Piston Ring Choice; Unmodified Cast or Filed Down Chrome?

I'm surprised at the amount of misinformation mixed into this thread. 

Dongya supply professional and honest service.

First off, whether or not the rings get filed, gaps can and must be checked. 

The comment about 75mm rings being too big for the bore is just plain garbage. They would need ~1/16" filed off the end, and that's fine. If they were an inch too big, different story, but we're talking .020 in bore size here.

There have only ever been two reasons to run chrome rings. One is in Porsche motors with Alusil or Nikasil bore treatments (both very hard). The other is for off-road motors that see a lot of airborne particulates (dust). In both cases, the goal is to keep the top rings from wearing out quickly by using a very hard chrome plating on the face of the ring. The rings are not made of chrome, they're still iron, and have no performance benefit besides the face hardness. Chrome rings do take a long time to seat, and may never seat with improper breakin. Also require different bore finish.

I'd just plan on the plain rings and check gaps. If the last set didn't cause a problem, that says they're fine.

Nockenwelle said:

I'm surprised at the amount of misinformation mixed into this thread. 

First off, whether or not the rings get filed, gaps can and must be checked. 

The comment about 75mm rings being too big for the bore is just plain garbage. They would need ~1/16" filed off the end, and that's fine. If they were an inch too big, different story, but we're talking .020 in bore size here.

There have only ever been two reasons to run chrome rings. One is in Porsche motors with Alusil or Nikasil bore treatments (both very hard). The other is for off-road motors that see a lot of airborne particulates (dust). In both cases, the goal is to keep the top rings from wearing out quickly by using a very hard chrome plating on the face of the ring. The rings are not made of chrome, they're still iron, and have no performance benefit besides the face hardness. Chrome rings do take a long time to seat, and may never seat with improper breakin. Also require different bore finish.

I'd just plan on the plain rings and check gaps. If the last set didn't cause a problem, that says they're fine.

The problem with running rings that are 0.020" oversize for the bore isn't the end gap.  As you and others have pointed out it's pretty trivial to set the end gap.  The problem is that rings are manufactured so that they're round and have a specific tension when installed in a specific bore size.  When installed in a different bore size they're going to be less round and the tension will be effected.  Twenty plus years ago some ring manufactures specified a tolerance of up to + 0.010" for a given ring size but I've never seen a minus tolerance.  Here's a chart from a Hastings catalog.

Want more information on Custom Piston Ring? Feel free to contact us.

HOW TO SELECT CORRECT OVERSIZE RINGS
Hastings Piston Rings are available in Std. size and the following oversizes:
.020", .030", .040", .060", .080", .100", .120" where required.
Contact Hastings Piston Ring Engineering Department at factory for non-cataloged ring applications, or unusual
oversizes. For sets in stock the following chart can be used.
The chart below gives the proper oversize rings to install for various oversize cylinders.
BORE DIAMETER USE RING SIZE
Std. to .010" ................................................STD
.020" to .029" .............................................. .020"
.030" to .039" .............................................. .030"
.040" to .049" .............................................. .040"
.060" to .069" .............................................. .060"
.080" to .089" .............................................. .080"
.100" to .109" .............................................. .100"
.120" to .129" .............................................. .120"

So, what happens if you use an oversize ring in a smaller bore? The ring tension will be higher than spec and they won't seal correctly.  How bad will it be?  I don't really know.  I'm sure the engine would run and maybe it would be OK for a street motor where you had no other choice but it's clearly not the correct way to do it and since we're talking about a race motor why would you do that?

As to ring types, you're correct.  We're talking coatings not ring material.  A plain cast ring is not a bad choice in this application and I should have said that in my earlier posts.  My excuse is that I was typing on my and I was going to clarify my recommendation if or when Tom came back with some piston specs. 

I typically use moly coated rings in vintage race motors when they're legal but it depends on the exact application including what part of the country their running in.  Here in the southwest where we're often racing in very dusty conditions and chrome rings may be appropriate. 

Tom said:

In reply to APEowner :

The 74.5mm pistons have 2mm first and second groove and a 4mm oil groove.

It took 4 months for a set to pop up. Toyota 4K engines use the same rings. Mitsubishi 4G36 is the same as well but finding those is even harder.

Most rings available for that bore size are to thin; motorcycles use 1mm. Honda & Toyota engines are typically 1.5mm thick.

Yeah, that's an unusual configuration.  I'm not seeing anything in the catalogs I have.  My next step would be to reach out to Total Seal and see if they have a standard part that would fit.  They can make anything you want but for your application if you're doing custom it would make more sense to spring for custom pistons with a more standard ring size.

I'm happy to reach out to Total Seal for you but if you want to just do it yourself here's the link Total Seal - Find a ring.  They'll need the grove depths in addition to the information you've provided already.

Contact us to discuss your requirements of Piston Ring Material. Our experienced sales team can help you identify the options that best suit your needs.

Ray can you walk us through the procedure for making piston ring? This is something I have wanted to try for a long time.

I have a set of rings ordered from Niagara right now. The last I spoke with them she told me that they have finished moving there shop and are in the process of getting back to business. Said I should have my rings in about 4 weeks. I have ordered many set from them and they have always been more than freindly and very helpful. I can't claim to be an expert on it but I got my info from this page http://www.oldengine.org/members/holland/images/PistonRings/Thumbnails.html
I've made a number of sets and they have all turned out well. One alteration to the instructions I do is not wedge them open as far as what the instructions say. I find with a lot of the engine rings being heavier built than modern engines they had to much tension. To split them after machining I use a medium size pair of bolt cutters and apply a bit of pressure and they snap cleanly. Andy, I am also working on a Bulldog that I believe to be a 12hp. Can you supply me with the bore size of yours to help confirm my engines hp. I just had it sleeved and will need rings as well. Could be that the guy who sleeved it for me can make the rings also. Just finished the sleeve this last week. Thanks, Mike Hello to All

For those of you that would like to try your hand at making
cast iron piston rings, I found a very good source of information on Ebay. I bought a book titled " American Machinist Handbook" authored by Calvin & Stanley 7th Edition
Published by McGraw & Hill Book Co. copyright It gives all the required information to make piston rings for both internal combustion engines and steam engines from 2 inch diameter bore up to and including 36 inch diameter bore. The book states information was provided by the United States Naval Yard, Boston Mass. This book has a wealth of information on a vast amount of machining methods from just before WWII in it's pages. I think I paid around $8.00
for it. Also covers a lot of information on machining practices and repairs by the Pennsylvania Railroad during the steam days.
Just my 2 cents.
LeRoy Now that Niagara has moved they don't want to spend the money to relocate and connect their smaller machines. The lady from Niagara told me that it is not cost effective. They don't make enough money on the smaller size pistons rings. So they will no longer be making piston rings 10 inches in Diameter and under. I would imagine if you wanted a very large quanity of small diameter rings made they would find away to do it.

I don't believe Dave Reed does custom size rings anymore. He has standard size rings only if he has them in stock.

I called Case machine out of North Carolina and he wants $65.00 for a single (one) ring. 5.250 X .406 step cut. I need six of these rings. It would cost me $ 390.00 plus tax. Thats not reasonable to me.

I called Auto Diesel Piston Rings who advertises they will make custom size rings but can not make the .406 width I need said their material does not come in that size. They did offer to sell me two rings to make one.

It's starting to look like I might have to make these rings myself. Hi John-
I don't remember you asking me about these rings. If you had I would have offered a 5 1/4" x 3/8" butt cut compression ring and a .030" wide spacer to put on top of the ring to make .405". I can't imagine why this would not work. That is unless you are building a space shuttle or an Indianapolis racer. I have these rings in stock so you don't have to wait for anything to be made. Your total cost for 6 rings and spacers would be about one fourth of the cost quoted below for the six rings. :shrug: I must be selling them too cheap. I knew I was doing something wrong but I couldn't figure out what it was. I will be looking forward to hearing from you.
Thank you,
Dave Reed
Otto Gas Engine Works
Blue Ball Road
Elkton MD -
410-398-
http://www.pistonrings.net
Now that Niagra has moved, does anyone have the new contact information for them? If they don't want to move their smaller machines because it wouldn't be "cost effective" for them, I might just be interested in inquiring as to whether they would be interested in selling their equipment for making the smaller sizes of rings. Somehow, we have GOT to keep our resources for parts alive, or none of us will be able to afford to preserve our mechanical historic treasures. I don't think there's any advantage to using a step cut ring, it doesn't hold compression and makes it hard to adjust the butt gap. On pistons with pinned rings if the pin is on the lower side of the pistons you are really increasing the gap. On my 8hp Titan you can see where it equals a 1/4 inch gap, whenever I machine the grooves I move the pin to the top. The gap can then be set like a normal ring.

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