lost a piece of piston...Stumped?

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Yeah I hate when people say how great their car is and you show up and it's junk. Especially long distance wasting all your time and money. Pull the pistons and check the top ring gap. There is a factor to calculate how big it should be if they are the hypers.
 
The clearance between the top of the piston to the cylinder wall is meaningless. It has zero to do with piston stability. Not one thing.

Piston stability comes from the piston skirt. The skirt is where piston to cylinder wall clearance is measured.

Although it looks like a lot of room between the piston top and cylinder wall, and may be, the only correct place to measure clearance is between the skirt and bore and nowhere else.

Hypereutectic pistons (specifically Keith Black) have smaller piston heads to allow for greater expansion. The reason for this is they have a higher percentage of silicon alloy. This is why ring gap is so critical and why they can also appear to have too much clearance at the top.

The Speed Pro Hypereutectics are different in that they do not require special ring gaps, because they do not have the high percentage of silicon alloy as the KB. So not all Hypereutectic pistons are created equally.

You did not specify which pistons you have, or if you did, I missed it.

My guess as to the cause of the damage is incorrect (too tight in this case) ring gap. Hypereutectic pistons have such a great rate of expansion at the top, that they will butt the ring ends together and cause the damage shown unless the gaps are within the specified specification.

Too many people blame hypereutectic pistons and call them "junk" when it is incorrect ring gaps that usually cause the problem.

If that engine was mine, It would come all the way back down and every single clearance double and triple checked. I think whoever set the ring gaps up, did it wrong. Simple as that.
 
Mad Dart said:
Shoot, I've lost a complete piston, Rod, cylinder wall & a valve in one whack. They disappeared into thin air. I found pieces of parts in the carb! After I put the new motor in and fired it off, there were pieces and schrapnel flying out the exhaust... A lot of it was caught in the mufflers.
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Louis,
Was that the motor from the 70?
 
There may something funny with the picture, but the crown of that piston appears to be 1/8" away from the cylinder wall. No 4" piston, cast or hypereutectic or otherwise is going to grow that much. If the picture is accurate, that's the wrong slug for the hole.

I'm curious to see a picture of that piston out of the motor, and some measurements.
 
Unless you are absolutely 100% sure that this was caused by a foreign object in the combustion chamber of that cylinder alone, as opposed to possible incorrect ring gaps, skirt clearance or detonation. You are going to need a full set of 8 new pistons.

Logic dictates that if you have one broken piston then the other 7 are probably not far behind. :sad:
 
Well it was a slow moving day I didn't get much done on it, took me awhile to pull the motor by myself and I got a late start. So I just barely got the engine on a stand before calling it quits.

But we measured bore and it measure out to be 4.60. Will have the pistons out tomorrow, sorry for this taking so long :(

Also a good thing this happened cause look what I found on the cam.....

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id check the wholes to see if they are in round ,like it was plate bored I think they under bored the holes went .020 over when it needed .030 over or went .030 over and put oversized rings on .020 over pistons, wow I did that to my very first car 37 years ago ,was a 69 Camaro that I always over reved it ,until 1 night it got real slow I took off the head s and had 3 pistons that looked like that mike from performance research just finished my motor if you want a new bad *** 360 +.030 with RHS X HEADS 2.02all done up 62cc heads / cc 525 20-228-4cam m1 intake I could sell you and have another 1 built quik and would come with a warrentee . I know that feeling that sux and I would rebuild a new motor if it was mine , I hate to see what other damage is done ,trying to just thro a new sleve and cylinder in it .that's beyond bandaids but I don't know much about building motors with more than 2 cylinders in them . ive seen them a lot worse at 13000 rpm any 1 down south would love that rush right now down the roads lol what a bummer I do have old cheap pistons if you want to put that engine back together pm me if interested or want performance researches phone # 3/4 of what he builds is mopar , midget and sprint and modified engines.G/L WITH THAT 1 bummer
 

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Use forged pistons for your next build.
Did you have a possible coolant leak in
that cylinder?
 
how do you have a 4.60 bore. when standard bore is 4.00. something is wrong with your measurement.
 
I with a few others that said it looks like the piston was to small for cylinder . Looking at the pic looks like there is a huge gap between the piston and cylinder wall. Almost like throwing a hotdog down a hallway lol
 
moparisbest said:
I with a few others that said it looks like the piston was to small for cylinder . Looking at the pic looks like there is a huge gap between the piston and cylinder wall. Almost like throwing a hotdog down a hallway lol
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as posted a couple of times..the clearance is at the skirt..not the top of the pistons...LOL
 
HOOCH said:
Well it was a slow moving day I didn't get much done on it, took me awhile to pull the motor by myself and I got a late start. So I just barely got the engine on a stand before calling it quits.

But we measured bore and it measure out to be 4.60. Will have the pistons out tomorrow, sorry for this taking so long :(

Also a good thing this happened cause look what I found on the cam.....

Posted via Topify using iPhone/iPad
Click to expand...

That looks like Valve Bounce damage. Lifter smashing into the cam when the valves FLOAT! Lol haaaa
 
Mad Dart said:
HOOCH said:
Well it was a slow moving day I didn't get much done on it, took me awhile to pull the motor by myself and I got a late start. So I just barely got the engine on a stand before calling it quits.

But we measured bore and it measure out to be 4.60. Will have the pistons out tomorrow, sorry for this taking so long
icon_sad.gif


Also a good thing this happened cause look what I found on the cam.....

Posted via Topify using iPhone/iPad
Click to expand...

That looks like Valve Bounce damage. Lifter smashing into the cam when the valves FLOAT! Lol haaaa
Click to expand...


We checked the valves and they were fine. Going to have it all apart today and we will know the size

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HOOCH said:
We checked the valves and they were fine. Going to have it all apart today and we will know the size

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Valve Bounce/Float won't mess up the valves unless it is so bad they hang open long enough for a piston to smash into them. Look at the bottom of your lifters that ride on the cam, that is where you would see damage…..Roll all your pushrods on a piece of glass to see if they are bent also. It's no big deal and part of the game, out with the old and in with the new!:D
 
Well this is the post everyone has been waiting for, and it's with a sad heart that I say she is toast :(

Bore measurements were anywhere from 4.050-4.055 at the top with a caliper, and I used a lil bore tool then measured the tool and got 4.060 in the center.

Piston measures 4.030 @ the skirt and is a KB190 here are some pics I was able to snap!

Also it's kinda hard to tell but the close up of the break it appears that the piston is slightly melted.

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How the hell could somebody make that mistake? Damn. You have to start from scratch. That really blows mega chunks.
 
That motor's fucked in more ways than one, and I'm betting you find more wrong as you start looking. Toss it on your local Toyota dealer's lot and start over. You don't want to find out what else they screwed up after you rebuild it, especially when it's .060" over.
 
look at the end gap of the top ring is it me
or something look weird???

the cylinder bore little scratch as we can call them doesnt affraid me much,little honing will do the job as I can see

new cam and 8 pistons later with rings will do the job!!

the cranck seem to be ok

you can get KB 190 for less than 400$
Doug herbert selling cam for pretty chip so...
http://www.dougherbert.com/index.php?main_page=index&cPath=83_84_85_623
 
I'd start with a fresh block as well. I stay away from sixty over 360's. Seen several locally that liked to run hot. Mine at 30 over runs nice & cool.
 
That really sucks! You might be able to reuse some of the pistons in another .030 over 360 block to save some money.
 
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