FM 124 ring gaps
#13
01-12-2020 | 05:27 PM
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2nd Gear
Joined: Aug 2018
Posts: 6
Likes: 3
From: Ks
Did you make a typo on when you said .045" end gap on the top ring .005" on the second?! This CAN'T be right, these are WAY over and under the correct end gap. Rule of thumb is .003" to .004" end gap per every 1" diameter bore,this would put you at a minimum of .013" to a max of .017" (unless you're building strictly for racing) . These were the typical parameters I used back years ago while engine building was still my profession, maybe these animals are a bit different but I still advise you seek out these specs from a trustworthy source before you go any further. Man,---.045" you could measure that with a carpenter's tape measure! In this game a half of one thousand'th (.0005) can make or break your engine. I think you should definitely not rush into this one.
#14
01-12-2020 | 07:23 PM
Tourer
Joined: Oct 2018
Posts: 470
Likes: 237
From: Coldstream B.C. CA.
Your post has taken me back in time to those days in the re-build shop, I recall as well that free air cooled engines would almost always call for more clearance than the forced air or liquid cooled engines. Also, I hope you don't get a different reading when you check at different distances up & down your cylinder,(as per previous comment) specially if these are new bores. You probably already know they wear like an icecream cone over time (heavier wear at the top), and of course there are limits as to how much taper you can get away with till a re-bore is necessary.
Good luck on your build mate!
Good luck on your build mate!
#15
01-12-2020 | 09:48 PM
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Joined: Jan 2019
Posts: 57
Likes: 14
From: Some beach somewhere
Same part # they sent me. I ordered the correct gasket elsewhere and will return or just eat what they sent me. I did call them and they told me that is what they use on all big bore kits, I'm not going with it. No way I would be willing to live with .029 gap on the 2nd ring gap. Good job checking your ring gaps before installing. I bet most just bolt it together without checking. Thanks for the reply also, much appreciated. BTW I sourced my cylinders and pistons elsewhere.
#16
01-13-2020 | 12:25 PM
Big Kahuna HDF Member
Joined: Oct 2010
Posts: 51,362
Likes: 4,605
From: Texas
I sent an email to FM letting them know that the gap on the 2nd ring was .027" and here is my answer:
Good afternoon Larry, Travis here at Fuel Moto. Thank you for taking the time to reach out to us. The high end of the acceptable tolerance on the 2nd ring end gap is .028”, although I try to keep it as close to the low end of the tolerance as I can. The 2nd ring is really just an oil scraper ring, so if that 2nd ring is at .027”, it is still within tolerance and will be just fine to run that way.
Good afternoon Larry, Travis here at Fuel Moto. Thank you for taking the time to reach out to us. The high end of the acceptable tolerance on the 2nd ring end gap is .028”, although I try to keep it as close to the low end of the tolerance as I can. The 2nd ring is really just an oil scraper ring, so if that 2nd ring is at .027”, it is still within tolerance and will be just fine to run that way.
#17
01-13-2020 | 12:57 PM
The spec for the 2nd ring is .024-028", this spec was established in the S&S engine test cell. Our Wiseco 4.250" pistons share the same ring pack as theirs and they also do bore finish work for us. We like to run the 2nd ring gaps toward the larger end of this spec on these air cooled engines. If anyone has any additional questions or requires assistance they are welcome to contact us at 920-423-3309 or info@fuelmotousa.com
__________________
Jamie Long / Fuel Moto USA
The USA's Leader V-Twin EFI & Performance www.fuelmotousa.com
Contact 920-423-3309
Email jamie@fuelmotousa.com
Jamie Long / Fuel Moto USA
The USA's Leader V-Twin EFI & Performance www.fuelmotousa.com
Contact 920-423-3309
Email jamie@fuelmotousa.com
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