Im on motor #2 in the last 3 weeks and both of them now have started slapping the pistons bad. They are both jy 05 5.3's. Is it just normal for them to rattle like ****? Cold it sounds like a bad rod knock when its warm like loud valvetrain. I hear stories nonstop of how great they are but this has happened twice now in 3 three weeks. Why?

 

my motor does it cold but goes away hot...been like that for 2 years and still runs strong...common problem

http://www.pistonslap.com/

 

Since you posted in the forced induction forum, are we to assume you have some sort of a blower, turbo, on it??
If so, maybe your tune is doing the damage..What did the first failure look like??

 

Got any vids?

 

Yes its boosted by an s475, no vids. The first motor didn't make a tick until I overheated it badly they in knocked so I pulled it to find no damage anywhere except that I can rock the pistons in the bores almost an eighth inch. This second motor ran great no noise for a week. Last weekend I was beating on it alot with the boost all the way down to 7 trying to get the carb dialed in. Got it good so I turned it up to 11 and after the first pull it started rattling. Now it sounds like a really loud rod knock when cold then when warn really loud valvetrain noise. Im sure its the same thing as the first motor. My afr was 11.1 and my timing at 11lbs would've been 24° I just need to know why this is happening?

 

I am on corn by the way as well.

 

That timing seems pretty high

 

^^^^^^^ What Goat said. That is alot of timing for a stock engine...
Do you read the plugs ??

 

That's been the thought but I've always heard pulling the timing on a 1:1 ratio is very safe. I've been researching ballpark figures for similar setups and mine is higher than anyone elses though. Ill have to hook my map sensor up to read vacuum also and redo my curve.

 

1:1 on a blowthrough E85 set up is pretty conservative. I cant imagine your IAT's are very high either.

 

Really I am looking for an explanation of why they started slapping as both motors were quiet at first and what exactly has happened since the pistons out of the first motor still appear perfectly fine. Are my rings going to hell from the heat and failing to stabilize the pistons or something? Im really looking for answers cause at this rate ill eat up 4 more engines this season alone.

 

disassemble the engine[s], look to see if the pistons have cracked, collapsed, scored, etc. Check brg condition. Brg shells pulled away from the bores, burned, etc?
Main caps walking?
Check the rings in the bores to see if they have collapsed.
Do the rings show the end gaps to have closed up, and made contact?
Are they loose in the piston grooves?
Cut the oil filters open. What's in there???

Just because the engine didn't cough up it's guts prior to making it to the junkyard, [knocking, etc], having it pushed to double it's rated output, very well was more than it could handle...[Obviously. Since you have 2 dead "players".]

Time for the "medical examiner" to go to work!

Beating on it, and not keeping CLOSE watch on the plugs, is not an "upwardly mobile move"....

 

I have taken apart the first motor the main and rod bearings were in great shape. A few cam bearing were worn to the copper but not spun. The pistons measure .008 below bore size in the skirt area and about .035 smaller than bore size at the top, which I've been told is typical. The bores are round and concentric within a thou and they have no scuffs scratches or any type of damage. The rings move freely in their lands and do not appear to have touched ends.

 

Old Geezer is right!
I believe this is what caused my engines ultimate demise.
After a year of listening to cold knock ( which seemed to develop overnight)
My engine melted a piston, #7 after too much boost and no intercooler.
I decided to remove the others and found this on 2 others pistons. You might have a broken ring land and not know it.

 

Too much timing=too much cylinder pressure which probably has broken the ring lands.

Running it rich will also weaken the ring's. 11.1 to me is rich.

 

24*..... is perfectly fine for lighting that motors fuse.

 

Its not pig rich, but could probably be leaned out .5-.75.. Though I've read a few tech articles that 11.o-11.1 on boost makes the most power as far as E85 is concerned. This is straight from yellowbullet, though the numbers are a bit rich IMO

Lambda E85 AFR Gas AFR
0.500 4.880 7.350
0.510 4.978 7.497
0.520 5.075 7.644
0.530 5.173 7.791
0.540 5.270 7.938
0.550 5.368 8.085
0.560 5.466 8.232
0.570 5.563 8.379
0.580 5.661 8.526
0.590 5.758 8.673
0.600 5.856 8.820
0.610 5.954 8.967
0.620 6.051 9.114
0.630 6.149 9.261
0.640 6.246 9.408
0.650 6.344 9.555
0.660 6.442 9.702
0.670 6.539 9.849
0.680 6.637 9.996
0.690 6.734 10.143
0.700 6.832 10.290
0.710 6.930 10.437
0.720 7.027 10.584
0.730 7.125 10.731 @ Max Power Multi Turbo
0.740 7.222 10.878
0.750 7.320 11.025 @ Supercharged/Turbo
0.760 7.418 11.172
0.770 7.515 11.319 @ Max Power NA
0.780 7.613 11.466
0.790 7.710 11.613
0.800 7.808 11.760 @ Consistant Race
0.810 7.906 11.907
0.820 8.003 12.054
0.830 8.101 12.201
0.840 8.198 12.348 @ Part throttle RACE
0.850 8.296 12.495
0.860 8.394 12.642
0.870 8.491 12.789 @ Idle
0.880 8.589 12.936
0.890 8.686 13.083
0.900 8.784 13.230
0.910 8.882 13.377 @ Part throttle STREET (economy)
0.920 8.979 13.524
0.930 9.077 13.671
0.940 9.174 13.818
0.950 9.272 13.965
0.960 9.370 14.112
0.970 9.467 14.259
0.980 9.565 14.406
0.990 9.662 14.553
1.000 9.760 14.700
1.010 9.858 14.847
1.020 9.955 14.994
1.030 10.053 15.141
1.040 10.150 15.288
1.050 10.248 15.435
1.060 10.346 15.582
1.070 10.443 15.729
1.080 10.541 15.876
1.090 10.638 16.023
1.100 10.736 16.170
1.110 10.834 16.317
1.120 10.931 16.464
1.130 11.029 16.611
1.140 11.126 16.758
1.150 11.224 16.905
1.160 11.322 17.052
1.170 11.419 17.199
1.180 11.517 17.346
1.190 11.614 17.493
1.200 11.712 17.640

 

Those numbers add up very well with how the engine responds. Thanks for posting that I will have to pull the rest of the pistons to check them.

 

Mark Sullens info?

And to the guy that said 24* is "perfectly fine" how do you know it's perfect if you aren't reading the plugs? You don't. The guy is on his 2nd motor in 3 weeks. There are people running these things for years without that kind of issue.

 

Well to the guys running them for years, ill assume most of them aren't just letting them slap the whole time right? Cause I am getting alot of "that's just what they do" type comments also.