| Author |
 Topic  |
|
|
DSW
Germany
95 Posts |
 Posted - 29/01/2009 : 19:37:04
|
Can anyone shed some light on the correct style of the brass dashpot screw caps for a PA?
I have 2 differing ones (one in brass with a slot, one of black plastic), and have seen all sorts around (hexagonal, knurled edge, with writing stamped in, etc.).
As I must now rebuild the carbs I thought I would donate them the proper cap(s) too.
David
|
|
|
Peter Green
United Kingdom
1682 Posts |
Posted - 29/01/2009 : 19:45:36
|
David,
As far as I know they should be round with a knurled edge. The Hexagonal and black plastic ones are to modern.
Peter. |
 |
|
|
ags
United Kingdom
275 Posts |
Posted - 29/01/2009 : 20:26:40
|
Hi David,
I am sure that Peter is correct. The original caps were circular brass with a knurled edge. Some of those that I have seen have had screw driver slots and a small hole for light oil to lubricate the piston in the central guide boss, and others merely the oil hole. Our carburettors did not have the oil filled dashpot damper as original, and I am fairly sure that all the black plastic caps will either have the piston for these or else will show where it has been removed.
The use of these dampers has been debated in this forum, and I certainly found that they helped me to tune my 11/4" H2 carburettor set up, but that I do not really miss them if things are right with the original 1" OMs.
Good luck with your search for the brass caps. Whilst not quite in the hen's teeth category, they are certainly not common and should be snapped up on sight.
More technical ramblings from
Andrew Smith MMM571 |
|
|
|
tholden
United Kingdom
1638 Posts |
Posted - 29/01/2009 : 22:46:17
|
David the correct ones as described by Peter are available from Burlen Services of Salisbury.
TH |
|
|
|
Peter Green
United Kingdom
1682 Posts |
Posted - 29/01/2009 : 23:12:22
|
David,
I have posted a picture on the Technical Information forum.
Peter. |
|
|
|
DSW
Germany
95 Posts |
Posted - 30/01/2009 : 17:20:56
|
Thank you very much everyone.
I was not expecting such quick and detailed responses and especially the instant photography by Peter.
Interestingly the Burlen carburettor web page does not assign the cap a part number, and searching for "dashpot" and "damper" cap gave a blank. However now that I have been given the number, entering just "AUC 2144" lists many cap variants. It is obviously not so easy to make perfect web pages! I will get a smart pair of "Bicycle oil" ones sent.
Now, who can explain the original spec. of bicycle oil ..... (no, I don't want to start anything!)
David |
|
|
|
Peter Scott
United Kingdom
1240 Posts |
Posted - 30/01/2009 : 18:53:39
|
David
When I were a lad, we used "3 in 1" oil for our bikes. I have a tin on the shelf over my bench as I still use it extensively including for my carbs.
Peter |
|
|
|
ags
United Kingdom
275 Posts |
Posted - 30/01/2009 : 19:54:08
|
Hi Peter,
"3 in 1" oil as such was indeed recommended for some varieties of the hydraulic piston dampers. I think that these were the earlier ones as an unreliable memory says that some post war dampers needed 20W-50 SAE engine oil to delay the rise of the dashpot piston even more and thus increase the enrichening effect.
More technical ramblings from
Andrew Smith MMM571 |
|
|
|
Peter Scott
United Kingdom
1240 Posts |
Posted - 31/01/2009 : 10:09:06
|
Andy
I agree that SU dampers need SAE30 or thereabouts. As we have no dampers on our cars the 3in1 is used for lubrication purposes only.
Peter |
|
|
|
bahnisch
Australia
674 Posts |
Posted - 31/01/2009 : 10:14:29
|
| My TC (car no 3885, engine no 4543) left the factory in October 1947 without piston dampers but these were fitted free of charge by the dealers here in Adelaide during its first service. I have conducted quite a few experiments on my F-type Magna and found that the car accelerates at its best (by far) when using the (original)heavy brass pistons (which do not have dampers). I have found that the behaviour of the piston (and mixture needle) do not seem to be very well understood by many MG owners. The taper of the needle really only affects the fuel/air ratio at constant engine speeds, under acceleration etc the speed of the air over the jet has a far greater influence and keeping the piston down increases this speed (and "suction") and therefore results in richer mixture. Damper oil viscosity is a much debated topic, suffice it to say that in our temperate climate, engine oil seems to give by far the best acceleration in piston-dampened MGA's and MGB's. |
|
|
| |
Topic |
|
Forum Locked
Topic Locked
