Box Stock

Predator 212 piston

Y

Yanko

New member
Hello, I have been building predators for a good amount of time. But just recently I’ve gotten into high compression applications.

My setup includes:
Rattlesnake cam: 230D and 251L
26lb Valve springs
14cc high compression head w/ porting
Stainless steel valves
Chromally push rods
flattop piston
Stock length billet rod
Billet flywheel
Billete side cover
Mikuni 22mm
Pulse pump

The top of my piston blew into pieces, and I would like to figure out why. I’m not sure if I have clearance issues or what. something to consider, the side cover on the engine blew off prior to the piston breaking. I wasn’t aware that the side cover came off my block and drove it for 1/2 mile, then the engine started getting very loud(I shut it off). I then looked on the inside of the short block and everything seemed to be fine. So I got a billet side cover and called it a day. After that I Decided to make the engine a hi-compression engine. Once I switched to the 14cc I felt a drop in power, only able to go 31 compared to 55. I did another top speed run and my piston broke. The cylinder walls didn’t even seem to be bad, even after the pistons broke(somehow). When I drained the oil it was black(seemed to be blow by).

also: I’m not sure this is a big deal, but also grinded off the top of my valve stem to make my rocker stay on the valve. Hopefully that didn’t make a difference but wanted to throw that in there.

I’m just confused and I probably did something really dumb lol. I don’t know how high compression stuff works I just tried it out of nowhere.Thanks for your time.
 

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The side cover coming off . Most likely allowed it to contact the head . Which caused it too fracture .
What's the head look like?
How many pieces were left that's a big chunk .
 
The head is a little beat up but I think its still savable. There is no major chunks taken out of it and it.
 
Get yourself some modeling clay. Place a few dabs around the piston and under the valves , assemble head . roll it over a couple times . Pull head . See what you have for clearance.
 
On that billet side cover, what was the end-play on the crank when you put it back together? What was it originally with the stock side cover? Use the gasket thickness to set end play at about 0.010" for the slop you need on the crank. Too tight will blow the cover every time at higher rpm's. If you don't check it, you won't know what it is...
Zeroed.jpg
 
With more compression there's other things you need. More octane, (there's a limit) colder plug, less timing and adequate valve clearance. There are limits. You can raise the compression pressure to a point that even race gas will detonate. Detonation looks like the top of the piston was sandblasted in places. Same for the head. Because my eyes are getting so bad, it's Hard for me to tell from your picture.
More details on your build are needed. If you don't know just say so.
 
So the side cover coming loose you ran it without oil for who knows how long. So after the side cover loosening and it getting hot did you put new rings/pistons? Did you look at the rod? I have a hard time telling from that first post if you just looked inside and bought a new cover and bolted it back together or if you checked anything.
 
How far in the hole was the piston at TDC? If you had it close to zero deck and from the picture I can see a thin steel .009 head gasket it won't work. You have to have at least .030 piston to cylinder head clearance, otherwise the piston will contact the head at high rpm. The results are what you have. I've seen it on many motors.
 
racinnut15xm said:
So the side cover coming loose you ran it without oil for who knows how long. So after the side cover loosening and it getting hot did you put new rings/pistons? Did you look at the rod? I have a hard time telling from that first post if you just looked inside and bought a new cover and bolted it back together or if you checked anything.
Click to expand...
When I shut it off It was loud but still running so I bolted it back together and ran it
 
As per the picture above the piston failure is Detonation from to low of Octane fuel. have seen it way to many times to count. A 14cc head and a thin head gasket needs 110 fuel depending on the deck height and timing.
 
bpoirier said:
How far in the hole was the piston at TDC? If you had it close to zero deck and from the picture I can see a thin steel .009 head gasket it won't work. You have to have at least .030 piston to cylinder head clearance, otherwise the piston will contact the head at high rpm. The results are what you have. I've seen it on many motors.
Click to expand...
It was a standard sized head gasket
 
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