I have a freshly built LD9 motor with the 2.3 oil pump swap. We were on the dyno tuning, and after about 8 runs, #4 bearing started hammering. I am now tearing the motor down and looking for the reason why. All the passages were blown out and all the bearing clearances were double checked during assembly. Eagle rods, Wiseco 10.5:1 pop ups. HO cams, cut and ported head. The motor was performing well. It was making 130hp on a Mustang dyno. The oil pressure was holding steady at 60, never fluctuated. On the last dyno pass it started knocking. It was shut down immediately. The motor spun the #4 bearing on the stock pump originally, that is why it was rebuilt. Now the question is why?
After I tore it down, I noticed something that might be the cause. It appears that the pistons were hitting the head enough to put the machine marks that are in the head on the tops of the pistons.
I tore the motor down for the rebuild. It looked like it was never torn down before. I did not have the block decked for the rebuild. However the head was cut, I don't know how much. I told the guy who did my head, to just enough to clean it up. The rods are supposed to be stock length. The motor was only taken to 7400 RPM.
Thats just weird.
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I forgot to add it had an .030 Cometic MLS headgasket.
^^ . there is your problem right there. .030 head gasket and a decked block is playing with fire. you did not have enough piston head clearance (quench) for the rock that your pistons had.
clean up the pistons, check for cracks, if good, throw in either a stock head gasket (or fel pro) or get a thicker cometic. problem should be solved after that. well... either that or get a new block and you could run the .030 again if you really want to.
the head surfacing doesnt come into play because the area that the pistons hit has always been flat and can never come any closer no matter how much you shave off. now... the valves, definitely can....
actually, i hate to say it but im glad this finally has been a posted up problem. now we KNOW our engines definitely need a good amount of quench clearance.
PS.... why are you using what looks like stock intake valves and stainless exhaust valves?
Edited 2 time(s). Last edited Tuesday, January 18, 2011 8:46 PM
If it takes forever.... I will die trying. Underdog Racing
I did not have the block decked for this rebuild. I planned on just getting a thicker Cometic. The exhaust valves are just new stock ones.
Ouch. That sucks.
If the pistons are forged, they will likely not crack from this, but they may bend, in that the upper ring land will be pinched downward and crimp the top ring. I'd toss the pistons and wrist pins, frankly...after this catastrophe, they are very suspect.
The rods may have survived, but they should be inspected by a reputable machine shop for damage in terms of still holding the correct center-to-center distance and paralellism of the big to small ends, as well as big and small end roundness. Magnaflux inspection for cracks is a strong suggestion as well.
Lesson here for everyone: ALWAYS check piston deck height when replacing pistons, whether you machine the block or not. Rule of thumb is about .040" clearance to accomodate rod strectch at high RPM. More may be required for high-revving and/or larger engines: consult with a skilled engine machinist for details.
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
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www.turbosystem.com
Bill speaks! OP: listen to this man.....
If it takes forever.... I will die trying. Underdog Racing
I know ford 302 guys recommend 0.060" clearance for anything above 7,500RPM.
A different animal I know, but should be similar.
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The pistons appear to be fine. None of the top rings have been pinched. The rods will be checked. The #4 rod is also going to be resized to make sure that the bearing seats correctly. I didn't really damage anything other than the rod journal, witch can be polished. I have a new crank and bearings here, so I'm going to throw them in. I'm having everything inspected first, just to be sure before it goes back together. I've built many other engines with 0 deck clearance before and had no issues because when you add the gasket it USUALLY give you enough room. Not this engine apparently. Oh well, its getting an .051 gasket this time.
the crank might be able to be polished but it could very well be out of round now... definitely check that.
If it takes forever.... I will die trying. Underdog Racing
Brian Erb wrote: Oh well, its getting an .051 gasket this time.
.030 gasket and you where hitting the head, .051 gasket nets less then .021 quench, N/A w/high compression motor should have no less then .030 (usual recommendation anyhow). Please go thicker...
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z yaaaa wrote:^^ . there is your problem right there. .030 head gasket and a decked block is playing with fire. you did not have enough piston head clearance (quench) for the rock that your pistons had.
I have a .030 HG with decked block
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WHITECAVY wrote:z yaaaa wrote:^^ . there is your problem right there. .030 head gasket and a decked block is playing with fire. you did not have enough piston head clearance (quench) for the rock that your pistons had.
I have a .030 HG with decked block
You also have 9-1 pistons with a dish instead of a dome and therefore more clearance.
Zs Z wrote:WHITECAVY wrote:z yaaaa wrote:^^ . there is your problem right there. .030 head gasket and a decked block is playing with fire. you did not have enough piston head clearance (quench) for the rock that your pistons had.
I have a .030 HG with decked block
You also have 9-1 pistons with a dish instead of a dome and therefore more clearance.
But they should still have the same height at the edges.
1994 Saturn SL2 Home Coming Edition: backup car
2002 Chevy Cavalier LS Sport Coupe: In a Junk Yard
1995 Mazda Miata R-package Class=STR
Sponsored by:
Kronos Performance
WPI Class of '12 Mechanical Engineering
WPI SAE Risk and Sustainability Management Officer
Leafy wrote:Zs Z wrote:WHITECAVY wrote:z yaaaa wrote:^^ . there is your problem right there. .030 head gasket and a decked block is playing with fire. you did not have enough piston head clearance (quench) for the rock that your pistons had.
I have a .030 HG with decked block
You also have 9-1 pistons with a dish instead of a dome and therefore more clearance.
But they should still have the same height at the edges.
These look to have less clearance around the edges than my 9-1s. They slope up immediately while the 9-1s are flat then go into the dish. To me it looks like the head is mushed to conform to the slope of the piston where it goes up.
Hmm. Looks like the piston dug more than .020 into the head, and that's all you're gaining by going to an .051" gasket.
Something weird is up. Suggest you slow down and analyze more before tossing it back together. That contact at the edge of the chamber, between the intake and exhaust valves, concerns me. It's almost as if the head was cut enough to be now into the inward slope of the hemisperical chamber contour. Do you know how much was taken off the head?
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
Also the piston head damage could have occurred after the bearing went out, I have seen that before. The thickness of the bearing is a void space where the bearing no longer is allowing the piston/rod to smack into the head.
david- the edges of ur pistons are at the same level as his are.....regardless of compression ratio. also.. you may not have had ur block decked as much as his OR have as much piston rock as his. every engine is different. who knows, yours might be at the very maximum allowed for quench clearance (which is optimum for performance so great job!
)
how much was removed from you're deck anyway?
if you have a real tight engine and know what you are doing you can run less than the recommend amount of quench clearance and get away with it. its all in the math, the expansion rates of the pistons, the stretching of the rods, the give of the crank, the give of the block, even the give of the head as well as head gasket all come into play.
brian- i honestly think you'll be ok with an .052 but its all going to come down to the math.... this time definitely have ur piston rock and pop up measured and account for it.
If it takes forever.... I will die trying. Underdog Racing
Zs Z wrote:Also the piston head damage could have occurred after the bearing went out, I have seen that before. The thickness of the bearing is a void space where the bearing no longer is allowing the piston/rod to smack into the head.
Good point. The piston would indeed be able to travel farther upward with sufficient bearing damage...but he said the crank seems re-usable. Were the bearing that wiped out, I'd expect significant bearing journal damage on the crank.
Bill Hahn Jr.
Hahn RaceCraft
World's Quickest and Fastest Street J-Bodies
Turbocharging GM FWD's since 1988
www.turbosystem.com
The pictures I posted were of the cylinder that had the bearing go away. The rest of the pistons look like they hit the head ever so slightly. All the pistons look like they have a slightly different clearance, because the marks are different. I haven't had time to measure anything today, I went back to work after being laid off for a month. I can't believe I'm having these issues with an undecked block. I've built many engines, never had this problem. I'll get some pictures of the crank and bearing tomorrow. After looking at the crank again, it will need to be ground to be used again. Good thing I have that other crank, I just have to put the 2.3 gear on the crank.
...so you DID or DID NOT have a decked block?
If it takes forever.... I will die trying. Underdog Racing
I've torn down more than a few stock LD9's that the pistons where +.002 - +.005 above the deck. Always measure.
"The FACTS are always subject to CHANGE once the TRUTH is applied"
"In the entire history of man the only stupid questions are the ones that don't get asked"
z yaaaa wrote:...so you DID or DID NOT have a decked block?
did not... he said it a couple times lol
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yeah i see that now..
im at a loss now, the cometic .030 should have provided ample clearance.
brian - the block was not decked THIS TIME, but has it ever been? and are you 100% positive on that? (i realise thats a stupid question cuz you prolly would have told us, just trying to get all the info correct here.... )
If it takes forever.... I will die trying. Underdog Racing
Maybe the timing jumped for some reason, that's what happend when my pistons smacked the head in my engine the first time.
~2014 New Z under the knife, same heart different body~
______________________
WHITECAVY no more
2012 numbers - 4SPD AUTOMATIC!!
328 HP
306 TQ
