|
|
Post by tommydp on Jan 16, 2014 14:25:02 GMT
|
|
|
|
Post by threelitre on Jan 16, 2014 21:41:22 GMT
Yup, I think it's the greasing of the piston. Later HIFs, that should never be filled to a level above the damper, have a little ball bearing instead. The damping action will - as we all most likely know - only get weak if there is only a very little oil inside the piston.
Regards,
Alexander
|
|
|
|
Post by dave1800 on Jan 17, 2014 5:53:21 GMT
There are many debates in the internet about the best type of oil to use in the dashpot. I like Tony's suggestion that the use of an oil that becomes thinner with temperature as was the norm when the cars were designed automatically compensates for the engine's needs. As far as the level is concerned, I suggest that if you slowly manually raise the piston to it's full height and the oil comes out of the breather hole in the cap then it's too full! David |
|
crabmaster
Member
Posts: 44
Attribute: http://www.austineighteenhundred.com.au
|
Post by crabmaster on Jan 17, 2014 6:32:47 GMT
I believe the intention of the oil level was to provide a bit of lubrication of the damper centre rod (the reservoir) in the bore of the suction chamber but I've noticed various workshop manuals show it above, and sometimes below, the level of the top of the reservoir. I think David is probably describing the way most of us set the level: Just fill it up and let the excess come out the top breather hole with the piston pushed up to maximum height, and there you are...
Like many, I've struggled with different oils to use, but if you've had a chance to read my last newsletter, I found that the original "SU" oil from Burlen and is surprisingly thick compared to commonly used oils like auto tranmission fluid, Singer sewing machine oil, etc.
Tony
|
|
|
|
Post by dave1800 on Jan 18, 2014 2:08:19 GMT
I don't think I ever knowingly saw the original SU oil; how does its viscosity compare with say SAE30 for example? David EDIT I'll answer by own question. The Burlen website states that it is a straight 20 grade oil. Burlen SUDavid Like many, I've struggled with different oils to use, but if you've had a chance to read my last newsletter, I found that the original "SU" oil from Burlen and is surprisingly thick compared to commonly used oils like auto tranmission fluid, Singer sewing machine oil, etc. Tony |
|
|
|
Post by Penguin45 on Jan 18, 2014 13:24:40 GMT
I've always used engine oil - 20W/50 - over the years. Interesting stuff.
Chris.
|
|
|
|
Post by charlypm on Jan 18, 2014 15:53:23 GMT
|
|
|
|
Post by dave1800 on Jan 19, 2014 2:48:00 GMT
Yes, I've seen all kinds of suggestions for racing which may possibly be better for engines running flat out all the time. Running dry wouldn't affect the piston height (opening) and air fuel mix other than when accelerating when it would cause it to be weak and cause hesitation. I suggest this would be better addressed by properly matching the needle to the engine set up. Removing the spring would allow the piston to rise further for a given load. I suspect what is happening here is that the racing engine is running the SU not as a constant depression device other than at low rpm but allowing full air flow at moderate rpm (piston fully open) and then increased fuelling as the rpm increases, ie similar to a fixed jet carb. However, for normal use the SU does a remarkable job of meeting the engine's fuelling requirements compared with a fixed jet car with improved economy. Have you ever considered using a wide band meter oxygen sensor to monitor the AFR and match your needles? Regards David |
|
|
|
Post by dave1800 on Jan 22, 2014 0:50:12 GMT
You may have seen this on the Moss website? Using a wideband oxygen sensor and experimenting with SU carbs' dashpot oil, springs etc the conclusion is that only the needle profile and adjustment really affect how they function. I've not been able to find the follow up article, if indeed there is one, and I am surprised with the experimental conclusion as I would have thought that the spring strength is critical. Moss SU experimentDavid |
|
