Honing cyl bore to increase piston to wall clearance

[ruff ruff]

Everybody would agree that heat causes the pistons to expand into the cylinder walls. Addressing coolant flow to the rear cylinders helps. Other cooling mods help. Having a good safe tune helps. Not making banzi top speed runs definitly helps. None of these actualy address the fact that a forged piston is very tight to an iron cylinder wall. Bore diameters and piston diameter varies which could result in very tight clearances.

What I'm getting at is alot of people replace their pistons either to avoid this problem or after damage has taken place. I keep seeing that "pistons are the weak link" and "pistons should be on everyones mod list" ect.

I'm wondering if piston replacement is even needed. Would disassembly of the motor having each cylinder torque plate finish honed to match it's individual piston and increase the clearance be a solution? It seems like the pistons themselves are not the week link in the motor, just the clearance. Is there any reason why the pistons themselves can not take the same strain as the rods and crank?

If increased clearance and a new set of rings is all it takes to prevent this you can get off a whole lot cheaper than what larger pistons rings a bore and hone would cost you.


On a related note those of you who have seen your cylinder walls, how much ring ridge is generated at the end of the sweep of the rings in the cylinder???

 

[ShelbyGuy]

but the pistons ARE a weak link, and not just the clearanace. the pinston's ring lands are placed for emissions compliance, not for strength. when a piston lets go, what happens? the compression ring land blows right off.

I suppose if you have lots of time and no money, you could get the hone out, but if you have lots of time and no money, trade the car in on a focus and get a job.



If the pistons were't already a weak link, then yes, what you're suggesting would make perfect sense. It all depends on how crazy you wanted to get with the boost.

 

[dougwg]

If you are going to go through all the trouble of taking the motor apart....pistons don't cost that much.

It's like installing a new clutch and not replacing the Throw out bearing

 

[bigbadwolff66]

Does anyone know what the depth of the first ring land is on the stock piston? Measurement would be from the top of the piston to the top of the first ring land.

 

[ruff ruff]

but the pistons ARE a weak link, and not just the clearanace. the pinston's ring lands are placed for emissions compliance, not for strength. when a piston lets go, what happens? the compression ring land blows right off.

Could you please show me an instance of the ring land failing on a stock 03-04 cobra motor not attributed to detonation or piston to wall clearance issues? I would like to see pictures if avalable. All failure pictures I have seen involved piston to wall clearance or poor tuning.

Like you said importance is placed on emissions. That would also dictate a small compression ring gap and probably a tight ring groove as well. If betwen the piston expanding and the compression ring expanding the ring has nowhere to go then the ring land breaks that is not a piston failure that is still a clearance failure. Either piston to wall(since the ring groove depth expands along with the piston) or too small of a ring end gap.

I suppose if you have lots of time and no money, you could get the hone out, but if you have lots of time and no money, trade the car in on a focus and get a job.

I guess you have money to burn. We arn't talking a $5 diffrence here. Pistons can set you back something like $500-$900 for one of these cars. It costs money to get the rotating assembly balanced and if you can't use aftermarket stock diameter pistons you'll have to bore the block .020" over that costs money too.

If there is no reason to spend that money, why would you? You can spend it elsewhere.
If all it takes is rod bolts some new rings and a hone to be able to make 700 or 800 horsepower at the wheels why replace the pistons?

 

[ruff ruff]

Does anyone know what the depth of the first ring land is on the stock piston? Measurement would be from the top of the piston to the top of the first ring land.

Also what is the groove depth the grove thickness and what kind of diffrence is there between the skirt and head diameter on the stock pistons?

 

[jtripp]

I ponder the same things as ruff ruff. I have a job but also value my money

 

[01yellercobra]

Holy necro thread.

Not sure what there is to ponder anymore. Plenty of people making 700+ on stock engines. If you're making back to back to back 160mph+ runs I think pistons are the least of your concerns.

 

[badcobra]

If I am tearing the engine down and honing cylinders, last thing I would ever do is put stock pistons back in. The skirts on stock pistons are paper thin and they are very low compression. The other consideration is, after all those heat cycles, the pistons have differing diameters, meaning each piston will measure different requiring you to have to hone each cylinder accordingly to hit target ptw clearance. While the '03/04 Cobra OEM piston was a decent offering, it was a mass produced part and the cheapest Ford could find to do the job.

 

[MalcolmV8]

If I am tearing the engine down and honing cylinders, last thing I would ever do is put stock pistons back in. The skirts on stock pistons are paper thin and they are very low compression.

This right here.

 

[Wings65288]

Lmfao whoa blast from the past of when i joined here back in '04. I started reading this thread just now and saw ShelbyGuy, Doug and i was like "oh WOW these guys are back on here now?!".