Cracks in LA and Magnum heads....Have you tried running them anyway?

[Kern Dog]

Many years back, I was rebuilding a mid 70s 360 and could not find a clean set of used LA or Magnum heads in the junkyards. I pulled 14-15 heads before finding a pair that had no cracks.
My Machinist said that cracks between valve seats is common with the Magnum heads. He thought that while these cracks often don't spread, it made more sense to start with uncracked heads.
I have wondered about that several times over the years.
With all of these engines in trucks and vans out there, it seems that many of them are currently running fine with the cracked heads posing no problems.
Who has installed heads that they knew had cracks ? I've never heard of people replacing heads due to these cracks, I've never heard of failures except blown head gaskets like these:

In the case of the blowouts above, the heads were fine.

 

[PRH]

The few sets of used magnum heads I’ve seen not only had cracks between the seats, but also had noticeable exhaust valve seat recession.

I can kinda see doing a head gasket replacement with the engine in the vehicle(without servicing the heads), just don’t look the heads over too carefully…….. cross your fingers and hope for the best.

Many shops don’t want to get involved with reconditioning heads that are cracked.

 

[CFD244]

I sold a set of X heads to a guy who had them magnafluxed. They found a couple of cracks near the spark plug holes. I gave him back his $$ and told him to pitch them....Not sure if he did, or used them anyway.

 

[Kern Dog]

Thanks.
I wasn't aiming to do hack work, I just wondered what the risks are since I rarely hear that these engines fail.

 

[PRH]

20 or so years ago, one of the dirt track classes around here used Dart Iron Eagle SBC heads.
After a season or two most of them would develop cracks between the seats in at least one chamber.
Initially we were pressure testing them, and if they didn’t leak they got reused.
Eventually we stopped bothering to pressure test them, since none had ever leaked.

 

[RustyRatRod]

If the crack extends into the valve seats, I wouldn't run them. Heat finds those cracks and burns valves.

 

[PRH]

As I said, you may find its a challenge to get someone to work on cracked heads…….. even if that work is to install seats.

 

[Kern Dog]

That makes sense since it could be a waste of time when the cracks get even worse.

 

[PRH]

The ones I’ve seen, the cracks seemed to originate at the seats, like this one(only the cracks were bigger/wider)-

 

[RustyRatRod]

As I said, you may find its a challenge to get someone to work on cracked heads…….. even if that work is to install seats.

Yup, because you still have cracked heads. lol

 

[RustyRatRod]

The ones I’ve seen, the cracks seemed to originate at the seats, like this one(only the cracks were bigger/wider)-

View attachment 1716486348

That's just how the head on my 351M cracked and it burned the exhaust valve right at the crack.

 

[PRH]

Yup, because you still have cracked heads. lol

The only way I’d work on something like that is cash(full payment) up front…….. and an understanding of zero warranty.

The cracks in the Dart heads from the dirt track motors were usually waaay bigger than the above pics.

 

[junkyardhero]

the common party line is that if they're not pushing water is that they're okay to run. however, as PRH noted the seats are usually beat into the heads as well-- common with a work truck-- so now you've got cracked heads, that even though they're fine to run have less than ideal sealing. so you're gonna give up something there.

a lot of machinists won't touch the seats for a clean up cut due to them being recessed and the cracking so that leaves you in the position of running them as is with as much hand lapping as you're patient to endure or attempting the fools errand of hunting down a non cracked set.

good news to that bad news is that reman heads are only about 6~700 which in the grand scheme of things isn't the worst thing in the world.

so if it's a rattle bomb rebuild? clean 'em up as best as possible and ship 'em.

 

[PRH]

Be interesting to section one of those cracked magnum heads right thru where it’s cracked…….. see just how far away the water is.

 

[PRH]

I’m sure there are tons of success stories of people running the Chinese replacement magnums ootb……… but I wouldn’t risk that myself.
The main fear being having some stuck valves in short order.

I suppose some guide honing might suffice, but I’d be much more comfortable with some bronze liners, but then the seats need to get recut………and by then you’re well beyond a set of $700 bolt on heads.

 

[273]

Be interesting to section one of those cracked magnum heads right thru where it’s cracked…….. see just how far away the water is.

Here's a magnum head cut apart, don't know if you can tell by the way he cut it.

 

[Kern Dog]

 

[PRH]

I was thinking more like right across the wall between the int/ex bowls……… basically right next to the crack.

It would be interesting……… but not interesting enough to actually do it myself.

Especially since I’m not really looking to increase my cracked iron head repair capabilities.

 

[PRH]

Back to the original question…

Have you tried running them anyway?​

I’d say………. There’s likely a 90%+ chance that any high mileage magnum running the roads with its original heads……… is running with at least one crack in one chamber.
So, yes……. They’re running them anyway

 

[Kern Dog]

It was 2008 when I built that 360. The original '596 heads had cracks, just one in each head. My machinist advised me to look for another pair. I pulled two sets from Magnum engines and 5 sets from LA engines before I found a pair that were not cracked.

 

[PRH]

And now they’ve got 17 years more wear and tear on them.

 

[Kern Dog]

You mean that they aren't self healing ?

 

[Hellrats]

My 5.9 in my Dakota has cracked heads. Been like that for 2 years and about 5000 miles. Runs fine. Put and camshaft in it and new gaskets. Work truck so it gets abused.

 

[RustyRatRod]

You mean that they aren't self healing ?

Oh darn. lol

 

[Kern Dog]

The Roadkill guys SWEAR by that”K-Seal” stuff.