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SU Damper Cap Vented vs Non-Vented

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AUSMHLY

AUSMHLY

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My 1964 3000 MkIII has SU HD8 carburetors. Mine have the black plastic damper cap. It has a vent hole in the cap.
My friend has a 1960 3000 with SU HD6 carburetors. His has the brass damper cap. It is not vented.

Why are some vent caps brass vs plastic?
Why are some vent caps vented vs non-vented?
 
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AUSMHLY said:
My 1964 3000 MkIII has SU HD8 carburetors. Mine have the black plastic damper cap. It has a vent hole in the cap.
My friend has a 1960 3000 with SU HD6 carburetors. His has the brass damper cap. It is not vented.

Why are some vent caps brass vs plastic?*
Why are some vent caps vented vs non-vented?**
Click to expand...

*plastic is cheaper; brass is stronger - plastic caps have been known to blow out in a backfire (unlikely).

**non-vented caps go with carbs that have a little hole drilled per this. Vented caps don't have the little angled hole. You must have one or the other.

VentAngle.jpg
 
I read about that in an article by Jim Taylor.

Where is that hole? I can't tell exactly where the arrow you drew is pointing to. (The other two arrows are pointing to the piston oil fill level.)
Should the hole be on the flanged part of the neck?
If there is no hole, I think it would be best to drill a 1/16" hole in the cap.
It's my friends HD6 carb and I didn't see any holes. His brass cap is non vented and he tells me these are the original carbs with original brass caps. But, he's not the original owner, so there's that.
 
AUSMHLY said:
I read about that in an article by Jim Taylor.

Where is that hole? I can't tell exactly where the arrow you drew is pointing to. (The other two arrows are pointing to the piston oil fill level.)
Should the hole be on the flanged part of the neck?
If there is no hole, I think it would be best to drill a 1/16" hole in the cap.
It's my friends HD6 carb and I didn't see any holes. His brass cap is non vented and he tells me these are the original carbs with original brass caps. But, he's not the original owner, so there's that.
Click to expand...

Sorry, should have circled the slanted hole my arrow is just touching. Ignore the two big arrows. If you don't see it, it's not there. You could also take the dome off and see it from the bottom, if it's there.

My original HD6's have the vented brass cap and no slant-drilled hole. Will upload pix later today.
 
The hole is not visible on the outside of the dome I'll assume. The tube the hole makes is from the inside of the neck to the bottom of the dome?
 
AUSMHLY said:
The hole is not visible on the outside of the dome I'll assume. The tube the hole makes is from the inside of the neck to the bottom of the dome?
Click to expand...

Correct. Here's a better dwg:
HDsectDwgCallouts.jpg

screenshot.2261.jpg


screenshot.2262.jpg

1/16" hole as measured with drill bit

screenshot.2263.jpg

If hole were present would be directly above, or at, the bright lower ring

screenshot.2264.jpg

Hole would show in circled area - in the area of the sharpie mark at the 3 o'clock position
 
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Sometimes :

An owner would replace the plastic caps with the brass ones so when he polished his carbs he could also polish the caps , adds a bit of glitter under the bonnet .
 
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I'm certainly confused. I asked, The hole is not visible on the outside of the dome I'll assume. You replied correct.
Is this the circled area?

screenshot.2261.jpegscreenshot.2264.jpeg
 
AUSMHLY said:
I'm certainly confused. I asked, The hole is not visible on the outside of the dome I'll assume. You replied correct.
Is this the circled area?

View attachment 64145View attachment 64146
Click to expand...

The circled area is on the right-hand picture. Referring to the drawing above, that is where the hole, if there were a hole, would appear. The circle I drew aligns with the "web" visible in the left-hand picture and the drawing above. My HD6's came with the hole in the cap, not the internal one. Only one hole is necessary.

If your friend's HD6's don't have the slanted internal holes, they'll need holes drilled in the caps.
 
Jerry said:
HD8 carbs. Brass vs Plastic dampers on a BJ8. At what time did they use Brass?
Click to expand...

Looking at all the old road tests in Brooklands' Austin Healey 3000 Ultimate Portfolio, the brass caps are seen through the MkI BT7; from the tri-carbs onward, the caps are all black plastic.
 
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Previous owner glued a copper coin from some foreign currency (Canadian?) - selected because it fit nicely within the plastic damper center ring - then drilled a vent hole through original position. You could have your bling for pennies!
 
steveg said:
*plastic is cheaper; brass is stronger - plastic caps have been known to blow out in a backfire (unlikely).
Click to expand...
Not so unlikely. I've had the rods on both of my plastic ones punch out from backfire. A PO of my HD8s had glued coins (dimes, IIRC) to the top of the plastic caps. Covered the holes.
 
John Turney said:
Not so unlikely. I've had the rods on both of my plastic ones punch out from backfire. A PO of my HD8s had glued coins (dimes, IIRC) to the top of the plastic caps. Covered the holes.
Click to expand...

I've had the stems push thru the plastic ones too. The stems on both types are the same diameter and are just a press fit into the caps, so you can press your stems into brass caps and permanently solve the problem.
IMO the brass looks better too.

Dave
 
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