Project LookOwt: Saving a piece of 3.0 history

[Force Fed Mopar]

I'll look it over again today, I don't remember any pistons being broke, but didn't look that close the other day.

I don't think it's pieces of a hammer.

[Force Fed Mopar]

Plastic bits are wrist pin buttons.



That's why it looked like a broken skirt in the pic, because the buttons had fallen apart and allowed the wrist pin to slide over.

[Force Fed Mopar]

Thinking I'm gonna buy a set of 10:1 SOHC Diamante pistons to go back in it. Rock auto has a set of DNJ pistons for about 100 bucks. Finish tearing it down to the block and clean it up so I can repaint it, and then build it back right. Crank and bearings look great still.

[Force Fed Mopar]

Or maybe I'll just spring for some custom forged pistons. I dunno yet lol. See what kind of money I can come up with in the next month or so.

[Reaper1]

Holy crap! What the hell were they thinking? There's no reason for those pistons to need Teflon pin buttons. Good think you caught this before running it more! That would have eventually trashed the block.

[Force Fed Mopar]

Yeap. There's no grooves for pin locks, and the pins are full floating, so I guess this was their only option? Really not sure why they used a DOHC piston/bottom end anyway, seems like it would have been just as easy to buy a SOHC Diamante engine as a DOHC version... I wonder if they were press fit originally and they honed them to be full floating.

Rods do look very clean and like they may have had work done on them. They do have ARP bolts in them.

[Ondonti]

Yeap. There's no grooves for pin locks, and the pins are full floating, so I guess this was their only option? Really not sure why they used a DOHC piston/bottom end anyway, seems like it would have been just as easy to buy a SOHC Diamante engine as a DOHC version... I wonder if they were press fit originally and they honed them to be full floating.

Rods do look very clean and like they may have had work done on them. They do have ARP bolts in them.

BTW, maybe rick had those rods done first while waiting for pistons that...never arrived or were never actually ordered. When you don't do your own work or inspect what work was performed you can get seriously taken advantage of.
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You do have a broken skirt in those pictures, My 10:1 broke the skirt in the same place. I just threw it back together after replacing the crankshaft. I bent a crankshaft so I figured that I had some interference. Maybe there is a design problem with 10:1 pistons and the cast crank. Leftover piece was sitting in the oil pan. Just chips off the bottom of one side.

No reason to have ARP bolts in stock rods, they don't need them plus you still have a stock cast crankshaft. Those rods were machined to be floating. I asked my machine shop to bush my reconditioned rods for floating when I got my forged pistons and they said it would be better to use that money to fully balance the rotating assembly and just press the rods on.

I would go for a set of forged flattops if you can afford them and get ring heights set properly for a large dose of nitrous (not like the OEM ring locations). . Get the biggest oversize you can find rings for if your machine shops will do large overbores for cheap. Errybody does 3.1 builds for double and triple the HP this is at. Your rods are ready for floating pins so proper pistons will work together with your rods.

Assuming you have a set of stock rods that are press fit.....
If you go with rockauto 10:1's then I would run insane large ring gaps. The OEM 10:1's are much stronger than the 8.85/8.9's because they don't have that massive intake valve relief near the ringland. I don't know about the aftermarket stuff out there. OEM 10:1's with big gaps bent my crankshaft and all they suffered was a chipped skirt. 8.85/8.9's would have checked out long before. I would order the largest available oversize for aftermarket cast pistons.

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If you have forged pistons and kill a rod for some reason, then you would also have the proper setup to bother upgrading your rods to some of the cheap options out there.

[Force Fed Mopar]

That's what I was thinking of doing, was just run stock 10:1 SOHC pistons with large gaps, like .035 or so. Forged would be nice insurance, just costs $500 or so more.

If I go forged I'll move the compression up to 11:1 or so. Nobody I found has an off-the-shelf SOHC piston, so it'll be a custom forging anyway. We'll see how my money goes in the next few weeks...

[Ondonti]

That's what I was thinking of doing, was just run stock 10:1 SOHC pistons with large gaps, like .035 or so. Forged would be nice insurance, just costs $500 or so more.

If I go forged I'll move the compression up to 11:1 or so. Nobody I found has an off-the-shelf SOHC piston, so it'll be a custom forging anyway. We'll see how my money goes in the next few weeks...

Remember the rod problem, you need some stock press fit rods to use stock pistons. I would go high 20's and then a few thou bigger on 2nd rings for nitrous. .025 top took a beating on a 10:1 stocker.

[bakes]

As a friend to friend don't run big globs of Nos on cast pistons as the higher silicon % in them makes them stronger to cylinder pressure but at the cost being weaker to nitrous detonation ring they shatter like glass leaving the rod ends to poke windows in the block.

[Force Fed Mopar]

Going to have to re-bore it, wrist pins got the cyl walls



And one of the skirts is broke



I may just end up throwing some OEM 10:1's in it for now to get it up and running and get it tuned on motor this year. Tax money is mostly already allotted to other stuff I have another short block I can get rods from. Actually could use the whole block if this one is too scarred to save. Thought about doing so anyway just to go back to a Chrysler block, since this Mitsu one isn't anything special anyway...may end up doing so.

Actually, for that matter I have a complete running engine I could drop in, just to get it going again... that way I could spend money now on getting the trans fixed, which is just as important... decisions decisions

[135sohc]

Actually, for that matter I have a complete running engine I could drop in, just to get it going again... that way I could spend money now on getting the trans fixed, which is just as important... decisions decisions

I like that idea. Throwing money down a rat hole into an engine that is nothing special but an odd mis match cobble job of parts seems like a waste IMO.

[Reaper1]

Man, whoever assembled that engine was smoking crack or something! I can't believe what I'm seeing! Seriously. These are all mistakes and moves that a totally oblivious person, or totally careless person would do when assembling the engine! It really makes you wonder about the shop that did the work. It really actually upsets me that somebody would let that go out the door!

[Vigo]

I would just put the stock engine you have in it and focus on the trans. You can always build this one back up at your leisure, and as said i see no huge advantage to getting it back up and running on this exact engine since it doesn't seem to have any huge advantages over an engine you already know runs right.

[bakes]

I would just put the stock engine you have in it and focus on the trans. You can always build this one back up at your leisure, and as said i see no huge advantage to getting it back up and running on this exact engine since it doesn't seem to have any huge advantages over an engine you already know runs right.

i have to agree it the time best spent ver cost

[Ondonti]

Stock engine with big gaps is fine.

I don't understand why you wouldn't want the biggest overbore you can get, especially if you have cylinder scarring. 1000whp has been achieved with near .100 overbores. Big overbores are the standard build for anyone making big power.

Get the biggest 10:1 pistons they sell if you are going stock. If you are going custom, go with something near .080-.100 overbore that has a good ringpack available. I went .096" for 3.13 liters of displacement.
You are thinking about tossing the block so you don't even have the excuse of trying to save cylinder material for future rebuilds. They sell cylinder liners for 6g72's if you ever needed one and the rest of the millions of engines on the road disappeared.

If you want to go really cheap, just keep the current pistons and put the proper stock press fit rods in. Totally acceptable but boring. I wouldn't even sweat that poor cylinder while you are working out transmission issues.

[Force Fed Mopar]

Because boring really doesn't gain that much. I'd rather not use the current pistons since they are totally mismatched to the SOHC heads. I suppose a .100 over bore might make a noticeable difference, when I go forged I'll consider it. Generally I like to use as close to stock bore as I can to maintain as much cylinder rigidity, although I have no problem with a .030-.040 overbore.

I keep changing my mind, but I'm pretty certain at this point that I'm just gonna order some stock bore 10:1 pistons and throw them in the Chrysler short block I have sitting around doing nothing. It has a fresh crank and rings in it, just needs honing again and clean up the crank nose, as it's been sitting. Or I could use the crank out of the Diamante block, it's clean and fresh. Not sure if it's any better than the Chrysler crank.

[Vigo]

Same motor that was running in that 86 daytona? Or you sold that? I like the cheap and fast route because honestly making it more complicated then it needs to be is the whole reason this car has sat for what, most of a decade? Just get it running and upgrade from there.

[Ondonti]

Because boring really doesn't gain that much. I'd rather not use the current pistons since they are totally mismatched to the SOHC heads. I suppose a .100 over bore might make a noticeable difference, when I go forged I'll consider it. Generally I like to use as close to stock bore as I can to maintain as much cylinder rigidity, although I have no problem with a .030-.040 overbore.

I keep changing my mind, but I'm pretty certain at this point that I'm just gonna order some stock bore 10:1 pistons and throw them in the Chrysler short block I have sitting around doing nothing. It has a fresh crank and rings in it, just needs honing again and clean up the crank nose, as it's been sitting. Or I could use the crank out of the Diamante block, it's clean and fresh. Not sure if it's any better than the Chrysler crank.

Well you don't need to even consider cylinder rigidity at .100 overbore because its one of the strongest blocks in existence cylinder wise. I have only heard of one block that was even partial filled EVER (guy mentioned below). Consider the fact that they really don't sell 6g72 shortblocks that are not near .100 overbore for any high HP applications. The higher HP rated shortblocks are all large overbores and sometimes with a stroker crank added in.

One person did once consider running a .200" overbore with sleeves but I think it was too much machine work. That was for a 2000hp setup. He still runs a huge overbore in his even weaker 6g74 block.

You will be putting down 1/3 the HP of what people expect those big overbores to handle.

[Force Fed Mopar]

Same motor that was running in that 86 daytona? Or you sold that? I like the cheap and fast route because honestly making it more complicated then it needs to be is the whole reason this car has sat for what, most of a decade? Just get it running and upgrade from there.

Yeap same one. Runs on all 6 now though lol.

Well you don't need to even consider cylinder rigidity at .100 overbore because its one of the strongest blocks in existence cylinder wise. I have only heard of one block that was even partial filled EVER (guy mentioned below). Consider the fact that they really don't sell 6g72 shortblocks that are not near .100 overbore for any high HP applications. The higher HP rated shortblocks are all large overbores and sometimes with a stroker crank added in.

One person did once consider running a .200" overbore with sleeves but I think it was too much machine work. That was for a 2000hp setup. He still runs a huge overbore in his even weaker 6g74 block.

You will be putting down 1/3 the HP of what people expect those big overbores to handle.

Well that's good to know. I'll do that when I get serious and go forged.