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MG MGA - Carburetter dampers

I am trying to get hold of the correct dampers for the carbs on my 1500 and am getting conflicting information from various sources. My carbs are standard AUC 784 (with internal venting) and require un-vented dampers, i.e. the ones without the hole. Do I need AUC8102 or AUC8103? The people at SU say I need AUC8103 but MGOC list AUC8102 as the un-vented ones (the picture of the AUC8102 on the SU site is shown as vented!) This is driving me mad, can someone please tell me definitely the number of the dampers WITHOUT the hole!
Lindsay Sampford

Lindsay

I bought a pair of unvented brass caps from Burlen on the 4 Apr 2007. My invoice says AUC 1028HB and the washer AUC 4900.

I then had to drill holes in them!

Steve
Steve Gyles

Lindsay

Have a look at this Burlen link:

http://tinyurl.com/d2wxx8f

Steve
Steve Gyles

The original official BMC SU listing says AUC 8102 for AUC784 carb set.

FRM
FR Millmore

Hi Lindsay

I can confirm that AUC8102HB are non-vented (HB for brass hexagonal). I bought a pair in august 2011 from MGOC (Spares) Ltd.

André

A.M. Kunz

Lindsay
That's what the bottom looks like:

André

A.M. Kunz

Just a thought Lindsay, are you wanting the complete assembly or just the cap? I transferred the shaft and damper from my old plastic cap to the brass cap.

Steve
Steve Gyles

I have used the brass MG logo caps from Moss to replace plastic caps and filled the vent hole with a dab of black silicone.
Mike











Mike Ellsmore

Thanks FRM and especially Andre. Both Moss and MGOC say it should be AUC8102, so it looks like it's the SU people that have got it wrong! http://tinyurl.com/d4nehla

Lindsay Sampford

Interesting point here:
Andre's pic seems to be the early long piston damper. This was subsequently replaced by a shorter piston, for improved carb response. The change was detailed and suggested to be applied to earlier carbs (shorten the piston), per factory TSB. If the supplied 8102 is long piston, then there is another number to cover the now correct short damper piston. Sometimes changed parts continue the earlier number despite the change.
Since my BMC SU book was after the change,I assumed it included the change; it may well have and the aftermarket ones are still to the earlier spec. I reckon Barney has something on this, and somebody recently posted pics of both damper piston configurations, possibly Andre, as the pics are similar size.

Looked up Barney : http://mgaguru.com/mgtech/carbs/cb105.htm
Great fun and more number confusion from TSB!!

"The original dampers (AUC8103) could cause uneven running and a restriction in maximum speed but are interchangeable with the new ones (AUC8114) giving an improved performance. Alternaterly, the old type can be converted to the later specification by machining .070" (1.78 mm.) off of the lower face of the piston. "

But read it all!

FRM
FR Millmore

I was almost about to show my limited knowledge of SU carbs by asking the question "Does it matter if you have a vented cap on internally vented H4 carbs?"

My thinking was that, "at least you would be certain that it was vented!"

But now I have read FRMs post and the MGAguru link he recommended I can see how important the correct level of venting is.

When you get your new dampers Lyndsay, I would mike them up to see if they are correct dimensionally.
With so many part numbers being thrown at you it may be the best way to be sure you have the correct size.

Colyn

See you in Wales?




Colyn Firth

Hi all
To summarize it:
8102 = long piston, non-vented
8103 = long piston, vented
8114 = short piston, vented
8115 = short piston, non-vented
Cap has to be specified separately (brass hex = HB)
Is that correct?
Once more the pic with short and lng piston.
André

A.M. Kunz

Hi
Sorry, one more question;
Does anybody know when exactly they changed from brass cap to plastic?
André
A.M. Kunz

I always thought that the H carbs were all brass.
N McGurk

For those who did not read the following page to FRM's link to Barney's site.

http://mgaguru.com/mgtech/carbs/cb105a.htm


Mick
M F Anderson

brass caps through MGA production (H carbs) Plastic from MGB production (HS)
But, the actual dampers can be interchanged between these and many other carbs. So it is common and sometimes functionally correct to have either cap on either carb.
The "HB" designation is a modern aberration to cover two part numbers.
Note the fine point in the TSB re the "o" marking. This must have been done as OEM, because I remember a lot of those; I'm pretty sure the aftermarket was not rigorous about marking them, and all with the same stamp.
I am not certain that there actually were any plastic caps with no vents; the "dustproof" design was dropped.

FRM
FR Millmore

Andre, you are a mine of information when it comes to carb dampers! So for the sake of better carb performance it looks like I ought to go for AUC8115 rather than AUC8102?
Lindsay Sampford

Lindsay
I have ordered a pair of AUC8115 non vented (AUC8114 are the same but vented) from Burlen. They are on the way. In a couple of days I hopefully can confirm that they are the short piston type (improved version from 8102 and 8103). When ordering I forgot to mention that I would like the brass caps, so I'll probably get the plastic ones. I'm not sure though if they are actually available with brass caps. I'll have to find out from Burlen.
André
A.M. Kunz

Andre

Plastic caps I believe. You needed to order AUC8115HB.

Steve
Steve Gyles

Andre, that's where I was getting mine from, but you will notice that the picture of the brass cap shows a vent regardless of the part number of the damper! That was what was throwing me, I guess it's a picture version of a 'typo' whatever that is called.
As Steve says, you have to add the suffix 'HB' and a bit more money to get brass. I'll wait until you get yours before I order mine, I'm after brass and want to be sure I get the right ones first time!
Lindsay Sampford

Hi all
I received the AUC8115 from Burlen today. As I mentioned before I forgot to add "HB" so I got the plastic caps, but "short Piston, non vented", thats good for a start. So if you go for the brass then order AUC8115HB!
Image again for comparison reasons:
Top AUC8114 (have been in the car for 40? years)
Middle AUC8115 (new)
Low AUC8102 (new)
André

A.M. Kunz

Andre

You can buy the caps separately. That is what I did and simply transferred the shafts.

I don't have long and short shafts to compare. Can you tell me the correct length for our carbs please. That said, my old plastic caps have AUC8115 stamped on them so I suspect I have the correct length.

Steve
Steve Gyles

Andre

Sorry I may be confusing the issue. I am up to speed with the shorter piston length. I was referring to what looks like a longer shaft (middle on your photo) or is that just for photographic purposes?

Steve
Steve Gyles

Steve
Overall length is all the same.
The difference is only in the dimension of the small brass piston at the end.
See: MGAguru - CB 105 (Service memo MG/264)
André
A.M. Kunz

Transfer of cap
Steve
You mentioned that you transferred the caps from one shaft to another. What is the best method to get the shaft out of the cap? Do you use heat or just grab and pull them out? How do you get them in the new shaft (without bending the shaft accidentally)? I'm afraid to experiment - don't want to ruin them.
Thank you for your advice.
André
A.M. Kunz

Andre

Too long ago to remember precisely but judging by the lack of damage to the plastic cap (photo) I think they are just a tight fit. I probably put the cap in a vice and pulled the shaft with pliers held at right angles loosely round the shaft butting up against the end of the top of the piston assembly protected by a bit of cloth or suchlike. I don't recall there being any issue. Incidentally, the plastic cap is embossed AUC8114 and you can probably see from the photo that it has 15 inside. I must have just gently tapped the shaft into the brass cap. There is no damage (bending) to my shafts.

I am okay with the piston length.

Steve

Steve Gyles

Thank you steve.
One day I'll try do the conversion.
Now, I believe all damper questions and problems are solved and everybody is happy!
Thank you all!
André
A.M. Kunz

The plastic caps on my AUC8102 dampers seem to be attached to the shaft by a tight ball-and-socket self-aligning arrangement, so if those were pulled out I think it would be difficult to re-fit them into a brass hex cap.
Lindsay Sampford

Hi all
After all I decided to go all the way and got another pair of dampers from Burlen!
AUC8115HB / improved short piston / dustproof non-vented / Hex brass cap.
So, now with Steves stub stacks, K&N Filters and correct dampers my MkII should go like a rocket!
Andr

A.M. Kunz

Andre,

With the non-vented caps make sure that you have the internal venting passage.
Also ensure that you fit the air cleaners correctly so that you do not block the venting hole in the mating face.

Mick
M F Anderson


Thank you Mick. I'm fully aware of what you mention. Thats how the whole thing started:

http://mgaguru.com/mgtech/carbs/cb105a.htm

I detected that I had both holes. Thats why I wanted the correct dampers so badly.

André
A.M. Kunz

Image of internal damper ventilation hole of "dustfree" carburetor H4

André



A.M. Kunz

Hi all
One more important point:

Filling the dust-proofed damper correctly:

"On dust-proofed carburettors ... the oil level should be 0.5 in / 13 mm below the top of the hollow piston rod."

Non dust-proofed carbs (with the hole in the cap):

"Finally top up the piston damper with thin engine oil grade 20W/50 until the level is 0.5 in / 13mm above the top of the hollow piston rod."

(from "SU Carburetors, Owners Workshop Manual", Haynes, page 35).

Only two words make the difference: below / above!

Andr
A.M. Kunz

You don't even need to look at the damper oil level to know it it works. Just unscrew the damper, lift up 1/2 inch, and press down. If you feel the resistance before it hits the threads, it has enough oil.
Barney Gaylord

I am having brain failure here, struggling to remember discussions on posts gone by. Mick reminded us about the problems of fitting the rear air filter upside down thereby blocking the vent holes; a point which I also regularly post as a possible solution to various aliments. However, please remind me if this only relevant to carbs with the internal drilling (no vent hole in the cap) or does it apply to both types?

Steve

Steve Gyles

This thread was discussed between 30/04/2012 and 17/05/2012

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