401 is FU#^ED

[theredneckwiththe401cherokeeS]

previous owner boogered my bores up
i will have to get it bored and buy new pistons
how far can i bore this 401 block,safely?

[trickc]

I believe max is .020 over, otherwise cyl walls get too thin and have overheating problems.

P.s. sorry to hear about your 401. If I remember correctly oversize pistons for these can be pricey also.

[ August 29, 2003, 09:53 AM: Message edited by: trickc ]

[theredneckwiththe401cherokeeS]

the guy i buy pistons from, sell 30,40,and 60 over pistons for this motor. im not sure how a 20 overbore can cause overheating, elaborate please

[Gwamp]

You can also get the cylinders sleeved if you want. The 401 does not liked to be bored out more than .20 or so. The walls of the cylinders get too thin.

[LRRH]

many have tried it and many have overheated. the reasons he lists the pistons is because it's the same block as the 360. there are a few who have had success going 030 over.

[Elliott]

"They" say that 401s bored are more suseptible to overheating. Given that 401s and 360s are suseptible to overheating by the fact they are AMC engines alone should always inspire you to maintain or build an exception cooling system in the first place. Every AMC I've owned, 401, 360, bored or not had a tendancy to spike unless I modified the cooling system.
That said, going 60 over may be really pushing it, but I've never gone there. You can also have the cylinders sleeved to standard. I don't think I'd worry about up to 40 over, with adequate cooling mods.
I don't know what the factual basis is for saying that 401s are more prone to overheating, have to assume "they" would cite cylinder wall thickness being marginal, but don't know that is actually a fact.
Not real up on the physics of heat transfer, but I do know (from what I've been told by an AMC racer/machinist) that the 401 has the highest nickle content of any block made (which is why moly rings don't seat well). Maybe that high nickle content actually retains a higher proportion of heat then other motors?????

Who's got the facts?

[Hump]

"They" would be old SnakeEyesTX. He bored his 401 .060 over, added a four core radiator, pusher and puller fans, lower thermostat, and everything else in the book. His engine ruined itself in a hurry.

The AMC car guys do the big overbores, but they are only running 1/4 before shutting it down.

[Elliott]

Don't aluminum manifolds also block off two coolant ports, because the manifold does not use them... and could disrupt total flow?

It is not the same block as the 360, it's a separate casting and uses higher nickle content. The dimensions for the cylinders may be the same as the 360 in the 401 casting however. If the dimensions were the same and then AMC just bored them up to 401... well then, that would explain why going past 20 over would cause problems.

Who has actual standard specs on what the 401 cylinder wall thickness is compared to a 360?

[ August 29, 2003, 10:32 AM: Message edited by: Elliott ]

[Midnightwagon]

well sleeve all 8 holes or try and find a better shape core to work with.

[Glenn_tx]

Originally posted by Hump:
"They" would be old SnakeEyesTX. He bored his 401 .060 over, added a four core radiator, pusher and puller fans, lower thermostat, and everything else in the book. His engine ruined itself in a hurry.

The AMC car guys do the big overbores, but they are only running 1/4 before shutting it down.Hmm. I have that very motor sitting in my backyard. Anybody want it?

[jeepsr4ever]

ive seen 304's and 360's bored .090 over, it really depends on the block, 401 ive had 1 at .060 and 2 at .030 never overheated even with 10-1's aluminum intakes do not block the water ports unless they are hard core drag racing intakes, most people just get the block bored but forget that the deck is very important as well, so they get a crappy head seal and blow a head gasket, the engine overheats and they blame the bore. Its not always the bore! you can go up to .120 over and get it xrayed for a bad boy stroker 700hp and up, i wouldnt hesitate to bore it .030........good luck

[theredneckwiththe401cherokeeS]

i talked to a guy in cocoa fla. been building these motors since the 60s says some of these 401's are succeptible to "core shift" whatever the hell that means. im taking it to be bored, i hope 30 over does it, if it dont, ill sleeve it
if this Great Googley MoogleyGreat Googley MoogleyGreat Googley MoogleyGreat Googley MoogleyGreat Googley Moogley dont obliterate the tires when i get done with it. napa just told me $75 each bore to sleeve, that sucks.

[flatbackdragon]

an article in June 98 HotRod discusses that a little along with oiling problem. can email you the article if you wish

[Chero77]

I ran my 401 bored .060 over for three years with a stock cooling system and never saw any sign of overheating even in 100 plus desert heat.

I only discovered it had been bored .060 after I took it in for a rebuild. Its now sleeved to standard bore with a slightly larger than stock cam. If anything, it runs a little hotter now than it did at .060 over. However, still well within the capacity of the stock cooling system.

By the way, the cost of sleeving all eight cylinders was only $150 additional.

[ August 29, 2003, 03:01 PM: Message edited by: Chero77 ]

[tgreese]

I've read that overboring really depends on the condition of the particular block. Some blocks have the water passages nicely centered around the bore, some don't. It's just normal production variability. The block can be tested (sonic testing? must be a sonogram) to measure the bore wall thickness and determine the suitability for overbore. Race car builders should be able to refer you to a shop that does this.

hth :cool: Tim

PS at 8 * $75 = $600 you should be able to find a better core... are 401s that dear?

[ August 29, 2003, 03:03 PM: Message edited by: tgreese ]

[BIG BAD JON]

Ouch!

[Wesdog]

Make sure whoever does the cylinder bore uses a torque plate.

[Elliott]

Originally posted by flatbackdragon:
an article in June 98 HotRod discusses that a little along with oiling problem. can email you the article if you wishThere's a few things in that article ain't zactly straight, but it's decent for a reference... it wasn't written by a machinist or an AMC expert and not all his sources jibe.

[Stuka]

The 304 has lots of sidewall, you can bore it 90 over and it still has a smaller bore then a 401 with a 60 over bore.

[tgreese]

BTW re core shift

"Core is a sand shape inserted into the mold to produce the internal features of the part such as holes or internal passages."

If it shifts, the water passages won't be centered around the cylinder.

http://www.efunda.com/processes/metal_processing/sand_casting_intro.cfm

hth :cool: Tim

[Elliott]

Originally posted by tgreese:
BTW re core shift

"Core is a sand shape inserted into the mold to produce the internal features of the part such as holes or internal passages."

If it shifts, the water passages won't be centered around the cylinder.

http://www.efunda.com/processes/metal_processing/sand_casting_intro.cfm

hth :cool: TimSo, the 401 having "thin walls" is a myth?
or not?

Problems with sand casting would effect any cast block... not just the 401.
I'm pretty sure my last one was 30 over, had no trouble with it.
Seems you could anticipate any engine having a potential for problems going more then 40 over, but I'm not an engine builder... just have a hard time believing that when they put a forged crank into a high nickle content engine and did some up with 4 bolt mains that AMC would overbore them to start with.

[tgreese]

Elliot, I don't know specifically about the 401. I was just answering theredneck...'s sort-of question "core shift" whatever the hell that means.

By the basic geometry of the block, if the cylinder centers stay the same, as the bore gets larger, the walls have to get thinner unless the water passage design is changed. Unless AMC redesigned the water passages for the 401, the cylinder walls have to be thinner than the 360 by (4.165 - 4.08) / 2 = 0.0425. A 360 block bored 80-over, but a stronger alloy.

Can't say much more than that without knowing how thick the 360 walls were to begin with.

[ August 29, 2003, 05:55 PM: Message edited by: tgreese ]

[Elliott]

From just the "success" stories above with significant overbores it sounds like the deck height issues, failure to use a torque plate when boring and casting abnormalities contribute to overheating as opposed to it simply being a thin wall issue.
Granted a thinner wall would make the casting abnormalities have a more significant contribution to over heating, but it doesn't sound like a thinner wall is the actual problem or every 401 would suffer from overboring.
I don't think I'd trouble myself with any special testing other then a routine dye penetrant for any oversizing up to 40 thou.
Would like to hear from some racers on this, I'd think the majority of them run their AMCs on the street.

[Elliott]

Originally posted by Chero77:
I ran my 401 bored .060 over for three years with a stock cooling system and never saw any sign of overheating even in 100 plus desert heat.

I only discovered it had been bored .060 after I took it in for a rebuild. Its now sleeved to standard bore with a slightly larger than stock cam. If anything, it runs a little hotter now than it did at .060 over. However, still well within the capacity of the stock cooling system.

By the way, the cost of sleeving all eight cylinders was only $150 additional.

[Elliott]

Originally posted by Chero77:
I ran my 401 bored .060 over for three years with a stock cooling system and never saw any sign of overheating even in 100 plus desert heat.

I only discovered it had been bored .060 after I took it in for a rebuild. Its now sleeved to standard bore with a slightly larger than stock cam. If anything, it runs a little hotter now than it did at .060 over. However, still well within the capacity of the stock cooling system.

By the way, the cost of sleeving all eight cylinders was only $150 additional.This is a good example of what I'm attempting get across about the 401. I will however... happily take any 401 30 over cores with rods and the factory forged cranks that anyone wishes to discard.

[NomadJack]

Dumb noobie question:
My impression is that the 360 and 401 are essentially the same size block with the bores on the 401 slightly larger and the stroke slightly longer to account for the additional 41cid. Is this correct? I've heard a few people recommend that 360's only be bored .045 over before potential cooling issues arise, so wouldn't a 401 have an even smaller range it can go before there are concerns?

[Elliott]

Originally posted by NomadJack:
Dumb noobie question:
My impression is that the 360 and 401 are essentially the same size block with the bores on the 401 slightly larger and the stroke slightly longer to account for the additional 41cid. Is this correct? I've heard a few people recommend that 360's only be bored .045 over before potential cooling issues arise, so wouldn't a 401 have an even smaller range it can go before there are concerns?Correct on the first statement.
On the second statement, it is probably slightly truer for the 401 given that it is a casting issue which could effect the 360 block just the same as the 401. IMO ;)
If you have even one guy boring a 401 60 over and running in 100+ heat with a stock cooling system for years without trouble... it is hardly a thin wall issue for the 401. Obviously there was minimal casting abnormalities in his block. If a 360 had severe casting abnomalities it could overheat and melt down with thicker walls and a std bore.
Does Chevy have the same issues with the 350 and 400?

[ August 29, 2003, 07:46 PM: Message edited by: Elliott ]

[Wesdog]

As I understand it the standard AMC 401 is a different cast than the standard AMC 360. They have the raised 306 or 401 numbers cast into the sides of the blocks. However, there are some 'service' blocks out there that are actually bored to the desired size (304, 360, 390, 401 etc.) and then stamped with the actual size. These service block 401s appear to be a different cast then those that have 401 cast on each side of the blocks.
I don't claim to be an AMC expert so this info may or may not be exactly correct.
The point of this being that those using a service block may get different results when overboring than those using a standard cast 401 block.

[ August 29, 2003, 07:50 PM: Message edited by: Wesdog ]

[Elliott]

Every 401 I've seen was of a different cast. However, possibly the early blocks (~70) were bored out service blocks? I haven't seen any early ones.

[Don S]

..
… My 401 is .030 over. It can pull a heavy trailer in a 4th of July parade with an outside temperature of 105 degrees. My engine builder only rebuilds engines and has been doing it 30 + years. He claims he can bore my 401 to .060 over and no problems.

... He rebuilt mine in late 1986 and its’ still in great shape. It leaks a little oil but doesn’t burn it. I heard all the horror stories about overheating (after the rebuild) so I made a little cooling modification but that was mainly to help prevent vapor lock…

see link>OVERHEATING & AIRFLOW 101 (http://groups.msn.com/JEEPTECH101/jeeptech.msnw)

Good luck and http://www.michiganjeepers.com/forums/images/graemlins/wave.gif and … CUL.. Don S..

[Elliott]

Thanks for the info Don.

Here is a link to some actual measurements from machinists that race: http://pub186.ezboard.com/famcforumfrm31.showMessage?topicID=321.topic

I would add that cylinder wall failure really sucks when that piston hydraulics on compression, the block can't be rebuilt. It happened to my stock, std bore 360. Some blocks are just crap, maybe AMC had a little more problem with this then other engine manufacturers..... I don't know, doubt it though.

[steven79]

No snakeyes motor did just fine when i installed it and set everything, it was snakeyes that could not stop messing with it by screwing with the timeing and putting a hi rise intake on it with a bad carb, other wise it would rum a little warm sitting in traffic, but 220 is not to hot. ;)

[Elliott]

Originally posted by Wesdog:
As I understand it the standard AMC 401 is a different cast than the standard AMC 360. They have the raised 306 or 401 numbers cast into the sides of the blocks. However, there are some 'service' blocks out there that are actually bored to the desired size (304, 360, 390, 401 etc.) and then stamped with the actual size. These service block 401s appear to be a different cast then those that have 401 cast on each side of the blocks.
I don't claim to be an AMC expert so this info may or may not be exactly correct.
The point of this being that those using a service block may get different results when overboring than those using a standard cast 401 block.Info on service blocks, and AMC history: http://home.att.net/~farna/amtech/engines.html#V-8

"The cubic inch size of all GEN-2 and GEN-3 engines is cast into each side of the block just behind the engine mount plates in the center of the engine. An exception is the 1970 thick cast 360 which was used in some Donohue Javelins to homologate the thick wall 360 block for Trans-Am racing. These were also used as service replacement engines. They are essentially a 401 casting (they have the same casting number as the 401) with a 360 bore. This block could be bored to 360 or 401 specs, hence its use as a service replacement, and why it didn't have to be used in all the 1970 Donohue Javelins. Homologation wasn't required because it was a standard service part, not a race only item."

With all the above said and after more searching, earlier posts are correct that the AMC Performance Manual apparently recommends overbores on the 401 do not exceed .0225 :eek:
As far as sonic testing for overbore I've read that a final wall thickness of .20-.25" is recommended. That's about all I can find tongue.gif
Wall thickness will be a factor where there has been significant core shifting and core shifting can be a factor where wall thickness was not (ie: the 360 blocks). ;)

[ August 30, 2003, 11:46 AM: Message edited by: Elliott ]