Datsun Roadster Forum-311s.org

I just removed my first piston and noticed this in the top ring. It looks like the groove has been widened? Is this normal, or is it time for new pistons as well as rings?


And on the crankshaft there are many holes that have been bored on each part of the crank. What the heck? Balanced? Lightened? Any info and suggestions are greatly appreciated!


Thanks,
Ron

Ron it looks like its time for some new pistons as well . That crease is not a good sign!

That crank has been balanced. The pistons, I'm not sure.

Will

Ring groove looks as if it had a section of broken ring on that area.
If that was the case, the cylinder bore would more than likely have a local scoring along the stroke length of the bore in that area.
The picture clearly shows a section of blowby path running from the piston crown thru the damaged section onto the space between the compression ring and second ring.
Localized cooked oil above the oil ring also leads me to believe a hot spot was created by a cracked ring.

Was the ring intact or has someone re-ringed the piston after the fact?

Are you in the process of re-building the engine or trouble shooting a oil smoking tailpipe?

What was the compression on the cylinders before you took it apart?

Ray B.

1990 I overheated a ford engine and cracked the heads. Had the heads repaired but the engine had a ticking sound in it. I figured it was a valvetrain related noise and ignored it for 15 years. This year rebuilt the motor because the oil pressure was going down and engine was starting to run rough. Found a piston that looked much worse than that. It seems I also broke some rings and they bounced around and hammered the ring grove. What amazed me was the cylinder was not scored.

Ray,

I've had a lot of blow-by since I had the car. I changed the valve seals but it didn't help. Compression in #1 (the piston in the pic) was 120-135 and all others were 170-180 so I figured it was a ring. I was suprised to see the piston damaged as it was though.

With the crank being balanced, and some not too old blue case paint, it's obvious the PO had some engine work done. Maybe #1 just didn't seat right? The ring is intact and not broken at all. The cylinder looks good and there wasn't even a ridge at the top so it can't have that many miles.

I think I'm going to hone the cylinders and put in new h20 pistons and rings and run it like that. Even with the bad piston this engine never ran hot and was one of the quickest.

Ron

DELETED

Every crank that I have seen is balanced in that manner. Occasionally you will see a weld spot where heavy metal was welded in too.

On the cylinder, it is very possible that the cylinder is fine. I bought a 1500 core once that came with all of the parts. I pulled the pistons out and HUGE chunks of the lands between the rings were gone. The rings had a catastrophic failure. The cylinders checked out fine. The engine is now in a 1500 motoring somewhere around in Texas....

If a cheap and dirty is required, could you throw a single used piston and rod from another engine into this one ?
You know like Willy Nelson's Song " On the Road Again"

Ray B.

I have a block here with the same pistons you have. with the 3 on top. If you want to try the cheap way let me know..

That looks like either detonation damage, (Pre ignition severe pinging) or someone banged the piston into the cylinder without a ring compressor and the end of the ring did that. Was the gap of the ring at that point? Is it a dent, or is the metal chipped out?

Yeah that's where the gap was. It looks like it was pressed into that shape. Like maybe the ring was sticking somewhere during the stroke. It was still in one piece. I haven't pulled the others yet but that's next.

My other thought was that the gap was too big or the groove was too big or the wrong thickness ring was used and allowed it to rub the groove into that shape.

Thankfully I sourced an old block from Joaquin (THANKS!!) with intact pistons. So I'm gonna try a swap with some new rings.

If the ring was there, most likley it was done when the piston was installed and the ring caught on the deck. Either no ring compressor, or BIGGER HAMMER. If the rebuilder did that, better check everything you're going to reuse.