970s block machining
Posted: Mon Apr 11, 2011 12:36 pm
Ne??
mk1-forum.net
A friendly international forum for people interested in the tuning & modification of classic BMC vehicles
https://mk1-forum.net/
970s block machining
Page 1 of 3
Re: 970s block machining
Posted: Mon Apr 11, 2011 1:20 pm
225 thou...... What - nearly a 1/4 of an inch?
Re: 970s block machining
Posted: Mon Apr 11, 2011 1:20 pm
1071 rods?? 
Re: 970s block machining
Posted: Mon Apr 11, 2011 1:21 pm
That is exactly what I was thinking.....
Re: 970s block machining
Posted: Mon Apr 11, 2011 1:32 pm
ditto
i bet this block has 'autograss history'
i bet this block has 'autograss history'
Re: 970s block machining
Posted: Mon Apr 11, 2011 1:52 pm
1071 rods?Vegard wrote:1071 rods??
Is it not just the 970s rods are longer?
aeg 521 off the look of it but they are highly polished so ???
Re: 970s block machining
Posted: Mon Apr 11, 2011 1:53 pm
yep!ChrisM wrote:225 thou...... What - nearly a 1/4 of an inch?
Re: 970s block machining
Posted: Mon Apr 11, 2011 2:09 pm
Fit 1071 rods, that's what I meant. I guess that's what has been done previously as well.
Re: 970s block machining
Posted: Mon Apr 11, 2011 3:34 pm
Sounds like a huge understatement to me and I'd have thought they'd insist you check this before they machined that block any further .rosepetal wrote: They did comment that the newly (standard) three ring dished pistons would possibly require a skim to suit the block
Re: 970s block machining
Posted: Mon Apr 11, 2011 3:52 pm
Aye.Surf 1275 wrote:Sounds like a huge understatement to me and I'd have thought they'd insist you check this before they machined that block any further .rosepetal wrote: They did comment that the newly (standard) three ring dished pistons would possibly require a skim to suit the block
Me too Pete.
Re: 970s block machining
Posted: Mon Apr 11, 2011 3:54 pm
you may well find that impossible to skim the pistons by such a large amount without breaking through to the other side - or leaving the crowns very very thin.
i would either be looking for a set of 1071/1275 length rods to suit the block, or looking for another block
sounds like a mess, either way!
i would either be looking for a set of 1071/1275 length rods to suit the block, or looking for another block
sounds like a mess, either way!
Re: 970s block machining
Posted: Mon Apr 11, 2011 4:31 pm
Thanks guru. I have plenty of rods to choose from, but cant quite get my head round the engine characteristic's of a 970 with a set of these rods?guru_1071 wrote:you may well find that impossible to skim the pistons by such a large amount without breaking through to the other side - or leaving the crowns very very thin.
i would either be looking for a set of 1071/1275 length rods to suit the block, or looking for another block
sounds like a mess, either way!
Will it rev? how will effect the engine size, would I have to machine the followers down to suit, etc etc....oh eck.
Feel another block coming on. Anybody????
Think I may be looking for a re-imbursement from the said Mini sporty place.
Re: 970s block machining
Posted: Mon Apr 11, 2011 4:43 pm
it was a trick done by auto grass racers in the early 1990s due to the engine class size (which have since changed, so they became a redundant engine size - they all use 1071's now as the class limit is 1130cc),
i guess it was easy to find a 970 crank but the rods where harder to get, so they would use the (cheaper & more common i guess) shorter rods and deck the block to suit - ive had a couple of s blocks through my hands that have been 'wrecked' like this - its hard to do anything with them as the blocks have often been overskimmed, so even with short rods you still have piston problems.
the engine would run ok, but you would probably have to spend some time sorting the rocker ratios out due to the unknown block height.
i guess it was easy to find a 970 crank but the rods where harder to get, so they would use the (cheaper & more common i guess) shorter rods and deck the block to suit - ive had a couple of s blocks through my hands that have been 'wrecked' like this - its hard to do anything with them as the blocks have often been overskimmed, so even with short rods you still have piston problems.
the engine would run ok, but you would probably have to spend some time sorting the rocker ratios out due to the unknown block height.
Re: 970s block machining
Posted: Mon Apr 11, 2011 6:56 pm
Hello
Are you 100% sure that the stroke of the crank and the rod centres are correct . Unmachined / part machined crank and rod forgings were available from the factory years ago .
I have seen standard looking cooper s rods with 6 inch centres . Also at the moment we have a crank with AEG 330 forged on it but is actually a 1071 stroke .
If the block has been decked that much the head face will be nearly in to the water pump bolt holes . What is the thickness of the block from gearbox to head face ?
When special saloon,s were at there height , it was comon to built 999 and 850cc motors with big bore,s and short ( 54mm ) billet cranks .
This is just part of the " fun " of building engines out of near 50 year old parts .
Where are you in the UK?
Are you 100% sure that the stroke of the crank and the rod centres are correct . Unmachined / part machined crank and rod forgings were available from the factory years ago .
I have seen standard looking cooper s rods with 6 inch centres . Also at the moment we have a crank with AEG 330 forged on it but is actually a 1071 stroke .
If the block has been decked that much the head face will be nearly in to the water pump bolt holes . What is the thickness of the block from gearbox to head face ?
When special saloon,s were at there height , it was comon to built 999 and 850cc motors with big bore,s and short ( 54mm ) billet cranks .
This is just part of the " fun " of building engines out of near 50 year old parts .
Where are you in the UK?
Re: 970s block machining
Posted: Tue Apr 12, 2011 7:05 pm
251 ENG wrote:Hello
Are you 100% sure that the stroke of the crank and the rod centres are correct . Unmachined / part machined crank and rod forgings were available from the factory years ago .
I have seen standard looking cooper s rods with 6 inch centres . Also at the moment we have a crank with AEG 330 forged on it but is actually a 1071 stroke .
If the block has been decked that much the head face will be nearly in to the water pump bolt holes . What is the thickness of the block from gearbox to head face ?
When special saloon,s were at there height , it was comon to built 999 and 850cc motors with big bore,s and short ( 54mm ) billet cranks .
This is just part of the " fun " of building engines out of near 50 year old parts .
Just measured the centres of the rods...big end to little end centres..250mm.
The block is 213mm from gearbox to head face so your correct in saying its been heavily decked. Have you any idea its correct height? That info seems not readily available for some reason.
Then again thinking about it, the correct block height is probably this dim plus the extended piston height!!!
Thanks for all the info by the way, .....my
Where are you in the UK?
Re: 970s block machining
Posted: Wed Apr 13, 2011 7:52 am
Hello
The block " thickness " on a standard unmachined 1071/970 block is 218.36mm ( 8.597" )
Con rod centres on a 970 rod is 149.23mm ( 5.875" )
Con rod centres on a 1071 / 1275 rod is 146.05 ( 5.750" )
The comprssion height on most 1275 type pistons is about 38mm ( 1.500" )
So , if you have 970 rods you could gain a bit by changing rods and may be able to get the rest of the top off the pistons , but I don,t think it,s going to be a long lasting engine.
I work at Southam mini metro centre ( 01926 815681 )in warwickshire , doing all the engine maching . We do loads of cooper s engines , got engines for at least 5 people who post on here at the moment . No very local to you though .
If the block has been machined that much it will be a bit thin on the top .
The block " thickness " on a standard unmachined 1071/970 block is 218.36mm ( 8.597" )
Con rod centres on a 970 rod is 149.23mm ( 5.875" )
Con rod centres on a 1071 / 1275 rod is 146.05 ( 5.750" )
The comprssion height on most 1275 type pistons is about 38mm ( 1.500" )
So , if you have 970 rods you could gain a bit by changing rods and may be able to get the rest of the top off the pistons , but I don,t think it,s going to be a long lasting engine.
I work at Southam mini metro centre ( 01926 815681 )in warwickshire , doing all the engine maching . We do loads of cooper s engines , got engines for at least 5 people who post on here at the moment . No very local to you though .
If the block has been machined that much it will be a bit thin on the top .
Re: 970s block machining
Posted: Wed Apr 13, 2011 9:17 am
Thanks again for the info
I have just physically measured the difference in the the two conrod internal gudgeon pin to big end, ie 970/1071,1275, and there is 190thou difference between the two.
OK, my next question is ..why the difference? Why did they make the 970 conrods slightly larger?
I know what you are saying about using a set of these rods and it makes sense as it would mean only skimming about 30thou off the top of the pistons, but, what other effect in your estimation would it have on other components/charicteristic's..would I be able to skim the followers if I used iski to compensate for the lack in height etc etc etc.......
Do you think all this is worth it in the end or do I just machine a suitable A series block to suit?
I have just physically measured the difference in the the two conrod internal gudgeon pin to big end, ie 970/1071,1275, and there is 190thou difference between the two.
OK, my next question is ..why the difference? Why did they make the 970 conrods slightly larger?
I know what you are saying about using a set of these rods and it makes sense as it would mean only skimming about 30thou off the top of the pistons, but, what other effect in your estimation would it have on other components/charicteristic's..would I be able to skim the followers if I used iski to compensate for the lack in height etc etc etc.......
Do you think all this is worth it in the end or do I just machine a suitable A series block to suit?
Re: 970s block machining
Posted: Wed Apr 13, 2011 9:27 am
rosepetal wrote:Thanks again for the info
I have just physically measured the difference in the the two conrod internal gudgeon pin to big end, ie 970/1071,1275, and there is 190thou difference between the two.
OK, my next question is ..why the difference? Why did they make the 970 conrods slightly larger?
I know what you are saying about using a set of these rods and it makes sense as it would mean only skimming about 30thou off the top of the pistons, but, what other effect in your estimation would it have on other components/charicteristic's..would I be able to skim the followers if I used iski to compensate for the lack in height etc etc etc.......
Do you think all this is worth it in the end or do I just machine a suitable A series block to suit?
rp
you wouldnt need to alter the followers at all, you would alter the length of the push rods to correct the rocker ratios
970 rods where made longer as this helps with the piston speeds/loads at the extremes of the stroke - the short stroke / longer rod combo is what makes them rev so well, i guess the bmc engineers balanced the stroke/rod length with the amount that they felt coulbe be removed of the face of a block.
Re: 970s block machining
Posted: Wed Apr 13, 2011 9:43 am
just thought about that one....
I suppose by making the rods longer as well, they could minimise decking the block..think thats what you have just said as well ??
I suppose by making the rods longer as well, they could minimise decking the block..think thats what you have just said as well ??
Re: 970s block machining
Posted: Wed Apr 13, 2011 9:57 am
No, you need shorter rods. (i.e 1071/1275 type)
Or you could have custom pistons made up from billets.... gonna cost though.
Or you could have custom pistons made up from billets.... gonna cost though.