Carb body to intake runner...

Lineslinger · Jan 10, 2020

I have read and received various recommendations in regards to creating a good seal between the carb body and the intake runner.

Some say the O-ring works fine, others say a good fiber gasket material and still others recommend filling the O-ring groove with one of the various gasket forming offerings, usually in a tube.

How did you connect your setup?

maylar · Jan 10, 2020

I use the o-rings with a smear of RTV on the flange.

concours · Jan 10, 2020

The stainless steel button heads are a poor choice here. Cannot tighten enough.

RoadScholar · Jan 10, 2020

concours said:
The stainless steel button heads are a poor choice here. Cannot tighten enough.

I realize that most Norton fasteners are set by "feel", but a 5/16-18 fastener grade 5 max torque is listed as 17 ft/lb, a grade 8 is listed as 25 ft/lb and plated 5/16-18 (which were OE) are 13 and 18 respectively. An 18-8 stainless fastener rated at 11 ft/lb is, probably not a good match, a 316 fastener rated at 12 ft/lb should be acceptable. Rocky Point sold stainless Allens for years with no reports of failure (316), the 2-->1 Mikuni manifolds all came with stainless manifold to head Allens, again no failure reports. I readily admit that the button heads have slightly less drive depth, but given the torques involved would be surprised if they couldn't be properly tightened.

I don't disagree with your post, but would like to know more.

Best

jseng1 · Jan 10, 2020

It helps to use a quality carb that doesn't bend and warp where it bolts on to the flange like the Amal does. Carbs connected to the manifold with a rubber tube don't have this problem.

Problem is that there are few if any quality carb choices that will fit into the small space requirements.

The only twin carbs that fit without clearance issues are the Amals and the Chinese PWKs (require mods).

Lineslinger · Jan 10, 2020

concours said:
The stainless steel button heads are a poor choice here. Cannot tighten enough.

Huh, and here I was thinking about reading a response regarding gasket material.

I understand fasteners reasonably well and disagree with your observation.

acadian · Jan 10, 2020

If the carb flange is not warped due to over tightening, and the inlet manifold surface is flat and smooth, than the standard o-rings with a little bit of hi temp grease has always worked for me. Try to get some allen heads for the inboard carb mounts, make removal much easier

maylar · Jan 10, 2020

acadian said:
Try to get some allen heads for the inboard carb mounts, make removal much easier

Yeah, and get knurled ones, so you can manipulate them with your fingers.

concours · Jan 10, 2020

RoadScholar said:
I realize that most Norton fasteners are set by "feel", but a 5/16-18 fastener grade 5 max torque is listed as 17 ft/lb, a grade 8 is listed as 25 ft/lb and plated 5/16-18 (which were OE) are 13 and 18 respectively. An 18-8 stainless fastener rated at 11 ft/lb is, probably not a good match, a 316 fastener rated at 12 ft/lb should be acceptable. Rocky Point sold stainless Allens for years with no reports of failure (316), the 2-->1 Mikuni manifolds all came with stainless manifold to head Allens, again no failure reports. I readily admit that the button heads have slightly less drive depth, but given the torques involved would be surprised if they couldn't be properly tightened.

I don't disagree with your post, but would like to know more.

Best

Your post uses “Allens” sales history interchangeably with the BUTTON heads referenced in my post.
Whole different deal.

Looks like 123 inch lbs., or 10.25 ft.lbs., rated by a top supplier, Unbrako brand.

40+ years and a dumptruck load of SS fastener experience, much of it button head.

I stand by my statement.
I have them holding license plates on, and a few other superfluous uses.

Reference the general notes in image 1.

http://www.unbrako.com/images/downloads/engguide.pdf

Also, note the softer values in the hardness properties.

Together with the DECREASED depth of socket AND hex bit radius, it’s recipe for swearing, wasted time, breakdowns (fall aparts) and more.

I acknowledge the publics thirst for fastener jewelry, but in so many cases, it’s a DOWNGRADE in functionality.

concours · Jan 10, 2020

Lineslinger said:
Huh, and here I was thinking about reading a response regarding gasket material.

I understand fasteners reasonably well and disagree with your observation.

Sure didn’t mean to call your baby ugly.
Just sharing knowledge, based on lots of experience. The good news is, you can simply disregard as internet engineer BS.

And, please, explain WHY you disagree, so I can benefit too.

acotrel · Jan 10, 2020

My carbs are not flange mounted, they are the push-in type. And I use Japanese type rubberised mounts. Vibration can cause flooding which can cause rich mixture and adversely affect performance. I bought my set-up from Mick Hemmings.