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RivNut

401 vs 430 piston rings

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I've always been under the belief that 401 Nailhead and 430 big block piston rings are the same (interchangeable.) They both have the same 4.1875" diameter bore.  Tonight I watched a couple of episodes of a Hagerty Redline rebuild of a nailhead. In the episode where the host is assembling the pistons and rings, he claims that the 401 nailhead rings are unique. 

 

Can someone confirm which case is true?  

 

I also think that 425 nailhead and 455 big block pistons can use the same rings - 4.3175" diameter bore

 

I also thought that 413 Chrysler rings can be used in a 401. ??? 4.1875 diameter

 

Thanks,

Ed

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So if the bores are the same , are the higher cubes a result of longer stroke? If yes I would opine that you are correct ed

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Yes, the additional cubic inches come from a longer stroke.  The 401/425 share a 3.64" stroke and the  430/455  share a 3.90" stroke. The bore increases on a 401 to 425, and a 430 to 455 is .125" (1/8".) Maximum safe overbore for each engine is .060" (.0625" = 1/16".)

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Aside from the bore, what other differences are there between the 401 block and the 425 block?

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None that I'm aware of, except piston assemblies, in some years a cam with a different profile (but profiles changed for engines with the same cubes over the years,) and Carter carbs that have different jetting.  Nothing that really won't interchange.  When I got my 64, it had an Edlebrock carb on it.  I got a good deal on a rebuilt Carter AFB for a '64 401 and have been running it ever since.  I have no idea what difference I might notice if it was running a correct 425 carb. Of course the casting for the block to accommodate the bigger pistons.

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What's the difference between the castings other than the bore -- which is largely a machining operation.  IOW, if you bore out a 401 block to 4.3175", do you or do you not have a 425 block?  If not, why not?

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The block castings between 401/425 are the same in many instances.  The diff. was being core shift in the blocks.  The blocks that came from casting with better centered bores had the hump in the rear designating to be bored for a 425.  IF I remember correctly the casting with the last 3 numbers being 705, I think, could be either a 401 or 425.   Normally the 401's CAN'T be bored to 425,1/8th. inch, because you end up with way to thin cylinder walls.  Same with a +.060" overbore without sonic testing 1st.   You got to sonic test BEFORE doing ANY OVER BORING.  EVEN A STOCK REBUILD. The weight of the reciprocating assembly dictates a minimum cylinder wall thickness of at least .150".  Many of the blocks didn't have this from the factory new.  I've tested a number of blocks that were only .105" thickness on one side & .300+ on the other.  Too thin a cylinder wall & the block has a tendency to "Wiggle" at the bottom causing early ring wear & longevity of the rebuild.

That's one reason I use an epoxy filler in the bottom of the block which lessens the tendency & promotes a longer lasting rebuild.

 

Cams are diff. between 401 & 425. In the early years of the 425 there was a TSB (technical service bulletin) stating that if a customer with a 425 was complaining of too rough an idle & all other parameters were OK to replace the cam with a 401 cam.

 

The diff. in carbs. are things that cannot be normally changed like idle air bleeds, etc.   Not just jetting & metering rods.  IF you look in the chassis manual & look at the carb. section with the specs. you can clearly see the differences. I think there are about half a dozen of them.

 

Tom T.

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Tom (Telriv)

Can you confirm the crossover between the 401 and 430 rings?

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21 minutes ago, telriv said:

The block castings between 401/425 are the same in many instances.  The diff. was being core shift in the blocks.  The blocks that came from casting with better centered bores had the hump in the rear designating to be bored for a 425.  IF I remember correctly the casting with the last 3 numbers being 705, I think, could be either a 401 or 425.   Normally the 401's CAN'T be bored to 425,1/8th. inch, because you end up with way to thin cylinder walls.

That's the thing: if the castings are the same, the cylinder spacing in the blocks is the same, and the spacing between all adjacent cylinders is equidistant, then it makes no sense that walls would be of a different thickness.  Now, if there's inconsistent casting or sloppy (off-center) machining when boring out the cylinders, then the wall between 2 and 4 could well be thicker than the wall between 4 and 6 -- but if that's an issue that would apply irrespective of the bore diameter.  More to the point, if a 401 block can't be bored out to 425 specs,  then it never could have been a 425 to begin with.  The only way that could be is if the blocks are different or there's such inconsistent casting/machining that they can't hold tolerances and they need to cherry-pick 425 blocks.  If the latter is the case, then the 425 is problematic from the get-go, because that means that all of these supposedly identical blocks need to be individually inspected to see which ones can be bored out to 4.3125, which are limited to 4.1875,  and (inevitably) which ones must be scrapped because they're out of spec for either.  Maybe that's the best they could do then, but that sounds like an incredibly wasteful and time-consuming process.

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Tim,

All nailheads - 264, 322, 364, 401, and 425 share the same external dimensions.  I imagine that the water jackets in the smaller engines have more room between the cylinder walls.  They all share the same bore spacing but there's no way you're going to put a 425 piston in a 264.  

 Chevy stretched their 265 small block to 400 cubic inches but the had to siamese some cylinder walls to do it.  When a casting is bored, a cylinder wall thickness is determined.  I think that is done to ensure that the cylinder walls are not so thick that the pistons can't be cooled. 

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Chip,

 

   Do as many rebuilds as I have & you will become more familiar with the capabilities of the blocks.  Yes there have been 401's bored .125" over, BUT mostly/normally didn't last very long because the bottom of the block had so much give too it.   IF you had a block solidly mounted & used precise measuring tools you could measure how much the bottom of the block moves with just hand pressure. Think of how much more stress is going on with ALL the reciprocating parts in motion.

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I get all that, but this is the essential question: Suppose that in 1964 there's a freshly cast nailhead block in the factory.  How is it decided that it will be a 401 or a 425?  Seems to me there are three choices:

- All the raw castings are the same; it can be whatever they want it to be.

- The 401 casting and the 425 casting are different; the 401 block cannot be bored out to be a 425.

- It's supposed to be one casting for either engine, but there's so much variation in the castings that only some of them are suitable for the larger bore of the 425.  This means the blocks must be individually inspected and sorted.

 

Am I missing something here?  If I'm not, what's the answer?

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The raw castings are not the same. Different sand casts for each different bore size. If you're thinking that a 401 block is the same casting as a 425 block and you can bore a 425 block 0.060" over, then theoretically if they are both the same casting, you could bore the 401 the 0.125" to bring it out to 425, THEN go another 0.060" over like you can on a 425 to bring close to 440 cubic inches..  That would be a total over bore of 0.185 or roughly 3/16". Now your measuring in fractions rather than thousandths. Ain't gonna happen. 

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So, I have seen this Youtube clip before but because of this discussion watched it again with many replays:

https://www.hagerty.com/articles-videos/articles/2019/07/24/watch-this-buick-nailhead-go-from-rusty-mess-to-a-v-8-blessed

Entertaining but even the write-up doesn't come near to the details we encounter on our nailheads.

  1. They re-used the timing cover as the donor engine didn't come with one. This surprises me as the engine was badly corroded. At least 1 bolt needed torching to get the timing cover off.
  2. No mention of using a roller timing chain
  3. Used an Edelbrock AFB Clone Carb (what size?). Must have used an adapter to mount the original aircleaner.
  4. No Exhaust manifold gaskets installed as it should be. But, what is that copper coloured goop?
  5. No Exhaust valve inserts as it should be according to Centerville Auto Repair's 15 mistakes. There is discussion on this on the Hagerty site and they say the inserts would actually fall out. Before kids came along when my Riviera went into a 25 year sleep, I had my heads re-done with SS exhaust seat inserts. Oh no! When my Riviera is ready to run (and it did before I took it apart). I'll do a compression test.
  6. They cut off the torque converter. Hopefully it wasn't trashed. Switch-pitch torque converters are becoming scarce!
  7. They fitted the main bearings. Then re-fitted with studs in-place of bolts and upper main bearing shells with red?

Hmm, I'm learning more but perplexed on why all this trouble without a Buick car in mind?

 

John B.

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9 hours ago, telriv said:

The block castings between 401/425 are the same in many instances.  … IF I remember correctly the casting with the last 3 numbers being 705, I think, could be either a 401 or 425.

 

4 hours ago, RivNut said:

The raw castings are not the same.

 

You can't both be right. 😛

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On 3/7/2020 at 10:09 PM, XframeFX said:

Entertaining but even the write-up doesn't come near to the details we encounter on our nailheads.

 

I just watched the video. Constant has been guitar and percussion in videos is making me weary. I turned the sound on when the guy running around the machine shop in a t shirt and shorts appeared to be talking, but it really wasn't worth the click. Seven sleeves? They should have spent the time used to make the dancing wrenches to find a better core, maybe a big job for a movie production assistant.

 

Twenty-five years ago you probably had stellite valve seats installed. There shouldn't be a worry. An overheated Jaguar aluminum head might drop a valve seat. The script writer's uncle may have experienced that. And now the holiday tale is part of his automotive repertoire.

 

If I went to an engine shop and found four or more guys working on one engine and a half dressed boss making odd facial gestures the two guys in the corner with the drums and guitar would give me a drum roll and I'd be gone.

 

Bernie

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Parts that were used is the norm.  Because of them if the compression is 8-1 they would be lucky not to mention the quench/squish area way out of bonds with pistons in the hole at .060" in the hole +or-.

No wonder MANY call me with the question, 'I just rebuilt my original engine & it has less power than the worn out engine I took out.

I've said it MANY times,  " it's all in the details, when you figured you have covered them all, go back I'm willing the bet you missed a few".

For the most part it's engine rebuild 101,  they ALL have there own idiosyncrasy's BUT just like anything else it takes time & time is $$$$$

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Some years back I had a conversation with Carmen Fasso (I think) and asked if a 401 could be bored to 425.  His response was 63-64 used different castings for the two motors, but 65 could be bored.  It makes no sense that. GM would have used different castings, except they did those kinds of things.

 

For what its worth.  

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23 hours ago, telriv said:

I've said it MANY times,  " it's all in the details, when you figured you have covered them all, go back I'm willing the bet you missed a few".

 

There was a period in time when I thought farming out some work to "professionals" would be a good idea. When I thought it was appropriate I would drop off the car, parts if required, and the shop manual. Most often the manual was lying in the same spot on the counter and the details overlooked. The first disappointment was in 1972 and , hopefully, the last time was 2013. I am a slow learner.

I have lost confidence in anything but the book and me. I will take the money I was going to pay some Gemoke (as my Dad called them) and buy tools and books.

 

Remembering those old blowhards make me smile. I once heard a recommendation for a transmission mechanic (probably in a bar) "He can tear such and such automatic transmission apart, throw all the parts in a corner, and come back six months later and put it together". Today I would have no interest in a guy who might throw all my parts for anything in a corner for even a day.

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20 minutes ago, 60FlatTop said:

I have lost confidence in anything but the book and me. I will take the money I was going to pay some Gemoke (as my Dad called them) and buy tools and books.

Concur.  Take the money you were going to drop on labor costs and buy tools.  You'll end up money ahead, potentially with a quicker conclusion, and quite likely superior results.  And some new tools.

 

If you look at a job like rebuilding an engine, there are two kinds of work: that you probably can't do yourself, and that you can.  The former is stuff like reboring cylinders, truing heads, etc.  It doesn't make sense to buy the expensive machinery needed for those jobs, so farm them out.  (Dirty little secret: most "engine rebuilders" farm that work out as well.)   The rest of the project requires little more than hand tools, plastigage, a torque wrench, and attention to detail (which is pretty much all there in the manual).

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3 hours ago, KongaMan said:

Concur.  Take the money you were going to drop on labor costs and buy tools.  You'll end up money ahead, potentially with a quicker conclusion, and quite likely superior results.  And some new tools.

 

If you look at a job like rebuilding an engine, there are two kinds of work: that you probably can't do yourself, and that you can.  The former is stuff like reboring cylinders, truing heads, etc.  It doesn't make sense to buy the expensive machinery needed for those jobs, so farm them out.  (Dirty little secret: most "engine rebuilders" farm that work out as well.)   The rest of the project requires little more than hand tools, plastigage, a torque wrench, and attention to detail (which is pretty much all there in the manual).

I just found the machine shop that the rebuilders use.  Saves money and you have a direct line of communication. You can say "no hardened seats", get a confirmation and not worry about the instructions being passed on.

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There is enough nickle in the iron that a nailhead shouldn't need hardened seats installed.  Its something Chevy engine rebuilders do therefore they think every engine needs the same. 

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Correct, I learned about the high nickel content when I got back into the project a few years ago. Another regret, it was all about unleaded fuel back then. " I wish I knew then what I know now".

I looked up the receipt, March 1993 - 27 years ago! Among the items in the BOM is "8 each SB1562 Exhaust Seat Inserts".

Small valves and the seats are not stellite!

Googled it:

SB1562-1
High-Chrome Premium Grade Material with 1-9/16"
(1.562 Nominal O.D.)

SB1562-1N
Same as SB1562-1 except Star Series material.

SB1562-1PM
Same as SB1562-1 except Powdered Metal Material

 

 

 

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On 3/10/2020 at 6:39 PM, RivNut said:

You can say "no hardened seats", get a confirmation and not worry about the instructions being passed on.

 

...or ignored entirely.  :unsure:

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