FM 124 ring gaps

Reply Subscribe

Thread Tools

Search this Thread

Jan 12, 2020 | 05:08 PM

#11

skills

Road Captain

Joined: Oct 2018

Posts: 539

Likes: 284

From: Coldstream B.C. CA.

Ok, now this is looking much more realistic. As for six digit numbers in this context (ie .019125" ring but gap), LOL that's funny.

Jan 12, 2020 | 05:18 PM

#12

Cncsparky

Thread Starter

2nd Gear

Joined: Aug 2018

Posts: 6

Likes: 3

From: Ks

Quote:

Originally Posted by Mopower

They sent me a 4.50" bore .014 base gasket for mine, what base gasket did you get?

Same. Cometic C10195

Jan 12, 2020 | 05:27 PM

#13

Cncsparky

Thread Starter

2nd Gear

Joined: Aug 2018

Posts: 6

Likes: 3

From: Ks

Quote:

Originally Posted by skills

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.

Yes that’s obviously a typo 😉. Should be .0045”

Jan 12, 2020 | 07:23 PM

#14

skills

Road Captain

Joined: Oct 2018

Posts: 539

Likes: 284

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!

Jan 12, 2020 | 09:48 PM

#15

Mopower

Advanced

Joined: Jan 2019

Posts: 57

Likes: 14

From: Some beach somewhere

Quote:

Originally Posted by Cncsparky

Same. Cometic C10195

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.

Jan 13, 2020 | 12:25 PM

#16

Hairy Larry

Big Kahuna HDF Member

Joined: Oct 2010

Posts: 51,364

Likes: 4,614

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.

Jan 13, 2020 | 12:57 PM

#17

fuelmoto

Platinum Sponsor

Joined: Feb 2007

Posts: 7,287

Likes: 4,286

From: Little Chute, WI

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

__________________