Piston ID

[Wrath]

Previous owner of my GN "Freshened up" the motor at some point... Anyone know what pistons these are? Thanks

 

[forcefed3.8's]

Stock

 

[dank GN]

Yep definitely look stock . Did he say he put different pistons in? What did he actually do with this freash in up?

 

[Wrath]

Previous owner didn't know much about what was done to it besides the bolt-ons seen under the hood... i have no idea what "freshened up" is but when I received the car it had some pretty bad exhaust/oil/tranny fluid leaks so I just assumed the worst... I have gone through most of the car but am looking at rebuilding the engine soon as it has a slight ticking/knocking noise at idle when warm and in park/neutral, in drive/under load you don't hear it. Ran engine without belt to ensure it wasn't any accessories causing the noise either. The compression test checked out and I don't have any smoke on start up or anything, but I'm afraid to take it past 10psi or enjoy the car for fear of causing additional damage from a unknown worn out bearing or something causing the knocking noise. Sounds like its coming from the lower end, already checked out flywheel for cracks and torqued down the torque converter bolts...

 

[dank GN]

Here is a good link to check out . Great info
http://www.gnttype.org/techarea/techpage.html
And this one aswell
http://www.vortexbuicks-etc.com/

 

[dank GN]

Here is a good link to check out . Great info
http://www.gnttype.org/techarea/techpage.html
And this one aswell
http://www.vortexbuicks-etc.com/

 

[Wrath]

From what I have researched, I was under the impression that the factory pistons were not notched on the bottom under where the pin is held and has steel reinforcing there that was easy to see... I found a pic of some Speed Pro Hyper pistons which look nearly identical to what I have. Not saying you guys are wrong or anything, just trying to convince myself

 

[turbo87adam]

Unfortunately the only way to figure out what pistons are in your motor is to find a part# and that usely means pulling a piston. I wouldn't go down that road until your completely dedicated to a rebuild. That being said my recommendation is to bring it to a well known and respected builder. As the old saying goes you usely get what you pay for.

 

[Wrath]

Thanks for the recommendation. I actually met with Jack Laswell in Royce City, TX back in March and showed him the first two pictures of my engine and he confirmed they were not stock pistons, even pulled one off the shelf to show me the differences. He just didn't know which pistons they were at the time so I was just interested to see if anyone here knew so I can get an idea on what I have.

 

[Buick Mark]

Those for sure are not the original Buick pistons.
Yes, you can easily see the steel strut in the Buick pistons from the underside.

 

[750H.P.V6]

It's a cast piston. It looks like a Speed pro replacement part.

Neal

 

[MAK507]

good luck man! I started chasing that “tapping/knocking sound” and kept throwing money at it with all of the different suggestions. I finally called it quits and sold the car. I would definitely not be driving the car with that until you figure out (and solve) it. My tapping/knocking sound got louder and louder the longer I waited. It got ridiculously loud at idle when I’d stop at a red. I should’ve pulled the motor out but I had no time. Again, good luck!

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[750H.P.V6]

Hyperutectic pistons are cast from a high silicon content aluminum alloy. They are much more dimensionally stable over a wide temperature range and typically run tight piston to wall clearance. If they were installed loose they will always make noise since they don't expand like a forged piston would as the engine reaches operating temperature. You might have other issues but possibly what you're hearing is just piston noise.

Neal

 

[Wrath]

Thanks for the replies. I have a video of the Tapping/Knocking noise Here , which I originally had on my Introduction Post. Sound familiar MAK507? Neal would you say that these pistons are an upgrade from stock? I have seen a bunch of posts about Hyperutectic pistons being poor quality/melting or failing on them... but I don't plan on racing, just looking towards a rebuild for street use, possibly reusing these pistons if they are in good condition, maybe to differ based on recommendations.

 

[earlbrown]

would you say that these pistons are an upgrade from stock?

Nowhere close. I'm pretty sure those are some FMO replacement pistons. Those are pretty much crap and nowhere near as strong as a stock slug.

The oil return grooves are huge and damn near run from pin to pin on both sides. That means the skirts are held on by two small points on each side. If the piston is loose in the bore and ever wants to rock over, that's where the crack will form.

You'll know if it happens because it'll pinch the rings and compression will go into the toilet. The breathers will smoke like a freight train from all the pressure shooting into the pan.

 

[jamesmac]

You may want to try removing the belt again to see if you can move the crank pulley back & forth by hand. could be something going on with the keyway, crank pulley bolts, or that funky cover over the crank pulley,

 

[750H.P.V6]

Neal would you say that these pistons are an upgrade from stock? I have seen a bunch of posts about Hyperutectic pistons being poor quality/melting or failing on them... but I don't plan on racing, just looking towards a rebuild for street use, possibly reusing these pistons if they are in good condition, maybe to differ based on recommendations.

I wouldn't use them in the first place and they aren't worth re-using after the fact. When you decide to rebuild you should look at getting a good set of forged pistons and go with those.

Neal

 

[MAK507]

Thanks for the replies. I have a video of the Tapping/Knocking noise Here , which I originally had on my Introduction Post. Sound familiar MAK507? Neal would you say that these pistons are an upgrade from stock? I have seen a bunch of posts about Hyperutectic pistons being poor quality/melting or failing on them... but I don't plan on racing, just looking towards a rebuild for street use, possibly reusing these pistons if they are in good condition, maybe to differ based on recommendations.

Not at all! Yours doesn’t sound internal. Sounds like something is maybe loose? Hard to pinpoint sounds [emoji22]


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[Wrath]

You may want to try removing the belt again to see if you can move the crank pulley back & forth by hand. could be something going on with the keyway, crank pulley bolts, or that funky cover over the crank pulley,

Not at all! Yours doesn’t sound internal. Sounds like something is maybe loose? Hard to pinpoint sounds

Yeah it has a under-drive pulley 75% size of the stock one, I'll try taking that cover off of it along with the belt to investigate.

Guess i'll also be on the lookout for any deals on Forged pistons too