So a few months back I had read an article here regarding mopar crankshafts being out of spec causing random misfires & pings because of increased or decreased pressures in a cylinder.

"Most OEM crankshafts are out of stroke spec, some by as much as 0.025 to 0.050 ! That means you'll be down on cubes in one or all cylinders. Indexing the crank is a time-honored way of ensuring you engine makes all the cubic inches advertised. Additionally, the as-delivered factory cranks seldom place the rod journals at 90-degree intervals, so timing the ignition and cam is off. " ------------------ (end quote)


The website goes on to say this was intriguing but also quite possibly hype to bring business to shop who made those comments and promote crank indexing sales.

Well anyway I'm in the middle of rebuilding my sisters 2000 Ram 360 at the moment, it had spun a main bearing after her husband told her the oil level was fine and she did some donuts in her yard last winter trying to get out of the snowy ditch (it was 2 quarts low for the record, I checked it after it was spun...yes oil starvation caused).

So now her engine is at the machine shop and in light of reading that article about 2-3 months ago I decided to have the shop check the stroke of the crank and guess what? every single one of the crank journals measured out to 3.58 stroke, and the machinist also went on to state that every mopar crank as far back as he can remember in his 25 years of machining were in spec unless an issue such as rod bearing failure caused crank distortion or some sort of destruction or previous machine work as been performed. He also said if a Magnum engine has a chronic ping that cannot be solved by conventional methods then he would look at getting a new set of heads because that is as he stated "9 times out of 10 the reason for chronic pinging in a magnum motor" if plenum gasket was replaced and full tune up has been performed. Cracked heads sounded more reasonable to him for what that myth was trying to state.

So with that said he grounded the mains .20 to clean up the surfaces and the rod journals .10 as standard procedure and also did a full race balance on the rotating assembly for $130. Quite pleased with the results, I also had the block baked & boiled and checked for cracks and the bores light honed, thing looks absolutely beautiful!.

Anyway one mopar motor out of the millions made and one machine shops veteran testimonials certainly isn't a big enough sample to say the myth of the uneven stroked cranks is true or untrue but I also think if your magnum motor is misfiring after all reasonable options have been exercised, your heads may be cracked and they should be checked out!.

This should make people who've read that article feel a little better about their pinging problem worries being contributed by un even cranks lol.

 

You mean our cranks aren't made by drunk UP ice fishermen with die grinders in their home garages?

 

That article is just trying to sell. Like you already suspected.

 

Haha That visual is great!. You'd think after 140+ years of using piston & crank technology on steam and internal combustion engines we as humans would at least get equal stroke right between cylinders

Honestly that sounded so rediculous to me, but I just had to share some first hand machine shop proof that our cranks should be fine ;-) Its the crack prone heads we gotta worry about. Speaking of wasn't that just for a few years of Rams the cracked heads?

 

The prone to cracking heads is for any magnum engine. So 94-01 and a couple years after but that's when they started phasing them out.

These engines are too well know for being workhorses to have a major problem with bad cranks.

 

Magnum 5.2 - '92-'03
Magnum 5.9 - '93-'03