Poking the B3?

[sketchman]

As I suspected, the valves are good and my hillbilly head shave held up just fine for about 6 months so far. Everyone who knew about it before it happened said it would never work so I'm happy about that.

The pistons are nice and sloppy. Now just gotta find a beater. Harder than I thought it'd be.

[sketchman]

sketch, B6 pistons are NOT an option in a B3. if you were to bore a B3 block to accept a B6 piston, you would cut into the water jackets and ruin the block.

Do you know specifics on average wall thickness? I had forgotten these engines were closed deck, so measuring it is a bit annoying with a mic. I think I have an idea how to do it. I just haven't tried it yet.

[FB71]

the B3 doesn't have the cyl wall thickness cast into it to allow for anything over +.030" without severly weakening the walls and thus making it a ticking time bomb. If i were you, i would look into a +.020" piston and then offset grind the crank with oversize rod bearings to add stroke. doing so may require custom pistons to give proper clearance and quench.

they'll tolerate 1mm/0.040" overbore.

[FB71]

Do you know specifics on average wall thickness? I had forgotten these engines were closed deck, so measuring it is a bit annoying with a mic. I think I have an idea how to do it. I just haven't tried it yet.

about 0.120" - 0.150" wall thickness.

[sketchman]

about 0.120" - 0.150" wall thickness.

Not much to work with at all if that's the case. What's your source? Not calling you a liar. I'd just like to be thoroughly certain, because everything I keep learning seems to agree with the admittedly rough measurements I just took.

I'm not even going to say how far I think it can be taken, because no one would believe it, and I don't even know yet if I'll be able to pull off all that's needed to support the bore, so we'll just have to wait and see what happens.

[FestYboy]

FB71 is a master ford tech, i don't question him on these things. and to bolster his statements and mine, a B3 is 71mm bore, a B6 is 78mm bore.... so to put B6 pistons in means a .280" overbore: you're into the water jackets.

[sketchman]

I think we can agree that even master techs are imperfect humans like the rest of us. Humans have a tendency to pass on things that seem to be sound ideas without checking them out first. Not saying that's the case, but it's almost always a possibility. Which is why I asked for the source. Didn't mean anything derogatory by it.

so to put B6 pistons in means a .280" overbore: you're into the water jackets.

Yes, IF the walls are just .120"-.150" thick. A few things won't let me believe that yet. One being that(even erring on the side of safety) my own personal measurements highly disagree with it. I'm willing to admit that I'm wrong and that my measurements were off etc, if I can be proved wrong. So far, no one has done that IMO.

[FestYboy]

the nominal wall thickness is listed in the factory manual, and if you don't believe that, then what will you believe? that and the B3 cyls are seperate (a gap between) where the B6 block cyls are siamesed, which allows for the greater bore dia.

[sketchman]

Would that be in any year manual? I have a 91, and I can't seem to find it. I would have no trouble believing that if someone had said that and mentioned at least the section in the manual where these specs are located, or somewhere else where they were located, or some kind of verifiable data. None had been offered.

[JPT]

Get an old block, carve it up and measure. Removes all doubt.

[sketchman]

The problem here is availability. There are no old blocks that I can just hack away at or I would have by now. If I just can't get a definite verifiable answer I will go with what my own eyes tell me, explain it to the machine shop, and ask that they bore one cylinder first and stop if it won't work.

[Safety Guy]

Not sure if this will help, but here's some pics.

First, a 1994 B6:



My old 1989 B3 block:



Okay, something tells me this will be no help.

Karl

[blkfordsedan]

The problem here is availability. There are no old blocks that I can just hack away at or I would have by now. If I just can't get a definite verifiable answer I will go with what my own eyes tell me, explain it to the machine shop, and ask that they bore one cylinder first and stop if it won't work.

Just take your block to a good machine shop that has a sonic tester. They can take a few readings on the cylinders and tell you exactly what the wall thickness is. It usually varies around the cylinder. This is very useful in older engines like the FE Ford that may suffer from core shift during the casting process. I doubt the B series Mazda suffers from core shift, but it will tell you what you want to know.

[sketchman]

I've emailed a guy who may be able to help, and I'll look into the sonic testing, though being as it is a spare block, it will probably be cheaper to just tell them what the deal is and try a cylinder to see what happens.

[sketchman]

Not sure if this will help, but here's some pics.

Okay, something tells me this will be no help.

Karl

It won't but thanks anyway. Problem with trying to measure the engine's cylinder walls is that there is no coolant hole that is flush with any wall, so what I did was bend a piece of stiff wire into a shape like below and lay the flat side on the deck with the hooked end reaching around to touch the cylinder. Then mic from inside the cylinder to the bend of the hook. Take that measurement and then subtract what you get by mic'ing the length of the "triangle" that the hook makes and the thickness of the wire(also mic'ed) to get wall thickness. It's a lot simpler to do than to type and read.