Engine bore centres
- gazza82
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Engine bore centres
This may sound an odd (or daft) question but is the centre of the bore the same distance on all engine sizes?
"If you're driving on the edge ... you're leaving too much room!"
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Re: Engine bore centres
Can,t find the bore centre distances at the moment, but it is inconceivable that the 803, with a bore of 58mm could share the same bore centre with a 1275 with a bore of 70.62 mm.
Even 950 to 1275 ( 62.9mm to 70.62mm) is imposssible.
I know that 1098,s have been stretched to 1251cc , using Hillman Imp pistons) but the problem with large A series overbores has always been sealing the bores between No 2 and No 3 cylinders.
Big overbores on 1275,s are often achieved by offsetting the bores to each other to gain a little more "meat" between 2 and 3.
I,m sure you know that there is a basic difference between the "small bore" A series blocks (803/948/998/1098 and the "big bore" ones (970/1275)
Why do you ask ?
Even 950 to 1275 ( 62.9mm to 70.62mm) is imposssible.
I know that 1098,s have been stretched to 1251cc , using Hillman Imp pistons) but the problem with large A series overbores has always been sealing the bores between No 2 and No 3 cylinders.
Big overbores on 1275,s are often achieved by offsetting the bores to each other to gain a little more "meat" between 2 and 3.
I,m sure you know that there is a basic difference between the "small bore" A series blocks (803/948/998/1098 and the "big bore" ones (970/1275)
Why do you ask ?
- gazza82
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Re: Engine bore centres
A question someone asked me. Trying to find out why they want to know but triggered my inquisitive side. I will look through my various manuals later.
"If you're driving on the edge ... you're leaving too much room!"
Club WebEditor.
Cars: "Project 757" '59 A35 2-door bought in 1971 & Subaru BRZ SE LUX Auto plus "family fleet": Alfa MiTo, Peugeot 206, (Ex '98 Alfa Romeo 156 2.0 TS)
Club WebEditor.
Cars: "Project 757" '59 A35 2-door bought in 1971 & Subaru BRZ SE LUX Auto plus "family fleet": Alfa MiTo, Peugeot 206, (Ex '98 Alfa Romeo 156 2.0 TS)
Re: Engine bore centres
I couldn't find any data on A-seies bore centres either...Dave Clark wrote:Can,t find the bore centre distances at the moment, but it is inconceivable that the 803, with a bore of 58mm could share the same bore centre with a 1275 with a bore of 70.62 mm.
But I have a suspicion that bore centres are common across all A-series engine capacities, partially backed up by experience of fitting a Marina 12G940 head to 948 block. It's common industry practice for each engine family (eg A-Series, B-Series or Kent) to maintain common bore centres.
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Re: Engine bore centres
Maybe small bores have the same centres and the large bore ditto, but I still cant see them all having common centres.
12G940 to 948 requires block pocketing as the valves overlap the bore and may also be offset - not sure about that though. Offering a 1275 head gasket up to a 948 block could be illuminating.
12G940 to 948 requires block pocketing as the valves overlap the bore and may also be offset - not sure about that though. Offering a 1275 head gasket up to a 948 block could be illuminating.
Re: Engine bore centres
Found this thread from another forum which may give a clue (second post).
http://retrorides.proboards.com/thread/ ... re-spacing
http://retrorides.proboards.com/thread/ ... re-spacing
Felicity and Sam, Owners of 'Nelly', 1955 Black 4-Door A30
Owner and Club Member Since 2014
Southampton & New Forest Club Member
Owner and Club Member Since 2014
Southampton & New Forest Club Member
- gazza82
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Re: Engine bore centres
Which says:-
Many thanks for the link!- 998cc A-Series (64.58mm bore): cyl.1&2/3&4: 5.5mm, 2&3: 18mm
- 1275cc A-Series (70.66mm bore): 6.5mm
The smal-bore engines (848, 948, 998, 1098) have paired bores, hence a bigger spacing between 2 and 3. The big bore engines have even spacing (970, 1071, 1275). P.e. 848cc vs. 1275cc:
"If you're driving on the edge ... you're leaving too much room!"
Club WebEditor.
Cars: "Project 757" '59 A35 2-door bought in 1971 & Subaru BRZ SE LUX Auto plus "family fleet": Alfa MiTo, Peugeot 206, (Ex '98 Alfa Romeo 156 2.0 TS)
Club WebEditor.
Cars: "Project 757" '59 A35 2-door bought in 1971 & Subaru BRZ SE LUX Auto plus "family fleet": Alfa MiTo, Peugeot 206, (Ex '98 Alfa Romeo 156 2.0 TS)
- David Swain
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Re: Engine bore centres
I have a Mini 850 cylinder head, on my Ex 948, now 1030 Engine. All seems to line up OK
David Swain. Member No. A1743
Contact for 'The Suffolk Group'.
Contact Email suffolk@austina30a35ownersclub.co.uk
A30 van 55 'R.G. Swain', A35 4 Door 59 'Little Gem', A35 2 Door 59 'The Rev' '+1'
Contact for 'The Suffolk Group'.
Contact Email suffolk@austina30a35ownersclub.co.uk
A30 van 55 'R.G. Swain', A35 4 Door 59 'Little Gem', A35 2 Door 59 'The Rev' '+1'
Re: Engine bore centres
You're correct Dave - I should have known better than to debate such issues with an A-series expertDave Clark wrote:Maybe small bores have the same centres and the large bore ditto, but I still cant see them all having common centres.
Photos below clearly show difference in bore centres between small and large A-series. This means different capacity A-series blocks could not go down the same machining lines unless fundamental tooling was changed. That's an expensive penalty and would not be tolerated by any manufacturer focused on making profit. No wonder BMC, BLMC, Austin et al went out of business...