Well done!

very interesting

so is it the piston itself that makes the most difference, or the shape of the bevel as well?

IE did you try putting the 2085 piston onto the 1505 shaft and drive it?

The engine/car the 2085 is in is not registered atm so no, I haven't tried swamping things about and testing them on the road but I would guess that the bevel shape does play some part as the mating surface on the corresponding piston matches the larger radius of the bevel.

I am obviously guessing but I think you would get most of the benefit of the 2085 by reducing the outer diameter of the bevel on a 1505 to match to let more oil past.

Maybe get the Doc to spin one up in a lathe and have a play!

cheers

Kev (who has found yet another use for a lathe I don't have )

Hi Kevin

Firstly thanks very much for such a detailed breakdown of the parts and talking the time to share the knowledge

Essentailly from your description all they have done is made the taper greater which would allow more oil to pass at a given point increasing the speed the piston can travel.

Hence by allowing the piston to travel faster and the flat spot is therefore elliminated

The flat spot is therefore most likley caused by a rich mixture at the stall spot of the piston

From your dimensions I should be able to work out the angle of the champer

It should be easy to modify a standard one and save me some cash

Is'nt Ausmini a great place

Cheers

Kiwiinwgtn
:

Your welcome

Hummm,

Not quite, I don't think the radius/chamfer/bevel would make that much difference. From the measurements, it is the diameter of the bevel at its widest point being slightly narrower on the 2085 than the 1505 that lets more oil past. Not the oil flow between the damper rod and the floating piston as this is essentially the same on both.

So, to be clear, from the reference photo below, the shaft bevel (from the top in the photo down) starts at its narrowest point and draws an arc perpendicular to the rest of the shaft which becomes parallel at its base, then there is a short section that is parallel (to the suction chamber piston bore). The 1505 is the same diameter as the piston which is a close fit inside the suction chamber piston and restricts more oil flow, the 2085 at this point is slightly narrower and allows more oil to flow past allowing the suction chamber piston to fall more quickly but rise at the same rate.



or is that what you meant and i'm not paying attention?

I wonder how different the effect this might have on a H/HS carb considering the HIF Suction Chamber piston runs on ball bearings rather than a plain bush.

cheers

Kev

the taper here


or

edit - whoops, missed the second photo, but yes - the second photo!


Ahh, no, the one on the main shaft! Not on the piston. Its the main 'shaft bevel/taper diameter' that's different (smaller on the 2085) as well as the radius and height of the 'taper/bevel' again on the main shaft (That you can see in the dismantled photos).

how about this?



cheers

Kev

And looking at the second photo again, the taper probably doesn't do anything much at all in terms of allowing the oil to flow easier seeing as as the suction chamber piston falls, the oil has to pass in the opposite direction to the bevel/ taper and when its rising, the piston is jammed up against it restricting flow. So really its only the diameter which allows more oil to flow as the suction chamber piston falls that counts. The radius of the shaft bevel may be designed to better restrict the piston rising however....

cheers

Kev

Your not going mad I posted the first pic and modified it for the 2nd

It looks like they took the sharp edge off the piston

also increasing the taper on the other piston would reduce the weight which should help

I took a close up of my one and it has a pronounced step the 2805 one has a nice raduis

LOL! My other half might argue about that!

The radius under the step appears to be the same as my 2085. Looks like you could just reduce the diameter until the step/sharp edge is gone and you would be all sorted!

cheers

Kev

thats what i was thinking of doing (I have set myself a goal of getting a small lathe by the end of the year)

so the tapers on the pistons are the same and the only difference is the grooves

The pics make the taper look bigger on the 2805 one

is the radius of the piston where the shaft sits the same

Very interesting!

I've got the standard part on my car. My engine and car are from an MG Metro. When I put the 1.5 ratio rockers in and did some head work, the idle got quite lumpy. I put a stiffer damper spring in and different needle and the car seemed to run well. The idle was terrible though. I could hear the damper bouncing on the inner carb ramp. I followed the Yellow Bible and added a small washer between the E-clip and the piston which took a lot of the slack out of the travel so it is now better damped. It cured the damper bounce but I wonder if the mixture on gear changes is now out??

If my car wasn't beset by electrical gremlins I'd try this other type of damper.

M