Overhaulling a L36, pistons not marked for front of engine. Help

[tech3627]

I am overhauling a 3800 L36 for my 01 GP. I already replaced the engine a year ago with a used engine, but it threw a rod through the side of the block so I am building one this time. I had 2 extra engines in the garage, the original one from this car, and the one out of my wrecked 97 GP. I disassembled both extra engines to decide which one to build. I marked all the rods for which cylinder they came out of, but not the tops of the pistons. I did not realize these pistons are not marked on top to identify which side is the front. Here is the top of the piston.

I do see a couple of marks on the bottom of the piston.

If I remember correctly from my days rebuilding small block Chevys the notches for the rod bearings went towards the outside of the block. If I do that to this motor the mark on the bottom of the left bank pistons will be towards the front of the engine, but the right bank will be towards the back of the engine. Does anyone know for sure which way these pistons go? I can pull the blown engine out of the car and tear it down to look, but I would rather have the new engine built and ready to drop in when I pull that one out.

 

[sixpackofwags]

I was wondering if you found out the orientation of pistons and rods. I have the same question about the marks. I had to buy two new pistons that have arrows on them that are on the same side as the mark on the bottom of piston has seen in your pic. but not sure if all arrows are suppose too point towards front, or odd side front,even side towards rear of engine.

 

[MoarkatsINmuhtrailer]

Why in the hell are you building an engine???

You know it is gonna blow up again.


Go to junk yard, pick up a new engine, refresh gaskets and be done.

 

[tech3627]

I am building one because it is about the same price to build one as it is to buy a used one with 130,000 miles on it. The biggest problem with these engines is the bearings getting washed out and they start to knock. If I can start with new bearings I expect to get a lot more miles out of it. I have another vehicle to drive, so there is no reason not to build it. It is also a great opportunity to teach my 12 year old son how an engine works and how to fix it.

 

[Fivefingerdeathpunch]

Aslong as the proper machine work was done, by all means build it.

 

[dbextreme]

I bet no one knows the answer to this for one of two reasons:

1) Few rebuild these motors. I got a quote for machine work and an LS builder to build my bottom end and I about crapped myself. My 17K mile 2007 L26 replacement motor was only $500. No brainer there.
2) IF these motors are rebuilt, better internals are used meaning the stock piston and rods are trashed.

That's just what I get from reading. You are correct regarding bearing washing, but if the proper machine work is not done on the bottom end it will fall apart rather quickly.

If you have all the proper machine work done, then go for it, but watch tolerances... I understand letting the son learn to. My two boys a great pit crew.. LOL We are planning a new project now. I have a 82K 1976 model 460 motor sitting on an engine stand now, just wondering what to make... Cab truck to play in the woods or use my Thunderbird to back half and put the motor in it.

 

[tech3627]

I pulled the other engine out of the car tonight to check which way the pistons are in that motor. All the pistons are installed with the mark on the bottom of the piston to the front of the engine. That makes all the notches for the rod bearings on the left side of the engine, but the notches on the main bearings are on the right side of the engine. I thought the marks on the bottom of the pistons would go to the front, but the notches were throwing me off. I am used to the notches being toward the outside of the engine, not all on the same side of the engine.