It's alive! Finally.

[optmaxx]

It fired up today after changing the PCM, and 30 amp Engine Control 1 fuse in the PDC at the same time, so I don't know which one fixed it. I did the break in procedure by running it up to 1500-2000 rpm for about 20 min, and I bled the coolant with a homemade burping funnel. It runs pretty good, I don't notice any hiccups or misses. It does feel a little tight though, I'm guessing that's from being rebuilt though right...?

I'm going to have to get used to what I'm assuming is piston slap, it kind of sounds like a diesel. It gave me a scare when I went to go start it up again from taking a trip to the auto shop because it started to make a pretty good clapping sound. My heart sank thinking that something went wrong with my engine internals because it wasn't that loud when I first fired it up. It got much better after driving it a bit, so I figured that it was the piston slap.

I put in 89 octane to start with, and I did get pinging but only because I forgot to plug in my VSS. Once that was plugged in, there was no pinging at all, so the Bulltear pistons deliver, and I am also running 24lbs injectors . Aside from the piston slap making me nervous, the stroker runs great and it has good power. I might need a new battery because the crank kept getting weaker as the day progressed, and my volt gauge shows that it is getting charged, so I'm guessing the it has low cranking amps. Thanks for the help.

[optmaxx]

I was hoping if anyone can tell me how loud stroker piston slap is supposed to be on start up? This is my first stroker build so I would like to be able to have some kind of reference to go by because mine sounds pretty loud, but it does quiet down after some driving and warming up, however it's still there. It not noticeable at higher RPMs though.

[optmaxx]

I wasn't sure if I should post this video because it's not a very good one, it seems to make the noise louder than it really is. I wanted to take another video with a better camera, but my Jeep battery is completely dead, so it's probably not staying charged because my Jeeps volt meter reads fine when its running.

Anyways, this a video of what my stroker sounds like with forged pistons. I'm assuming it's piston slap because it has all of the characteristics of it, like being louder when starting it up cold, the noise lowers to a diesel like sound when warm, and it goes away completely at higher RPMs. In this video it sounds louder, but in person it does sound more like a diesel and it doesn't really bother me unless I really focus on it...actually, the sound sort of reminds me of my friend's 4 banger turbo. I don't know if you can tell but it idles smooth, and the power is consistent throughout. I put in 8 gallons of 89 octane and I get no pinging, but there's also 8+ month old gas in there. I've only driven yesterday and today, but I can't keep it on the road too long because of my tags, so it's all pretty much fresh.

I put a stethoscope on the valve cover, and it all sounds normal to me. The noise didn't seem to be coming from the the valve cover, so I just figured it was piston slap; I didn't go under to hear what it sounds like yet. So, this is what my Jeep sounds like with Bulltear forged pistons with no offset pin.

https://www.youtube.com/watch?v=UvUO_8FvJDI

[nicpaige]

That sounds excessive unless like you say it is being exaggerated by the microphone on the camera.

[optmaxx]

It does sound louder in the video, and in person my exhaust sounds loud too but I can barely hear it in the video. I've been trying to look for videos to compare it to, but I've only been able to find other videos (that aren't jeeps) that have forged pistons that sound similar.

It doesn't sound that bad in person, but I just don't know what to compare it to either, and I hope that I'm not in denial haha. I even looked up info on pistons with no offset pin (Centered pin pistons?) because mine are not offset, and I guess they are supposed to slap more going up and down...but have less resistance than offset pistons. Anyways, it does sound louder in the video, and I was disappointed that it didn't sound like what I thought it sounded like. The noise doesn't bother me if that's the way it's supposed to be, because the power is awesome, I mean inside the Jeep it's barely noticeable and on the highway it's not even there.

To be honest I'm just assuming it's piston slap too, because I've never heard it before, I just know that it's confused with other bad symptoms haha. The oil pressure is great and it doesn't over heat. I'll try to get a better video with hopefully better sound

[Cheromaniac]

Yeah that's definitely piston slap but nothing out of the ordinary. The engine will sound like a diesel when cold so just go easy on it until it's warmed up. At higher rpm other mechanical noises will drown out piston slap so you won't be able to reliably tell if it's gone.

[optmaxx]

Yeah that's definitely piston slap but nothing out of the ordinary. The engine will sound like a diesel when cold so just go easy on it until it's warmed up. At higher rpm other mechanical noises will drown out piston slap so you won't be able to reliably tell if it's gone.

I'm glad that it's piston slap. If it turns out that my Stroker is louder than most, could it be because I'm running pistons with centered pins instead of offset? I probably just need a louder exhaust haha.

[optmaxx]

Here's another video. I suppose it's a bit better, I guess my stroker is just louder? It does sound like a diesel, but I don't mind if it's normal. I took off the valve cover to double check if the the rocker bolts were torqued to spec and they were, and I ran it without the valve cover and I was able to confirm oil was coming out of the push rods, but I confirmed that when I primed it. Again, I'm still curious if center pin pistons are like this. Excuse the mess, I was diagnosing a no spark condition. https://www.youtube.com/watch?v=od9tNik ... e=youtu.be

[SilverXJ]

Both of the videos sound like a noisy valve train to me. But it may just be the camera. However, the 4.0L is not what is considered a quiet engine. Add that with an aftermarket cam with a fast ramp rate and possibly roller rockers and the noise gets louder. Still, pretty normal.

If the piston clearances are set correctly the slap should go away with in minutes of driving. My pistons are set at .005" clearance and in this 80* weather I don't even hear them when cold. Now, in the winter it is pretty loud but it goes away with in minutes of being started.

[optmaxx]

Both of the videos sound like a noisy valve train to me. But it may just be the camera. However, the 4.0L is not what is considered a quiet engine. Add that with an aftermarket cam with a fast ramp rate and possibly roller rockers and the noise gets louder. Still, pretty normal.

If the piston clearances are set correctly the slap should go away with in minutes of driving. My pistons are set at .005" clearance and in this 80* weather I don't even hear them when cold. Now, in the winter it is pretty loud but it goes away with in minutes of being started.

If it's the valve train, could it be the lifers? I couldn't feel any play in the rockers, and the rods looked straight so I don't know how else to diagnose that. I agree that the 4.0s aren't quiet engines, and even my 4.2 with the mpi wasn't quiet, I just hope that the pistons are making it seem louder. The noise does goes away when driving, but it comes back, but it could be because it's harder to hear when driving. When I stick a tube against the valve cover, it doesn't sound loud, just normal rocker noise, I'll check again; I haven't been able to drive it much either....could the oil be too thick? I'm using Lucas SAE 30 break in oil.

I have been looking up info on pistons with no offset pin, and supposedly they always slap going up and down. I know i keep going back to that, but I just hope that someone can confirm that those type of pistons always make noise. If what I have is piston slap, it does make it a bit harder to diagnose car noise.

I forgot to mention that I did reuse the 4.2 rockers, but those are interchangeable. I am using 4.0 push rods for a 1996 4.0, I got those off of ebay. Thanks again, it does drive awesome though.

[jeepxj3]

Why do forged pistons 'slap' and stock pistons do not? Is it a clearance issue? Stock are fit tighter because they expand less?

[Cheromaniac]

Why do forged pistons 'slap' and stock pistons do not? Is it a clearance issue? Stock are fit tighter because they expand less?

Yeah, it's a clearance issue. Forged pistons expand at a faster rate than cast or hypereutectic pistons and require a greater piston-to-bore clearance. Most modern engines are fitted with hypereutectics to minimize the clearance and make the engine quieter. They also reduce emissions and allow the oil change intervals to be extended.

[optmaxx]

Both of the videos sound like a noisy valve train to me. But it may just be the camera. However, the 4.0L is not what is considered a quiet engine. Add that with an aftermarket cam with a fast ramp rate and possibly roller rockers and the noise gets louder. Still, pretty normal.

If the piston clearances are set correctly the slap should go away with in minutes of driving. My pistons are set at .005" clearance and in this 80* weather I don't even hear them when cold. Now, in the winter it is pretty loud but it goes away with in minutes of being started.

Sorry, were you saying that my noise was normal?

I remember when I did my 4.0 head to 4.2 block conversion, my engine seemed a little more noisy, and I was worried about rocker clearance. I even took it to my mechanic so that he could adjust the rocker clearance, but he ended up telling me to keep on driving it to let the lifters adjust. I did what he told me to do and sure enough, the engine quieted down considerably. Should I just keep driving it and see if it quiets down?

[SilverXJ]

Why do forged pistons 'slap' and stock pistons do not? Is it a clearance issue? Stock are fit tighter because they expand less?

The slap comes from the extra clearance when cold. The piston expands after a few minutes and the nose goes away. Stock cast piston have been know to make slapping sounds as well.

Sorry, were you saying that my noise was normal?

From what I can hear in the vidoe, yes.

Should I just keep driving it and see if it quiets down?

Just check things over such as preload and valve train clearances. If all checks out then drive it. The lifters would have already adjusted.

[6TIME]

I vote valvetrain as well....definitely. That noise is coming from the top end of the motor. The ticking at idle speed is much to high frequency for piston slap. Piston slap sounds deep and hollow, and like Silver said it's gone once the pistons are expanded and up to temp.