Piston orientation
 

Stupid question but will become clear why I ask.

What are the issues with running a piston installed 180* backwards??

And now the rest of the story. I purchased a set of TRW L2359 .060 pistons many years ago from H-O Racking. Tells yo how long this project has been going. They were dished 16cc's. I was going to run 670 heads on my 455 and figured that would help with compression. I now will run KRE 74cc heads. I also at the time was offered a set of forged H-beam rods that where honed for floating pins. So as my project got going I sent the rods, pistons, and pins to a respected Pontiac builder cross state to machine the pistons and pins to fit the rods. I also had a little more cut in the top for valve relief due to worrying about the cam I will run. Got everything back and assembled my engine. But as life goes the project stalled and the engine sat for several years. Project going forward now. But I was concerned about the engine sitting and pulled the heads. Was relieved to find eight shiny cylinders and no bugs. But the #5 piston looked off. Further inspection seems to indicate it was installed 180* off. The extra valve relief matched the other pistons on that side. But the factory stamping was on the opposite side of the piston. I did a search and found a pic on ebay of a L2359. The arrow points to the front when the factory stamping is on the bottom. I attached a pic. The 16cc dish removed the arrow.

So what do I do now ??? If I remove it and reinstall it the correct way the extra valve clearance is on the wrong side. My cam specs are below. Is this really an issue, valve clearance that is?? If valve clearance is not really an issue is balance?? I'm really bummed but glad I pulled the heads and found this.

Any thoughts/suggestions??

I be curled up in a corner with a stiff drink.

The Piston-Pin Offset. Supposedly the Pin is offset to neutralize Side-wall loading during the Power Stroke.

180* and the sidewall is loded more than Stock design. Just means more HP is scrubbed-off into little bits of gray metallic gravy in the oil.

At this point you can also be concerned about rod orientation as well.

I think I would pull the pan and check everything with your more experienced eyes

I agree pull them all. My old machinist felt there was a slight performance edge to running them pointed the wrong way, but in you case pistons valve notches were not machined for that.

I would take the short block apart and verify everything is put back together correctly. I will mention that since these pistons and pins are almost certainly press fit, that any requiring removal and re-installation could be a bit of an issue. You will need to find a machine shop that has the Sunnen pin removal system or equivalent. Many shops simply have a press and some rudimentary plugs and supports for pressing pistons off. This ruins the pistons because usually it doesn't matter, they are going in the scrap pile anyway. With your pistons, you are hoping to re-use them, so the pin bore needs to be supported to not crush and distort the pin hole. When I have to do this, even with the Sunnen equipment, you have to be very careful. Not unusual to have to touch-up the pin bores with the rod hone or every now and then needing a .001 or .003" oversize pin to restore the press. Choose a good shop.

Why didn't you call your machinist who did the job and ask him? If he is really reputable, he will correct the error. Easy enough to UPS ship the complete piston/rod to him and let him correct it, or drive back and give it to him.

I know my machinist would honor his work and correct his mistake without question.

Hold On
 

Four valve reliefs means pistons work on either bank.

No left/right with these pistons. If they did have offset pins....Four arrows would point forwards and the opposite bank would point to the rear.

Could pull that one piston and measure for any offset just for peace of mind.

If none, just put it back and forget about arrows and part numbers.

Make sense?
Clay

TRW/Sealed pros do have an offset. But if all the others have the valve reliefs correct he must have put one on the wrong way on the rods if the chamfer is correct to the crank side.

Bad info
 

Offset would follow rotation. So above info is wrong.

Skip is correct. These pistons have .062" pin offset.

I must have been thinking about SD pistons that didn't have offset.

My bad
Clay

I 90% agree with you. If things are pressed-on and installed incorrectly, that is a defect in "material and workmanship". Agree 100%. The only little hic-up is the OP says this is a very old project that has been sitting for a long time. Is the shop even in business anymore? Good possibility the person who put the items together wrong isn't even there anymore. (no excuse). A receipt would go a long way to getting this fixed. If a piston isn't damaged removing and pressing the pin back in-it's a pretty easy fix. About 20 minutes for the first one for set-up and about 5 minutes for any others. If it was my shop and the customer had a receipt, I would fix it free with my apology. No receipt, and many years later, I would still fix it for free but may want an agreement that the customer may have to pay for a replacement piston or two if they get ruined in the process. Labor free.

Here's a little follow up info.

Looks like he closed his shop. But am trying to contact him.
Rods are not pressed in. They are floating pins.
Original pistons had four valve reliefs since they did need to be installed with one part facing the front. But I did have the reliefs increased for valve clearance. This was done on one side only.
Based on images of originals I can tell the other 7 are orientated in the correct direction. As for mounting on the rods I'm pretty sure they are all correct. I mounted them. But I'm pulling all eight just to make sure.

I have a couple of options floating around in my head to correct this issue. Just need for Monday to roll around so I can make a few phone calls. My hope is that since I'm now using different heads is there better valve clearance than the 670's I was planning to use when I had the work done. Since the head gasket I was going to use was the standard Fel Pro 1016 can I go to a cometic .060 thick gasket and pick up some clearance. If this is the case Ill just spin #5 around and reassemble. Just need to slow down and take my time and weigh the options and ask all the right questions to the right folks. Of course the crazy outlier is to get a 501 stroker kit from Butler :)

Thanks for all the replies. Ill let ya know how this works out.

I guess it's a bad news/good news situation. Bad news is to be totally safe new pistons. Which means either new rods or more piston work to mount on my rods. Which means re-balance everything. Good news - Looks like a 501 is in my future ... LOL.

Before you go too crazy pull them out and check rod orientation. All pistons got the new notches right and on the right off set side for both banks? If not then since floating just swap pistons to where notches are correct. My 455 I used the RAIV heads on had backward TRWs in it. Ran pretty darned good.

I will probaly try that and hope I don't have a valve clearance issue with that piston since the extra clearance will be in the wrong location. Like I said previously I'm not too concerned with rod orientation since I installed the pistons on the rods. But I'll probably be pro-active and check the other seven. If I do have clearance with #5 then that changes the ball game. Cutting #5 changes the balance. the other seven will then need to be cut. Complete rotating assembly will need to be re-balanced. Plus most places won't touch anything that someone else worked on. I'll know better later this week once I have had a change to check valve clearance on #5 with it switched around the right direction.



As for the direction indicators. These had an arrow that points to the front as you can see in the pic in a previous post. These no longer exist since they were dished 16CCs. But I'll check #5 since I need to pull it anyway to see if there are any other indicators visible. I'm just resigning myself to the worst case scenario ...

If you put the pistons on the rods, you were the one to install it wrong?
What were you going by to put the valve relief on backwards?
The arrow or the valve relief?
(the machinist may have ground the wrong reliefs, but to install on rods should be what is used)

I'd just take the piston off and turn it around.
The offset, if it has one, won't affect it as much as the valve relief in the wrong spot.

:confused:

I'd just take the piston off and turn it around.
The offset, if it has one, won't affect it as much as the valve relief in the wrong spot.

Yep!

I think my machinist felt swapping offset changed rod angle slightly like longer rods.

I'm going by where the arrow would point if it was still there based on the pic I posted above. But, due to the 16cc dish that arrow is gone. So' I'm going by the factory stamping of part number and over size. based on that pic #5 is in the wrong orientation. When I installed the pistons I was told that the NEW valve reliefs went on the intake manifold side. I didn't pay much attention to the original stamping. didn't really think about it. I'm currently trying to determine if I ever really did have a valve clearance issue. It's sounding like I was given some bad advice. And not by the machinist either. If that turns out to be the result I'll be happy and can just turn #5 around. I'll probably still check rod orientation on the other seven since I have the bottom end all apart anyway.

The "NEW" valve relief is in the right spot. That's my concern if I just spin it around. But sounds like I may have been given bad advice, not from machinist, and didn't need the extra valve relief. Waiting for one more confirmation. Will still check rods just to be safe.

Where is the 'good' machined relief at right now in the engine?
(intake side or exhaust side)

If it is already in right position, I'd let it go.
(if rod itself is in correct orientation on crank)


:)

Re-read 1st post.
:D

If it is in correct position in engine, to heck with the piston offset if it has any.

:)

Just make sure the rod is in correct orientation on crank.


:)