JE Wrist Pin Choices?

[KTL]

I see JE has a pretty extensive selection of wrist pin choices. The typical SC 22mm pins that come with their "off the shelf" JE pistons are the 866-2500-15-93C

That number means:

>0.866" dia. pin (22mm)
>2.500" length
>0.15" wall thickness
>93 series pin material "Manufactured from case-hardened high-nickel carbon steel, these pins are popular in high horsepower circle track, road racing and endurance racing due to good ductility and fatigue characteristics."
>C = lock type= chamfered pin end

This pin is straight wall and weighs 108g ea. Searching thru the other pins they offer, same 0.866" dia., same 2.500" length, they have a 0.10" and a 0.12" wall thickness pin in 52 series steel material.

52 series steel is a step below 93 series "Often referred to as "Tool Steel", 52 Series pins are through-hardened 52100 high-carbon bearing steel and are an affordable upgrade for forced induction or nitrous-fed drag racing applications. 52 Series pins offer high-strength but low ductility."

What got me thinking about the thinner pins is not only their lower weight (0.10" wall thk pin is 77g each, 0.12" wall thk pin is 90g each) but the fact that all the Carrera JE piston kits use 52 series steel.

For comparision:

Carrera 3.2L JE piston pin is spec'd for 23mm (0.905") pin number 905-2500-15-52C which means it is same 0.15" wall thk as my SC "off the shelf" pin but is 52 series tool steel like the lighter pins they offer. Strange that the Carrera spec pistons use the lesser 52 series material compared to the SC spec pistons.

930 3.3L JE piston pin is also 23mm and number 905-2500-18-93C which means it is 0.18" wall thk and 93 series steel. The thicker 0.18" pin makes sense here since the 930 has higher cylinder pressure.

Just wondering if it is possible to consider the lighter pin for my application. Engine is a 10.5 C/R 3.0L with carbs, Web 120/104 cams, Pauter rods, lightened crank used for sprint racing kept under 8000 rpms.

I know there were some problems with JE pistons way back when and I believe that was traced to the tapered wall pins? The two lighter pins they offer are straight wall. The 0.10" pin (33% reduction in thickness..... ) @ 77g seems like a risk, so i'd be considering the 0.12" pin, which saves a considerable 18g per pin.

Plan is not to just throw the engine together and run it forever. It'll be timed-out at a fairly strict 80 hr. interval (timed via actual rpm-triggered hour meter) so that's one reason why i'm considering cutting weight on the piston pins.

Was also planning to lighten the pistons so that also plays a role in considering the lighter pins. I should have gotten the FSR (Forged Side Relief) piston design, but I dropped the ball and missed checking that on my build sheet....... me = moron because I really wanted that feature & just plain forgot to confirm. So have to wait to use that feature next time around.

Thanks,
Kevin

[Mark Henry]

Not really sure Kevin, but I'd say go with the lighter pin.

My specs for the engine I'm building for my 914 is close to yours, although I'm just building for a street car and plan to keep the rpm's in the stock-ish range. I'm using Mahle RSR (style) pistons, I could weigh a pin for you if you like.

[KTL]

Thanks for the thoughts Mark. I did weigh all my pins. That's actually something I need to call JE about. I was a bit disappointed to find the spread in weight.

109.0
108.4
109.6
109.1
109.7
108.5

As far as pin diameter, they all meas'd OK at either 0.8658 or 0.8659. With my rod small ends at 0.8666 to 0.8668, i'm content with the 0.0008 or 0.0009 clearance

Pauter did a nice job honing the small ends because I asked Brian to hone them with consideration for JE's 0.8660 spec'd pin diameter, so i'd have a 0.0006 to 0.0007 pin fit

[Mark Henry]

Those numbers are close to +/- 1g, what's the difference when you swap the pistons around trying for balance.

I didn't weighed each pin but the one I did weighs 92g, the piston 554g for a total of 646g. I'll see what the spread are on mine, I'm sending the whole engine out for balancing next week.

[Mark Henry]

My pins are dead nuts on, my pistons are 0.0, +0.2, +0.7, +0.8, +0.9, +1.2 grams.

My question is where is the best area to remove material for balancing?
Maybe I should start my own thread....

[KTL]

I would remove material up in the crown. JE has a page (last one) that shows where they lighten pistons. So you should be able to use any one of those locations to cut weight?

http://www.jepistons.com/PDFs/TechCorner/SCPDrawings/JE_Piston_terminology_and_features.pdf

Dang, all your pins are spot on? I'll be sending mine to JE to replace them. Something as small & seemingly simple as the pin should be closer than mine are.