Bore and Stroke ?

[WS6LOVE]

im trying to build a 60 to the largest displacement i can and still be able to be driven everyday. my plan so far is to take a 3.4 (duh) and bore it out to the same as a 3900 (so i can get new pistons easier, since its a factory bore) and use a 3.6 crank.

i could be wrong, but thats why im here. i come from the land of v8s, so i need me some big displacement if im ever gonna respect myself with a v6, haha.

[montess408]

well it is a 3400 block but he used a 3500 crank but every thing elese is 3400 as far as i know

[ForcedFirebird]

He's talking about offset grinding a 3400 crank that starts out with 2" pins, if you turn anything off of it you certainly will not have a 2" pin afterwards, and he certainly will not be able to use the same rods and pistons unless as I mentioned he can do so without the piston coming into contact with the cylinder head.

Without a doubt. That's why I mentioned forgetting the nodular iron, specially for welding.

Welding a cast crank improperly is not much unlike taking glass out of the oven and running it under water.

Did I mention we can do dry-heat treating at the shop as well? We can make metal so hard it will crack if you look at it wrong

Why are we having yet another discussion on this?

Joseph, Dave, the total change in stroke that can be achieved with perfect machining can be as much as .25" without a doubt. If you use the current surface of a 3500 rod pin, you can move the rod center .125". This gives you .125" more on the up and down stroke of the rod centerline (in relation to the crank centerline) making 1/4" possible - ever so slightly possible.

gectek, but unless you have access to equipment that can grind to the neighborhood of 50 millionths, this won't happen. Don't waste your time with a nodular iron crank when the 3500 crank is steel and is over 40 rockwell (making it forged according to the machinery handbook). Just press the timing ring off the crank and press a ring on mimicking the 3400 crank, like Joseph did for his 3900 swap.

I see that we might get slightly over .2" maximum.

*BUT* this might not be a bad thing since this can now use 3400 rods with 3500 pistons and the deck height will remain the same. 3500 pistons protrude .010" out of the deck.

I agree with Joseph that it does cost more to machine 6 throws vs. four. The crank has to be offset indexed to turn a rod pin. This means a fixture is made with a locating hole at each throw to make it concentric and able to be turned (you have to find center of each pin). This is actually a long tedious process, especially to make it true with both ends of the crank being variable, with both ends of the crank needing to change centerline -- and -- to be within .0002" (standard machining tolerance). The V8 crank has four centers (four setups), and the 60* crank has 6. Taking into consideration my shop charges $100-150 per setup, the 60* crank WILL cost more to turn - about 50% more.

He's talking about offset grinding a 3400 crank that starts out with 2" pins, if you turn anything off of it you certainly will not have a 2" pin afterwards, and he certainly will not be able to use the same rods and pistons unless as I mentioned he can do so without the piston coming into contact with the cylinder head.

[ForcedFirebird]

Why are we having yet another discussion on this?

Joseph, Dave, the total change in stroke that can be achieved with perfect machining can be as much as .25" without a doubt. If you use the current surface of a 3500 rod pin, you can move the rod center .125". This gives you .125" more on the up and down stroke of the rod centerline (in relation to the crank centerline) making 1/4" possible - ever so slightly possible.

gectek, but unless you have access to equipment that can grind to the neighborhood of 50 millionths, this won't happen. Don't waste your time with a nodular iron crank when the 3500 crank is steel and is over 40 rockwell (making it forged according to the machinery handbook). Just press the timing ring off the crank and press a ring on mimicking the 3400 crank, like Joseph did for his 3900 swap.

I see that we might get slightly over .2" maximum.

*BUT* this might not be a bad thing since this can now use 3400 rods with 3500 pistons and the deck height will remain the same. 3500 pistons protrude .010" out of the deck.

I agree with Joseph that it does cost more to machine 6 throws vs. four. The crank has to be offset indexed to turn a rod pin. This means a fixture is made with a locating hole at each throw to make it concentric and able to be turned (you have to find center of each pin). This is actually a long tedious process, especially to make it true with both ends of the crank being variable, with both ends of the crank needing to change centerline -- and -- to be within .0002" (standard machining tolerance). The V8 crank has four centers (four setups), and the 60* crank has 6. Taking into consideration my shop charges $100-150 per setup, the 60* crank WILL cost more to turn - about 50% more.

how much can you off set a 3400 crank b4 you get problems ? .125 ?

i was talking to a guy that has a stroker motor and he said that his stroke is now 3.510 and as far as i know he is using stock lengt rods and pistons

Impossible, you can't use the same piston and rod in any engine that has crank stroke increased unless you have at least that much clearance plus some above the piston in the stock engine at TDC before hitting the cylinder head.

[montess408]

Not to mention it will cost about twice as much to do considering the price quotes I've received for welding the steel crank in an effort to achieve the 3.48" stroke, over $650 as opposed to as low as $225 to offset grind the steel crank to the max possible.

how much can you off set a 3400 crank b4 you get problems ? .125 ?

i was talking to a guy that has a stroker motor and he said that his stroke is now 3.510 and as far as i know he is using stock lengt rods and pistons

[gectek]

well i have a few connections at some awesome crank builders...and yah you are talking about stress relieveing if i am correct....maybe

If your talking about welding up the older model cranks like the 3400 then I would be very cautious. Cast iron is particular metal and unless the welder properly pre heats and post heats it you could be in for some problems.

Not to mention it will cost about twice as much to do considering the price quotes I've received for welding the steel crank in an effort to achieve the 3.48" stroke, over $650 as opposed to as low as $225 to offset grind the steel crank to the max possible.

[geoffinbc]

If your talking about welding up the older model cranks like the 3400 then I would be very cautious. Cast iron is particular metal and unless the welder properly pre heats and post heats it you could be in for some problems.

[gectek]

that might be a better option...but a little on the expensive side. oh well...i have the resources to do it if i want i guess. I think itll be exciting. I can see it already, lots of TQ and revvin it to 7 grand...sounds like fun esp with lightweight pistons and rods

im talking about welding it up and offset grinding then redrilling the oil holes and then having it chamfered, polished and balanced accordingly, of course with custom pistons with the pin height already compensated...i like the thought of the 3500, but i really want a clean and easy install. if i can get mile high to cut the timing marks into the crank, then that would be better...then i wouldnt have to worry about the difference in the timing reference, and it would be a drop in engine, but otherwise ill have to go with the TCE piece, which wouldnt be that bad. I am torn between two ideas...but a stroker would be very nice...esp a 3.8 or 3.9 stroker...yah the rod ratio might have gone a little off, but even a 383 has a not so average rod ratio and they still produce good power

If you do this with a 3900 block, rod ratio will not be a problem because you can use LS1 pistons which come with several different compression heights as low as 1.030 still leaving room for use with a 6" connecting rod. Welding up the crank and regrinding will run in the $600 ball park due to the need to address 6 individual throws, I've already looked into this in an effort to create a 60 degree 4.3L.

[gectek]

im talking about welding it up and offset grinding then redrilling the oil holes and then having it chamfered, polished and balanced accordingly, of course with custom pistons with the pin height already compensated...i like the thought of the 3500, but i really want a clean and easy install. if i can get mile high to cut the timing marks into the crank, then that would be better...then i wouldnt have to worry about the difference in the timing reference, and it would be a drop in engine, but otherwise ill have to go with the TCE piece, which wouldnt be that bad. I am torn between two ideas...but a stroker would be very nice...esp a 3.8 or 3.9 stroker...yah the rod ratio might have gone a little off, but even a 383 has a not so average rod ratio and they still produce good power

if you cut .25" off the backside and use 2" journal rods it should work.. or maybe i'm thinking wrong...

You're dealing with a circle so if you start at center you have .1125" above and below the 2" perimeter inside the 2.250 crank pin. You can't offset grind a total of .250" as in the piston moves .250 inches further up in the bore with the same rod.

If you count the added distance of .1 above and below then yes, but I'm talking about the pin circle center being shifted the indicated distance of .250", you can't do that without welding the crank or going to a journal diameter smaller than 2.00". I guess we're just looking at it from two different aspects that are in a sense correct.

[Superdave]

You can only offset grind the crank to ~.100 increase, you have to divide the .250 by 2 giving .1125 and then clean up the crank after the offset which will net about a .100 offset.

if you cut .25" off the backside and use 2" journal rods it should work.. or maybe i'm thinking wrong...