Head gasket size for TC 106" build.

[Adam76]

Hi, I'm getting the parts together for a 96" to 106" build that gives me a bore size of 3.915 (KB 103" + .040 oversize pistons).

The closest .030" MLA had gasket size I can find is the 3.937" size that is used for 107" builds.

Is this HG size ideal? Doesn't seem like a good match to me. 22 thou too big by my calculations...

I don't want to go to 107" because I want to keep compression around 10.2

Thanks.

[Ohio HD]

3.915" x 4.375" = 105.3 cu in.

Use a 3.937" head gasket.

[Ohio HD]

FYI, the 3.937" cylinder bore (107 cu in) uses a 3.954" head gasket as I recall.

[Adam76]

3.915" x 4.375" = 105.3 cu in.

Use a 3.937" head gasket.

OK thanks.

That will make things a lot easier.

I would rather just go to 107" but can't find a flat top piston that keeps compression at 10.2... They are all 10.35 / 10.4 which is too much for the cams I have. And I want to stick with the .030 head gasket for a tighter squish.

[guydoc77]

Suburban Speed has 107" flat top Mahle pistons.

[Adam76]

Suburban Speed has 107" flat top Mahle pistons.

Thanks.
KB and Wiseco also both do flat top 107" pistons, but using the compression calculator it always ends up around 10.3 - 10.4 even with stock heads.

[guydoc77]

Hmmm.
Well flat top is, well flat top.
So are you looking for a dished piston?
That will be difficult I'm sure.
I wouldn't limit myself to static CR by a tenth or two.
In other words, I wouldn't predict 10.0 to act a whole lot different manners wise than 10.3.
Other than slightly bumped up left side of curve.

[guydoc77]

Just out of curiosity, what is the IC of the cams you wanna keep?

[rigidthumper]

Suburban Speed shows their flat top 107 @ 10:1part #: SS082937F02 with stock heads.

[JSD]

Have you looked at the Wiseco 3.397 black pistons . They claim 10 to 1 comp 

[Adam76]

Have you looked at the Wiseco 3.397 black pistons . They claim 10 to 1 comp

Thanks, I'll have a look and see if I can find them.

[Adam76]

They all say 10 to 1 but you put them into the compression calculator and they come out with 10.3 ?

What am I missing?
Cheers

[rigidthumper]

Are you using the same data?
86cc chambers, -1.5 to -2.5 cc (depending on how big the valve reliefs are) pistons down .007-.009 from 0 deck typically, 3.950 x.030 head gasket, 3.937 bore x 4.375 stroke, 7.659 rods

[Adam76]

Are you using the same data?
86cc chambers, -1.5 to -2.5 cc (depending on how big the valve reliefs are) pistons down .007-.009 from 0 deck typically, 3.950 x.030 head gasket, 3.937 bore x 4.375 stroke, 7.659 rods

Thanks.
I was using 85cc chambers,  -1.5 cc, with 3.937 had gasket with pistons down 006.

I guess I had a few off

[Ohio HD]

Thanks.
I was using 85cc chambers,  -1.5 cc, with 3.937 had gasket with pistons down 006.

I guess I had a few off

3.954" not 3.937"

[Adam76]

Thanks.
I was using 85cc chambers,  -1.5 cc, with 3.937 had gasket with pistons down 006.

I guess I had a few off

3.954" not 3.937"

OK thanks.

Can't seem to find that size HG listed for sale anywhere?

[Ohio HD]

Can't seem to find that size HG listed for sale anywhere?

C9894 Cometic.

[Adam76]

Can't seem to find that size HG listed for sale anywhere?

C9894 Cometic.

"Head Gasket, Multi-Layer Stainless Steel, 3.937 in. Bore, 0.030 in. Thick, Harley-Davidson®, Pair"

Ah, they list them for a 3.397 bore size - I thought that was referring to the actual HG size 

[98fxstc]

bit of difference between 3.397 and 3.937   

[Adam76]

bit of difference between 3.397 and 3.937 

Yeah, that was a typo.... Obviously meant 3.937.

[JSD]

Shim the base 

[Adam76]

Shim the base

Hey JSD, do you mean use cylinder base gaskets?

[JSD]

No I made shims to go under cylinders to get the compression i wanted on a customersTC

[kd]

Cometic will make you base gaskets in any thickness they have stock for.  No surcharge.

Do an accurate measurement of your deck height and call them and ask if they can do it or how close they can get.

[Adam76]

Cometic will make you base gaskets in any thickness they have stock for.  No surcharge.

Do an accurate measurement of your deck height and call them and ask if they can do it or how close they can get.

Thanks, that's easier than machining the base of the cylinders.
Cheers

[Ohio HD]

Thanks, that's easier than machining the base of the cylinders.
Cheers

Adding a shim adds to the base of the cylinder. Machining removes from the base. Not the same thing.

Stick with the o-ring seal and set the cylinders properly.

[kd]

I agree.  I thought those cylinders and cases used the standard size .020 base gasket by the sound of the previous discussion.

My 4.060 barrels did but had +.003 deck height that I dialed in with the base gaskets.

[Adam76]

Thanks, that's easier than machining the base of the cylinders.
Cheers

Adding a shim adds to the base of the cylinder. Machining removes from the base. Not the same thing.

Stick with the o-ring seal and set the cylinders properly.

OK, thanks. Got it.

[kd]

 

[Adam76]

FYI, the 3.937" cylinder bore (107 cu in) uses a 3.954" head gasket as I recall.

Hey Ohio, just out of curiosity - if I was using a piston with a bore size of 3.915 (oversize 103" piston) what HG would I use? Would the 3.954" be too big? Does Cometic even make a HG that would suit that bore size?
Thanks.

[Ohio HD]

Hey Ohio, just out of curiosity - if I was using a piston with a bore size of 3.915 (oversize 103" piston) what HG would I use? Would the 3.954" be too big? Does Cometic even make a HG that would suit that bore size?
Thanks.

Adam, it might be easier if you called Cometic, give them the gasket ID and thickness that you want, and see if they have them or will make them.

[Adam76]

Hey Ohio, just out of curiosity - if I was using a piston with a bore size of 3.915 (oversize 103" piston) what HG would I use? Would the 3.954" be too big? Does Cometic even make a HG that would suit that bore size?
Thanks.

Adam, it might be easier if you called Cometic, give them the gasket ID and thickness that you want, and see if they have them or will make them.

Thanks. That's the obvious answer  .
I'll probably just go down the 107" route as it seems easier to work things out and get parts for.
I've found the KB V-Twin KB714LCA.STD flat top pistons which look pretty good and reasonably priced. So I'll probably just use those.
Cheers

[60Gunner]

What cam are you using? 10.1, 10.3?
Have you CC'd the heads. If so, I missed it.
What's the concern here?

[Adam76]

What cam are you using? 10.1, 10.3?
Have you CC'd the heads. If so, I missed it.
What's the concern here?

Using stock heads, assuming they are around 85cc / 86cc, haven't got them cc'd yet. Aiming for 10.2 compression. Main concern was keeping compression at 10.2 with a 107" build...

[jsachs1]

I just finished a .040" 88" top end.3.915" bore. You need to use Twin Cam 100MM bore head gaskets.
Cometic # C9894 = .030"
Cometic #C9894-.036".
They are the same head gaskets as the gaskets used for 96" and 107"
John

[60Gunner]

What cam are you using? 10.1, 10.3?
Have you CC'd the heads. If so, I missed it.
What's the concern here?

Using stock heads, assuming they are around 85cc / 86cc, haven't got them cc'd yet. Aiming for 10.2 compression. Main concern was keeping compression at 10.2 with a 107" build...

10.2 is the target because???. 
Make the valve pockets a little deeper/bigger and you're back to 10.2 if you're worried about going over 200psi CCP. That's if it actually IS 10.4.

[Adam76]

I just finished a .040" 88" top end.3.915" bore. You need to use Twin Cam 100MM bore head gaskets.
Cometic # C9894 = .030"
Cometic #C9894-.036".
They are the same head gaskets as the gaskets used for 96" and 107"
John

Thanks John.

So if I'm reading you correctly,  it's the same C9894 gasket whether I have bore size of 3.915 or 3.937.... Thanks for clarifying.
Cheers

[jsachs1]

100 % correct. The same.
John