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Antique Gas Engine Discussion

O/S rings or sleeve?


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  #1  
Old 06-17-2005, 06:22:38 PM
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Jebaroni Jebaroni is offline
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Unhappy O/S rings or sleeve?

Hey guys, after cleaning up my taylor engine block, I put the rings back in the cylinder to check the end gap. My feeler gauges stop at 0.025" and it looked like another 10-15 thousandths could easily fit in there. These are the original sized stock rings that i purchased about 5 engine hours ago. Since i'm restoring this engine, should I just have some oversized rings made or try to have the cylinder sleeved (haven't mic'd it yet) and worry about what to do about the port for the spark plug? Or do you think I should just live with some blow-by? Thanks in advance.

Jeb
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Old 06-17-2005, 08:12:54 PM
Neale Behm Neale Behm is offline
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Default Re: O/S rings or sleeve?

There are a number of threads in the archives on this subject.

The first question is...do you have decent compression (enough to run)? If so, most would advise you to live with it as it is. If not you'll need to measure the clearance between the piston and ring in the groove. Dave Reid...at Otto Engine Works... says if it's over .005 you'll need to have the groove cut oversize and a spacer installed. (I followed that advice and now have plenty of compression with over .045 end gap in the rings)

Go ahead and search the archives for topics on rings and compression and you'll find tons of other comments on this subject

Thanks Harry
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Old 06-17-2005, 09:20:29 PM
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Default Re: O/S rings or sleeve?

Thanks Harry;

I have right at 0.005" piston to ring clearance but the engine was running pretty well. I just noticed that when I was tearing everything down, i had pretty bad carbon build up on the SIDE of the piston (probably from some blow-by?). I'll examine the rings a little better once I get the piston really clean. Thanks for the help!

Jeb
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Old 06-17-2005, 11:10:39 PM
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Default Re: O/S rings or sleeve?

Hi Jeb-
It boils down to are you satisfied with the current compression that you are getting or not. For a show engine you may be good enough to go with it. Let's face it, we aren't making our living with these old engines and they are not "mission critical". It sounds like you are at the top max for ring side clearance at 5 thou. 6 or more means machine work usually. I am glad to hear that you actually checked the ring side clearance. Wise move. Lets do some calculations from your measurements.
You have approx .040 end gap on the new rings.
Subtract the normal expected end gap for a 3 1/2" ring. Assume 4 thou per inch in a new ring or .004" times 3.5" or lets call it .015" for round numbers.
0.040" less .015" = .025" of circumference more than STD.
0.025" divided by 3 (approxomate for pi) leaves a diameter difference of approx .008" . This means that your cylinder may be as much as 8 thou oversized. Note that the new rings may come with as much as .007" per inch of bore end clearance built in so the calculation may slide around a little.
Running the calculation again at .007" per inch of bore in the new rings:
.007" times 3.5"= .0245" or .025".
.040" end gap less .025" made into the new rings leaves 0.015" of difference in circumference divided by 3 (pi) leaving 0.005" of actual cylinder wear.
This 0.005" to 0.008" oversize is not an alarming size. STD rings will work in a bore up to .020" oversized. I would not waste the resources on a new sleeve at this point. If you want to do anything go for the oversized rings. This may give you a 1 or 2 percent compression increase which isn't much. If you really want to fix it right go with ring spacers in re machined grooves. You could re use the rings you have now or go with oversize. I may have some 3 1/2" x 3/16" rings in .010 or .020 over here somewhere. This will give you the most bang for the buck if you excuse the pun. You may decide to put the extra work and money in another engine if this one runs good enough for you now. One suggestion is to use a heavier lube oil to take up a little more wear. The downside may be carbon forming on the ignition system or a wet top end. If you don't mind a little oil smoke, the carbon formed may actually fill in some of the "wear" on the piston. Experiment a little and see what happens. Wishing you luck. Have fun with your engine.
Thank you,
Dave Reed
Otto Gas Engine Works
2167 Blue Ball Road
Elkton MD 21921-3330
phone 410-398-7340 http://www.pistonrings.net
http://www.pistonring.net
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Old 06-18-2005, 04:31:40 AM
Neale Behm Neale Behm is offline
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Default Re: O/S rings or sleeve?

Sorry about misspelling your name Dave! Thanks again for the good advice.
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Old 06-18-2005, 07:54:39 AM
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Default Re: O/S rings or sleeve?

Hey Dave; I was hoping that you would chime in and I was thinking that rings would be the most economical way to go anyway. The 0.005" clearance I measured on the ring side gap is actually still in a sort of dirty piston groove, so it could be more than that if I polished everything up good. So it looks like i'll be going with either wider rings or a ring spacer. If I went the spacer route, what sort of thicknesses would I be looking at? Since I am probably going to reuse the existing rings (less than 5 hours run time on them), are spacers available in thousandth sizes or how does this work? This is all new and wonderful and exciting to me and i'm still learning a lot about the finer points of engine work so please bear with me. If you would like me to call you, i can do that as well rather than eat up space here, but I leave these things to you. Please advise me as to how much I should open up the width of the ring grooves. That, or I may just send you the whole piston along with my rings. Then we'd have to discus pricing. Thanks for the help!

Jeb
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Old 06-18-2005, 11:52:20 AM
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Default Re: O/S rings or sleeve?

Hi Jeb-
I'll post the meat of it here so that everyone can benefit from the information. The most economical fix is as you said to go with the spacers first. You can always come back later and put in the oversized rings easily if you want. I have been planning to put up a page on ring spacers but it has not happened yet. Hopefully soon. Most spacers are .030" in width so the groove would need to be machined nominal width plus .030". In your case this is 0.2175" if you have 3/16" rings now. The 3 1/2" spacers are 0.180" radially deep so you need to allow at least 0.185" of groove depth at the top edge of the groove. Note that ring spacers always go at the top side of a ring in the groove. The spacer doesn't actually touch the cylinder wall and needs to be on the top side for the ring to still seal.

I usually recommend you having the spacers in hand to use as a gauge when doing the machine work. This involves putting the piston in a lathe after removing the conn rod. The biggest reason for the lathe work is to make the ring grooves have parallel sides again. As a ring wears the groove it becomes like a ditch. Wide at the top and narrow at the bottom. Since one of the sealing surfaces of the ring is on the flat bottom side the ring is not sealing across the whole flat face. This allows the compression to bypass around the bottom of the ring making blowby. Straightening the grooves and taking up the extra space with spacers restores the proper ring to piston clearances and puts you back in business.

I like to see most people either do the work themselves or find a local buddy that has a lathe in their shop. The whole job usually takes about an hour including getting the cutters ready and centering the piston in the lathe. Also the lathe can be worn and old and still do the job well if the piston can be centered accurately. I prefer not to have people ship me the pistons as they can get lost or damaged in shipment. This causes bigger and more problems. If you absolutely don't know anyone local I can do it but you may be better off to enter a plea here on the Stak. There are lots of guys on here with the facilities to do it. Besides you may strike up a new friendship which is one of the best things about this hobby.
Thanks to Harry we have a forum to get timely assistance here and to hook up with some guys that appreciate the same things that we do. Let me know if you have any problems or questions and I will be glad to help.
Thank you,
Dave Reed
Otto Gas Engine Works
2167 Blue Ball Road
Elkton MD 21921-3330
phone 410-398-7340 http://www.pistonrings.net
http://www.pistonring.net
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Old 06-19-2005, 08:02:51 PM
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Default Re: O/S rings or sleeve?

Yeah, i'll ask around locally, but the only machine shops that I know of haven't ever dealt with machining pistons (that I know of), or are ridiculously expensive. I may know of one local guy and i'll ask him, but other than that, it's go to another city or ship it to someone that knows what they're doing (you). I'll keep you posted and let you know what I find out. Appreciate the help!

Jeb
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Old 06-19-2005, 10:20:02 PM
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Default Re: O/S rings or sleeve?

Jeb-
Try the stackers. I am sure that there is someone reading this somewhere near Tarboro NC that has a lathe that could help you out. It doesn't have to be a big fancy lathe either. An old worn 9 inch South Bend or Atlas lathe would do fine. C'mon guys, Lets see what we can do for a fellow Stacker in need. Anybody got any suggestions?
Thanks,
Dave Reed
Elkton MD
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