350 Mag broke a rod.

[Elmerfudd]

My checkmate blew up a week or so ago, and I'm having the engine rebuilt, I don't wanna slap it all back together just to have it happen again. Any ideas on what I should be checking before I stick it back in? It happened while I was heading down the lake at about 30mph/3000RPMs. That's about all I can tell ya for conditions.

Thanks for any help.

Corey

 

[winter]

There are far too many things that can cause an engine failure to be able to tell you what hapened, but a broken rod in a 350 mag is harsh. Those motors are generally very tough. Lack of proper oiling in and around that rod is perhaps the most possible reason. If the engine is getting rebuilt, a reputable builder will spec out any original parts to make sure they are sound before reuse, and that includes the block and heads. It will also be hot tanked to clean out all the water and oil ports/galleys. There are countless other things a good builder should do, but try to make sure you give him leeway and extra $$$ to do a proper job, not just a 'patch-up'.

 

[Elmerfudd]

Thanks for the advice, I've brought it to a famous engine builder in my area, he's the leading builder for all stock car engines and marine engines around here, he's expensive but assures me a HP gain in return.

 

[Big Red]

How do you know you broke a rod. At 3000 rpms under load of a boat I would say the hole block is trash. Last time I broke a rod it came out the oil pan for a clean get away.

Like Winter breaking a rod is harsh

 

[Old Navy]

"Clean get away" HeHe......

Mag the block and any other parts you want to reuse. "broken" rods usually leave a path of destruction behind, making scrap out of the bottom end. Might be cheaper to get a reman or new GM shortblock in that case.

 

[Elmerfudd]

We hauled the engine out and removed the oil pan, the rod broke in a strange place saving the block as far is we could tell. i should have taken pictures. Best I can explain it is that the rod broke right where it connects to the crank, at the thickest part of the rod, But managed to remain attached at the crank and also at the wristpin nice and high up in the cylinder. Doesn't look like much if any damage at all done to the block, but we'll have to wait and see. Thanks for the replys.

 

[ezstriper]

Hey Red, we call that terminal oil pan failure !!!! anyway on yours if the block is ok, I would buy a 383 stroker kit now, cost about the same as you are going to need to fix what you have...and those work great in boats because of the more torque...Rob

 

[Elmerfudd]

Hey Red, we call that terminal oil pan failure !!!! anyway on yours if the block is ok, I would buy a 383 stroker kit now, cost about the same as you are going to need to fix what you have...and those work great in boats because of the more torque...Rob

Yeah that sounds like a good idea, I'll have to mention that to him. Will that suffer the reliability of the engine? The engine that was in it went 19 years without a rebuild. But I would say it was gettin pretty tired.

 

[winter]

Yeah, as i started thinking about this, rod failures come in many varieties, but usually end up making quite a mess, sending bits and pieces everywhere, until the motor actually comes to s stop. A boat will simply shut down. a manual trannny car doing 80mph will likely keep spinning the mill till the car comes to a stop or the clutch is depressed

Maybe someone else can chime in, but in some cases a chevy crate motor or some remans can end up being a more economical choice, depending on how many parts in your old engine were damaged. I'll be pulling my 350mag this winter for a major upgrade to 425hp. I looked into crate engines, but in my case, with a perfectly running motor (at least now), it's better to rebuild. Let us know how it goes!

 

[wca_tim]

I'm very happy with the 383 I had built for my boat. Haven't had it in for long enough to say much about longevity, but I do remember the engine builder making it clear that for a 383 marine engine to last you need to go with all forged lower end, that you can't get away with the cheaper cast cranks like you can in a street car...

 

[Big Red]

Hey Red, we call that terminal oil pan failure !!!!

That hole engine is trashed. It got everything, it even trashed the left valve cover I guess where it slammed the piston into a open valve and it crammed the rocker and push rod into the valve cover. My weakest link was the rod bolts and thats what gave away.

Cheapest marine engines I have found.

http://www.affordablemarine.com/gm.htm

==

 

[ezstriper]

I think with the rpm we see in the boats the 383 would be a great choice..even merc selling then now too, 6.2 is a 383...Rob

 

[Elmerfudd]

I've mentioned the 383 option to my builder, he said he's so busy he hasn't had a chance to tear it down yet. But he'll lay out my options depending on how everything looks.

 

[Big Red]

Glad to see your engine builder is busy everybody around here is sitting around with their thumb up their ??? because of the economy

 

[ezstriper]

around here to red.....

 

[yellowfiero88]

My builder is busy here in cincy. He is about 2-3 weeks behind right now.

As for the stroker, I was considering it for my enchanter but after considering that a short crank motor is a better option for high RPM i decided against it. The way I look at it, I like to go fast and for a motor turning 4500+ for extended periods of time a long stroke would just not hold up like a shorter stroke. I think a high HP,high reving 327 with a supercharger would be a wicked motor in a boat.

As for my motor, I went with a 4 bolt 350, +.030, 9.0:1 compression, Comp extreme cam, port matched and polished heads, full roller 1.6 rockers for starters. Down the road, depending on how it runs, I am going to upgrade to large 2.08" aftermarket heads.

 

[Wide Open]

The 6.2 is a 377CID engine. It's not stroked as far as a 383. They do work well though. I'd like to see merc build a 383 and set it up to turn out about 340-350 h.p.! That would make a perfect "gap filler" in the horsepower range that they currently have. With the 350MAG at 300h.p. and the 6.2 at 320h.p., there's hardly a noticeable difference in performance. But look at the price increase for the 6.2 and you'll see why they don't see very many.

 

[yellowfiero88]

The 6.2 is a 377CID engine. It's not stroked as far as a 383. They do work well though. I'd like to see merc build a 383 and set it up to turn out about 340-350 h.p.! That would make a perfect "gap filler" in the horsepower range that they currently have. With the 350MAG at 300h.p. and the 6.2 at 320h.p., there's hardly a noticeable difference in performance. But look at the price increase for the 6.2 and you'll see why they don't see very many.

The difference is not in the stroke (well when your talking CID) but the bore.
377 = 350 w/400 crank stock bore
383 = 350 w/400 crank + .030 bore
388 = 350 w/400 crank + .060 bore

Its pretty easy to reach the 400HP mark with a 350. Bump the compression a little and make it breath and your most of the way there. Or buy this http://store.summitracing.com/partdetail.asp?part=EDL-2098&autoview=sku . Dont know about aluminum heads, if I like them or not but 410hp/408tq on a 350 done with a case of brews on a friday night:cheers

 

[wca_tim]

the shop that built my 383 is well known in the area for offshore and circle track engines. He told me I could run it at 5200 - 5500 rpms without worrying about it coming apart, but that if I was going to run it hard, I needed to put a good sized oil cooler in it. The rotating assembly and valve train would take quite a bit more, but we focused on usable power that would last...

It's probably making something over 400 horsepower and 425+ ft pounds of torque as sits. that's ca. 9.5: cr, wp 200 cc, 2.02 heads, comp cams xtreme cam, scat forged rotating assembly, torker2 intake and imco powerflows. great manners and pulls like a train from idle to 5000+ rpms depending on prop.

I'm very happy with the choice.

 

[winter]

the shop that built my 383 is well known in the area for offshore and circle track engines. He told me I could run it at 5200 - 5500 rpms without worrying about it coming apart, but that if I was going to run it hard, I needed to put a good sized oil cooler in it. The rotating assembly and valve train would take quite a bit more, but we focused on usable power that would last...

It's probably making something over 400 horsepower and 425+ ft pounds of torque as sits. that's ca. 9.5: cr, wp 200 cc, 2.02 heads, comp cams xtreme cam, scat forged rotating assembly, torker2 intake and imco powerflows. great manners and pulls like a train from idle to 5000+ rpms depending on prop.

I'm very happy with the choice.

What speeds are you seeing? I'm contemplating the same move in my Persuader. My builder also memtioned an easy 400hp with some internal guts and proper heads. He noted the bulk of the power will be found in the heads, we'll see!