401 vs 430 piston rings

[RivNut]

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

[arnulfo de l.a.]

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

[RivNut]

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".)

[KongaMan]

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

[RivNut]

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.

[KongaMan]

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?

[telriv]

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.

[RivNut]

Tom (Telriv)

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

[KongaMan]

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.

[RivNut]

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. 

[telriv]

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.

[KongaMan]

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?

[RivNut]

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. 

[XframeFX]

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.

[KongaMan]

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. 😛

[60FlatTop]

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

[telriv]

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 $$$$$

[Zimm63]

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.  

[60FlatTop]

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.

[KongaMan]

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).

[RivNut]

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.

[arnulfo de l.a.]

what seats are recommended when seats are needed?

[RivNut]

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. 

[XframeFX]

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

 

 

 

[EmTee]

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. 

[Turbinator]

On 3/7/2020 at 5:04 PM, KongaMan said:

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.

Are there other ways to boost horse power of a 401 to equal the horse power of a 425 without worrying about overboring? It would seem to me other things could be considered to increase engine performance such as compression ratio of each cylinder. I do not know other things, but I would guess there are other improvements. Maybe forged pistons as opposed to cast pistons could add to performance. I’m rebuilding my engine and I’m thinking the parts that go back in the 401 should be better than what came out.

[60FlatTop]

I have had both 401's and 425's. If you are hauling around a 4,000 to 4,500 pound Riviera or Electra you are never going to notice the difference.

 

Since Tachometers have become standard in most cars I noticed I rarely exceed 3,500 to 3,800 RPM. 4,000 RPM maybe a couple times a year out at the lonely end of the Parkway.

 

I have had a couple of 401's that felt better than the 425.

 

Bernie

Edited March 23, 2020 by 60FlatTop (see edit history)

[Turbinator]

3 hours ago, 60FlatTop said:

I have had both 401's and 425's. If you are hauling around a 4,000 to 4,500 pound Riviera or Electra you are never going to notice the difference.

 

Since Tachometers have become standard in most cars I noticed I rarely exceed 3,500 to 3,800 RPM. 4,000 RPM maybe a couple times a year out at the lonely end of the Parkway.

 

I have had a couple of 401's that felt better than the 424.

 

Bernie

Bernie, I’ve heard when a 401 gets up to 5000 RPM’s things start to come apart.  I doubt I’ll ever get my 401 up to 5000 RPM’s. It seems if you rebuild a 401 there are things you can do boost performance w/o boring the cylinders too big.

Turbinator

[Turbinator]

On 3/10/2020 at 8:35 PM, RivNut said:

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. 

Ed, the builder that has my engine wanted to put hardened seats in my nailhead. I told the builder no, do not put hardened seats in. He said, ok. 

[60FlatTop]

The 445 torque comes in around 3,000 RPM. That's what you feel on your pants. Money is better spent bumping the ring and pinion a ratio or two.

 

The western extension of the expressway used to end about 7 miles from my house. As soon as I get off the truck goes out of overdrive the rest of the way home. I like it, feels like the Riviera. One of my favorite things about the old Buicks, no overdrive, always feel peppy.

[KongaMan]

3 hours ago, Turbinator said:

Are there other ways to boost horse power of a 401 to equal the horse power of a 425 without worrying about overboring? It would seem to me other things could be considered to increase engine performance such as compression ratio of each cylinder. I do not know other things, but I would guess there are other improvements. Maybe forged pistons as opposed to cast pistons could add to performance. I’m rebuilding my engine and I’m thinking the parts that go back in the 401 should be better than what came out.

The question about boring out a 401 to 425 spec was academic.  I was just wondering if the 401 and 425 ever used a common block.  I have no need or interest in attempting it.

 

The parts in the stock engine are fine quality -- and there wouldn't seem to be an obvious need for a performance improvement.  Is it not quick enough now?

[RivNut]

5 hours ago, Turbinator said:

Are there other ways to boost horse power of a 401 to equal the horse power of a 425 without worrying about overboring? It would seem to me other things could be considered to increase engine performance such as compression ratio of each cylinder. I do not know other things, but I would guess there are other improvements. Maybe forged pistons as opposed to cast pistons could add to performance. I’m rebuilding my engine and I’m thinking the parts that go back in the 401 should be better than what came out.

Different profile cam, professionally ported heads, matching intake manifold to head ports, roller lifters, roller rockers, free flowing headers, bigger exhaust pipes, EFI.  You're already at 10.25 compression ratio which, when new, called for premium gas.  You cant go much higher without 'ping.'

 

In 1966, Buick built a couple of production "400" engines for the Skylark GS.  Exact same bore and stroke as a 401 but on paper it was a 400.  400 was mandated as the maximum cubic inches for an intermediate body.  Oldsmobile & Pontianc had their 400s, Buick had its 'on paper' 400, and Chevy had its 402 which they called a 396.  In 67 Buick had its 400 big block, to go with the 430 when the nailhead went bye-bye.

 

Besides the 325 hp MT engine like in your Riviera, in 66 there were MU and an MR engines, both "400s."  One of which was rated at 360 hp.  Quadrajet carb from the Riviera, and the Super Wildcat (2x4 bbl) camshaft and distributor.  Basically sold to dealerships who would sponsor a car for drag racing.  I think the other 401 had 11:1 compression. 

 

Buick experimented with turbocharging nailhead but at the time GM did not have a transmission that could handle the torque.

Edited March 23, 2020 by RivNut (see edit history)

[60FlatTop]

If a guy who looked like this was giving advice on how engines held together I'd kind of take it with a grain of salt.

 

He'd have his baler cranked down to put out 120 pound bales and tell you the wire wasn't strong enough. And that ain't Tommy Ivo.

 

[rocky5517]

I just watched a video on you tube with a young guy/ his site is "engineering explained". He spent 20 minutes explaining the relationship between bore and stroke, and the effects on HP. I was getting dizzy but I understood most of it. You guys would really get a kick out of it. 

[Turbinator]

On 3/23/2020 at 5:06 PM, KongaMan said:

The question about boring out a 401 to 425 spec was academic.  I was just wondering if the 401 and 425 ever used a common block.  I have no need or interest in attempting it.

 

The parts in the stock engine are fine quality -- and there wouldn't seem to be an obvious need for a performance improvement.  Is it not quick enough now?

Oh, the car engine is plenty quick at the stock level. Performance in car talk means speed to most . I was looking for performance in reliability, much less oil use, and quite frankly a higher comfort level knowing the engine is hopefully stronger and more dependable. Anytime an engine Ive had in the past used a 1 1/2 quarts of oil in less than a thousand miles something was up.

Id like to take long trips knowing the engine is reliable.

Edited March 25, 2020 by Turbinator (see edit history)

[Turbinator]

On 3/23/2020 at 6:30 PM, RivNut said:

Different profile cam, professionally ported heads, matching intake manifold to head ports, roller lifters, roller rockers, free flowing headers, bigger exhaust pipes, EFI.  You're already at 10.25 compression ratio which, when new, called for premium gas.  You cant go much higher without 'ping.'

 

In 1966, Buick built a couple of production "400" engines for the Skylark GS.  Exact same bore and stroke as a 401 but on paper it was a 400.  400 was mandated as the maximum cubic inches for an intermediate body.  Oldsmobile & Pontianc had their 400s, Buick had its 'on paper' 400, and Chevy had its 402 which they called a 396.  In 67 Buick had its 400 big block, to go with the 430 when the nailhead went bye-bye.

 

Besides the 325 hp MT engine like in your Riviera, in 66 there were MU and an MR engines, both "400s."  One of which was rated at 360 hp.  Quadrajet carb from the Riviera, and the Super Wildcat (2x4 bbl) camshaft and distributor.  Basically sold to dealerships who would sponsor a car for drag racing.  I think the other 401 had 11:1 compression. 

 

Buick experimented with turbocharging nailhead but at the time GM did not have a transmission that could handle the torque.

Amazing. So boring the cylinders in a car engine is not the main thing to increase power and speed. Many modifications can be made to achieve the speed some are looking for.

I thought a person who wanted to make a 425 out of a 401 was chasing the speed and power. So to the point, why bore if you can get more speed and power without boring the cylinders. I’m trying to have my cylinders bored as little as possible.

Edited March 25, 2020 by Turbinator (see edit history)

[1965rivgs]

5 hours ago, Turbinator said:

Oh, the car engine is plenty quick at the stock level. Performance in car talk means speed to most . I was looking for performance in reliability, much less oil use, and quite frankly a higher comfort level knowing the engine is hopefully stronger and more dependable. Anytime an engine Ive had in the past used a 1 1/2 quarts of oil in less than a thousand miles something was up.

Id like to take long trips knowing the engine is reliable.

Hi Bob,

  That sort of oil usage for a Nailhead seems to be quite common. Cant remember whether it was `64, `65 or `66 but there is a service bulletin regarding oil usage that states anything over 500 miles per quart is "normal". The best "oil economy" I ever got with a Nailhead on the highway was 1 quart in a thousand miles from Florida to Chicago.

Tom

[kegart]

I can remember that I checked the oil level every time I got gas. Chevrolets usually got 800-900 miles to a quart. The first car that I had that didn't need to add oil between oil changes was a 1973 Olds.

 

Kevin

 

[johnrex]

49 minutes ago, 1965rivgs said:

Hi Bob,

  That sort of oil usage for a Nailhead seems to be quite common. Cant remember whether it was `64, `65 or `66 but there is a service bulletin regarding oil usage that states anything over 500 miles per quart is "normal". The best "oil economy" I ever got with a Nailhead on the highway was 1 quart in a thousand miles from Florida to Chicago.

Tom

My brand new 1965 Wildcat averaged a quart every 500-1000 miles. Perfectly normal, in fact, some mechanics told me if you didn't burn oil, something was wrong.

[60FlatTop]

Nailhead valve guides get a lot of side pressure just from the valve train angle. If you take the rocker arm assembly off it is not hard to find one or two that you can wiggle with your fingertip from the top of the stem. And the umbrella stem seals are usually in the oil pan. But the stems need a little lube. Heck, one of my cars has 48 valves. A drop or two for each is going to use a bit.

 

The trick is knowing when the wear gets unbalanced between all 8 cylinders. I used to have an Allen Engine Analyzer with a oscilloscope and look pretty deeply into each cylinder. It really took up more space than it was worth. Now I used an older inductive high voltage meter on the plug wires and look for variation. My '64 Riviera will run around 3,000 volts. If it gets up toward 4,000 on a cylinder I dig in. Most cars run about there. And a compression test is always step one of a tuneup.

 

I have seen a lot of speed parts bolted on, but the simple smooth drivability of the car is a lot more important to me. Have a plug wire slip off when you arrive at a cruise night and try to keep it running to get into a parking space. "Wow, man, you got a cam in that thing?"

Bernie