began. Other than a bit of sludge (from coolant mixing with oil) the engine seems ok. Upon tear down, one of the head gaskets was leaking. Had the heads pressure checked, new stem seals, and surfaced. Should be good to go soon and then the fun starts!

But, if I was going to rebuild the 350 SBC, I would stroke it for sure.

[GASoline71]

350 hp out of a 350 is EZPZ on a fairly tight budget too.

I never though I'd see the day where an LS swap is considered easier than rebuilding a 350. But here we are...

Gary

[geezer#99]

[QUOTE=LT7A;8910825/Just my two cents, but I got to thinking about 500 horsepower in a pickup truck, even with posi. Definitely not a wet weather vehicle, and no winter driving. That said, it sure sounds fun. I think your initial 400 / 400 is a good balance of power to driveability.[/QUOTE]

Utter nonsense!
LOL!
Back in ‘78 I used my 70 chevelle ss LS6 as an only vehicle for one winter in 40 below country.
It’s all about control of that loud pedal!