how much more can I overbore?

[BrendellaJet]

Yanked the motor this weekend-getting ready to re-gel the boat. Pulled the heads off for some engine detailing and found that all cylinders had a very definite pattern that was created by the up/down motion of the pistons/rings(some that I can catch a fingernail on.) Crosshatch marks are still evident. The pistons are .060" overbored. Looks like some machine work is in order, how much more can I overbore? is it possible this could be fixed just with a hone? I can get the block serial # if that makes a difference, I know the block is a 4 bolt, and it has "Hi Per Pass" cast into the back of the block, which I assume stands for Hi Performance Passeger car. Hopefully this block can still be used. What do you guys think?

[Fiat48]

I'm gathering we are talking a big block chevy here. Most block will go .100 over with no problem. I've seen .125 over but don't recommend it. Speed Pro used to make a .090 over piston also. Another thing that can be done is to hone the block .005 or .010 and have custom pistons made if you're concerned about cylinder wall thickness. Depending on how deep any scores are, honing may be all that's needed.

[MikeF]

BJet, I'd venture to say that you can bore it out (at least) one more time. If you want to know for sure how much "meat" are on the cyl walls, you need to Sonic Check the block. That can usually be done at a reputable machine shop.
I had to do this w/ mine (just to make sure!). I ended up only having to go .070 over (was .060) to clean up the scratches from the rings on #4. SRP makes some forged pistons #139516 that are approx 10/1 for stock length rods and open chamber heads. These are what I have in my engine. W/ my engine, they are @ 9.61/1 :cool: .

[BrendellaJet]

Yes, we are talking BBC here. Thanks for the info!.

[HBjet]

Fiat48:
Most block will go .100 over with no problemFiat48, are you talking about un-sonic checked blocks that are already .060 over? If so how do you figure it would be no problem? Thanks
HBjet

[Fiat48]

I've never had a problem boring any Big Block Chevy (Mark IV) to .100 over be it low deck or tall deck. Naturally, sonic checking is a good idea if you have it available to you. I've done sonic testing on several, but never found .100 over to be a problem. But I do consider it the end of the line. I know many at .125 over but I have never done that. Actually, I prefer the .090 over as it leaves .010 for cleanup if something happens. Bigger is better with bore size, long as you have the cylinder wall thickness to do so. Increased breathing due to valve unshouding in the cylinder.
[ February 10, 2003, 09:21 PM: Message edited by: Fiat48 ]

[intimidator]

YEA B.J. IT WOULD BE ON THE SAFE TO U.T. IT MINE WAS BODERLINE .125 IT WAS SUGGESTED TO HARD BLOCK IT. I BOUGHT THE HALF FILL. FOR TEN DOLLAR'S MORE I COULD HAVE GOT THE FULL FILL. HALF ONLY PUT ABOUT 2 TO 3 INCHES I THINK 4'' WOULD HAVE BEEN BETTER? I HAVE 6 TRW .100 OVER 12.5 TO 1 PISTON'S FOR $ 200 ABOUT 5 HOUR'S TOTAL ON THESE PISTON'S

[HBjet]

Fiat48, what would you say is the minimum cylinder wall thickness a block should have?
HBjet

[revndave]

I had my motor bored .100 over.Just found out has pin hole in 1 hole.Sonic did'nt show it last year when motor was built.Back at machine shop to sonic and possible sleeve.This all came about last weekend.Did warm up on trailer and found water in oil.Should find out today about block.

[DansBlown73Nordic]

A friend has a pulling tractor that had a 427 tall deck bored .125 over. It made a funny noise at about 7500 rpm,s. eek! we pulled it apart and one cylinder was gone. I mean nothing left but the cylinder walls on either side. Not a prtty site.....

[superV]

I am a "ASNT-TC1A Level III" UT And MagParticle inspector and have all my own equipment if anyone needs a MPI or A UT let me know?

[superV]

P.S. Its Ultrasonic L-wave Inspection. :D

[roco racing]

bore it slightly and have custom pistons made.

[cyclone]

my GEV IV BBC is .100 over and I have no clue if it was ever sonic checked. so far so good though.

[BGMAN203]

I wouldn't go over .070 with a motor you plan on squeezing or have a huffer on top of. Sonic check or not. wink

[wsm9808]

HBjet:
Fiat48, what would you say is the minimum cylinder wall thickness a block should have?
HBjet That depends on what you are going to do with the motor and the intended HP range. Most cylinder sleeves used to repair blocks with are sold in .093 wall and .125 wall and have worked for decades in most engines even if one whole side of the bore had been knocked out and repaired with a sleeve.
The original wall on most 350 chevys is usually around .110 to .125 on the side next to another cylinder and average around .225 on the thrust side.
Stock BBC bores are around .280 and Merlins if I remember correctly are in the range of .375.
When you bore a block .100 you are only taking .050 from the wall and the BBC is normally concidered safe to bore to .100 up to 500HP, up around 650HP most stock blocks are really testing their reliable limits, bored or not. For more power than that, and/or a lot of squeeze I would defenantly want a Merlin or Bowtie block.
Sonic testing is nice, but, about the only time you will find a block thin is if there is a huge amount of core shift. You can usually spot core shift by checking the lifter bores. If they are way off center of the lifter bore boss on the block, then you may have a block that could have bores that are thin on one side and thick on the other.
Brendella, if it were my block, I would see if it would clean at .070 and go that way. Not because i would be worried about a .100 block, but because that would make the block still able to go one more bore job if it should ever be damaged or worn and need boring again.

[revndave]

FOUND OUT WONT TAKE SLEEVE.TOO THIN.GOING TO FILL BLOCK 1/2 WAY TO SEAL PIN HOLE.HOPEFULLY WILL WORK

[HBjet]

So lets say you have a BBC stock bore (.280 wall thickness as stated) but you have core/casting shift when the block was made. From the get go the cylinder wall thicknesses are not going to be the same (say side to side) Then someone takes it out .030 over and without sonic checking the block, just bores down the center of the existing cylinder. Now the thinner sides are even thinner. Then they decided to take it .060 over and again just bore down the center, resulting in even thinner sides....
You see what I'm getting at?
So the question as to how much you can over really depends on cylinder wall thickness, and the only way to find that out is by sonic checking it. If BrendellaJet's block was sonic checked the first time it was taken from std. to .030 and the bore was offset to remove more from the thicker cylinder side and very little of the thinner, and repeated the same time it was taken to .060 then I would agree that you can take it to .100 over.
If none of that was done, you could possible have a block that was taken .060 over with 1 cylinder or 2 that now has a wall thicknesses between .050 - .030 and that is way to thin.
If the above was true, then the answer of taking it to .100 over not being a problem would be false, especially comming from a Race Engine Builder!
Based upon this info, sonic checking the block is the only way to determine how much over you can bore a block.
HBjet

[schiada96]

HB if the block has .1 of core shift, most are not even close to this much. A over bore of .1 will still leave a 3/16 wall plenty strong enough for a lake motor. The way you are talking about putting the bore in the wrong spot would throw a lot more off than worring about a thin wall.
[ February 12, 2003, 11:32 AM: Message edited by: schiada96 ]

[HBjet]

schiada96:
HB if the block has .1 of core shift, most are not even close to this much. A over bore of .1 will still leave a 3/16 wall plenty strong enough for a lake motor. The way you are talking about putting the bore in the wrong spot would throw a lot more off than worring about a thin wall. So, are you saying forget the sonic check and center off the existing cylinders and just bore away to .100 over and you will not have one problem?
Does anyone know for sure what a stock STD. block cylinder wall thickness is and how accurately are the thicknesses on each side of the cylinder the same when stock?
I ask because I've seen 454 blocks with .030 over and a cylinder wall thickness of .050 on one side and .220 on another! Would you say you can take this block to .100 over? And this block wasn't sonic checked the first time it was bored.
HBjet
[ February 12, 2003, 01:31 PM: Message edited by: HBjet ]

[wsm9808]

The original question was "How much more can I over bore(An 060 block)"
Had he asked what is the best NDT(non distructive test) way to know what my wall thickness is and what would be the minimun thickness needed for a 400 HP motor. THEN, I believe most replies would have been suggesting sonic testing. But you still wouldnt know if there are any tiny casting flaws in the bore that another .020 might open up and allow water to leak into the bore through a mase of tiny holes in the casting that play connect the dots all the way to the water jacket. So lets pressure test it after boring too, hell, lets pressure test and sonic test every block in the world to be bored from now on because it upsets HB if you dont.
Myself and others spoke from experiance that in most cases a BBC will bore to .100. He is not building a $25,000 motor and going from .060 to .100 should not be a problem. There is a tiny chance it might split a wall, but there is also a chance a piece of the space shuttle could drop out of the sky and knock a hole in the side of his block too. LMAO
Excuse me, while I go check my PCV valve. :)

[Fiat48]

revndave:
FOUND OUT WONT TAKE SLEEVE.TOO THIN.GOING TO FILL BLOCK 1/2 WAY TO SEAL PIN HOLE.HOPEFULLY WILL WORK Are you sure you want to put all your good stuff in a block you already know is too thin to sleeve?
Now, I have filled blocks with Quik Crete to fix split cylinders or pin hole cylinders but alwasy has been a temporary fix for me. The water at Firebird raceway in Phoenix has caused more pin holed cylinders than I care to count.
wsm9808: You are right. :D
Once at a race in Phoenix we had two cylinders pin hole, side by side. We had a guy bore and sleeve them, but had him set up the boring bar offset slightly to bore less material off the thin side. That may go against all you ever learned, but it worked. But after the race, we gave the block a decent burial.
[ February 12, 2003, 07:00 PM: Message edited by: Fiat48 ]

[revndave]

QUICK FIX FOR NOW.WE'LL BE SAVING FOR DART BLOCK.ALSO DE-TUNING MOTOR.ONLY 7LBS OF BOOST.THIS TUNE UP MADE 920 AT 7000RPM.

[HBjet]

wsm9808:
400 HP motorWhere does he say a 400HP motor?
BTW, I'm not arguing, I just think telling people they can take there BBC's .100 over without checking cylinder wall thickness and telling them they won't have any problems is not good advice. Maybe there won't be a problem right away, but who know's what someone has planned for there motor or how long they plan on running it. To me, sonic checking is a small price to pay for piece of mind!
HBjet
[ February 13, 2003, 08:16 AM: Message edited by: HBjet ]

[superV]

wsm9808:
The original question was "How much more can I over bore(An 060 block)"
Had he asked what is the best NDT(non distructive test) way to know what my wall thickness is and what would be the minimun thickness needed for a 400 HP motor. I see you are familiar with NDT I do not know to many people that are other than in the Bizz. Its funny when I tell people I do NDT they are like whats that? But being certified in 9 areas i just say im in QA.

[hack job]

revndave:
QUICK FIX FOR NOW.WE'LL BE SAVING FOR DART BLOCK.ALSO DE-TUNING MOTOR.ONLY 7LBS OF BOOST.THIS TUNE UP MADE 920 AT 7000RPM. dave iam glad to see that you will most likly be on the water for the summer . i cant wait too see that boat run over 100. it should be no prob. hope it all works out.

[wsm9808]

HB, no one said sonic testing was a bad idea. It is a great plan, but not definative, and neither is experiance. We all all trying to help and are telling what we have learned over the years. I dont concider advice from what has worked for years as "bad" from seasoned professionals. And as for the "no prblems right away", Actually, most pin holes and dangerously thin walls show up right away or after only a few full power burst, not years later. Hell, it breaks years later, you got your moneys worth IMO.
No one said 400HP motor, I pulled that out of the air to make the question more specific for that example. But you know that, you are just being you and splitting hairs that dont need splitting. But debates are good, it draws out information.
SuperV, I used to build NDT pipe testing Equipment. Pipe X-ray machines, to check oil field pipe thickness and integrity before they dropped them down a hole. (sonic testers?)
welp, we are gone sking for a few days, see yall monday night.

[Cs19]

whats that 920 horse motor going in?

[revndave]

IT GOES IN A 19FT CARRIBEAN/SPECTRA(BLOWN WAGES)