Hypatec / Hypatech pistons
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(can't remember which is the right spelling) :)

Finally made a start machining them, these are the 73mm ones (so 1360cc engine) from Australia



I've taken the original dish deepest point as a datum and machined a flat bottom dish, radiused out to the original dish diameter.

Went from 7.4 cc to 14.0 cc (within 0.5 cc of my caculations before starting)

Maximum crown thickness (centre) remains as initially at 6.6mm and minimum thickness is in two small areas near the outside diameter perpendicular to the pin (so where the oil will be thrown up from the gearbox) at 4.2mm.

Schrödinger's cat - so which one am I ???

Intresting. how much would you estimate the machineing costs of these pistons to be?

thanks

Sam.

Hi Sam,

I really don't know.... When I was having the block bored to match them I did ask the machine shop how much to do them on their CNC lathe if I gave them a proper drawing and they said (as I expected) that it would just have to be hourly rate, time unknown, as it would take longer to set them up accurately in the machine (because of their shape), than it would to machine them.

So I decided to do it myself and (as expected) I took longer setting up my lathe and making a suitable jig to hold them, than my total machining time will be.

Schrödinger's cat - so which one am I ???

Nice work there. :)

WWW.TURBO-MINI.COM

you taking orders?

I,m sorry that I didnt wait until you had shown this because I gave up on these pistons for turbo,as I couldnt see how to get the C/R down. Looks like a straightforward turning or milling job,which I could have done at home. Mini 13 will now know how to use them -good luck Joe !

Schrödinger's cat - so which one am I ???

We made up an adaptor which fits the gudgeon pin , much like the con rod normally would, & have it grabbed up in the chuck, so all the turning force is in the gudgeon pin & not grabbing the normally "out of round" piston skirts,,, & in doing so we`r not damaging the skirt in any way

Dam good little pistons hey???

www.miniman.com.au

"""LazyGoodForNothingSmartArseKnowItAllBackYardMiniMechanic"""

Similar to my own technique -Ihave a threaded bar through the lathe mandrel which I can use to pull the piston firmly on to the chuck then clock it up and away you go.

I paid about £40 to have a similar thing done to mine if that helps.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

So you milled these then?

if so i'm impressed, i've never got good results from milling on mine!

Schrödinger's cat - so which one am I ???

So Rod how deep is the dish in these? 5.6mm?

Dig's out his notes (yes I keep everything...)

My datum was 5.3mm off the small circular bit in the middle - but it was raised, say 0.1 - 0.2mm above the rest of the dish.

So, if you look closely at the photos you can see I "nearly" removed the middle bit so my average depth was probably 5.5mm ???

From my calculations before machining and end result of measured cc, that would be about right.

Schrödinger's cat - so which one am I ???

good stuff, cheers!

dished the first one of mine today, used Tadge44's method of a draw bar pulling the piston against the chuck, works an absolute treat!

took mine down so the std marked on the pip in the middle is still just visible. I think the dish "corners" are a bit more abrupt in mine due to a smaller tool radius, i also have a little chatter too but what does that matter?

I'm positive the pistons will be fine this thin, after all the thinest bit is near the edge and will get oil splash, especially as I will be using them with oil jets.

I have an interest in these pistons so could you let us see some more pics,please ?.

Yes, I think I probably went a tiny bit lower then you as I got rid of the "STD" mark and most of the "pip" in the middle.

I ground my tool put to a 6mm radius, ie, to cut the corner in one go... so I'm not surprised it chattered a bit but, as you say, I can't see those few marks will matter.

No more photos from me I'm afraid, as they are well buried inside an engine now !!!


EDIT - edited for typo only

Edited by Rod S on 5th Nov, 2008.

Schrödinger's cat - so which one am I ???

i'll get some pics up of mine.

here we go, dish is about 15cc (calculated) to get a bit more you could tak the dish outward a bit, here it is 60mm diameter, if you took it to 63 the dish would be approx 18cc.

Edited by Joe C on 6th Nov, 2008.

aww look at my old pistons.

You certainly have a much smaller radius than me in the corners of the dish but the depth looks pretty similar to mine judging from the centre bit.

I stopped at 59mm dia (where I measured my original shallow dish to be).

Combined with the different radius, that would account for the 1cc difference between us.

I don't think I would want to increase the dish diameter any more than 60mm just to gain a few cc, they need to take a lot of heat away from that raised outer bit and, even with oil jets (which I don't have) the cooling in that area is probably marginal, especially at TDC when that area is above the water jacket.

Schrödinger's cat - so which one am I ???

ah, mine might be 59 then.

Thanks for your pics too, Joe.I wish I had thought of this before I got rid.

has everyone worked out how thick it is between the bottom of the top ring slot and the corner of the recess in the top ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

I did at the time (but I can't find my notes !!!)

The top ring is well down and the groove is not that deep.

I remember that I used a large radius (6mm) for the corner of the dish to maximise the slot to dish distance, but it was still much bigger than the minimum crown thickness I had to accept.

Schrödinger's cat - so which one am I ???

Its going to interesting to see how these modified pistons hold up, eventually.They are so well priced and relatively easy to modify for low compression they could become a real asset.Please let us know in due course.