.01 Ring with Standard Piston

[Patcon]

It's been a long time since I've been up that way.

Beautiful area but not close to anything

Blown budget or not, I probably wouldn't pursue this path. It's pretty cheap to have a block machined.

The piston rings are a wash either way but you would need new pistons. You need new bearings any way, so it doesn't add a lot of cost to just go ahead and redo the lower end right. If you try to do what you are suggesting you will end up paying twice to do basically the same work

[Captain Obvious]

10 hours ago, Trnelson said:

I know they would have to be filed down to get the right gap.  I've read that this used to be common practice on older engines.  Obviously I have zero experience with it but it seems to me that if the target gap is .030 - .043 and as it stands now with new standard size rings set in the bore my gap range is .48 to .53  The oversized rings are .25mm larger then it would require filing off .07-.02 to get to the .030 gap.  I would want to cheat that up to probably .035 to be safe on the bottom end of the stroke.

Current gap= .53 with standard ring, .28 with a .25 larger ring so file off .07 to get .030

You care more about the circumference than the diameter. The difference in circumference between the 83mm and the 83.25mm ring is 0.785mm.

If your current gap is .53 mm with the standard ring, then an 83.25mm ring would result in a .25 mm overlap. You would have to remove that overlap and then enough more to end up with the desired gap.

That said, I have no idea if using the oversized rings would actually work or not. I'm just here for the math.  

[Trnelson]

Thank you for the mathematical clarification!  Math has never been my strong suit.  I have decided for the sake of experimentation to get a set of oversize rings and a filing tool and see what happens.  My premonition is that it will take no less than a month of Sundays to file that much off of each ring, I will lose faith, confidence and ambition and wind up going with the stock rings.  Supposed to have the supplies by Sunday, stay tuned...

[jonbill]

not only will it take a lot of filing, I imagine it'll be under quite a bit of stress, being that compressed. 

And if the bore isn't round, it'll still not seal, as @zedhead pointed out. 

Edited January 15, 2021 by jonbill

[Zed Head]

Considering all you could look at it this way - standard rings will be slightly larger, better, than the worn-out rings you are replacing, just because they aren't worn.  So you'll get a small amount of improved sealing.  With a hone the new rings will seat and seal to the new bore but with a slightly too large gap.  So, you'll be basically back to where you started, but with new bearings and whatever other work you're planning.  Probably valve guides and seals and other things.  So, overall, you'll probably be less smoky but it will run as well or better than it did when you took it apart.  When the time comes in a couple of years, if you really have only put a few thousand miles on it, you can take it apart and do the bores and pistons and just leave the work you already did.  Because the old work will still be almost new.

Basically, just hone it and use new standard size rings, then finish the job in a few years.  Or, odds are good, it will just run so well that you don't get back to it for ten years.

Trying to fit oversize rings probably won't really buy you much, is what I'm saying.  Although it would be interesting to try.

I don't think you said if you ever heard the engine run or used it.  How bad was it?

[Trnelson]

It actually ran pretty well when I pulled it, a little smokey but surprisingly little considering it’s level of oil consumption (+ - 1 quart per 300 miles.  When I got it the fumes would make your eyes bleed, that all but disappeared  once I got the carbs leaned out to the correct mixture. I’m not sure if that was the cause of tremendous carbon build up in the head or not but it looked like the valves and runners had been sprayed with bed liner! 
To reiterate, this whole process was and is a learning experience for me. I learn by touching, feeling and doing WAY better than by reading books alone.  I  know that there will be some wasteful spending but I’m fine with that knowing that I can now at least speak somewhat knowledgeably to engine builders, machinists etc on what I want on my next go-round. 
At present my goal is basically a through cleaning, new bearings, gaskets, seals. I’ve removed some casting flash from the head, polished the exhaust runners and bowls, lapped the valves, CC’d the combustion chambers ( just for kicks as I haven’t touched them with a grinder) cleaned, polished, painted virtually every piece I’ve removed.  I have a lightweight flywheel, new clutch assembly, oil pump, water pump and some other parts I’m forgetting right now to be installed as I put everything back together. I’m sure I have made some mistakes and will probably make more, like stuffing a .010 ring in a sloppy standard bore!, but that’s how I learn best. I was the kid who had to touch the fire to be sure that it was in fact hot. 
I do appreciate all the helpful information and advice that y’all provide on a daily basis in these forums. Without this knowledge base I would be completely lost in this whole Zcar project. I plan to take some pics of the ring experiment as it develops and I’m sure I will be asking for more help ✌🏻

[jonbill]

If it was smokey, make sure you change the valve stem seals. Maybe even check the guides aren't too worn. 

It won't be the compression rings. 

[Captain Obvious]

Considering how much you have to compress the rings to get them into the bore, I would guess* that compressing them .010 more wouldn't even be noticeable.  How much would the expansion force change with an additional .010 compression? I mean... five thousandths more compression per side really isn't much at all.

Makes me wonder... Do the ring manufacturers have different fixtures for each ring size, or are they just grinding off more of the tips for the oversized rings? Maybe at the extremes there are different castings, but each raw casting can be machined into a couple different size categories or something? That's a common manufacturing technique.

Bottom line... In a pinch, I'd be willing to try the same thing you're doing.

 

 *Strictly a guess since I've never done it

[Trnelson]

3 hours ago, jonbill said:

If it was smokey, make sure you change the valve stem seals. Maybe even check the guides aren't too worn. 

It won't be the compression rings. 

I’m working more on the head today, the guides pass the “wiggle” test so I think I’m ok there. Having to re-lap a few valves due to them failing the diesel fuel leak down test. I hope to finish that today and put the head back together after a through cleaning. 
I honestly believe that the carbon build up was so bad on the valves that it was, at least in part, contributing to the oil consumption. 
Thanks for the input. 
 

Tom
 

 

[Captain Obvious]

Make sure you clean all the carbon off the valve stems and guides before you run your wiggle test. I've seen situations where the built up coating of carbon was helping take up the gap. I could definitely feel a difference between dirty and clean.

[Trnelson]

Yes sir, I’ve been cleaning them up during the lapping/ de-carboning process and they still feel ok, very little wiggle and they all feel consistent. Learned a new trick on checking valve seats, the “bounce test”. When the valves and seats are in good condition the valve will bounce a little when dropped into the seat. A poor sealing seat will land with more of a thud. Sounded hokey but I have confirmed it with a diesel fuel leak check. I’m sure it’s not 100% accurate but it does seem to be a good indicator of valve and seat condition. 
Now back to lapping...

[Captain Obvious]

And if you do decide to move forward with the oversized rings and get to the ring grinding portion of the show... Just remember that details are important. You want nice clean parallel edges. You want square corners but you don't want burrs or knife edges. You need to remove the burrs, but you don't want to break the corners any more than that.

It sounds easy. "File or grind the tips until you get the desired gap." But execution isn't as easy as the description. Plenty of info on the web to learn from.

An admission from me... I've never done it. I have a ring grinder here (thanks @240260280), but after testing and measurement, I found that my ring gaps worked out fine without grinding. So I wasn't looking forward to doing it, and thankfully, I didn't have to.