Pistons

dmcguire

New Member
Joined
Jan 31, 2018
Hello all,

I just put together my 87' Regal and found out that cylinder 3 has no compression. After taking a snake camera down the spark plug hole I found out a portion of my cylinder is mission on the top side. I have a set of pistons by diamond, attached are a few pictures. It looks like the bore is 3.810" and the stroke is 1.685". My question would be are these a drop in piston or would I have to bore out my heads? I am somewhat new to the inside of engines, I have been around the outside of engines my whole life just never opened one up.

Would I be better off just honing the cylinder? I know that if there are just light scratches honing will work, but if the scratches are deeper then either a proper honing machine or bore to the next size up would be best.
 

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You really need to get the engine out and apart to determine the extent of the damage. It appears you have a burnt piston which will need to be replaced and more than likely the block will need to be bored / honed. FWIW, the pistons you have won't work as the compression height is wrong for a stock stroke and rod length.

Neal
 
Good god, you sent a lot of aluminum through the turbo! That engine's going to have to come out and come apart. Once that's done you can measure your bores and know exactly what you have.

Also, your stroke isn't 1.685" (I'm guessing that's the compression height of the piston in the wrong box) The stock stroke is 3.400".
 
Thank you for the replies, apologies on the delay. I just got the motor out two days ago and am still working on the disassemble process. I do have different connecting rods as well. I am unsure what they are as I have not looked that much into them.

I do have stock pistons that have some use to them, but was looking forward to upgrading while having the engine out, but if these will not work for my application I will just sell these and use the stockers I have already after they are cleaned. Unless it would not be much more to make these work. As I said before I am new to the insides of these engines.

More background on the engine. This engine was bought by my dad before he passed last year and was never in this car that I have now. The turbo I have now is a larger aftermarket precision turbo, so it is in great shape. I was trying to get away with installing the engine and having it ready to go vs redo everything since I was tight on time when putting it together the first time.
 
Update: Looks like the piston melted and did not score or engrave the cylinder walls. Attached are a few pictures showing that the metal from the piston coated a portion of the cylinder wall. I believe I may just hone and clean the cylinder wall and use a stock piston again.

The coolant was from taking off the head. All gaskets are in good shape.
 

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I wish I could say that all you will need is a hone and re-assembly but she sure looks angry. She got really hot!! Of course no one can say by pics alone but my advise is you better take it completely apart and send it to a machine shop and get her checked. If it sucks doing it once the second time is a real ass reamer. And as Earl said if there is particles everywhere and in everything you would want to take it apart just to clean the oiling system. FWIW.
 
Thanks for the reply. I do plan on taking it apart and having it truly inspected by a machine shop. I checked all the other cylinders before taking it out of the car and all had great compression, 150-160. Cleaning out the oil pan, there were a few small chucks of metal, but that was it and the oil screen was clear.
 
Should have been chunks of plastic from the top timing gear. Does you pickup have a round trap door on the screen?
 
That piston isn't melted, it's broken. Then it looks like the ring was flame torched after it lost it's shield. If that picture is accurate, then the cylinder wall was subjected to the same thing.

You're on the verge of going through a lot of trouble to end up with a compromised engine right out of the bat. If you were slapping together a Corsica to sell it at tax refund time, I'd say go for it....

....but on a performance car like these, that's as finicky as these... I HIGHLY recommend building it as right as possible. ESP when messing with the bottom end. That's the foundation that everything else is bolted to.
 
Yep she's hurt pretty bad. You're looking at a complete rebuild with fresh bores and new slugs.

And you have to prevent it from happening again by finding out what went wrong with boost / fuel / timing to cause it.
 
Should have been chunks of plastic from the top timing gear. Does you pickup have a round trap door on the screen?

The pickup screen did have a small round bronze part on it. I did not see any plastic pieces. only small metal parts.
 
That would be the trap door letting all that crap in the oil system...
 
That would be the trap door letting all that crap in the oil system...

I will be going through the engine to see whats been moving around in there. I hope everything stayed in the pan.

Should have been chunks of plastic from the top timing gear. Does you pickup have a round trap door on the screen?

As far as the timing gear, apologies for the ignorance new to the insides of these engines, why would parts of the timing gear be in the oil pan? I may find out myself when removing items from the engine.
 
Since the engine has head stud it stands to reason it's been rebuilt before. What is the bore size right now?

Neal
 
Since the engine has head stud it stands to reason it's been rebuilt before. What is the bore size right now?

Neal


I have not measured it yet. But from what I would believe its stock, just had work done to improve the stock motor. So far it had a very nice multilayered metal head gaskets, new oil pan gasket, head studs, and a metal intake manifold gasket.
 
I will be going through the engine to see whats been moving around in there. I hope everything stayed in the pan.



As far as the timing gear, apologies for the ignorance new to the insides of these engines, why would parts of the timing gear be in the oil pan? I may find out myself when removing items from the engine.


The stock timing gear is made of aluminium that's coated in nylon. After 30 years, they time out and start to break apart.

Since you have head studs and MLS gaskets, I'm going to assUme that your timing set has been changed out in the past.


Now for more potential 'bad' news. To run MLS gaskets correctly, the block needs to be decked to a smoother than factory finish (and put back flat). So now, not only do you need to know the exact bore size you're working with, you need to know how tall your decks are.
 
Here are the connecting rods I have with the pistons in the first post. I am not sure what the stock length rod is.

The stock timing gear is made of aluminium that's coated in nylon. After 30 years, they time out and start to break apart.

Since you have head studs and MLS gaskets, I'm going to assUme that your timing set has been changed out in the past.


Now for more potential 'bad' news. To run MLS gaskets correctly, the block needs to be decked to a smoother than factory finish (and put back flat). So now, not only do you need to know the exact bore size you're working with, you need to know how tall your decks are.

Thank you for the information. I will have too look and see what that is. As I mentioned I plan on taking it to a shop and have them inspect it before anything goes back in.
 

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If you're wanting to run those 6.350" rods, you're definitely going to need a set of my slugs. Those things will have a normal piston sticking waaaaaaay out of the top of the engine.
 
If you're wanting to run those 6.350" rods, you're definitely going to need a set of my slugs. Those things will have a normal piston sticking waaaaaaay out of the top of the engine.

Would the pistons I have work with those rods? or would I still have to get different pistons? What would a set of yours run?
 
Unfortunately the pistons won't work with the rods you have the compression height is way off. You could run those rods but you'll need a custom piston like Earl stated.

Neal
 
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