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hilman imp pistons
https://www.ausmini.com/forums/viewtopic.php?f=2&t=72084		 Page 1 of 1
Author:  i got a mini [ Mon Jul 25, 2011 9:42 pm ]
Post subject:  hilman imp pistons
so i no were i can get a set of hilman imp piston for my 1100. how much would they increase my power buy and how far will i have to bore a 1100 out to fit them in there
Author:  drmini in aust [ Mon Jul 25, 2011 9:49 pm ]
Post subject: 
How much power is anyone's guess but the 120 extra cc definitely helps.
You need to offset bore it to 68.0mm, that is a 3.4mm overbore from stock size.
Get a copy of Vizard's book `tuning the A series engine', he explains the offset boring method and the pitfalls you may encounter.

And if they are `JP' pistons, I'd not rev it too hard... PM me if you want to know why.
Author:  i got a mini [ Mon Jul 25, 2011 9:57 pm ]
Post subject: 
ok so what is the difference between imp pistons and some 120 thou over sized piston
Author:  simon k [ Mon Jul 25, 2011 10:02 pm ]
Post subject: 
i got a mini wrote:
ok so what is the difference between imp pistons and some 120 thou over sized piston


the imp pistons are bigger - doc said 120cc, not .120"
Author:  drmini in aust [ Mon Jul 25, 2011 10:04 pm ]
Post subject: 
68mm is .134" oversize, not .120".

And most +.120" pistons suit a 998, not a 1098. Their gudgeon pin to crown height is too great by 3.75mm to go with a 1098 crank.
Author:  paul_ewins [ Mon Jul 25, 2011 10:40 pm ]
Post subject: 
I think it is all covered in the yellow Vizard book, but basically you have to offset the bores and then mill a large chunk off the top of the block. I think it is GR that has rebuilt the engine on one of the NSW Imps that usually comes down to Phillip Island each year so you could ask him which pistons he uses. Be aware though that they are 998cc Imps and the pistons for the 1220 conversion are from the smaller bore 875cc version. I had Bryan Pope rebuild a 998 Imp engine for my Bolwell mk4 and he had a lot of trouble getting good pistons.

I got a lot of stuff from Impwerks in NZ in the past, but the website is gone so he may have closed up shop. In the UK there is Malcolm Anderson: http://malcolmandersonimp.blogspot.com/ who had a good name amongst Imp owner from what I remember.
Author:  drmini in aust [ Mon Jul 25, 2011 10:58 pm ]
Post subject: 
Last time I tried buying 68mm Imp pistons from UK they were around A$800 a set. This was years ago, they would be even harder to find now.

I think TheMiniman said he used to use Suzuki bike ones, but what model I dunno.
Author:  Kyoda [ Tue Jul 26, 2011 4:25 pm ]
Post subject: 
Our Mini K runs Imp pistons. Engine size is 1220. 1275 head, 45 Weber.

Puts out 65hp at the wheels. :D

Very pleased. 8)
Author:  jester99 [ Tue Jul 26, 2011 5:14 pm ]
Post subject: 
I had much difficulty in finding a set of imp pistons when i rebuilt my engine recently. I ended up re-using the pistons i had as they were hardly worn, and found a guy who had a set of new old stock rings that he had sitting in his shed.

While researching a supplier for pistons i had many people give me feedback about certain piston brands, and what not to use. Be cautious here.

i found a few sets of pistons suitable and recommended by people in the know, but as drmini said, they were around the $800 mark from overseas.

i also recommend the Vizard A series book, it was very informative for me also. and yeh there is quite a bit more involved to this configuartion than just a rebore to 68mm. I heard many people recommend xraying the block to ensure that the block you have is suitable to be bored this large. I have also heard some people even went through multiple blocks until they acheived the desired result.

but the result is great once you get it right.

8)
Author:  jester99 [ Tue Jul 26, 2011 5:27 pm ]
Post subject: 
Something that might help, i also tried Impwerks in NZ, and had no luck contacting them by phone, fax or email.

Keep in mind also that your cylinder head will need to be configured to suit the bottom end, for example, vizard suggests machining the block flush with the tops of the pistons, and as the imp piston has a flat top, this changes the cylinders compressed voume. This means you may need to modify your head or even change to another head to get the deired compression ratio. something to think about. 8)

Here is a link that may interest you, for some visual references

http://www.ausmini.com/forums/viewtopic ... &start=105
Author:  TheMiniMan [ Tue Jul 26, 2011 5:31 pm ]
Post subject: 
i have an engine here with Imp pistons in it, but 2x of them are fly-cut & the other 2 arnt,,, some people are weired hey? :-) :-) :-)

However--> we did a few engines ages ago using some 2nd hand (2nd oversize) Suzuki GS750 (early model 2v) pistons (from memory)

they cleaned up well so we bored to suit, stuck some new rings on em & all was good, they`re a light piston & i think they were 67.5mm, so ended up really nice little donks

G/pins are smaller diam so we had little end bushes made for the con rods (fully floating) & bought new circlips (they were a bit tricky to get for some reason, but we got em) & all was well

who wants an imp-pistoned engine with 1100 crank in it???

it was running & didn`t smoke, but we stole the head & box off it :-)

it`s pretty old tho & has those 2-pistons with flycuts that i mentioned above, so maybe rip it down & sort that lot,,, maybe just flycut the other 2 pistons to balance things up ??? :-)

anyways, it`s there if someone wants to give me money for it :-)
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