When putting pistons on rods...

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eviper21

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318 pistons on rods...is there an easy way to know which way the pistons go? Obviously the rod has to face the correct direction incorrelation with the front of the piston...but both sides of the rod look the same to me. Any help??
 
With the notch or groove on the top of the piston pointing toward the front of the engine, the larger chamfer (bevel) on the connecting rod bore must be installed toward the crankshaft journal fillet (the crankshaft journal for that cylinder).

That means, for one bank of pistons, the rod chamfer will point towards the front of the engine, and the other bank, they'll point to the rear.
 

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hi, another way is make sure the notches for bearings face toward the out side of block.which will also make chamfer come out correct. just food for thought.
 
I believe the oil grooves face inwards (this is how the cam gets oiled) and the numbers face outward. A lot of replacement rod bearing shells do not have the notch for the oil groove. For a street or street strip engine, add it. For a racing engine which will spend most of it's time at high RPM it isn't needed or wanted.
 
70Duster440 said:
With the notch or groove on the top of the piston pointing toward the front of the engine, the larger chamfer (bevel) on the connecting rod bore must be installed toward the crankshaft journal fillet (the crankshaft journal for that cylinder).

That means, for one bank of pistons, the rod chamfer will point towards the front of the engine, and the other bank, they'll point to the rear.
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I agree, this is the best way to be sure.

Jack
 
Yup - you orient the rods to the crank, and the pistons to the front of the engine (notch to front). To be honest - I still mock them up by hand and number each part, and mark the front of the rod and an arrow on the bottom of the piston when I assemble...lol. Better safe than doing it twice...
 
moper said:
Yup - you orient the rods to the crank, and the pistons to the front of the engine (notch to front). To be honest - I still mock them up by hand and number each part, and mark the front of the rod and an arrow on the bottom of the piston when I assemble...lol. Better safe than doing it twice...
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Glad to someone is as anal as I am :D........Take's time, but I always double/triple checked everything when assembling.......even the rebuilds I did when working on commercial lawn equipment for 5yrs.....lol.
 
You guy's aren't alone, it usually takes me 2 days to assemble an engine, seeing as I check everything at least 3 times and then I am still worried.

Jack
 
What happens if you get them in the wrong way. Yet another thing to be paranoid about, as if all the "my rebuilt small block wont start" threads aren't enough.
 
coffeedart67 said:
What happens if you get them in the wrong way. Yet another thing to be paranoid about, as if all the "my rebuilt small block wont start" threads aren't enough.
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The biggest thing would be the fillet of the crank would chew away at the rod bearing. Not a good thing. If you put the pistons in backwards there may be clearance problems with the valves among other things.

Jack
 
Coyote Jack said:
The biggest thing would be the fillet of the crank would chew away at the rod bearing. Not a good thing. If you put the pistons in backwards there may be clearance problems with the valves among other things.

Jack
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why did your concerning catostrophic failure seem so casually toned when I read it? Lol

It's like, oh the biggest thing with WWIII we would ever face is nuclear warfare and an engine knock! No biggie!
 
You'll know if you're measuring everything and long before the heads go on. In some engines the rod side clearance is "used up" if the crank fillet is not adjacent to the rod's chamfer and either the crank won't turn (I always rotate the crank completely once after every rod get's torqued) or the rod side clearance will be non-existent or tight. Especially on strokers with performance cranks with big fillets the engine won't turn with two rods on a throw and one backwards.

And yes - I've got them backwards before...lol
 
Definitely double and triple check, and WRITE THINGS DOWN!!! If you keep a written journal of clearances, torque readings, etc., you will have the peace of knowing it got put together correctly. Once it's all buttoned up, you can't see any of the internals without tearing it all apart again. That way, if any problems occur, you know what the ACTUAL specs are because you documented them. Tracking any potential problems will be logical rather than guess work. ie: "Did I remember to torque those main caps?" :eek:ops:
 
i read about the larger chamfer on the rods, but i couldnt really tell the difference between either side of the rod. anyone have pics? the good part is, the old piston and rod assembly is still together (i needa put new pistons on the old rods). so if i do it one at a time im sure i can get it matched up ok. The thing is, i think the motor was previously rebuilt so i wanna make sure the previous builder put it together right!

thanks for all the info though
 
Another way to think of this is the oiling notch on the big end of the rod is supposed to face the opposite bank of cylinders.
 
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