Took a look inside my hemi

[Wild one]

Found this on Redditt.

https://www.reddit.com/r/EngineBuilding/comments/1bje27t/57_genii_hemi_snapped_a_connecting_rod_as_soon_as/?rdt=34573

5.7 genII Hemi snapped a connecting rod as soon as it started after rebuild.​

This came in with a broken rod and frozen wrist pins. I gave the machine shop an entire set of core rods (with pistons on them) that were in good shape, but they destroyed them trying to press out the old pins. These are the press fit pins, they don't float in the connecting rod. I took their word for it and got a new set of EngineTech connecting rods, but one broke the moment we started it and trashed the block this time. I don't like aftermarket parts, I would have preferred the cores. I'm not even sure if this is a defect with EngineTech. I wonder if this machine shop knows how to properly fit the pins to the rods. What do you guys think? This is our first time using them because the other machine shop was taking too long to turn things around for us.







Where did it snap? At the big end, or small end. This is very unusual.


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In your first 2 pictures, there is a gouge at the edge of the piston pin bore. This is probably from (I am guessing) whatever they used to drive the pins out in a press. They were not paying attention, or it slipped while pressing and that gouge is the result.

Over the years I have broken a few pistons pressing apart pins and rods. But they weren't the best to start with. I use a fixture from Kent Moore that you place the piston and rod onto. It supports the edge of the rod, there is no load or pressing on the piston. The pistons you have pictured look like they set them on a press, and started pushing out the in. Obviously the pistons shattered.

For reassembly I use a Sunnen rod heater. The pin end of the rod gets heated up, with the piston and pin ready to go. There is an insertion tool and stop you can set up, but I just do it by hand. Once the rod is hot, I quickly put it in the piston and slide the pin in place. One quick move. I can usually get them in all the way before the rod cools and grabs a piston. If they don't get in all the way they have to go in the press.

Rods or pistons that have damage like you picture but have not failed yet eventually will fail. This could be the reason your Hemi job failed on startup.


Stock rods are thin and cheap if not press off properly it bend the rod end with wrist pin and it will be bent and not know it and bam


Pistons broke from the machine shop trying to press out the pins

Ok… so the box of broken pistons is from the machine shop? You said the pistons broke when you started it and poked a hole in the block? The only other thing I can think is they cracked the piston putting the pins in and either didn’t know it or tried to cover it up?

​

 

[Xsen]

I'm not familiar with these HEMI engines, but with many others. Is it possible to have the rods facing the wrong way, stressing the pistons, like on some other engines?

You definitely can, but to avoid that, they've marked the rods with numbers and forward-facing arrows on the bearing caps, before taking them off the crank.

Found this on Redditt.

https://www.reddit.com/r/EngineBuilding/comments/1bje27t/57_genii_hemi_snapped_a_connecting_rod_as_soon_as/?rdt=34573

5.7 genII Hemi snapped a connecting rod as soon as it started after rebuild.​

In my case a pair of stock pistons also broke, when the wrist pins were pressed out. Old pins were discarded, of course. Could this bend the stock rod heads... Hm. I have to think it over.

Shop trying to press the pins into the cold rods - oh my. Some people should never even walk close to the engine.

 

[Xsen]

Brother, Kudos to You for your detailed and open thought process during this whole endeavor.
I for one appreciate all the time, thought and detail you've provided throughout your whole process, as well as our communities input, too!

I look forward to seeing how this all plays out. I for one am learning a lot of deeper internal nuances in this build thread and appreciate being able to share it with you and our community. Knowledge is power, Brother!

Thanks! I believe that's what forums are for - sharing knowledge and experience in a particular area.

I hope some certainty regarding the cause of this will eventually arrive.

 

[Wild one]

You definitely can, but to avoid that, they've marked the rods with numbers and forward-facing arrows on the bearing caps, before taking them off the crank.



In my case a pair of stock pistons also broke, when the wrist pins were pressed out. Old pins were discarded, of course. Could this bend the stock rod heads... Hm. I have to think it over.

Shop trying to press the pins into the cold rods - oh my. Some people should never even walk close to the engine.

By chance you're aftermarket Mahle pistons weren't sized for a 0.927 pin and the shop tried to press in the stock pins which are sized at 0.945. I can't see that happening,but something sure is suspect for the majority of your pistons to have cracked pin bores.

 

[Xsen]

Just a small update. Got another set of Mahle +0.25 pistons, this time I ordered'em via another supply chain to make sure they were 100% Mahle. Long story short - pistons, boxes and everything else are identical. So I assume, the first set of Mahle pistons was original as well.

Now the shop has started disassembling the connecting rods from the broken pistons, starting with the most damaged one - No. 3. Check out what was found:


The pin has spun in the rod, despite the press fit. Honestly, the amount of damage this engine did to itself in under 6 seconds is unbelievable.

I asked the shop to ship the new pistons, old rod-piston assemblies and the tools needed for assembling the pistons and rods back, and I will assemble everything myself.

 

[Xsen]

So I thought I should update this thread with the final ruling on the case of the broken pistons. After all this was a fun [not at all] journey over a year long.

I did buy another box of Mahle +0.25 pistons, but before actually dropping another set of pistons into this block I've found a reputable local machine shop that does engine blocks and heads for of all sorts of cars and trucks and took my block to them for measurements along with the new pistons. I thought this would be a good idea to verify that the clearance was still where I wanted it to be.

You bet it was. The shop called me the day after and said that they're done measuring. The mains, the crankshaft and the rod bearings were all in perfect shape and size. The cylinders though...



The measurements were done on three planes (A for top, B for mid-cylinder, and C for bottom) and using two perpendicular axis X and Y, giving six measurements per cylinder (all numbers above are metric).

And here it was, the answer to everything. Of course, I just couldn't believe these numbers, I mean, a negative clearance on a HEMI? Really?!

Next morning I was right there at the shop. Took a piston and shoved it into cylinder #3 as it would normally go - it went all the way down all right. So I asked them whether they were sure about these numbers on the sheet. And then the guy went like "Now turn the piston ninety degrees and try that again". And so I did. And the piston got stuck in the bore. Touche!

All the time and effort (and money of course) wasted just because previous shop managed to bore and hone the block just so the cylinders not only had both taper and out-of-round, but were too small for the pistons too. I don't know how did they manage to do so, but they certainly did. That squeaking noise that the engine made during its 6-second run? That was no pulley, that were the pistons trying to make it through the cylinders. When the engine finally fired up and the pistons started to really heat up, it took six seconds for cylinder 3 and a few others to lockup completely, while the others were trying to rotate the crankshaft which then was pulling the pistons down, hence the damage to the pins.

So there I was with my other set of +0.25 pistons and the block that could not be bored to fit them. All in all the final decision was to sleeve the block and then bore and hone the sleeves to fit the pistons I already had.

Fast-forward to June 2025, the block was ready, all the parts were in good order, and I even bought a cool rotating engine assemblly stand. Took a week off my job and spent it carefully putting the engine together. Man, working with the engine on a rotating stand is pure pleasure! Before closing the valve covers I pre-lubed all bearings and everything with new oil, pressure-fed through the oil pressure sensor hole, rotating the crankshaft until the oil came out of the nozzles in every rocker. Then I installed the engine back into the truck, got everything back together and put all the fluids in.

This was the first engine that I've assembled from the bare block to running and damn it felt good when it fired up almost instantly once the air was out of the injectors. Five months and 8000 miles later it really purrs at idle. So hopefully good oil, proper maintenance and care will keep it running for a long time now. We'll see.

A nice ending to this story, right?

Well, no, there's more looking inside HEMIs coming.

 

[Xsen]

I'll keep this post short as after all, this was a much easier case. I actually have two Rams - a 2014, the star of the previous episode, and a 2013. Same 5.7 with 8-speed tranny and 4wd, just no air suspension. 224k kilometers on the odo and some audible tick at idle, that has developed around last summer. Sad to say, I was hoping it's not the tick, maybe just one of lifters being a bit tired. I even got a 10452HV Melling oil pump, to help fix that.

First warning signs arrived last summer too. I was on a short drive when I heard some weird sounds from under the hood. Pulled over, popped the hood open and listened - a strong singular chirping sound, seemingly at random time, not periodic. Then it stopped chirping and sounded all normal again. I blamed the water pump bearing, that had awful play in it and was due to replacement next week.

Next warning sign appeared somewhere around March - I started hearing something really resembling knock sounds during mild acceleration while on the highway. Hooked up the scanner, only to see that Knock Ratio going up. I do run a custom tune, but the truck had never made that uncomfortable prolonged knock sound before. I did think that maybe it was some bad gas, so I switched the gas station. Then I reverted my spark maps to stock - and still the knock was there. Maybe a tad lighter, but there.

What's really weird - right on the night when we rolled the 2014 Ram out of the shop, and I was driving the 2013 home - I heard bad noises again. Loud ticking, sometimes chirping. The frequency of the ticks was right at the cam speed, but the loudness and the tone took random changes. I finished the trip, parked the truck and I already knew I was going down that rabbit hole again.

My engine stand was still at the shop, so no reason to delay. After a few days I drove the truck back to the shop, and pulled the engine. No surprises there.



The OCV has a ton of shavings on its screen.



Cylinder #2 intake lifter - dead. Roller stuck and pushed up into the lifter, the bearings gone. Cam lobe shaved off. This was the cylinder that was knocking due to lean conditions. It's not that the AF mixture in the charge was lean, it rather got too little of the charge as the valve was not opening enough.

Cylinder #3 and #5 intake lifters - almost dead. Both rollers have significant radial play, the bearings still there, but probably the needles are pretty square.

Other lifters look okayish, no visible damage.

Going deeper into the engine bottom - all pistons heavily worn on the skirts. Some worse than the others, but most look like this.



Oil rings on some pistons were stuck, which is definitely not a good sign. Guess it had some really bad oil in it at some point.

Cylinder walls have light vertical wear, nothing too crazy. However, when I took the engine block to the machine shop, all cylinders were out-of-round. Judging by both my engines - that's what HEMIs do at some point after 100-150k miles, which is unfortunate. GM's 5.3 LMG engine which also has a cast iron block never does that. Maybe it's just my luck, I don't know.

Both heads required the valve job, but unlike the previous engine, they were flat on the mating surface. All pushrods looked okay at first glance, but upon closer inspection some of their ends had wear. As for the crank bearings - they were in perfect shape, just like last time. I suppose HEMIs are not harsh on those, at least the NA engines.

Overall, the rebuild speclist came down to:

— +0.5 Mahle pistons set with pins and rings
— Mahle main bearings set, STD size
- Mahle rod bearings set, STD size
- Mopar MDS lifters
- Mopar MDS camshaft
- Mopar MDS solenoids
- Mahle pushrods
— Melling 10452HV oil pump with stock relief spring
— Seals & gaskets set (mostly Mopar, some Mahle)
— Mopar oil pressure and temperature sensors, Mopar ECT sensor
— New exhaust studs and bolts, manufactured locally
— Mopar EVAP Purge solenoid
- Liqui Moly KFS-13 Coolant
- Local brand 5W40 oil for first run for 20 minutes
- Mopar 899 oil filter
- Mobil1 FS 0W40 oil
- Fram XG2 oil filter
- 1L of ZF Lifeguard Fluid 8

One thing I would change if I had to do it again - I'd get the non-MDS setup. I'm not a fan of how the lubrication works with the MDS, and even if I would lose a bit of mpg - I'd deal with that. But this occured to me after all parts were already purchased, so this time the MDS stayed in.

A few pictures of the assembly process:



If you're rebuilding the engine, you definitely want to pluck out the magnets that hide beneath the MDS solenoids and clean them thoroughly.



I absolutely love working with the engine out and on the stand.



Ye, who installs the pickup tube before installing the windage tray, shall remove it again.



Ready for priming with oil




After reassembling everything and running the engine for about 20 minutes at 1500 - 2000 rpm, I've changed the oil and filter to m1 and Fram XG2, and topped the transmission with ZF fluid, as some was lost while disconnecting the cooler.

So far everything runs well.

I went with the 10452HV oil pump in hopes that it would do good to the freshly rebuilt engine. I won't bet that it would save me from hemitick, but well, maybe it would help somewhat. I put the softer spring in it though, as I don't think there would be any benefits in higher max oil pressure. My idle is currently set to 650 rpm, so I keep telling myself that all factors together will make it last longer.

My cold (about zero celsius) start oil pressure right after she fires up is about 75 PSI, warm idle oil pressure is around 41 PSI, depending on the oil temp of course. Typical highway speed oil pressure is 63 PSI.

 

[EdGs]

Nice writeup, good pics.

 

[04fxdwgi]

Very nice. Did you change out the timing chain and guides also?

 

[Hagar1]

I'm not familiar with these HEMI engines, but with many others. Is it possible to have the rods facing the wrong way, stressing the pistons, like on some other engines?

The only real risk of a piston installed backwards is valve interference on some. A lot of racing guys would intentionally turn the pistons around to reduce friction by moving the "pin offset" to the other side. Back in the day, I did that with a 2.2 that I built. I was surprisingly powerful, probably up over 120 hp, much better than the old 93 hp 2.2. I reversed the pistons, ported the head, back cut the valves and installed a mild cam. It made an engine out of it. The other thing that made a difference was installing a turbo 2.2 trans torque convertor.
Surprised a lot of people at the traffic lights.

 

[Xsen]

Very nice. Did you change out the timing chain and guides also?

Thanks!

No. I've checked the condition of the chain, the sprockets and the guides and decided to keep them.