1970 Dodge Dart 318 piston rings

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PikaPhantom

PikaPhantom

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hello everybody, currently i am replacing the piston rings on the original pistons from a 318 that has been honed out and the new rings seemed to have a significantly larger gap than what is recommended in the manual for a standard size. So thinking they were faulty i got another set but ended up having the same outcome. I'm not sure whether i need bore out the block even though it seems fine or get oversized rings and file them down to spec or if there is a science about piston rings that I'm missing. Any thoughts?

thank you
 
PikaPhantom said:
hello everybody, currently i am replacing the piston rings on the original pistons from a 318 that has been honed out and the new rings seemed to have a significantly larger gap than what is recommended in the manual for a standard size. So thinking they were faulty i got another set but ended up having the same outcome. I'm not sure whether i need bore out the block even though it seems fine or get oversized rings and file them down to spec or if there is a science about piston rings that I'm missing. Any thoughts?

thank you
Click to expand...

Have you measured your bore??? If you have two sets of rings that do not have the proper gap, then maybe your engine is overbored... You don't know what previous owners may have done before you got it, it's best to measure to see what you have and then go from there to get the proper ring size...
 
You're not missing anything except that your bores are worn. Measure the gap at the top of the bore, just below any ridge, and then measure again near the bottom of the bore; bet you'll find quite a difference and that is bore taper; it can be quite different for each bore so you need to check them all. If any of the bores are tapered, you need to fit any file-to-fit rings at the bottom of their stroke (about 4" down in the bore) and then live with the gap near the top; if you fit them at the top, then they close up and can seize in the bore near the bottom of the stroke when things get hot.

Know that tapered bores 'work' the rings and they won't last as long and don't tend to seal well. I've done a few hone-only jobs in the past when I was young and poor, with tapered and out-of-round bores, and the worn cylinders never operated nearly as well as the others, and those engine clearly had extra blowby . The ring grooves were corrected with rings spacers so the rings were held flat, but the worn bore issues could not be fixed by just new rings alone.
 
nm9stheham said:
You're not missing anything except that your bores are worn. Measure the gap at the top of the bore, just below any ridge, and then measure again near the bottom of the bore; bet you'll find quite a difference and that is bore taper; it can be quite different for each bore so you need to check them all. If any of the bores are tapered, you need to fit any file-to-fit rings at the bottom of their stroke (about 4" down in the bore) and then live with the gap near the top; if you fit them at the top, then they close up and can seize in the bore near the bottom of the stroke when things get hot.

Know that tapered bores 'work' the rings and they won't last as long and don't tend to seal well. I've done a few hone-only jobs in the past when I was young and poor, with tapered and out-of-round bores, and the worn cylinders never operated nearly as well as the others, and those engine clearly had extra blowby . The ring grooves were corrected with rings spacers so the rings were held flat, but the worn bore issues could not be fixed by just new rings alone.
Click to expand...

If you want to measure the taper in the bore, it's best to measure at the top, bottom, and middle of the piston travel of the bore... The maximum side load on the cylinder is when the crank is 90° to the bore, which is exactly at mid stroke, so the most taper should be in the middle of the piston travel area...
 
FWIW... don't think I've ever observed less wear at the top than in the middle.... but can't say I consistently paid attention to the middle.
 
nm9stheham said:
FWIW... don't think I've ever observed less wear at the top than in the middle.... but can't say I consistently paid attention to the middle.
Click to expand...

The piston speed is maximum at mid stroke, it's slowing down to change directions at the top and bottom of the bore.... Also by mechanics/physics, the maximum side load is when the crank is 90° from the bore... Those two together would typically mean that the greatest wear is in middle of the piston travel area when the crank is at 90°...
 
Sounds like another "re-ring a stock bore 318" thread. What you guys say is true. Unless you measure, you are just shooting from the hip and all your work will be wasted..
 
Kinda depends on the budget and the desired quality of the outcome. OP, can you give us an idea of what you want to end up with? Just running? Or a solid rebuild with longevity?
 
Well, with the 'significantly larger gap' issues you have found with the standard rings pointing to bore wear, then it's a no-brainer to bore and go to new, oversized pistons. Gaps will be right (though you need to still chekc and maybe touch up), ring side clearance will be right (no rings flopping up and down and wearing out in short order), break-in will be good, cylinders will all seal and operate right, and blowby will be normal. I haven't done a no-bore rebuild since 1978 after doing a couple due to limited funds and finding out how poorly some cylinders operated afterwards. Proper bore and piston fit, and ring operation, are fundamental to a good running engine.

Let me ask, when you say 'significantly larger gap', how much larger are these gaps vs. the upper limit?

Is this a rebuild for performance or just stock?
 
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nm9stheham said:
Well, with the 'significantly larger gap' issues you have found with the standard rings pointing to bore wear, then it's a no-brainer to bore and go to new, oversized pistons. Gaps will be right (though you need to still chekc and maybe touch up), ring side clearance will be right (no rings flopping up and down and wearing out in short order), break-in will be good, cylinders will all seal and operate right, and blowby will be normal. I haven't done a no-bore rebuild since 1978 after doing a couple due to limited funds and finding out how poorly some cylinders operated afterwards. Proper bore and piston fit, and ring operation, are fundamental to a good running engine.

Let me ask, when you say 'significantly larger gap', how much larger are these gaps vs. the upper limit?

Is this a rebuild for performance or just stock?
Click to expand...

This a just a stock rebuild.
The photos are the original rings that were in the block vs the new aftermarket ones.

56EF2746-05A3-468F-AFF1-68D4F6B3CD8F.jpeg


4C026F15-1478-47EB-9A72-010409BE03DB.jpeg
 
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Which photo is which?

If the upper photo is the new rings, then the new rings are very wrong, or the engine has been bored before or was bored in the factory to clean up a block issue. Clean up the piston heads and see if there is a '030' marking or similar on the top.

If you have a caliper, see if you can measure the piston diameter just below the ring grooves. Or check across the top of the bore. Seems like you need to do as recommended in post #3.

IMHO that is a very light honing job... I can barely discern the hone marks. It does not look to me to be sufficient.
 
nm9stheham said:
Which photo is which?

If the upper photo is the new rings, then the new rings are very wrong, or the engine has been bored before or was bored in the factory to clean up a block issue. Clean up the piston heads and see if there is a '030' marking or similar on the top.

If you have a caliper, see if you can measure the piston diameter just below the ring grooves. Or check across the top of the bore. Seems like you need to do as recommended in post #3.

IMHO that is a very light honing job... I can barely discern the hone marks. It does not look to me to be sufficient.
Click to expand...
top is suppose to be the new rings
oh wait a minute. i see the 030 stamps.
 
nm9stheham said:
There ya go! Problem solved....a nod to KK for calling it 1st.
Click to expand...
THANK YOU MY FRIEND YOU ARE AN ANGEL. I had no idea that was something to look for. I'm still relatively new to this so this was all a weird headache. thank you

and heres the honing job with better lighting not sure if you still think it should be rehoned so here it is. I was using a not so good rental tool so if it has to be rehoned ill find something better

IMG_3181[1].JPG
 
And if you don't mind me saying.... I'd still compare gap measurements (use a feeler gauge) up and down the bores using one ring and see how much the gap varies, to get an idea of the bores' taper. Each increase of .003" in the gap indicates approximately .001" of bore wear. Excess bore taper will wear out rings in a hurry.

And from what I see, I'd do more honing... too much shine and too much vertical scratching left IMHO in the original pix. And in the last pix the honing marks look too flat.... they should cross each other at about 45 degrees apart. Others may want to comment.
 
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