OK, I'd like to consider myself having an intermediate level of engine building knowledge as I'm a large diesel engine mechanic by trade and have done plenty of hot-rodding in my day, so I'd like to think I got the fundamentals of general engine building. However, I'm doing my first HD Twin Cam engine build so looking at getting some expert advice from all you wonderful folk.

Anyway, I'm converting my 2014 FXDB 103" to an S&S 106" using their big bore kit. Now, I'm also slightly bumping my compression so I'm going with a .030 head gasket. My issue is with which gasket to go with. According to the S&S literature in their catalog and website, S&S PN 900-0216 is the .030 gasket for their 106" which has a bore of 3.927". So I order that from a local vendor and when I receive it, I get a Cometic MLS gasket. Spoke to S&S and they said with the .030 gaskets, they just use Cometic instead of their own in-house brand. I'm fine with that as I like Cometic anyway. Well the problem comes up when I see the label on the gasket which has no S&S PN but has a Cometic PN of C9721 and says it's for the 3.875" bore (which is the stock 103" bore size). I started wondering if I may have gotten the wrong gasket as in my experience, it's preferred to NOT have the gasket protrude into the cylinder, which it would in this case were I to use this gasket. I've measured with my caliper micrometer and that is the case here.

So to clear up confusion to make sure the vendor didn't give me the wrong one, I contacted S&S to see if they can give me their PN cross reference to the Cometic one. They were unable to give me the cross reference but told me that I have the right gasket, but on their website it says this gasket is a 3.927" bore gasket. He said they have no issues with this gasket size on the 106 build and I know they have a great rep for HD engine builds, but all the fibers in my body are telling me, how can that be okay to have the gasket protrude into the cylinder? Am I just being over-concerned and should just shut up and build or do I have a valid concern?

I contacted Cometic and they do not offer a 3.927" MLS gasket but do have a 3.937" one (that is the bore for 107" Cometic PN C9894). In a perfect world, a gasket that is perfectly fit to the cylinder would be ideal, but if I had to pick the lesser of 2 problems I would personally pick the gasket that is only .010 larger rather than .052 smaller. Do you agree? What am I not considering here?

Am I splitting hairs here and being overly cautious or should I go with the larger head gasket?

Sorry for the long post and thanks for any insight you guys can provide.

 

Well you're in luck bud my thread right below yours I just got my S&S 106" cylinders on yesterday. I went out and took some pics for you of the gasket you want. It's for the 3.937" bore or 107":





I believe they sent you the wrong gaskets.

 

wow!! perfect...yup, looks like I got the wrong Part. Here's what I got and it actually measures at 3.875.





Convert 100mm to SAE and you get 3.937"....nice and short answer! Love it! THANKS!!!

 

No problem welcome to the forum. Check out my thread when you get a chance it's in my signature.

 

@mattVA Will do! Hey BTW, are you sticking with the base o-ring setup or changing to the Cometic Base Gasket?I'm hearing arguments in both directions and not sure which to go with.

 

Base o-rings. I haven't heard of any widespread failures using them. Think about how many 88"-107" engines are out there using the o-ring around the spigot.

 

Yeah, I was kind of going that direction myself. Saw your post and it's great stuff, you are doing pretty much my build and I will definitely reference it as I continue my build. I switched to the Timkin and also using the S&S crank, but also switched to the S&S TC3 Cam plate/oil pump and some gear drive 585 EZ start cams...

 

$18 for Cometic gaskets...that's great! Where'd you happen upon that deal?

 

I wish that's a 4 as in 48

 

CYCO (US Seal) sells quality seals and gaskets for Harleys for much less, including MLS head gaskets. All standard sizes but not sure if they inventory the 3.937" gasket.