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GR pistons
https://www.ausmini.com/forums/viewtopic.php?f=5&t=88104		 Page 1 of 2
Author:  wantafaster1 [ Tue Dec 23, 2014 9:10 pm ]
Post subject:  GR pistons
Hi from a very wet Ireland folks! I have got an 84mm crank and my Graham Russell pistons are on their way to me. Now, given the choice of a or a plus blocks, which is the best to use?
It's a steel crank and I think I can use it in either block if the correct thrusts are used, as far as I understand the blocks are a different height, therefore that is why there are different pin to crown dimensions with standard pistons.
I'm guessing GR pistons are made to suit the older blocks as that is what was used down under. Will all work out fine when I do a dry build but does this mean that less machining is needed in the a plus, but conversely is it really true that the older block is better material and therefore longer lasting?
Planning on using a piper 300 cam but have choice of 649 and 544 Leyland grinds, it's for racing by the way, but I like a strong pulling engine rather than one that only works at 7-8000 all the time. Have a very good cylinder head.

Thanks in advance for any sensible advice!
Author:  mickmini [ Tue Dec 23, 2014 10:18 pm ]
Post subject:  Re: GR pistons
I did not think there was a deck height difference for any of the 1275 blocks. That was only the case for the 970 and 1071 S blocks. These required different piston pin to crown height to account for the different rod/stroke ratio, if i recall correctly (waiting to be flamed on that one).

There were some known porosity problems with earlier A+ blocks, resulting in some of them being sleeved in all four cylinders by the factory.

Earlier 1275 A blocks had the smaller journal and later 1275, including A+ had the larger journal, which meant different rods for each, but the centres are still the same. You have a new crank, so presumably either have or will get the rods to suit.

The pistons you have on the way were designed to have plently of crown height so that you can machine the height and dish to suit the head and block combination that you have.

All in all, i think that you should get the 1275 block that is available and in good enough condition to bore to the pistons you have on the way. Bear in mind that if you are going to 73mm or above, offset boring will allow you to get further rebores to 73.5 and 74mm - and to get a block good enought to have that capacity.

We have a preference for the later 1275 A blocks here in Australia simply because there are more of them available than A+ without having to pay the Cooper S tax. But the pistons fit any of the 1275 blocks.

My engine is a 1275 A out of a Leyland 1275LS Mini, and therefore one of the later 1275 A blocks, 1978 vintage. I am using a reground large journal crank with Cooper S rods. The block was decked to ensure a flat face for the head, bored for 73mm pistons. I used Hypatec pistons, but these had the crown machined to the deck height and a small dish machined to mach the combustion chamber size in the head to get 10.9:1 compression.

Matching all this is a RE282 cam which is not available any more, but Graham has a newer cam that is similar. End result was 127hp and 113ftlb. See the dyno sheet here http://www.ausmini.com/forums/viewtopic.php?f=5&t=44857&hilit=wakefield and more details here http://www.ausmini.com/forums/viewtopic.php?f=5&t=31567&hilit=wakefield about what it has done on the track.

I limit to 7000rpm due to the crank material.

This engine is fantastically drivable. I took the car over to the Netherlands whilst i was living there and managed to win the class at the sprints and set fastest time of the day at the slalom on a couple of occasions.

Good luck with yours.

cheers
michael
Author:  wantafaster1 [ Tue Dec 23, 2014 11:00 pm ]
Post subject:  Re: GR pistons
The older pistons are 1.469 wrist pin height, a plus 1.526, so given the crank and rods are the same, either the pistons are further down the bore in the older motor or the blocks are different. It might need less machining in the a plus block, but then again would the older block last longer due to better material?
84mm minus 81.33 is 2.67, divided by 2 is 1.335.
Multiply by.0395 is .0527 thou.
The 84mm crank seems to be really popular down there.
Author:  wantafaster1 [ Wed Dec 24, 2014 3:56 am ]
Post subject:  Re: GR pistons
Okay have just discovered Keith Calver's instructions say they are made for a plus. Now, given that you folks like your 84mm cranks, how much has anyone successfully machined off the Graham Russell pistons?
Author:  9YaTaH [ Wed Dec 24, 2014 6:55 am ]
Post subject:  Re: GR pistons
wantafaster1 wrote:
Hi from a very wet Ireland folks! I have got an 84mm crank and my Graham Russell pistons are on their way to me. Now, given the choice of a or a plus blocks, which is the best to use?
It's a steel crank and I think I can use it in either block if the correct thrusts are used, as far as I understand the blocks are a different height, therefore that is why there are different pin to crown dimensions with standard pistons.
I'm guessing GR pistons are made to suit the older blocks as that is what was used down under. Will all work out fine when I do a dry build but does this mean that less machining is needed in the a plus, but conversely is it really true that the older block is better material and therefore longer lasting?
Planning on using a piper 300 cam but have choice of 649 and 544 Leyland grinds, it's for racing by the way, but I like a strong pulling engine rather than one that only works at 7-8000 all the time. Have a very good cylinder head.

Thanks in advance for any sensible advice!


Worst of all, the Irish tend to avoid using umbrellas (or they use to) so they all get wet walking between pubs! :D

wantafaster1 - why not write to Graeme Russell and outline what you are intending to do to the engine...he can advise you the best combination AND probably the best cam grind...Cheers, Mick

(Maybe someone from here is visiting Ireland soon and have space for a cam in their luggage! )

http://russellengineering.com.au/
Author:  drmini in aust [ Wed Dec 24, 2014 6:57 am ]
Post subject:  Re: GR pistons
A+ motors vary the C/R by altering the piston's pin to crown height. So the low C/R ones are way down the bore.

A series motors did this by varying the piston dish depth.

AFAIK the block heights are the same as mickmini said.

re decking the GR pistons, Graham says he prefers Hypatecs for this as the ring pack is further down the piston. But you can take 1.5mm off his, no problem.
I've built a few strokers with Hypatecs, my 1412 had 84.33mm stroke, I took 1.5mm off these pistons and reshaped the dish to GR piston's shape.

[edited] for syntax, because of the smartass post following this one. Merry Xmas Mick. :D
Author:  9YaTaH [ Thu Dec 25, 2014 11:02 am ]
Post subject:  Re: GR pistons
drmini in aust wrote:
I've built a few strokers with Hypatecs, my 1412 had 84.33mm stroke, I took 1.5mm off these pistons and reshaped the dish to GR's shape.


:lol: :lol: :lol: :arrow:
Author:  wantafaster1 [ Sun Dec 28, 2014 6:51 am ]
Post subject:  Re: GR pistons
Thanks guys, so is this what I need, with the chrome or cast rings?

http://minisport.com.au/1275-094-piston ... patec-1360

Now, I already had 1380cc with Omega pistons, in my wisdom I thought 72.5 bore with 84mm crank would give me 1387cc and that meant my existing cylinder head would be in the ball park regarding compression.
So, If I end up then at 1412cc, how do I "get rid" of compression? Sorry don't know the head volume offhand but as it was full race lets say it was at 12 to 1. Is it then the case of making the piston bowl deeper than ideal to get what I want?
Author:  Scoop [ Sun Dec 28, 2014 7:46 am ]
Post subject:  Re: GR pistons
Dont you have GR piston and rings on the way :?
Author:  mickmini [ Sun Dec 28, 2014 8:09 am ]
Post subject:  Re: GR pistons
wantafaster1 wrote:
Thanks guys, so is this what I need, with the chrome or cast rings?

http://minisport.com.au/1275-094-piston ... patec-1360

Now, I already had 1380cc with Omega pistons, in my wisdom I thought 72.5 bore with 84mm crank would give me 1387cc and that meant my existing cylinder head would be in the ball park regarding compression.
So, If I end up then at 1412cc, how do I "get rid" of compression? Sorry don't know the head volume offhand but as it was full race lets say it was at 12 to 1. Is it then the case of making the piston bowl deeper than ideal to get what I want?


Yes, machine a dish into the top of the piston to reduce the compression to the practical level based on your swept volume and chamber size.
Author:  wantafaster1 [ Sun Dec 28, 2014 8:56 am ]
Post subject:  Re: GR pistons
Good, hopefully they can stand a fair bit of metal coming off. Chrome or cast rings then?
Author:  9YaTaH [ Sun Dec 28, 2014 9:04 am ]
Post subject:  Re: decompress
What are peoples opinions on decompression plates or double head gaskets etc :?:
Author:  wantafaster1 [ Sun Dec 28, 2014 9:33 am ]
Post subject:  Re: GR pistons
Scoop I hadn't realised the GR and hypatecs were not the same design, from what I gather on this forum the Hypatecs are thicker on top and can stand more machining.

The GR pistons are here but can't get a block bored until the holidays are over, no dry building for the foreseeable future.
Author:  drmini in aust [ Sun Dec 28, 2014 10:09 am ]
Post subject:  Re: GR pistons
wantafaster1 wrote:
Scoop I hadn't realised the GR and hypatecs were not the same design, from what I gather on this forum the Hypatecs are thicker on top and can stand more machining.

The GR pistons are here but can't get a block bored until the holidays are over, no dry building for the foreseeable future.

They are both similar thickness in the crown, it's just that the GR ring grooves are a little further up.
You could also reduce compression by enlarging the head chambers..
Here's what I'm running on the 1360 with Hypatec pistons- it needs a lot of advance (39deg total) but works fine.

Image
Author:  wantafaster1 [ Sun Dec 28, 2014 7:21 pm ]
Post subject:  Re: GR pistons
My cyl head works brilliantly and I'm unwilling to alter it in any way.
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