I picked up an LS1 from a friend of mine, he had it in his 01 vette. He was saying that the engine had some bad blowby and im better of rebuilding it. I started to rebuild it and ran into a problem, well i dont know if it is a problem but you can move the piston side to side with in the bore. whats a good thing to do to fix this problem. will i have to bore it over and put new pistons and rings?

 

Based on the info you gave...its kinda hard to answer.

How much movement are we talking? A little wiggle? Or a lotta sloshing?

Is it all stock inside?

A tiny bit of wiggle is normal. The piston doesnt fit tightly into the bore without the rings, or else you'd have problems. The blowby happens when the seal between the rings and piston, piston and bore, or the ring gap becomes out of spec at running temperature. Those tolerances and clearances change quite a bit once its all warmed up.

At the same time, you dont want to be able to clank it back and forth like 1/8" or something. Any way you can take some measurements or take a video of the movement? Do you have an inside bore gauge and a set of calipers to get some numbers on the bores and pistons?

One thing about the alum ls1 motors. You cant just bore them like a standard chevy motor. At least not as much. So make sure if you are going to go that route, you take it to someone that knows. If you bore too far, you're in trouble. You're looking at boring the block and pressing in new sleeves.

J.

 

If you're actually doing a rebuild, then this will be a non-issue anyway. A true rebuild will include a honing of the cylinder walls, and new pistons with new rings, or at the very least, new rings on the original pistons, provided the machinist can do a small enough hone.

 

LS1s are known for some oil blowby. I would ask him if when the motor was cold did it sound like a rod was knocking until it warmed up, that would indicate piston slap, again for which LS1s are known for and could explain the movement of the piston in the cylinder. From my understanding when GM worked on a motor with bad piston slap they put a new set of pistons in that closed up the tolerance on the piston to wall clearance.

 

Thanks guy all this advice will make me look into the situation some more. When i was moving the piston its more of a wiggle then a slop. The bottom end is all factory. this engine had a supercharger on it for about 30km(maybe more)of its life and was driven hard. If anything ill put new piston rings and bearings. you can still see the hone marks from factory. When i get back to working on the engine, ill take a vid and some measurements of how much it moves.

 

Are you going to supercharge it again? Or just running it N/A?

If you are just running it N/A... you might benefit from a light hone on the cylinders just to give the rings a new surface to break into. Then maybe do file to fit rings, and tighten them up a bit.

Thats what I plan to do with my motor if I end up tearing it apart to fix it. Light hone, new rings probably file to fit. I have lots of blowby and oil in my intake.

J.

 

If your going to bore or rehone, GM recommends nothing more than 0.010" oversize on the LS1. Some DO get away with 0.020" if 10 thousands doesn't clean up. If you still had the motor together, a cylinder leakage test would be beneficial. On a cold motor with engine de-greened and rings sealed, you shouldn't want any more that 12 - 15 percent leakdown. With the cylinder pressurized w/ compressed air, listen to the oil fill, exhaust downpipe, and throttle body and it will tell you were your not sealing (Rings, exhaust or intake valves). With blowby being an issue, the rings would be suspect.

 

Thanks for all the input. I finally had some time to take apart the LS1, turns out that one side all the pistons are cracked and the other side is fine. That's why it was having the blow by on the one side. Now i'm in this rut i was wanting to get some opinions on what to do. I'm going to supercharge this engine just not right away. The crank is fine and i was not planing on changing it but the pistons and connecting rods i will be changing. whats a good combo to go with.