Cylander wall thickness "update"

I know somewhere on this forum this has been discussed before but for the life of me I don't remember where, so here go's,,I know thicker is better but what would be acceptable for minimum thrust side thickness after boring/honing to the size needed, 400 block out to a 4.375 bore.

The general rule I know is .200" minimum for thrust sides.

Bill.. I have heard of guys running .100 wall.. myself
I would like .120 or better.. its real hard to find a
factory production block with better than .120 when its
cleaned up
EDIT
my mega block had .200 on basically all cylinders with
a 4.5 bore(I wasnt going 4.5 but I did have it sonic
checked... 64 readings per cyl... that was $75)

Talked to my machinist today, he has one block checked and the other will be done in the morning and will pick them up in the afternoon,,sounds like mine are going to be real good then, at least the first one.

Just my $.02.

On another make I had a 715 HP stock block motor, did not know it at the time but the block had core shift. It was only a +.030" over bore. It came apart in a big way around 7,000 few months later. Measuring some of the block after, thrust side of the #1 cylinder was .080", the other was .300+". Basically anything that moved was ruined. Roller cam bent, roller lifters, valves hit pistons, crank bent, even bent snout on ATI balancer.

I will never do another motor without sonic checking. Last one I did was .250" and I still filled it.

having the sonic numbers will help me decide which block I will use, be nice if the second one is as good as the first.

I like to see .150 minimum after boring and honing on the major thrust side, I have ran blocks that had .120 on the minor thrust side with no failures with .150 on the major thrust sides, yet Thicker is way better

I posted some data on two RB blocks I checked HERE. You may find it of interest...

We generally consider anything above .180 on the thrust sides at finish bore a good block.Have we used block with less,yes but not for max performance use.

What is your minimum acceptable thickness for a NON-thrust measurement?

I can say that every cyl that has cracked on my stuff
has been on the NON thrust side.. every one.. they varied
from .125 to .160.. that was 5 cyls on multiple blocks(all
340 blocks at 4.070 bores)

I have one that`s at .118 non thrust 7000`+ r`s 14 years later.........better but a lottery ticket.......

We like to see minimal .180 all around but have used blocks at .160 on non thrust sides.Depending on the build and where the cylinder is thin we usually do a short fill.
We haven't had much luck with lottery tickets.

had two blocks one was a 1975 the other is a 1976 both came in with the numbers solidly in the .310-.320 range had a spot here and there that was in the mid 200 range worse being 245, and a couple around .260-.280,,95% are .300 or better.

Yes!!!! I will never build another engine blind again. QC at the Trenton plant back in the day was a joke at best and that is an understatement at best. Especially those 76-79 ultra ultra thin wall cast 400/440 blocks🤓

Dude, you got really lucky Maybe it is time for you to buy a lottery ticket while your luck is in town AKA, those are stout block castings Flog the dog snot out of both of them

That's great we usually only see those numbers on the 71 to 73 blocks.How many checks are you doing for each cylinder?Usually #1,#2,#7 and#8 non thrust to the front and back of those cylinders come up thin on those 74 and later blocks.

Do you guys factor in weather your checking a oem block vs a race block of better material in whats a go or no go block?

looking at the numbers the front and back numbers are consistantly a little thinner mostly in the mid to upper .200 range, when he checks each bore he will do 4 steps on the thrust and non thrust side and 3 on the front and back of each cylander.

I said somthing to him about doing a half fill and he promptly told me to not waste my time and money and that blocks like that don't need it besides he is not a proponant of using filler because of thermal issues in the cylander.

You shouldnt have ANY issues with those blocks..
they are THICK walls... in my SB stuff I havent ever
seen a production block that thick... just my race blocks
good luck with your build

Sounds like he did a comprehensive test.As far as the short fill,it has little effect on the thermal expansion since you are only filling to the core plugs.Thermal issues come into play in the upper portion of the cylinder where the heat from combustion occurs.We also do not like to fill any blocks but with the inconsistant values of the end cylinders can cause distortion from heat.The shorter the cylinder length the less heat effective area and with the short fill the less chance of an issue.We see pin holes and cracks develope within the lower part of the cylinder where the transition from the water jacket to the solid mass of the block is and that's where we are referring to.You could be lucky enough to not need this.For an all out race engine it might be wise,but that your decision.We just seen many later 400 and 440 blocks that could have been saved.

I don't use block filler for that exact reason The heat zone differences above and below the block filler ends up making the cylinder walls different internal diminsions above and below the filler, basically a small step in them

that must be why he explained about blocks that had a 1/2 fill showed a increased amount of skirt scuffing as opposed to ones that dont, and it all makes sense to me because of the difference in thermal expansion in those two areas.

Sorry, but ain't buyin all that. Based on water displacement, I run a 3/4 fill block. Never seen a "line of demarcation" on the cylinder walls. Never had any piston scuffing issues. With the temps we usually run ( under 200 degrees ) don't think there is a lot of thermal expansion / contraction to worry about. If there is any, it would all be on the expansion side, so don't see it scuffing piston walls. On wall thickness, I have run small block motors all out of E58 coded cars. Supposed to be "hand picked blocks", what ever that means. Had two sonic tested. All at .2 or thicker walls ( before boring ). Don't know if those two items are related, but just eyeballing lifter bore holes and castings in the lifter bore areas, looks like minimal core shift on these blocks.

Cement those blocks up then complain about heavy azz cars. LOL. Concrete's for swim-in pools.

I think I would be questioning the measuring equipment.




Chris.

Id kinda agree with Chris, Ive checked quite a few blocks and haven't been that lucky with wall thickness, on my last engine build I didn't find one with that good of numbers out of 10 blocks checked, makes me wonder if my checker is bad?

As far as questioning the test,it seems to be a very comprehensive test using minimally 12 checks per cylinder.We do 16 checks if we find thin areas.
Diffrent types of material have different inherent sound velosities,ie:steel velosity aprox.5918m/s and aluminium is 6350m/s.If the guage is not set correctly the measurements will be erroneous by a certain percentage.
There are 3 ways to calibrate a sonic meter.
1- Calibrate to a known thicknes/material
2-Calibrate to a known velosity
3- A 2 point calibration.
We generally use 1- calabration to the known thicknes, sincethe advent of added alloys and strengthen materials to the parent metal.ie: added nickel in cast iron.Cast iron having a sound velosity m/s of 4572 and nickel having a sound velosity of m/s 5639.
Depending on the amount of nickel interduced into the cast iron will negate using 2-calibration to a known velosity(chart value).The best way to measure a block is to find an area that can be measuered(known thickness)your probe should read the same value.
Other considerations are choosing the correct transducer probe size and diameter as well as a good copulant for seal.Keep in mind test should be done at nominal room tempertures.

To address heat distortion issues,even though we don't do or recommend a tall fill,a short fill does not have an adverse effect.Run a cylinder that is thin and you will see a lot of shadow areas because of heat.

On my .030 440, the old Mopar Performance Engines book had me paranoid about thin wall blocks since the block I used was a 78. It passed sonic check no problem. I can't recall how thick the walls were, but the machine shop said for mine, that .060 over on that block wouldn't have been an issue. Also the majority of BBM blocks they had tested were thin at .030, no matter what the casting date was. I was prepared to go and buy blocks of all different vintages, guess it doesn't matter.

I try to alwyas calibrate my sonic tester to a known thickness, not the posted velocity for the metal being tested I'll take a dremel tool or small hand held air powered high speed rotary grinder with a carbide bit to smooth out around the oil pan rail on the BB in the back near the bellhousing mounting starter areas or in the front near the timing cover ribs to get a smooth, flat surface I measure it with a set of dial calipers and get the meter reading within .005 or less on the meter

So far for me I am using the ears for the engine
mounts.. I touch them up with a 4" disc on my die
grinder for a flat surface.. this would be my known
thickness point to test... but I'm still playing with
my new tester... havent played much lately being I have
stuff thats not working on my junker... soon I will get
back to testing blocks since I have a few I want to look
at for up coming jobs... but so far I havent ever seen some
of the numbers posted

Mr p just curious as to what year 340 blocks did this.I have 2 340 blocks with 7/70 build dates.

I think they are a 68 and a 70.. I have 3 others
but havent looked at the wall thickness yet

One of the most common errors when sonic testing is the use of incorrect probes.Since we do roll cages as well as blocks we have various size probes.For cast iron we use .500-1MHz,for steel .250-7.5MHz amd for aluminium .250-2.25 MHz.The small diameter probes should be used when testing concaved or convexed surfaces as to not have any chance of gaps between the probe and surface.
We have seen some really thick blocks that have exceeded .500 and .400 in areas but they are certainly rare.Uncle Barry bought a hemi block from us that exceeded these numbers.
As for using hardblock on a short fill,it has more advantages than disavantages.As we mentioned we find casting irregularities at the bottom of the cylinders more than anywhere else.This is why you see many cracks at non thrust sides and below the ring travel area.It certanily doesn't hurt and is a bit of insurance.

Lots of good info from BG Racing. Thanks!

Your welcome

I can't wait, Bill. You're gonna shart yourself lol.

Well I spent a little time today investigating what the doubters have been saying about calibration's and testing of blocks that seem too good to be true, and what I found in the limited area that I was able to physically check my self and found that on the two cylanders at the rear of the block (#7-#8) mechanically checked out to be the same as what the paperwork said it was,, driverside, the paper said .290 and was real close to what my machinist's scale said it was and #7 had the same results,,so I have convinced myself that his calibration was correct and I have two good blocks to work with.

You are truly blest My brother I sent my best 400 block (out of the three I have)to the machine shop and it ended up having a pitting issue in one cylinder that the shop decided to put a sleeve in it without asking me before hand and then proceeded to braze and weld up two places on the deck without informing me of the damage which ended up requiring another sleeve in that block on the other side Maybe it is time for me to make a machine shop change

I have convinced myself that his calibration was correct and I have two good blocks to work with. [/quote]

Bill, maybe you should buy the lottery ticket! Oh, and don't forget to share when you win............https://board.moparts.org/ubbthreads/images/icons/default/laugh.gif

one requirement when I have any machine work done is "Here is my home and cell numbers, call me if there is ANY questions or concern's",,,recently I had to change machine shop's because the guy that has done my work finally retired after 35 years and I did a lot of digging and Doug's name kept coming up, so I went for a visit and was pretty impressed with what I heard and seen in his shop, I observed a lot of higher end stuff right along with the standard bracket build's, I have heard a lot of good about him so I am giving him a try and keeping my eyes and ears open and watching how he operates, I like what I have seen so far.
John, my father said once that a blind squirrel will find a nut once in a while, as far as a lottery ticket, well I do have to go and put gas in the truck here in a little while,,,,

Yea Been there done that. I told Bill before hand that what he would get. I think take .100 off them numbers would be closer.

Even if I did reduce the numbers by .100 both block's are good ones.

I think everything has been covered as far as the testing and if it was done correctly then you should have a great block.If you went over all the information with your machinist and are satisfied then get started on the build.
The only thing I question is not to use a short fill since your spending a lot of money on the block.The big issue we see is always on the tall fill and block not being clean inside and the cement not sealing against the block and cylinder walls or blocking water passages.But it's your decision as to what gets done.
Good luck with your build,and look forward to seeing you at the track.

What's the build plan for the block?
I like a little hard block in my stuff but I run my stuff hard.

I agree bill I do think the blocks will be fine. Heck I use one. It is in my car LOL It just the odds of me and you owning 4 blocks that check that good. Is pretty rare. I know guys with aftermarket blocks that say they are not that good. And I will add One of the block I got. Been check by two diff shops. Got me? I Quit worrying about it.