Logo
FULL SITE MENU

Broken crank on M360

D

dodgetkboy78

New member
"Last week, out of the blue, t

"Last week, out of the blue, the crankshaft broke, at the #8 rod journal, on my M360. Nothing out of the normal, 2600rpm, 1/3 throttle, just happened. Anyone seen this one before? The 360 replaced a 318, and I am not sure if they replaced the 318 flywheel with the external balanced 360 one, I have seen it done in a car, and it didn't vibrate that bad......

Anyway.

IF I just cant put a new crank in the 360, what would it take to marinize a 318. Mostly, this motor is RH. How do they deal with the oil pump, ect? Is there a gear set up to spin the cam the same way?

I have been building, working, driving, and modding SB chryslers since before I had my drivers lic, but the opposite spinning motor is new to me.

Also, if I do go the 318 route, the 360 pan wont work. What is the reason for the cast pan? Could I use a rear sump truck pan? (steel) Are they cast aluminum for rust issues? Or something else."
 
"Big difference between the tw

"Big difference between the two cranks: 318 is internally balanced, the 360 externally.

Why did it break? Most likely an inclusion in the casting, a flaw that showed up after years of stress cycles. It happens.

No way would I use that block again without having it line bored, and maybe not even then. Better line up a rebuilt long block--cost you less in the end, and they are cheaper than SB Chevies!

Jeff"
 
"I meant build a 318 for it. I

"I meant build a 318 for it. I have tons of steel crank 318 and 340 stuff. 360 has longer stroke, bigger bearings, ect.

Further investigation, the crank broke right at the back of the motor, all the main bearings are still holding the crank in place, I bet someone dropped the damn thing."
 
"Could be. A 340 would be nice

"Could be. A 340 would be nice, especially if it had good breathing heads.

Jeff"
 
"Hey Bobby - marinizing a 318

"Hey Bobby - marinizing a 318 or 340 is easy.....especially where a lot of the parts from your 360 will bolt right up. The cranks in 68-72 340's (and some 318’s marines from the same timeframe) were forged....so, if you’ve got one of those cranks, wouldn't have to worry about snapping one again.

As much of a wrench-turning junky as I am, unless you have a motor built and ready to go, I have to agree with Jeff about the long-block. When talking about a quality rebuild (as opposed to yanking a 178,000 mile 318 out of a Cordoba, for example), even when you can do most of the work yourself, the cost savings over a long-block is negligible at best. And if there are cost savings, they can often be canceled out by the fact that long-block comes with a warrantee.

That said, if you have the ability to drop in/pull out the engine pretty easily, you could get another 360 crank from a junkyard and see if you got lucky with the rest of the motor."
 
"If I replace the crank, I wil

"If I replace the crank, I will buy an eagle forged crank, and re-balance the rotating assembly. I have a sweet running 318, I built, oh, 12-14 years ago for a customer, and got it back, less than a thousand miles on it, still runs like a top, I may put it in. It was a 68 truck motor, steel crank, forged piston, balanced motor. Performance pistons do not have an offset pin either, so I really dont have to take the block apart. I have everything I need to rebuild, replace, measure, blueprint, time, degree a SB chrysler, so I will do it myself, and I don't trust the non chrysler guru's with my stuff either, look where it got this last motor!

still wondering, the purpose of the cast pan, and what do they do about the cam spinning backwards, as far as the distributer drive gear, oil pump, ect. Or is there a gear drive with a set of idlers in this motor?"
 
".."still wondering, the p

".."still wondering, the purpose of the cast pan?"

Corrosion resistance. I've seen sheet steel pans with holes rusted right through them.

..." and what do they do about the cam spinning backwards, as far as the distributer drive gear, oil pump, ect. Or is there a gear drive with a set of idlers in this motor?"

The gears on the camshaft are ground backwards, which turns the distributor and oil pump the 'normal' direction. A special distributor thrust housing keeps the oil pump gear from rising in the block (since the thrust on it is assbackwards).

Jeff"
 
"OK, from a sesame street pers

"OK, from a sesame street perspective like mine, the counter rotating motor is a mirror image of the other?

Looking at the firing order , aside from the 1 wire on my 318's, reverse water pumps, and some other things here, it looks like a mirror image."
 
"The main bearing oil seal sys

"The main bearing oil seal system is different somehow--I'm working on it!--along with the pistons being installed backwards (notch to the rear). The circulating pumps are the same.

Interesting, eh!

Jeff

PS: If you wanna get a real headache, check out how those morons at Chris Craft butchered S B Chevies in their boats. Not that the flywheel end does NOT attach to the tranny!
295174.jpg
"
 
""If I replace the crank,

""If I replace the crank, I will buy an eagle forged crank, and re-balance the rotating assembly."

Strictly option but…..unless the 360 has very low hours and/or you’re modding it, an Eagle forged would be good money after bad. The purchase price of the crank is more than the engine will be worth with it installed. The factory cast crank can easily handle the hp/tq/rpm’s that the marine 360 puts out. As you suggested, yours was probably dropped or poorly installed by a previous re-builder…….as opposed to failing because of load, etc.

Given the reverse rotation issues that you’re up against, I’d see if you can salvage the 360. Even if you have to break it down to examine it, it sounds like you’d have to do the same to your 318…..in order to convert it to RR."
 
"The 360 has less than 100 hou

"The 360 has less than 100 hours on it, since a rebuild, new pumps, risers, exchangers, ect. It was a balanced, blueprinted motor too, have the blueprints, and receipts. Ran absolutely perfect, never burned a drop of oil. Then Snappo.

More than likely I will just get a Eagle cast crank, if the block is good. So far, things are looking better, it's a bummer I have to re-ring it when I balance it."
 
"Would be nice if you could ma

"Would be nice if you could make it out of this mess with a $300 crank and some of your time.

Not sure where you are but there's a guy in NH selling a FWC marine 318 and 360 for $100 (no joke). I think both are parts motors or rebuilds but they're complete...carbs, exhaust, etc. The blocks could be good."
 
"The guy's in Derry NH. I

"The guy's in Derry NH. I think that both motors have gears on them but he said that, if the buyer was willing to do the work, he'd separate. Pick-up only deal I'm sure.

Here are pics he sent me.....

295191.jpg
318"">
295192.jpg
360
 
"Seeing it's FWCooled, goo

"Seeing it's FWCooled, good deal! Truck shipping on a pallet isn't as bad as you'd expect--especially if you pick up the motor yourself at their shipping depot.

Jeff"
 
Back
Top