Register now to get rid of these ads!

Max 392 Bore size

Discussion in 'The Hokey Ass Message Board' started by sgunlock, Oct 17, 2010.

  1. sgunlock
    Joined: Apr 11, 2010
    Posts: 9

    sgunlock
    Member

    I picked up my 58 392 hemi block which is already .060 over from the machine shop on friday. I was having them clean and check it out before I start to rebuild it. He told me that the cylinders have a small scratch in them and would need probably .010 more boring. I can feel the scratches with my fingernails. I would like to know what is the max bore you can do on a 392 and still be ok. This is not going be a blower motor or anything just a mild build hopefully around 400hp.
    What is a bummer is when I bought this motor along with it came 8 new Arias Forged pistons .060 over. Now I have to order new pistons when the time comes to bore. Any advice would be greatly appreciated.

    Steve Gunlock
     
  2. Jeff Norwell
    Joined: Aug 20, 2003
    Posts: 12,741

    Jeff Norwell
    MODERATOR
    Staff Member

    I believe 120 thou is around max....
    Another 10 over your 60 will be just fine
    Those early hemis are really beefy....
     
  3. Describe the "scratches''. How many, are they paralell with the bore, etc. You do not necessarily have to bore it/them out....
     
  4. sgunlock
    Joined: Apr 11, 2010
    Posts: 9

    sgunlock
    Member

    The scratches are vertical , I can feel scratches in 6 cylinders but not the other two. The six cylinders that do, it's only one scratch in each cylinder.
     
    Register now to get rid of these ads!

  5. Roger O'Dell
    Joined: Jan 21, 2008
    Posts: 1,037

    Roger O'Dell
    Member

    sonic test cyl for thickness
     
  6. I would very seriously consider running your Forged Arias pistons in the block the way it is...
     
  7. Vandy
    Joined: Nov 15, 2009
    Posts: 368

    Vandy
    Member
    from L.A. Ca

    I agree with 345 Desoto = Run It as is
     
  8. mart3406
    Joined: May 31, 2009
    Posts: 3,055

    mart3406
    Member
    from Canada

    ----------------------------
    No way on the .120 over. For a NA
    application .060 over is usually considered
    the safe maximum on a 392 and .030 or .040
    about the limit for a supercharged engine.
    Depending on how deep the scratches are and
    exactly what type, age and make the pistons
    are, you *might* be ok just honing the block
    and running the pistons on the loose side of the
    tolerances. Forged piston need more clearance
    than cast ones and especially, some of the older
    aftermarket racing pistons were designed to run
    really loose - with some of them calling for
    upwards of .008 to .010 piston to wall.

    Mart3406
    ==============
     
  9. Vandy
    Joined: Nov 15, 2009
    Posts: 368

    Vandy
    Member
    from L.A. Ca

    I have personally seen a few 92's at .125 over that were ran hard. Now days it's easy to sonic check a block and see what you have. I would just run what you have and save the re bore for another day.
     
  10. Jeff Norwell
    Joined: Aug 20, 2003
    Posts: 12,741

    Jeff Norwell
    MODERATOR
    Staff Member



    The OP asked how much a stock 392 can be bored.
    It is my understanding from my builder who did my engine(Tim Banning of FHO)....
    ... that they can be holed out to a .120.After .120.... well ...Kaboom.
    This was his info....and he has never steered anyone wrong.He really knows his stuff.
    My engine is cranked .70 over with forged pistons....
    The OP stated he was not supercharging.
    I do not know the specs on any early Dodge or Desoto, because my interest is in the 392.
    SUNGUNLOCK/If you need more questions answered.... feel free to call Tim..... http://www.forhemisonly.com/
     
  11. George
    Joined: Jan 1, 2005
    Posts: 7,017

    George
    Member

    That is the general consensus, that the 392s didn't have the thick walls of the 331/354s & shouldn't go over .060. On the 331s .120(354) is considered the safe limit, but I've heard of someone going out to 4"(392) & getting away with it. How much of a risk do you want to run?
     
  12. 73RR
    Joined: Jan 29, 2007
    Posts: 6,222

    73RR
    Member

    Without sonic testing you have NO idea how much material is left. I do know from years of experience that the 392's have major core shift problems. Maybe not all of them, but enough to be a big concern. Is 0.120 over safe? It will never happen in my shop.

    For a street engine I'd consider using what you have but there are practical limits on the wall clearance and you did not indicate if the existing 060 bore was cut/matched to the new pistons, or, if it is a finished bore. Check with the piston manufacture for wall clearance then see if your pistons can be used.

    .
     
  13. the SCROUNGER
    Joined: Nov 17, 2005
    Posts: 486

    the SCROUNGER
    Member
    from USA


    Topic worth reviving. I own a sonic tester and just checked a freshly built .060" over 392, that had some bore issues similar to your block. Egge Machine makes .080" pistons so the question becomes, can it be taken another .020" and clean it up ?

    After checking all 8 cylinders, it turned out that 3 of them were already too thin on the THRUST sides of the cylinders for high horsepower application, in this case the walls facing the lifter valley. One was only .117" on a major thrust wall. The other 2 were in the .120" to .125" range. I like to see .130" finished bore.

    So a 392 should really only be bored .030" unless a sonic tester tells you, there's enough meat there for a bigger bore size.

    On all other sidewalls, they were in the .200" to .250" range, which is typical of an early Chrysler hemi, they usually had lots of material to play with. A few were in the .150" to .180" range but after .060" over that's actually very good. You want at least .130" remaining at finished bore size.

    So to clean this one would mean another .020" and leave only .107" wall on a major thrust. That is a moderate risk. Take a caliper and open it to .107" and that's not a lot of thickness to hold combustion in at high rpm or high CR. OK for street driving on pump gas with 9:1 CR and around 400-500HP, but not for racing or boosted applications or high compression 13.5 CR.

    IMHO after seeing this, every 392 should be sonic checked first, before boring it out- and only bored minimal required to clean up the cylinders if needed. If it's already 060" definitely check it. If it's already .080" chances are it's a junk block. If you can find one and run it standard bore do so. They did experience core shift per the stories on the internet, in this case those rumors are true. The core on this one moved vertically i.e. the upper walls facing lifters were thinner, that is odd compared to most other engines where they shift left to right, and get thinner on the sides.

    I've run other makes with only .085" on a few sidewalls and made 500 HP and ran in the 12's on pump gas, but would not attempt it with thin major thrust walls. What happens is, instead of combustion pressure pushing the piston down, it swells the cylinder outward like a milk jug and flexes it. The side loading of the piston running on the bore also tries to push the side of the bore wall out. Ring seal suffers and the engine actually makes less power, even though the bigger bore has more CID. Eventually it will crack in the thin portion, or the wall stretches and the head pulls up and a head gasket will give in that area. The bore is what holds the deck down.
     
  14. the SCROUNGER
    Joined: Nov 17, 2005
    Posts: 486

    the SCROUNGER
    Member
    from USA


    I've checked them all. Your statement is true for the 331/354 blocks.

    331's will go to 354 no problem.

    Both 331 and 354 will go to the 3.90" to 3.94" bore size range, leaving .130" minimum remaining.

    The 331/354 blocks are really beefy, but the 392's obviously can have some serious core shift. I would not take a 392 more than .030" without sonic tester verification, it's a block that needs to be checked, and bored minimally, only enough to clean it up - not to look for more cubes at .060" or .120" a shot.

    A well calibrated sonic tester is the final arbiter.
     
    Last edited: May 19, 2012
  15. the SCROUNGER
    Joined: Nov 17, 2005
    Posts: 486

    the SCROUNGER
    Member
    from USA


    You got that right. Going another .060" over, to .120" over total, on the one I just checked, would put 3 cylinder walls all under .100" wall on thrust sides. It would take the thinnest one down to only .087" on a major thrust wall, and that would probably SPLIT OPEN very quickly.
     
  16. 73RR
    Joined: Jan 29, 2007
    Posts: 6,222

    73RR
    Member

    Containing combustion pressure, while a requirement, is not the only 'job' of the cylinder wall, either thick or thin.
    A thin wall, even if only a localized, will transfer combustion heat too quickly to the coolant, it will create a steam pocket and overheating will occur. Add in too much ignition advance and... It will be tough to diagnose.
    In extreme cases of thin wall, the heat produced is, IMHO, the main culprit in producing cracked walls. There are plenty of cracked exhaust manifolds to attest to this.
    Yes I know, higher cylinder pressure equals higher heat, but even nominal compression makes for high temps and the cast iron is there to absorb the heat and distribute it, hopefully, evenly, to the coolant.

    Bottom line: a stock bore block is best so minimize the cutting.

    .
     
  17. Jeff Norwell
    Joined: Aug 20, 2003
    Posts: 12,741

    Jeff Norwell
    MODERATOR
    Staff Member


    My 92 is punched 70.
    I did have it sonic tested and blueprinted.
    I have the engine stroked as well and the size is now roughly 422.
    So far no problems.
    The gentleman that did my engine work was Tim Banning who owns FHO.
    I was very pleased with what he did for me.
    He generally works on the 426 stuff.....
     
  18. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    X2. Really, I cant believe in this day and age that 1) this question gets asked over and over, and 2) that WHEN its asked, a bunch of guys start saying things like "Oh #.## is the max it will go". A sonic test is usually around $100. You are gonna drop at LEAST a grand in machine work, spend the extra goddam $100, and know how thick the walls are, and how bad the core shift is. End of speculation. And if the cores are shifted to the minor thrust side, its not as big a deal.
     
    Last edited: May 19, 2012
  19. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 8,979

    Rusty O'Toole
    Member

    On the subject of forged pistons. Way back around 1960 there was an answer to a letter in Hot Rod in which the author said he put forged, solid skirt pistons in his street driven 58 Corvette. They were fitted with the recommended clearance of .012 then knurled for a tighter fit. Said he had 30,000 miles on the motor, it did not burn oil and no piston slap when cold.
     
  20. the SCROUNGER
    Joined: Nov 17, 2005
    Posts: 486

    the SCROUNGER
    Member
    from USA


    if you look closely at an engine that failed with split cylinder walls, you'll see they crack in a way that appears to be caused by detonation of the fuel, from the explosive effects of combustion pressure. They'd have to be very, very thin, and the engine very, very lean, to break from heat alone. Like cherry red hot, the same way you heat something up with an acetylene torch.

    what I have seen from overheated engines is, a section of block between the cylinders on the deck, just burned away. The head gaskets gives out first, then the flame jumps across and if they keep running it, it erodes the block deck there

    ring seal is paramount. If cylinder pressure it getting past the rings, then it's not pushing down on the top of the piston and creating power, instead it's blowing by and coming out the breathers and seals in the crankcase.

    with this type engine (non sleeved, cylinders integral to block, cast iron) when the bore thickness gets below .130" finished bore size, the cylinders will begin flexing at high rpm/high CR applications.

    with most street rods/rat rods this is not a major issue, as many just get tooled around at slow speeds, but I'd still rather have .130" wall than .080" wall. If it does crack there's a lot of money wasted on a rebuild, that has to be done over again with another block, or patched with a sleeve and all its bad side effects- not to mention the most precious resource as one gets older- TIME. Time becomes more valuable than money, when you get up in age.
     
  21. the SCROUNGER
    Joined: Nov 17, 2005
    Posts: 486

    the SCROUNGER
    Member
    from USA


    the old forged pistons were a much looser fit, typically around .008", than today's forged pistons, so that would make sense. They expanded more.
     
  22. the SCROUNGER
    Joined: Nov 17, 2005
    Posts: 486

    the SCROUNGER
    Member
    from USA


    good advice. I got so tired of wondering "what if" that I bought my own tester.

    the reason there's so much speculation is, only 1 out of 20 shops has a sonic tester, and the ones that do have one, you have to trust they know how to calibrate it, and read the owners manual. I have caught shops in so many f-k ups it's no funny. One shop bored my Pontiac 455 out to Olds 455 specs on the oversize, no schitt it happened. Had to take it back and get it bored again. Another got me wrong parts. And many other things like that happened, like leaving glass bead inside parts, and not cleaning oil galleys. I'm a hobbyist now, but in the past it was like "taking golf lessons from someone, who can't golf as good as me." The sonic tester is not easy to calibrate. It's only as good as the guy using it, if he's a dumb asz, chances are he can't calibrate the tester, and the results will be incorrect. I have to read the manual EVERY TIME I use the darn thing. You have to set probe zero, then calibrate on the block you are testing. If you check a Chevy block, then go to a Ford block, guess what you have to recalibrate again.

    so hot rodders who don't have access to sonic testing just try to shoot from the hip, and get their engine together using common knowledge about the engine in question. Hence the speculation i.e. "can I just hit it another .060" and go" questions.

    My angle is this, if you can run the 392 standard bore and within specs on taper and ring end gap and piston/bore clearance, do it. Hone it and use it standard. Only bore it out if it really needs it. There's not a lot of wall thickness there to play with on the thrust sides in general.
     
    Last edited: May 20, 2012
  23. the SCROUNGER
    Joined: Nov 17, 2005
    Posts: 486

    the SCROUNGER
    Member
    from USA

    at .070" over, this one would have the thinnest holes at .112" which is ok for a low CR street driver on those few small areas. The thin area is only in one small section of each wall, not the entire wall from top to bottom. So it still has the rest of the very thick wall holding it.

    where other blocks are thin on the nonthrust sides, the 392 was very thick there. The 392 was thin on the major and minor thrust sides, which is sort of odd for an American V8. That's a sign of core shift.

    it depends on what the engine is being used for. 9:1 with pump gas 400 HP would run forever even with one wall at .100", it just would not be optimum for power and ring seal
     
    Last edited: May 20, 2012
  24. mickeyc
    Joined: Jul 8, 2008
    Posts: 847

    mickeyc
    Member

    What about sleeves? I had good luck with several sleeved small block chevy motors years ago. I do not know if this practice is still common or
    not.
     
  25. the SCROUNGER
    Joined: Nov 17, 2005
    Posts: 486

    the SCROUNGER
    Member
    from USA

    if the engine was designed to use sleeves from day one, like the modern aluminum V8's and diesels, they are a great way to just start with a "new" motor again. I worked as a diesel mechanic for 2 years, and we would resleeve the diesel tractors and install new pistons and bearings and rings, bolt on new reman heads, and away it would go for another 5 years or more.

    but if an engine is not designed for sleeves, here's what happens- when the new sleeve is pressed into the old cylinder, it cracks the original cylinder. The original cylinder is what holds the deck down. Now when the heads are torqued, instead of pulling the heads down tight, it pulls the deck UP in the area of the head bolt threads in the deck. And between the head bolts stays down, and compression leaks through there.

    we put 8 sleeves in a Pontiac and it would blow air into the radiator when doing a leakdown test on a cylinder, before we even fired it, it was already not sealing

    this is the dirty little secret the machine shops never tell you, they charge for the sleeves then say "oh well we tried" and it's not cheap either, that Pontiac sleeve job was $500

    if you sleeve a block, you can only sleeve every other hole, to keep one hole between each sleeve sound and unsleeved, to hold the deck down and hold the head gaskets. There may be some makes of blocks that have more rigidity, where this would not be a problem, but that's what we ran in to. It was an f-ing NIGHTMARE.

    a sleeve in a block is the kiss of death to me, I'd still buy a block with a sleeve or 2 in it, and try to run it, but it would have to be dirt cheap, because it could create problems, been there done that.

    basic rule, don't sleeve unless it's a very rare, hard to find, expensive block. Just get another block and start over, keep that one as a spare. A numbers matching original '70 Hemi Cuda with a cracked bore, that's a candidate for a sleeve, cuz the car is worth big money with the original block in it running. Sleeving a block not designed for it, is a compromise, not to mention it throws the cam bearing alignment out. I had to re-hone 3 blocks for cam fit, after they were sleeved, the cams would not go in the block.

    what an f-ing PITA !
     
    Last edited: May 20, 2012
  26. George
    Joined: Jan 1, 2005
    Posts: 7,017

    George
    Member

    Sleeving runs around $100 per hole, just a matter of if it is better to go buy another block vs $100-800 extra expense.
     
  27. TR Waters
    Joined: Nov 18, 2006
    Posts: 1,439

    TR Waters
    Member
    from Vermont
    1. Early Hemi Tech

    You need to find a new machine shop. Period.
     
  28. the SCROUNGER
    Joined: Nov 17, 2005
    Posts: 486

    the SCROUNGER
    Member
    from USA

    oh really ? Tell me who's better than Jensen and Morgantini. One has the fastest door car in the country that runs 6's, and the contract for Pocono NASCAR Racing School engines, the other did the hemi heads for Joe Amato on a regular basis, that won 5 NHRA Top Fuel Championships.

    It has nothing to do with the machine shop competence, it's the nature of the repair using a sleeve in the first place.

    these are highly competent machine shops better than any machine shop you probably ever walked in to up in VERMONT. They own their own dynos, flow benches, sonic testers, shot peeners, etc. One has been in the business around 40 years now.

    If you're never seen cracked walls before after sleeves are pressed in, you're just getting your block back with the soft plugs already in it, and don't see what happened to the original cylinder wall inside. Or you didn't look. The walls are PAPER THIN after they are bored to accept a sleeve.

    Take some soft plugs out, and look at what's left of the original cylinders after a sleeve is pressed in. That's the nature of the repair, it cracks the original wall. Ask yourself why a block is sleeve repaired to begin with ? Because there was a hole in it, or it was cracked.

    If it's already too thin, and you bore it to accept a sleeve, there's nothing left of the original wall now anyway. Get it ?

    it requires a .002" press to hold the sleeve in, meaning the bore is that much smaller than the sleeve. What do you think happens to the original wall when that larger sleeve is pressed in ?

    I've yet to see a single sleeved block, that the original bore wall was not cracked during installation of the sleeves, by any machine shop, period.

    it's a last resort fix patch job, putting a band aid on cancer.

    if the block is designed for sleeves, and to be changed out like a diesel is, that's a different story. They have o-rings on the sleeves and proper clearances. They can be pulled out easily with a puller from the top of the block, and new ones hammered in with a mallet and block of wood
     
    Last edited: May 21, 2012
  29. 73RR
    Joined: Jan 29, 2007
    Posts: 6,222

    73RR
    Member

    Gee Tom, what were you thinking ??[​IMG]

    While I agree with much of what has been offered, we have sleeved many engines, even those 'apparently' not designed for sleeves, and have had nothing bad happen. Have we ever sleeved all 8 holes? No. Very few blocks are worth that much. Have we ever placed sleeves next to each other? Many times.

    Like alot of 'things', this might be a matter of perception and expectations...

    .
     
  30. the SCROUNGER
    Joined: Nov 17, 2005
    Posts: 486

    the SCROUNGER
    Member
    from USA

    ok then ask yourself this, the hemi I sonic checked, has .117" walls on one thrust.

    you're going to bore that almost completely away, to put in a .093" thickness sleeve

    that leaves original wall thickness of only .024" - about the size of a spark plug gap there to hold the deck down and seal the head gasket

    and you're telling me, that's not going to crack when the sleeve is pressed in ?

    how much wall was left on the blocks you and your buddy above repaired with sleeves, did you measure it ? And why did you sleeve it in the first place ? Just for fun ? or was it thin, or cracked, or holed ? What's that do to block integrity and head gasket seal, in your opinion ? No effect at all, just like new ?

    you just never looked close enough.

    sure it'll "work"- but it certainly is not as good as just getting a new block

    we have a Pontiac w/2 sleeves in it, because it dropped a valve and broke a piston, and holed the block. It just ran 11.78's last weekend with the 2 sleeves in it, 470 CID w/aluminum E heads.

    the cam bore had to be rehoned to straighten it, just to get the cam in

    both original cylinders are cracked where it was sleeved, in addition to the holes from where it grenaded the first time- the sleeve replaces the original cylinder, one cylinder was totally bored out and the wall GONE in one section when the sleeve was pressed in, just top deck and bottom of block holding it at both ends.

    it's only a press slide fit, that won't hold the deck down like the original cylinder will. Put sleeves in next to each other, and you're going to start having head gasket problems there.

    you need to do some measuring and see what you really have left there holding that sleeve in place, what's left of the original wall ? nothing sometimes.

    cuz .117" minus .093" is .024" remaining, no matter how you cut it

    "no problems"

    just not yet...

    if a block is "too thin" at .100" so you bore the cylinder away to make room to press in a .093" sleeve, what's left, .007" ? I've seen them with nothing left after being bored for a sleeve, gaping air, cooling jacket. And what did you accomplish, besides just weakening the structure that holds the deck down when you torque the heads.

    that's assuming you use a thinner sleeve, use a .125" sleeve thickness on the hemi I checked, and guess what, there would be no original cylinder left after boring it to accept the sleeve. The sleeve would press into the bottom and top of deck only to hold it, like the Pontiac I described previously.

    IMO only sleeve when the wall is holed or cracked already. "Period" And never 2 sleeves next to each other. Unless you're doing it for free, then I have a few blocks you can try to fix. I sure won't pay $100 a hole to sleeve a boat anchor common block. 2 sleeves next to each other in a block, no thanks.
     
    Last edited: May 21, 2012

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2020 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.