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Bored Out A Series


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#1 danie garry

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Posted 05 December 2009 - 12:19 AM

is this actually possible???
click me!!!!!!!!!!!!

#2 Tim1970

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Posted 05 December 2009 - 12:43 AM

Very much so :thumbsup:
The capacity is not gained by an overbore alone it is stroked to 91mm
I think that's the longest stroke possible for the A series but may stand corrected.
As it says the pistons are 73.5mm which with standard stroke gives the common 1380cc
The largest possible i believe is 1596 with 74.7mm Triumph 2.5 pistons and 91mm stroke!
Hope this helps

Edited by Tim1970, 05 December 2009 - 12:51 AM.


#3 danie garry

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Posted 05 December 2009 - 12:50 AM

why do we not see more???

#4 The_Mistro

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Posted 05 December 2009 - 01:14 AM

it will prob need a LOT of maintaining!

#5 leadly

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Posted 05 December 2009 - 02:29 AM

it will prob need a LOT of maintaining!


and perhaps a healthy bank balance!!

#6 Tim1970

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Posted 05 December 2009 - 02:37 AM

Unfortunately my knowledge is patchy so i may stand corrected.
From what i undertand for the effort and cost involved there are generally not enough gains over a standard stroke engine or an engine stroked to say around 84mm (which can be achieved a lot cheaper and more reliably than the 91mm) to make it a viable option in most cases. Although torque improves power increases are small and reliability and revability generally decreases.
I would recomend reading from page 410 in Vizard's 'Tuning the A series engine' if you have, or can get hold of a copy.
Either way i think it's very interesting how it's done and everything would be a nice project in a money no object scenario.
Very interesting stuff

#7 Tim1970

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Posted 05 December 2009 - 02:41 AM

it will prob need a LOT of maintaining!

Depending on the bearings changing the crank at every service maybe? :thumbsup:

#8 puresmartie

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Posted 05 December 2009 - 04:14 PM

it will prob need a LOT of maintaining!

Depending on the bearings changing the crank at every service maybe? :)


what the hell?

#9 GraemeC

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Posted 05 December 2009 - 07:09 PM

I'm not sure you can stroke a standard cast crank to 91mm though - I'm sure you have to start with a specially forged jobby.

#10 Tim1970

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Posted 05 December 2009 - 07:24 PM

(Tim1970 @ Dec 5 2009, 02:49 AM)

(The_Mistro @ Dec 5 2009, 01:22 AM)
it will prob need a LOT of maintaining!

Depending on the bearings changing the crank at every service maybe?



what the hell?

Comment was made in jest really but the foundings for this are as follows.
When using a 91mm stroke the main bearings need to be larger than 'S' (2") sized ones (billet crank and block modified to accept ford 1600 crossflow (2 1/8"?) ) to get any longevity out of the crank. The 'S' size bearings give very little overlap of the journals so the crank is a lot more flexible and is more likely to fail prematurely. In vizard it talks about a billet crank lasting only 1500 miles on a race engine limited to 7500rpm with the 'S' bearings. With the larger bearings it states in excess of 4000 miles but i haven't found data that suggests the crank wouldn't last greatly in excess of this. For road use keeping revs low life should be greatly increased.
Hope that makes some sense. :)

Edited by Tim1970, 20 March 2011 - 07:20 PM.


#11 Tim1970

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Posted 05 December 2009 - 07:30 PM

I'm not sure you can stroke a standard cast crank to 91mm though - I'm sure you have to start with a specially forged jobby.


Yeah I think they use a specially made billet one.
I think the max for a standard crank is not much over 84mm or for an unmachined forging 86mm.
Not sure if more has been done successfully, but above that i think billet is the way.

Edited by Tim1970, 05 December 2009 - 07:34 PM.


#12 allen7

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Posted 07 December 2009 - 10:10 PM

I'm not sure you can stroke a standard cast crank to 91mm though - I'm sure you have to start with a specially forged jobby.


Yeah I think they use a specially made billet one.
I think the max for a standard crank is not much over 84mm or for an unmachined forging 86mm.
Not sure if more has been done successfully, but above that i think billet is the way.



Hi, again,

I'm obviously not a mini expert, I have quite a bit of paperwork - one bit, detailing the engine build (costing about £2,500 ithe early 9o's) it mentions the overbore and omega pistons and a turbo crank - I've measured the bore and the stroke and it is 91mm - I'm told this is not possible on a turbo crank - perhaps the engine was rebuilt with another crank and I don't have the paperwork?

A bit of a puzzle - but was running OK and, though not stripped, the oil pressure is good and the bearings seem fine.

Regards,

Allen

#13 mk1leg

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Posted 07 December 2009 - 11:12 PM

Read David Visard's book and there he tell you how to a chieve a 1600cc engine but its not a cheap job as a special crank costs in excess of £1500......... :-

#14 Tim1970

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Posted 08 December 2009 - 12:00 AM

Hi, again,

I'm obviously not a mini expert, I have quite a bit of paperwork - one bit, detailing the engine build (costing about £2,500 ithe early 9o's) it mentions the overbore and omega pistons and a turbo crank - I've measured the bore and the stroke and it is 91mm - I'm told this is not possible on a turbo crank - perhaps the engine was rebuilt with another crank and I don't have the paperwork?

A bit of a puzzle - but was running OK and, though not stripped, the oil pressure is good and the bearings seem fine.

Regards,

Allen


Hi Allen,

Not a problem does sound very interesting it may well be as you say that the crank has been changed at some point.
If you can get hold of a copy i'd recommend having a look in the section in David Vizard's book as 'mk1leg' suggests.
Should give you an idea of things to look at on the crank.
Best of luck with it all any more questions at all then ask away.

Tim

Edited by Tim1970, 08 December 2009 - 12:00 AM.


#15 allen7

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Posted 08 December 2009 - 07:58 PM

Guess I'd better seperate engine and box and look at the crank - that'll be a few days away -expect i'll be posting some photos.

Allen




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