Originally Posted by rockstar143

and of course...it's the rear precat, right? Did you tighten down the bolts in a cross bolt pattern? Might be as simple as loosening all 4 bolts and re-seating it...

I did freak out when he said cut it cut it too...I'm guess it was Manny? I guessed the tile cutting right!

Glad it's working, CrabsMan.

Originally Posted by justnspace

I felt the air coming out of the front precat

Originally Posted by KR3J//

Which may be just as well since the pistons should be replaced anyways. Can it run without doing it? Yes. Should it be ran with damaged pistons? No.

I could sit here and attempt to explain combustion chamber theory, how combustion occurs inside the chamber with a thermal video, and how the damage to the top of that piston went through a protective coating on the piston but it'll be tough. That damaged area -small as it may seem- will cause a hot spot and in time will crack. When fuel comes into that combustion chamber it will light the fuel early (before the spark plug fires) and cause pre-ignition. Now instead of lighting off properly at TDC the cylinders that have damage will be lighting off a few degrees before TDC. Your exhaust valves will not be able to scavenge all of the hot gases out because it is designed to withdraw at a certain rate and close to begin the next stroke. So now you have heat that is trying to find any other way out and a damage that is beginning to crack. The crack will leave tiny metal shavings which will rapidly act like sandpaper against your cylinder walls and damage your now very heated piston rings. (That's where the leftover unscavenged exhaust gases will try and go, past the rings.)
What happens when a cylinder ignites before TDC and the other cylinders are firing correctly at TDC? Basically it's putting an opposing force on that cylinder, piston rod, and your crankshaft, twisting it. Now it's slight but now there is increased heat and stress on the bearings on your entire rotating assembly. It's not a matter of if the bottom end will go, it's a matter of when.

I would recommend doing periodic compression checks and invest in a magnetic drain plug. It could be worth going as far as to install an exhaust gas temperature (EGT) gauge to monitor increasing exhaust temps. It's a good way to monitor what may be a bad to worse condition. If your EGTs go from say 650 degrees to 825 degrees you'll know the crack/heat/cylinder wall is getting worse and could pull the motor early and reuse what parts you can.

This is just knowledge I've gathered from being an ASE mechanic, AMP Aircraft Mechanic and now Engineer. Best of luck guys, I'm pulling for ya!

Originally Posted by rockstar143

What did Matt buy?

Originally Posted by justnspace

The only reason to run those tests, are if you are unsure.


I am positive I lost compression due to a over-rev.
No need to test for it.


I am positive swapping the heads fixed the lost compression.
No need to test for it.

a test will only confirm my suspicions....
Fucked up engine....

and now its fixed.
so, why test for what I already know?

Originally Posted by rockstar143

Why am i yelling!!?!?!?

Originally Posted by TLDude876

Not because it is running means it is properly fixed but hey what do I know

Originally Posted by justnspace

^it pulls.

remember, I havent driven it for a month or two.
it pulls hard in 2nd, 3rd and 4th! i havent pushed it hard in 5th or 6th.

butt, if you ask me to remember what it felt like before it was broken, I couldnt tell you.

Originally Posted by I hate cars

You want him to replace the pistons after valve interference? I just skimmed over this, maybe I missed something.

Justin never did do any diagnosing to confirm that this was a valve issue to begin with. No pics of the valves or pistons were ever shown on this thread. Without knowing the extent of the damage there it's hard to come to a conclusion. Anytime metal impacts metal the way it does in a valve to piston strike, those small bits of metal go somewhere and unfortunately have a way of finding the piston rings/lands and scoring the cylinder wall. My explanation of hot spots on that cylinder is extremely hard to explain without equipment like this: CLICK HERE & WATCH VID
Sure it can run okay but long term will have an effect vs. no damage being there at all.

I don't agree with your EGT theory.
This was more of an idea to monitor any increased temps from that cylinder and would have to be placed on the exhaust runner which after reading this thread is far above the OP's expertise. A more practical way is to do a compression check every once in awhile (3-6mos) to be on the safe side. A running engine can have slight compression loss -on the chance anything found its way to the ring lands -and seem fine. Some increased exhaust smoke may not be so obvious to the owner. (There's loose exhaust bolts not tightened down here, for example.)

The part about twisting the crankshaft was funny. I think that's the point in most piston engines lol. Crankshafts rotate and should not twist.

I know what you meant but it was still funny to me. On a more serious note, detonation and preignition are hard on the bottom end but it's usually the ring lands that let go first. I mentioned the rings first and you're right, that's the first place they'd go.
Rarely do you break a crank , especially such a robust forged fully counterweighted crank held in with splayed 6 bolt mains and a built in "girdle". Here I was referring more to bearing failure due to an imbalance as opposed to crank failure but the piston rings and damage to the cylinder walls would occur first.. likely long before this would come to light.

Most importantly, we can monitor knock (preignition not directly) so if there is no knock, the cosmetic damage to the pistons isn't hurting anything. Again without seeing the damage it's hard to tell how cosmetic it is. Chances are it'll be fine for awhile, hopefully a long while.
These engines don't run much in the way of cylinder pressures, and unlike airplane engines, we're coasting or idling as much as we're under load, he will be fine. I wasn't comparing any of this to airplane engines at all but will agree he should be fine IF the compression checks out now. Technically car engines are under a load as soon as you put it in drive but it is less of a load while idling/coasting, I knew what you meant.
Welcome to the board, it's good to have a mechanic/ engineer on here.


Good to see Justin got it done. Since I bought a new car, it's hard to keep an interest in the TL. I think my future mods will be limited to the roof rack I've always needed for my mountain bikes. I've had the idea to do a direct injection 3.5 turbo, this seems like the logical evolution. Can't blame you for calling it good with the roof rack. You have plenty of other toys that are more fun and have more potential.