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Discussion Starter · #1 ·
So I went down the road of no return. I bought a rebuild kit of eBay from lil red barn for the Onan b43G. Which has gaskets but not all of them missing oil filter and oil pump aswell as points gaskets I got my hands on the rest of the parts I needed. Also has 2 pistons and rings oversized. My question for anyone that might no are how do the rings go.. I can't get answers from red barn till Monday. The oil ring is good and installed but the top and secondary ring are exactly the same no markings at all both have a ridge on inside edge. They resemble nothing of original rings so looking into the manual is not going to help.. anyone else install these
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Chamfer faces top of piston. Don't forget to check ring end gaps and stagger gaps when installing. Bob

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2nd on checking the ring end gap and adjusting as necessary ....just fitting in the bore is not good enough as they expand when hot
 

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Discussion Starter · #4 ·
Okay so from what iam understanding is , face chamfer upwards on both rings ie. First and second compression rings. I do know to stagger the ring gaps and I still have to insert both first and secondary rings in the bore to check ring gaps
 

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Okay so from what iam understanding is , face chamfer upwards on both rings ie. First and second compression rings. I do know to stagger the ring gaps and I still have to insert both first and secondary rings in the bore to check ring gaps
spot on sir.....there will be a spec for ring end gap ...too tight is a engine killer....too loose and you lose a little compression...you can flat file the ends of rings to open up gap if needed just go slow rings are relatively soft
 

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Discussion Starter · #6 ·
Okay so end gap.is 0.010-0.020 for Onan rings does everyone agree thats correct for these lil red barn pistons
 

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Ring gap opening/end gap: If the spec for the ring gap is 0.010-0.020, it's correct. I tend to get long winded at times, so here I go again!!
Ring gap is based on bore diameter, the material used to make the rings, and the operating temperature. Different materials expand different amounts at a given temperature. You engine temp will be approx. the same, so that's out of the equation. Rings are typically made of similar materials, and even tough a slight material change will make a slightly different expansion, the difference will be so small you probably couldn't measure it if you wanted to!...so that too is out of the equation! So that leaves only bore diameter. Your b43 has a stock bore of 3.25". If you were to straighten your ring out, it would be 10.210" overall length (with "0" end gap). Bored .010 over, your ring, when straightened out, would be 10.241". The 0.031" difference in length will make some difference, but no enough to get concerned about. Use the 0.010-0.020 spec, favoring the larger gap as the ring is slightly longer and will grow a little more. Now the REASON for needing the end gap is to save your engine from total destruction! As metal is heated it "grows" in all directions. You can't measure the gap at operating temperature, so waay back when some Engineer sat down and said, "this" material, "this" bore, the ring will grow longer by "this" amount at operating temperature and needs to be "this" much shorter at room temperature. The gap will allow the ring to expand/grow longer when running and NOT push hard against the cylinder walls scoring them, and causing you to loose compression and re-bore your engine after only 15 minutes running time!.

To establish and measure the end cap, rings should be placed into the bore as square as possible. The easiest way to do this is to place the ring in the bore, slide a piston in and push the ring down until the ring sits square in the bore... approx. half way down Slide piston out of the way and check end gap with feeler gauge. If gap is 0.013" or less, I'd file it larger, just to be safe! Check end gap on the compression rings and the oil ring. I don't know if your oil ring is one piece or 3 pieces, but if 3 pieces, check gap on all 3 pieces.

Now, install rings. The top area of the pic I posted in #2 shows the position of the ring gaps with respect to the piston pin. If a one piece oil ring, place gap inline with piston pin. If 3 piece oil ring, place expander...zig-zag looking ring... ring gap at 6 or 12 o'clock, bottom flat oil ring gap at 3 o'clock, and top flat oil ring gap at 9'clock. The space between the short lines in the pic represent the approximate position of the ring gap(s). Install 1st & 2nd compression rings at locations shown, about 1:30 and 4:30.

As I started out, said that I get long winded, but I prefer to explain "why" something is done and not just, 'Yep". Keep asking about anything you're unsure of. Bob
 

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Discussion Starter · #8 ·
Perfect. Oil ring is a 3 piece and I will make sure to check all the rings for appropriate end gap. I don't want this thing to die in 15 minutes 😂.thanks for taking me to school!
 

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@rwmeyer Thanks for taking the time to explain!
 
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No problem guys. When I do things, I like to know "why". It's not always necessary, but it makes me feel better...knowing. It also gives me a better feeling to what I can let go as is if something isn't EXACTLY to spec. And here I go again!
End gap. Let's say I'm installing new rings, check the 0.010-0.020 spec and I find 0.030 end gap. Oh my, I need a whole new set of rings! Not really! Again some Engineer calculated what the gap should be in ideal conditions and also the max amount due to wear...in this case, 0.060 max gap worn, by Onan spec. So what does this end gap actually do? First, it prevents the ends of the rings coming together at operating temperature and forcing the rings tightly/hard against the cylinder walls. Next, it's a (hopefully!) calculated leakage rate. When your engine fires, the fuel explodes and drives your piston down. (I hope you guys are OK with math!) At 3600rpm, your piston is traveling down on the power stoke for 1/2 revolution which works out to .0167 seconds. Engineers, being as smart as they are, know how much pressure against the piston is actually exerted...which determines hp. They also know the every sealing surface is NOT 100% and that there is/may be a gap in the sealing surface at the ring gap. Through calculations, they can determine how much combustion gas/pressure escapes through the gap and it's affect on hp. The initial new gap of 0.010-0.020 is at room temperature (70ºF I believe) and the final "wear limit" is the maximum size that doesn't reduce engine hp (or increased oil consumption).

One more point, staggering ring gaps. As theses combustion gasses leak through the ring gap on the first ring, they must change direction in order to pass through the gap in the second ring, and then again change direction to pass by the oil ring gap(s). Each time the "fluid"...a gas is not a liquid, but for calculations, it's considered a "fluid"... changes direction, it looses pressure and velocity. The longer the path and the more changes in direction, the slower it's moving with reduced pressure. This adds up to less blow by into your crank case and max available hp.

I hope someone learns from my posts. On Forums like this, you never know what a person knows. They'll be people reading that say, 'Hell, any idiot knows that!' and they'll also be people that say, 'What's a piston ring?' I'm hoping to educate those that have no idea of why they're doing a particular task. Thanks for putting up with me! Bob
 
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No problem guys. When I do things, I like to know "why". It's not always necessary, but it makes me feel better...knowing. It also gives me a better feeling to what I can let go as is if something isn't EXACTLY to spec. And here I go again!
End gap. Let's say I'm installing new rings, check the 0.010-0.020 spec and I find 0.030 end gap. Oh my, I need a whole new set of rings! Not really! Again some Engineer calculated what the gap should be in ideal conditions and also the max amount due to wear...in this case, 0.060 max gap worn, by Onan spec. So what does this end gap actually do? First, it prevents the ends of the rings coming together at operating temperature and forcing the rings tightly/hard against the cylinder walls. Next, it's a (hopefully!) calculated leakage rate. When your engine fires, the fuel explodes and drives your piston down. (I hope you guys are OK with math!) At 3600rpm, your piston is traveling down on the power stoke for 1/2 revolution which works out to .0167 seconds. Engineers, being as smart as they are, know how much pressure against the piston is actually exerted...which determines hp. They also know the every sealing surface is NOT 100% and that there is/may be a gap in the sealing surface at the ring gap. Through calculations, they can determine how much combustion gas/pressure escapes through the gap and it's affect on hp. The initial new gap of 0.010-0.020 is at room temperature (70ºF I believe) and the final "wear limit" is the maximum size that doesn't reduce engine hp (or increased oil consumption).

One more point, staggering ring gaps. As theses combustion gasses leak through the ring gap on the first ring, they must change direction in order to pass through the gap in the second ring, and then again change direction to pass by the oil ring gap(s). Each time the "fluid"...a gas is not a liquid, but for calculations, it's considered a "fluid"... changes direction, it looses pressure and velocity. The longer the path and the more changes in direction, the slower it's moving with reduced pressure. This adds up to less blow by into your crank case and max available hp.

I hope someone learns from my posts. On Forums like this, you never know what a person knows. They'll be people reading that say, 'Hell, any idiot knows that!' and they'll also be people that say, 'What's a piston ring?' I'm hoping to educate those that have no idea of why they're doing a particular task. Thanks for putting up with me! Bob

LOL...BOB you got down in the weeds a bit on this, im glad you didnt get into ring side clearance in the piston groove and piston clearance in the bore LOL (y).........the crux of it is to small a ring end gap is a major problem...we do know how to have fun here dont we 🤣🚜
 

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ttaz, I couldn't find a spec for side clearance or I prolly would have!!! And then maybe "talk" about coefficients of thermal expansions of aluminum vs steel rings and then there's WHERE to measure piston side clearances! Lots of typing...which I'm NOT good at... but I REALLY enjoy ALL aspects and people in these Forums! I hopefully will teach someone something! Bob
 

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Discussion Starter · #13 ·
Well she's all assembled on the piston end and I posted my video to YouTube under always fixing john deer 318 rebuild. I appreciate the great info Bob. My tractor is gettin closer to being done home stretch lol.
 

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Rich, Sounds good, and you'll be mowing soon! One quick comment...and I MEAN quick! Check head for flat...I think spec is 0.005" Bob
 

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Discussion Starter · #15 ·
Rich, Sounds good, and you'll be mowing soon! One quick comment...and I MEAN quick! Check head for flat...I think spec is 0.005" Bob
Yep I will be checking that right on the suburban window. I have the tolerances written in my diary lol I believe your right with the 0.005.
 

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ttaz, I couldn't find a spec for side clearance or I prolly would have!!! And then maybe "talk" about coefficients of thermal expansions of aluminum vs steel rings and then there's WHERE to measure piston side clearances! Lots of typing...which I'm NOT good at... but I REALLY enjoy ALL aspects and people in these Forums! I hopefully will teach someone something! Bob
🤣 ...it is amazing the amount of knowledge you can accumulate over the years in varrying subjects.... one of my endeavors included building high performance engines and parts for them ....i know how deep those weeds can get on some things... i enjoy it also ...(y)
 
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