[STEELCITYFIREBIRD]

If the noise is more pronounced or audible at lower RPM, and as as you stated...
Get the idle down lower, adjust the idle mixture/speed in now that the vacuum leak is? repaired. Clean or replace spark plugs if needed to smooth out idle.

I agree Joe, experienced sets of ears hone in on problem area pretty quickly.

[Va68goat]

ponchjoe,
I've heard of CVM. They're about 2 1/2 hours away. At this point I'm not getting in the way of Paul and the guy they found to look at this motor. I want to avoid sending this motor back to Arizona if at all possible.

chiphead,
I agree. Since we now have a third party looking over this motor, I think it would be a good idea to continue to let him see this through, if he is willing. I really don't want to see this motor leave Virginia. As for the pistons, I don't know what it means to coat a piston but thats not what I paid for. I've spent a ton of money on parts that were suggested that I obviously didn't need and the knocking noise has never left.

STEELCITYFIREBIRD,
We'll get the idle down where it needs to be. I believe Paul said 900 rpm would be good for idle. Though I want to get to a point where I can enjoy this motor, I'm patient enough to let this play out.

[chiphead]

Originally Posted by Va68goat

chiphead,
I agree. Since we now have a third party looking over this motor, I think it would be a good idea to continue to let him see this through, if he is willing. I really don't want to see this motor leave Virginia. As for the pistons, I don't know what it means to coat a piston but thats not what I paid for. I've spent a ton of money on parts that were suggested that I obviously didn't need and the knocking noise has never left.

.

I get that, you don't want to throw more money down a hole. The challenge here is that if the engine gets diassembled, it's likely going to need major component replacement to rectify the noise. If it's a machining or assembly error, then the builder should rectify that for you.

The challenge with something like piston slap is that it can be acceptable from a technical standpoint. A 2618 forged piston with .005" skirt clearance is a common clearance, and it may slap depending on piston geometry. A 4032 piston with .005" has a good chance of slapping, even when warmed up. That's why I asked what the piston was made out of. We know you're at about .005" skirt to wall now.

My 400 motor slapped at .0055" and I ran the snot out of it for years on the street, incl making several nitrous passes at the track. My machinist warned me it might slap, and it did. The early LS motors slapped before they went to coated pistons and they ran 100K like that. Point being is if you have piston slap with no other issues, some of that is normal with a heavily modified engine.

Excessive piston slap is when the piston has enough clearance to rock A LOT in the bore as it goes over TDC and BDC. That's what causes the slap noise, as the skirt to wall clearance transitions from one side of the piston to the other as the piston changes direction in the cylinder. This will cause accelerated piston ring wear and upset ring sealing. In severe cases, piston rock can damage the skirt and require replacing the pistons. So checking the skirt clearances should definitely be done if the engine comes apart.

[Va68goat]

chiphead,
I never knew that piston slap would be considered acceptable (not that I even knew that term before I had this motor built). I think Paul realizes that the knocking noise is not normal for this build which explains him helping us diagnose the motor for 2 years. As much as I want to be driving this car, I've pretty much accepted the fact that it's likely that the motor will be pulled in the very near future.

[redhawk44]

I have heard you guys talking about piston slap and thought it was the piston coming too far up. After reading Chip I learned something new.

The challenge with something like piston slap is that it can be acceptable from a technical standpoint. A 2618 forged piston with .005" skirt clearance is a common clearance, and it may slap depending on piston geometry. A 4032 piston with .005" has a good chance of slapping, even when warmed up. That's why I asked what the piston was made out of. We know you're at about .005" skirt to wall now.


Thanks Chip.

[gtofreek]

I'll say it again, that noise is not piston slap. The pistons are 2618 material and they require a minimum of .0045" clearance and when I measured them they are at .0047" after honing it. It's not piston slap. Doesn't even sound like piston slap. Anyone that's heard piston slap would know that.

[grivera]

My 08 Tacoma with 4.0 engine has had piston slap since new - common with these engines - and sounds different than the tapping in Joe's engine.

[Sirrotica]

Originally Posted by gtofreek

I'll say it again, that noise is not piston slap. The pistons are 2618 material and they require a minimum of .0045" clearance and when I measured them they are at .0047" after honing it. It's not piston slap. Doesn't even sound like piston slap. Anyone that's heard piston slap would know that.

I agree, My LS2 in my GTO has had piston slap since I bought it new in 2006, and now has 140,000 miles on it. It sounds nothing like piston slap. Piston slap also varies with ambient temperature. At below 32 degrees mine makes tons of noise until it warms the internals up, and when up to operating temps you can just barely hear it at idle. LS engines are pretty well known for it, it seems to hurt nothing as proven by making 140,000 miles with no issues.

This engine (to my knowledge) has no change in the rapping noise based on engine temps, so clearance issues are kind of eliminated, as cold oil, more oil pressure at start up, and shrunken parts cold seem to make no difference in the noise.

I wish I knew what the noise was, but worrying about piston slap is, IMO, chasing a wish. As many Stratostreak engines as I'd laid my hands on in 50 years time, I've never had one making that noise, with the symptoms this engine has, and the noise seems centered on the distributor area, (by all accounts of the people that have worked on it). Which pretty much leaves out piston slap because there are no pistons in the distributor area.

In one of the early videos when the car was on a lift, and the phone/camera was being moved around under the car, to me the noise is in the rear of the engine near the rear of the pan around the flywheel area. It however does not sound like a cracked flexplate, and has proven that changing it made zero difference. I said before the flexplate was changed that I thought changing the flexplate would not fix it, and it didn't. I believe it's in the distributor oil pump area, but I can't think of what it is, and I've thought about it a good bit.

The only hint I have seen is the oil pump driveshaft is rubbed shiney only on one side, but unless the pilot hole that engages the top of the oil pump drive was off center when made it could make a noise hitting the cast lug in the block. I think that all those components have been replaced though in doing diagnosis elimination, so doubtful there would be 2 driveshafts made incorrectly If the shaft is off center it may be what caused the lower distributor bushing to fail also, but that is entirely conjecture on other peoples diagnosis during this problem.

Maybe the new guy will bring more insight into the mystery noise, I hope for everyone involved this ends soon.

[chiphead]

Originally Posted by gtofreek

I'll say it again, that noise is not piston slap. The pistons are 2618 material and they require a minimum of .0045" clearance and when I measured them they are at .0047" after honing it. It's not piston slap. Doesn't even sound like piston slap. Anyone that's heard piston slap would know that.

Confirmation of piston material is helpful. My motor made a dull double knock noise at TDC and BDC, especially when engine wasn't warmed up. Since (most? all?) 8 cylinders were doing it, it had a rhythmic double rap that I got used to. I just didn't hammer on it before it warmed up. When water temps were up, the noise would be hard to hear, kinda like Sirrotica said.

I'm not saying this is piston slap for sure. One of those videos Joe posted had a double knock sound on the driver's side that sure mimics what my motor would do, just louder.

I can't imagine what else could make this noise and not come apart. Sure it sounds like it's coming from the rear of the engine near the oil pump drive. There's not much there unless the driveshaft is smacking the block d-shaft loop hard enough to make that much noise???

[Sun Tuned]

Any chance this thing might have a cam drive gear pressed on the back of the cam?
Any chance it's pressed/ machined not quite right causing an elliptical deal?

Runout check on it if it comes out...

[Dragncar]

The 461 I am doing now will make a little noise until warm. .006 piston to wall. .004 is what Ross wanted and said add another .002 if hard blocked. It is. .002 more ring gap too.

[STEELCITYFIREBIRD]

Originally Posted by Sun Tuned

Any chance this thing might have a cam drive gear pressed on the back of the cam?
Any chance it's pressed/ machined not quite right causing an elliptical deal?

Runout check on it if it comes out...

Would that be a viable, probable cause, for rapid wear of lower distributor bushing?

With that, have you checked for a repeat failure there?

[grivera]

Originally Posted by Sun Tuned

Any chance this thing might have a cam drive gear pressed on the back of the cam?
Any chance it's pressed/ machined not quite right causing an elliptical deal?

Runout check on it if it comes out...

It's a Lunati billet roller cam and gear is not press on type

[Sirrotica]

They have spun the engine over with the distributor removed and observed for runout, reported no runout.

[MarkS57]

Originally Posted by Sirrotica

They have spun the engine over with the distributor removed and observed for runout, reported no runout.

I thought he same- the cam gear run out could be an issue but it looks true in the video they took. Its a real reach but it might be possible the cam gear teeth (or distributor gear teeth) might not be machined right such that the cut depth & width of the teeth changes along the circumference of the gear effectively pushing against the other gear when a narrow cut engages the other gear...like a said...its a real reach.

Anyway, listened to the videos of the knock again last night, to me, the sound and timing are that of a bad lifter tap..but its a roller so???

[grivera]

It's a shame that [before shipping it back] Paul didn't take a video/audio on a run stand with engine idling considering the history of this engine

[Holeshot71]

Feel like I'm kicking a dead horse here but has anyone taken a length of hose and listened around where the exhaust manifolds bolt to the heads? Specifically around cyl #8 and #2 flanges? This has been brought up by several people but don't think it's ever been answered?

[Va68goat]

STEELCITYFIREBIRD & Sun Tuned & MarkS57,
That's all pretty interesting. The polymer gear that was on the distributor when it failed on the dyno was the same one that was on the distributor when Paul located the bad distributor bushing. When Paul sent the distributor to MSD to have the bushing replaced, he had me send him a new polymer distributor gear. I bought the same one that was one that was on the distributor before. Paul installed that new distributor gear when he got the distributor back from MSD and ran it on the dyno. Right now this engine has less than two hours of idle time and ha never been driven. The tech inspected the distributor gear and he says he was surprised to see the gear in that condition because it only had less than two hours of idle time. He described the gear as having an "uneven wear pattern". I'll try to get some pictures of it.

grivera,
I believe Paul posted that he had a video of the engine idling on the dyno.

[Va68goat]

Holeshot71,
We've checked for exhaust leaks several times and it's definitely not an exhaust leak.

[Sirrotica]

Since the thread started it was suggested numerous times, and has been thoroughly checked more than once, from the owner, and the people doing the diagnostic work, there isn't an exhaust leak.

The noise is most pronounced in the distributor area and seems to be a metallic rapping. It has been listened to with a long rod and a mechanics stethoscope and when the engine was returned to the builder and disassembled there was a lower bushing destroyed in the distributor which was replaced by the manufacturer.

I wasn't aware that the latest guy doing the diagnostic work had pulled the distributor and noted that the newest gear was showing a uneven wear pattern after only 2 hours run time. There is a possibility that even though there is no runout of the drive gear on the cam as observed through the distributor hole, that there is a manufacturing defect of the teeth as far as the helical cut of them.