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miro
Senior Member
Username: miro
Post Number: 1245
Registered: 11-2001
| | Posted on Monday, February 12, 2024 - 11:25 am: | 
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I put this in at the head of the list of topics because I think it's a good article about piston rings.
https://vintagebikemagazine.com/wp-content/uploads/2019/12/Piston-Rings-for-Comb ustion-Engines_53094.pdf
I found it a good read especially for the section on used engines.
miro |
chris_spring
Senior Member
Username: chris_spring
Post Number: 283
Registered: 02-2019
| | Posted on Wednesday, February 14, 2024 - 04:06 pm: |
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Thx Miro.
I've put new rings in the Adams, changed one ring in the Kingfisher, and re-used rings in the St. Lawrence.
I will study this carefully to decide whether I need to re-visit any of the work performed.
Cheers! |
johnny
Senior Member
Username: johnny
Post Number: 657
Registered: 03-2006
| | Posted on Thursday, February 15, 2024 - 10:30 am: |
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Miro, Thank you for posting the link for piston rings. Some good info there however much of the information refers to new style piston rings & oil rings then what most of us are dealing with in the old early 1900's gasoline engines.
The information I'm posting below is from Dave Reed's website (Otto Gas Engine Works) Dave has been selling piston rings to engine collectors for many years & is very knowledgeable about the restoration of the older flywheel engines & piston rings. So for someone attempting to rebuild a old flywheel engine if you follow Daves tips below it will help you improve your engine compression.
Piston rings if not pinned will rotate in the cylinder when the ring side clearance to the ring land is excessive.
A NEW RING in a NEW GROOVE has 1 1/2 thousandths of clearance built into the ring. Once the piston grooves wear the ring is not held properly and will rotate. In a horizontal engine the force of gravity will work the gaps to the top. With proper clearances this will not happen. If you see all the gaps lined up you had better check for ring groove wear because trouble is just over the horizon. The greatest old wives tale about piston rings is that there is great importance to the gap whether in size or orientation. The gap is only about 5 percent of the equation that includes the ring side clearance. When there is compression leakage past a ring 95% goes past the sides of the rings and never enters the gap. If you bother to check the end gap why don't you check the most important thing - the fit of the ring to the groove? Most people don't. Then when they don't get any compression they call me. You can live with as much as 5 thousandths of side clearance but 6 or more means you will not be happy with your results. Machine work will be needed. Pins in the grooves will force a ring to seat in one spot but there again when the ring grooves wear the seal will fail. Gap size should be a minimum of 3 thou per inch of bore for easy break ins. Engines that will work hard and hot immediately after overhaul need 4 thou minimum end gap per inch of bore. As much as 8 thou per inch of bore is acceptable.
Honing
The other thing people overdo is hone. They want to see a pretty 350 chevy cross hatch pattern but that is not necessary in our old engines. You are grinding away precious cylinder wall material. The extra piston to cylinder wall clearance will allow the piston to cock around in the cylinder and will break the seal of the rings. If you can't resist the extra honing get a piece of emory paper and do it by hand. When your arm is tired you know that you are done. Leave the power honing to the professionals who have modern marvels like oversized pistons in their bag of tricks. |
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