JE pistons with press fit on stock rods? Anyone have any sort of fit issues ?

[Tim Cucci]

Just curious. I have 3.820 JE pistons with pressed pins in stock iron rods. Everything checks out so far but JE calls for a .050 min side clearance on the small end of the rod to the inside of the piston pin boss surface. Has anyone had a problem with this clearance when the piston is installed in the bore ? Just wondering due to crank being off center to the bore? I checked the skirt to wall fit and all holes were dead on .006 clearance up and down. I have not checked the inside minimum at .050 yet.

 

[Mike T]

Had a problem with this years ago and it ended up being 3 bent rods. They tend to be very close on one side anyway so a slightly bent rod will cause clearance issues.

 

[Tim Cucci]

I guess it is just a guess until I get the piston installed on the crank with rings and do a final check with feeler gauges. It does not look like I will have .050 min side clearance. Lots tighter than stock pistons. These Pistons are the stated pistons for the 87 GN Application per JE Specs. P/N131556. Hmmm?

 

[earlbrown]

The only way to know is to mock up the engine and check. The bad part is if you need to do some machining, the rod has to be removed in a press with a special tool that doesn't load the piston. (the reassembled after machining)


My 2618 pistons call for .040" per side and with a wide rod it's pretty tight.

 

[Tim Cucci]

just got the pistons put on the rods and everything balanced.

 

[Mike T]

The bad part is if you need to do some machining, the rod has to be removed in a press with a special tool that doesn't load the piston.

My rods had been cleaned, magnafluxed and resized but being bent still slipped by somehow. Pressed them back off myself and install K1's with floating pins.

 

[Tim Cucci]

Installed the pistons and rods yesterday. Wow! The small end under the pin has plenty of clearance but the very top of the rod over the pin and under the piston deck is extremely tight. There is clearance but I need to get a long feeler gauge to get a good check. The way the pistons are shaped above the pin does not work well with the stock rods.

 

[Tim Cucci]

All small end of the rods are to close to the inside of the piston pin boss fit. A couple have very very light rub marks where the very top of the stock rod had touched off while rotating the crank assembly. I just checked with a dental mirror and can see very little if any clearance on all six rods and pistons. On the crank all the mains are .0015 and all the rods to the crank are .0015. Crank turns great with no binding at 23ft. Lbs. of torque or less. Used Lucas assembly lube on bearings and tranny oil installing pistons. Side clearance is less than .015. This is terrible because all rotating parts have just been balanced and checked. Crank is stock standard and only polished . Thrust flange is fine and crank has .006 endplay. JE pistons are pressed on good stock rods. 1,3,5 dots face driver and 2,4,6, dots face front of the car. Anybody got any help here?

 

[dank GN]

I just got a set of custom pistons. I am dealing with something similar. My pistons call for .040 clearance all the way around the small end. If it's rubbing at all anywhere I wouldn't run it . It's easier and cheaper now to fix it then having to pull it again when something broken

 

[Tim Cucci]

Oh no. I'm not running it. Disappointing! I can't believe others haven't seen this issue with as many JE Buick GN pistons have been used with stock rods. Supposed to be a direct fit. I'm calling JE today. I don't know what would be different about mine. Im taking the pistons off the rods today and recheck the rods again. Im adding a couple of photos

 

[Rafs-T-Type]

Help a dummy out...what am I looking at here? What's the issue?

 

[Tim Cucci]

Side clearance on the small end of the rod. Above the wrist pin. Lots of clearance on one side and zero on the other.

 

[Mike T]

Same place mine hit. Are all of yours touching?

 

[Mike T]

The K1's were much more forgiving in this area.

 

[Mike T]

Help a dummy out...what am I looking at here? What's the issue?

He's referring to the area circled in red. The square boss on the small end of the rod rubs the side of the piston.

 

[Tim Cucci]

Thats it ! Right where the small end contacts the non machined surface.
I know one or two had a very very light rub and the others were very very close. I could get a .010 feeler in the gap but it's really hard to get an accurate feel. I just talked to JE Tech with not much help other than they said most people run aftermarket rods with these pistons but JE does not specify that. They recommend getting other rods or machining rods or pistons to clear.

 

[Tim Cucci]

The problem is the small end has the tall squared off end at the top. The K1's really do look to fit the piston much better. Is anyone out there running stock 3.8 rods with JE pistons? Can't believe this has not been brought up before?? Other than Mike T.

 

[Mike T]

Like Earl said you need a special tool to press the pistons back off of the rod. My machinist was not thrilled about doing this so he loaned me the tool.
Got them apart without hurting the piston but was not thrilled about putting that much pressure on a brand new piston.

The tool actually supports the rod so the pin can be pressed through but it take a lot of patience or you'll damage the piston.


Pins had a few scuffs so I replaced them along with the K1 rods.

 

[Tim Cucci]

Did you heat the rod? I've got a tool in mind to build and I think I can get the piston off without damage. If not I may just start over with new rods , pistons and rebalance everything. Looks like it's all gonna have to be redone anyway.
Man it's a shame cause everything else fits so good!

 

[Mike T]

No heat. The fixture has a hardened plate about 1/8th thick with a U shape cut out of it. The U goes between the rod and the piston and fits around the pin. You then press the pin out from the top in a hydraulic press.