03 Mustang, found dinged pistons, pics.

2003 mustang gt modded · Aug 8, 2025

Found a small ding 5-6mm, another piston had smaller ding.

I tested compression 150 psi, it took 30 compression strokes to get to 150. But it’s consistent on all pistons.

My car was heavily modified by previous owner. Supercharged and valves look thicker, I think transmission has been built,,so I’m assuming it has low compression pistons.

I think no damage has been done. What you think? Thank you.

2003 mustang gt modded · Aug 8, 2025

nickyb · Aug 8, 2025

Hard to tell from that pic, just pull the heads and take a good look.
Its better to be safe then sorry.

Noobz347 · Aug 8, 2025

nickyb said:
Hard to tell from that pic, just pull the heads and take a good look.
Its better to be safe then sorry.

I'm with nicky. Can't make out much from that.

It 'appears' to have lot of sludge and it 'appears' that your high mileage piston rings are worn out.

2003 mustang gt modded · Aug 8, 2025

You may see little better here, the arrow is pointing right to the ding, there is a lilttle tiny mountain.

I thought compression check will show if there is bent valve.

Noobz347 · Aug 8, 2025

Valve damage would be in the center of the piston if they had come in contact.

squeak93 · Aug 8, 2025

Check the blower impeller. Looks like debris has entered the chat and caused those. Dings/dents will cause hot spots and those lead to other issues that get exaggerated with boost. I agree with the others that at least pulling the heads is in order, but I'd be planning a full tear down if it were me.

2003 mustang gt modded · Aug 8, 2025

Noobz347 said:
Valve damage would be in the center of the piston if they had come in contact.

What about this pic. New edge Mustang that has valve ding very close to ring land.

2003 mustang gt modded · Aug 8, 2025

squeak93 said:
Check the blower impeller. Looks like debris has entered the chat and caused those. Dings/dents will cause hot spots and those lead to other issues that get exaggerated with boost. I agree with the others that at least pulling the heads is in order, but I'd be planning a full tear down if it were me.

Thanks to all for replying. Pulling the heads is a really big problem because I don’t have the space to do this type of major work and I have long tubes on there which means I have to drop subframe.

If compression checks out ok I think it should be alright, I do know it can create a hot spot but I don’t plan to rev the engine past 4.5k rpm, but if I do I can monitor it with knock gauge.

The impeller is all good.

With more expensive scope I could see valves perfectly, it allows you to see upside down. That might be an option without having to remove the heads.

Noobz347 · Aug 8, 2025

95 mustang gt 302 said:
What about this pic. New edge Mustang that has valve ding very close to ring land.

That looks like it might be possible with an oversized valve.

If you're getting valve interference, you would see marks in the areas where these pistons are fly-cut:

Those reliefs are intentionally made to prevent interference and also mark the location where the valves would interfere.

With the right head/valve combo, I could see where the image you posted could come from valve interference.

2003 mustang gt modded · Aug 9, 2025

Noobz347 said:
That looks like it might be possible with an oversized valve.

If you're getting valve interference, you would see marks in the areas where these pistons are fly-cut:

Those reliefs are intentionally made to prevent interference and also mark the location where the valves would interfere.

With the right head/valve combo, I could see where the image you posted could come from valve interference.

Cool. 150 psi on all cylinders indicates to me that there is no valve damage. Just a low compression motor that was fully built for boost.

Noobz347 · Aug 9, 2025

95 mustang gt 302 said:
Cool. 150 psi on all cylinders indicates to me that there is no valve damage. Just a low compression motor that was fully built for boost.

Are you going to clearance those valves that time?

2003 mustang gt modded · Aug 11, 2025

On 2003 isn’t it hydraulic? Self adjust?

Noobz347 · Aug 11, 2025

95 mustang gt 302 said:
On 2003 isn’t it hydraulic? Self adjust?

Uh... Wut?

Hydraulic does [not] mean self adjust.

2003 mustang gt modded · Aug 12, 2025

Noobz347 said:
Uh... Wut?

Hydraulic does [not] mean self adjust.

Using a feeler gauge, check the clearance between the lobe and the roller. Ok. How much clearance should I have?

2003 mustang gt modded · Aug 12, 2025

I’m not a Valve clearance expert, I consider my self a Mazda rotary guy and rotaries have no valves. Anyway I did try .0015” and .0025” feeler gauge and they didnt fit.

Am I suppose to press down on hydraulic lash adjuster firmly? And then take measurement? Thanks

Noobz347 · Aug 12, 2025

View: https://www.youtube.com/watch?v=9it1cokiHSc

2003 mustang gt modded · Aug 13, 2025

Ok so lash adjusters and followers auto self adjust? That’s what lash adjuster does is removes any lash? So nothing to measure there?

As far as piston to valve clearance, I don’t think I need to do that.

Here is more details on car. It looked like with scope that valves are very thick, I think they are aftermarket. The ding in piston looked like it was a small object. I can see it’s not valve.
It has a grove with 2 parallel markings. I’m pretty sure someone ran the car without a filter before the supercharger and something must have gotten inside the engine.

If they put racing valves, didn’t they check clearance? May be.

I drove the for around 6 k miles, I still have working pistons and valves.

Car has 120k.

Who ever had the car put lot of money into it, it has accufab TB, Bbk valve covers,
Aftermarket intake manifold, Bbk ceramic coated long tubes, racing fuel rails and lines. And I think manual transmission is built, 3:73. Reason I’m mentioning because I think if they put so much money into it and did work to engine internals they should have done proper job , because why would they cut corners.

I’m considering of selling the car.

squeak93 · Aug 14, 2025

There isn't any adjustment in stock type of parts. To your point the lash adjusters pump up with oil pressure and do their thing.

It's possible the pistons never cause an issue and run for 100k, it's also possible to create a hotspot and window the block tomorrow. I'd roll the dice too but I've also windowed 2 blocks on boost.

If all items check with a scope, no missing pieces are found upstream then it could have been assembled that way and likely not an issue. Just make sure you're not missing a 10mm. lol

2003 mustang gt modded · Aug 18, 2025

cool thx. Are the motors prone to detonation because of missing knock sensors? I know that after running hard everything gets hot and motor is prone to detonate even if it has a good tune but the tune doesn’t react to extreme temps and knock sensors is needed for that.

03 Mustang, found dinged pistons, pics.

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