Let me ask a question about cylinder walls

blykins · #1 (**permalink**) 11-21-2003, 02:50 PM

Which side is the thrust side? If I were standing looking down at the passenger side deck, which would be the thrust side? Left, right, down, up? This may be a stupid question, but I'm confused....

Mr.Fixit · #2 (**permalink**) 11-21-2003, 03:10 PM

Standing in front of the radiator of your car, the crank goes clockwise. (bottom of pass bank, top of driver's bank) If I understand your question

HighPlainsDrifter · #3 (**permalink**) 11-21-2003, 03:17 PM

Hi,
You will have side wall thrust as the piston goes down on power stroke and side thrust on the opposite wall as the piston goes up on the exhaust stroke, so both the left and right sides of the cylinder walls will have pressure on them, it wears more at the bottom of the cylinder, that's where the rod angle is the greatest.
Eventually the round cylinder will become an oval.
Perry.

blykins · #4 (**permalink**) 11-21-2003, 03:25 PM

So the piston wears the bore on the sides towards the intake manifold and the header....not towards the bellhousing and the water pump....right? If you think of a circle having 4 "sides", would this be correct?

Bob In Ct · #5 (**permalink**) 11-21-2003, 04:07 PM

I have no proof, but I would bet the condition is more pronounced in stroker engines due to more severe connecting rod angles.

Bob

blykins · #6 (**permalink**) 11-21-2003, 04:36 PM

Well...this is the reason I'm asking these questions. I have this 390 block that I've been tinkering with...and I thought it was a buy until last night. It's a 67 C7ME-A casting....and high nickel.

I had the thing magnafluxed last night...no cracks...I also had the cylinders sonic tested. Most of the cylinders were very beefy...(it is a stock 4.050" bore). The majority of the cylinder walls were in the .160"-.180" range. However, there was an area in the #1 cylinder about the size of a quarter where the thickness was .134". It was in what I call the bottom of the cylinder...if you're looking directly down at the passenger side cylinder deck, it would be at the bottom...towards the header or oil pan.

I really had my heart set on boring this thing .080" over and making a 427 out of it. However, if my buddy was right (he is a welding inspector with a $5k piece of equipment), taking .040" out of that side of the cylinder would make it .096". Ouch. I called the guys at Gessford, and they said for a street engine, they wouldn't wanna see anything at all less than .100" on a cylinder.

So basically I'm standing at the crossroads. I wish we would have skipped that cylinder...it was the last one we did.

What really sucks is the rest of the cylinder was anywhere from .154" to .179" on the other sides. It's just that small little section that worries me. I hate to scrap the block...I've got some money in it already from having it cleaned, etc...I could always just bore it .040" or .060" (machinist said it needs .030" to .040" to clean it up due to a few pits in the #1 cylinder), and end up with 418ci or 422ci with a 3.98" stroke. I really hate to do that though.

What would you guys do? I need some help. Basically I have two options...One is to just bore it what it needs to be cleaned up and end up shy of 427ci....or go ahead and bore it .080" and just hope that little quarter sized part doesn't blow out....

blykins · #7 (**permalink**) 11-21-2003, 04:39 PM

I guess I have a 3rd option...offset grind a new 3.98" stroke crankshaft to make up the difference. I figured out it would have to be lengthened about .043" to make it what I want. Would that be possible with a new crank? What about calling a crank manufacturer and asking them to custom make one for me?

CRZN427 · #8 (**permalink**) 11-22-2003, 12:11 AM

Like so many here I am no expert in the finer points of engine building, but your comments gave me reason to speak.

If you bore a 390 to get 427 you will probably have the same problems that Ford had with the "Center Oiler 427". That is, as I under stand it, oil starvation of the main bearings at the high end of the rpm band. Unless, of course, you provide additiional oil capacity to the mains, cross drill the mains and drill the rod throws for oil passages, like the 427 S/O.

In addition, without significant head work, the breathing of a 390 might not perform up to expectations for a 427 displacement.

If there is a thin spot on one of the cylinders, at the bottom of the bore, is it below the ring travel area? If so it won't have much affect on it by the cylinder pressures.

If that area is above ring travel it, might not have that much negative effect due to gas pressures any way since it is at the bottom of the piston travel where the pressure is less and near where the exhaust valve opens to relieve the pressure anyway.

Is the 0".004 that you are talking about in the inside or outside of the cylinder liner? If it is on the inside it will "go away" when the surface of the cylinder is bored.

Realistically, does a quarter size spot that is 0".004 thinner really make that much difference? Chances are that if you build this engine, and then (heaven forbid) you blow it, that it won't be the thin spot in the bottom of a cylinder that is the major cause of failure.

But again, I am no engine builder.

blykins · #9 (**permalink**) 11-22-2003, 01:44 AM

The thin spot is about an inch from the deck itself...close to the top of the bore. It's on the bottom "side" of the cylinder though...on the side of the cylinder that would be closest to the header...on the thrust side I guess I could say. That's what bothers me. I have always heard the cylinders were thinnest close to the top...and sure enough...it was.

Gessford said that .100" was the bare minimum for a cylinder wall thickness, and if I do take .080" out of the diameter of the cylinder, then taking .040" out of that side would leave me with .096". I think that's really taking a chance.

I was doing some searching last night, more than likely Scat would custom grind me a longer stroke than they offer (if I went with a .060" over block, I would need a 4.020" stroke crank) if I wanted to go that route....and also unbeknownst to me, they make some really nice forged cranks for FE motors...even in stock strokes. So I could just bore the block whatever it took to clean it up, and put a stock stroke back in it.

Didn't someone say that there were a few Cobras with 390's in them at some point in time....?

GEORGE ANDERSON · #10 (**permalink**) 11-22-2003, 04:39 AM

One of the problems with a preliminary sonic check is it's just an indicator...it doesn't tell you what will happen after you bore the block...pin holes can show up and other stuff.....the potential for years of water damage and rust damage on the back side of those 390 cylinder walls is GREAT..
perhaps a picture is worth a 1000 words...

Typical FE Cylinder wall

Another view of FE Cylinder Walls

So when you think of cylinder wall thickness you need to also consdier what will show up that the sonic check can't always pinpoint ahead of time...

more FE wall problems

My last comment....
(machinist said it needs .030" to .040" to clean it up due to a few pits in the #1 cylinder),

Listen to this machinist....because he's protecting himself....the potential is great for additional problems to show up...you can see the pin holes in the pictures above....my advice is if you want a 427 bore start with a 427 block.....
The 390 can build a great engine and some of the ideas above are possible.....
Not trying to cause a prblem with this post but if you do bore this block and things start showing up then you'll be sleeving every hole to be safe....then you'll end up like this image...

One last warning....

George

blykins · #11 (**permalink**) 11-22-2003, 07:14 AM

Man, those are some nasty pics. I don't even see how a block can have any integrity at all after all the cylinders are cut out in that last pic. Man, that would suck.

Well, I think I had already made up my mind, that I would just bore to clean up...but you have put some more red flags up...

I know by taking .030 or .040 out, I should be fine by looking at just thickness numbers alone...But I'll take a closer look inside the water jackets and survey the damage before I take it to the machine shop. Would you recommend doing another sonic test after the boring is complete?

Thanks for all the words and pics, George.

Faro · #12 (**permalink**) 11-22-2003, 08:32 AM

I'm no engine builder but I did stay at a Holiday Inn once.
Seriously though I did watch a TV show where they were showing how a block could be poured with some type of resin
to beef up the outer walls. The resin was said to be highly conductive so as to not hurt the cooling. Does any body out there
have any experience with it. Or perhaps a better memory than me. Might be an option worth exploring

arntztype4 · #13 (**permalink**) 11-22-2003, 11:11 AM

In regards to the thin cylinder wall, I also think that a quarter size spot in the wall that would end up being .004 too thin, at .096, is not a problem worth worrying about. However, I would closely examine the rest of the block in other areas. Such as how much are you going to have to deck the block to make it clean? Are the cam bores saveable? I had one block that had lifter bores that had to be bored to Mopar size lifters. That was an easy fix, that was better than the bores being sleeved.
Just be aware of other issues!
As far as "High Nickel Content". That's a bunch of fluff that most car buffs think they need, but the bottom line is, most guys won't ever run an engine hard enough, or long enough to have to worry about it. I drag raced a big block Chevy for years with a cast crank and a stock block, that never let me down!

blykins · #14 (**permalink**) 11-22-2003, 11:23 AM

The cylinder decks are fine...the machinist said that .010" would clean them up. As far as the cam bores and lifter bores, they were fine too. I got lucky there.

I kinda go along with you that a quarter sized spot may be fine...but I just don't wanna take a chance. The pics that George Anderson linked to kinda scared me. If the area was in another part of the cylinder, I wouldn't worry...but it's in a thin part of the casting anyway (close to the top) and the stupid thing is on the thrust side of the cylinder. Just my luck of course.

I think I'll just have it bored enough to clean it up, 30 or 40 over...and then make up the different with a longer stroke.

I'm waiting to hear back from Turk or Computerworks about how many original Cobras had 390's in them...hehee...

CRZN427 · #15 (**permalink**) 11-23-2003, 12:08 AM

The original 289 body that became the test mule for the big block car had a 390 for fitment, since the basic outside dimensions of the various FE big blocks are the same.

I don't believe that any of the "427" cars actually had a 390 from Shelby.

If you put in a stroked crank you will have to concern your self with different rods since the longer stroke will push the stock piston above the deck.

There were three stock stroke dimensions for the FE blocks.

3.500 for the 352 (4.000 bore)

3.780 for the 390 (4.050 bore)
3.780 for the 406 (4.130 bore)
3.780 for the 427 (4.230 bore)

3.980 for the 410 (4.050 bore)
3.980 for the 428 (4.130 bore)

There was also a 332 CID FE '57 and '58 but my book dosen't list that displacement.

My first Cobra had a 390 and it performed quite well.

If you are going to be concerned with showing every one else your clean rear end then you might as will get on with the dual paxton 427 like Shelby did. By the way, he found that an automatic made the dual paxton 427 drivable.