29 replies to this topic

[Corey96Williams]

Hi,

I've always fancied boring out my engine, but I know virtually nothing about it. Could anyone give me any information on it? Cost, where to take it, experience, pretty much anything helpful will be appreciated :)

Thanks,
Corey

[peter-b]

a little more info might help, what size engine etc. Why are you wanting to do it? Just boring it out doesn't make a great difference on its own unless you're going major oversize, even then it's marginal. Other things to concider is if its say a 998 then why not just fit 1275? You get a lot of people saying 'oh yeah, it's bored out and has 2 times the horsepower now', thats rubbish.

It's a combination of things, not just a case of drilling it for bigger pistons. My suggestion is unless you have bottomless pockets, and assuming you have a 1275, have a look into the best bang for buck options. If it is worn you may well need to get it bored, but don't go to the max size as it'll leave you room for future reboring. If it's not overly worn and comps are good, maybe some head work or cam/carbs, will get you what you're after?

In answer to your original question, it involves engine removal and a complete strip down. Then they'll clean and check block, measure it as to what size it is currently. Then bore and hone the cylinders to suit the pistons they or you supply. Basicly thats it, price varies heaps depending on the shop and the quality of the parts used. As for where, go to the best place you can afford or ask local workshops who they use or recommend. Don't forget theres more expense too, gaskets seals bearings, timing chain and or gears, crank grind maybe, oil pump, head overhaul or exchange, balancing, the list goes on.  

[Carlos W]

I'll echo the above, really good advice there.

 

It's all about accurately measuring to see if you need a rebore, if you do go to the next size up and then look at head work, and cam. If I was fitting a new cam I'd be replacing followers too.

 

Don't use a machine shop who don't want the pistons before they do the rebore. 

 

Whilst it's apart the crank will need inspecting, possibly regrinding and new shells fitted.

 

Have a read of some of Cooperman, or AC Dodds threads on these subjects because all I'd be doing is regurgitating their advice. 

 

You need to decide on budget and what you want from the car, depending upon you're ability will depend on what you can do yourself, but all the engineering part needs precision tools. 

[Fast Ivan]

A block is bored then honed to suit the pistons supplied by you to the machinist
Cost wise you're looking at around the £100 mark for the next size up
I would recommend AC Dodd for this work

[Spider]

There's a bit of info here

 

http://www.theminifo...gine-machining/

 

but no pricing, although it does say why!

[Corey96Williams]

a little more info might help, what size engine etc. Why are you wanting to do it? Just boring it out doesn't make a great difference on its own unless you're going major oversize, even then it's marginal. Other things to concider is if its say a 998 then why not just fit 1275? You get a lot of people saying 'oh yeah, it's bored out and has 2 times the horsepower now', thats rubbish.

It's a combination of things, not just a case of drilling it for bigger pistons. My suggestion is unless you have bottomless pockets, and assuming you have a 1275, have a look into the best bang for buck options. If it is worn you may well need to get it bored, but don't go to the max size as it'll leave you room for future reboring. If it's not overly worn and comps are good, maybe some head work or cam/carbs, will get you what you're after?

In answer to your original question, it involves engine removal and a complete strip down. Then they'll clean and check block, measure it as to what size it is currently. Then bore and hone the cylinders to suit the pistons they or you supply. Basicly thats it, price varies heaps depending on the shop and the quality of the parts used. As for where, go to the best place you can afford or ask local workshops who they use or recommend. Don't forget theres more expense too, gaskets seals bearings, timing chain and or gears, crank grind maybe, oil pump, head overhaul or exchange, balancing, the list goes on.  

I have a standard 1275cc, SPi. This will sound silly, but to be honest I don't know enough about it to give you a list of parts I'd like. It's a 85 thousand miler, and it's very reliable (touch wood). I don't necessarily need a rebore, but I want to do it to get more power. I've seen videos of 1340cc Minis and they look fast, and really good fun.  

 

A block is bored then honed to suit the pistons supplied by you to the machinist
Cost wise you're looking at around the £100 mark for the next size up
I would recommend AC Dodd for this work

Cheap compared to what I was expecting.

 

I'll echo the above, really good advice there.

 

It's all about accurately measuring to see if you need a rebore, if you do go to the next size up and then look at head work, and cam. If I was fitting a new cam I'd be replacing followers too.

 

Don't use a machine shop who don't want the pistons before they do the rebore. 

 

Whilst it's apart the crank will need inspecting, possibly regrinding and new shells fitted.

 

Have a read of some of Cooperman, or AC Dodds threads on these subjects because all I'd be doing is regurgitating their advice. 

 

You need to decide on budget and what you want from the car, depending upon you're ability will depend on what you can do yourself, but all the engineering part needs precision tools. 

Pretty much all I want is the extra power, the budget would depend on what sort of price bracket I will be looking at (As I'm still completely new to the idea, I don't know exactly what I'm after).

Edited by Corey96Williams, 28 May 2015 - 02:28 PM.

[Carlos W]

You don't necessarily need a rebore, you need to measure to see if you need a rebore.

 

As has been suggested, a rebore won't give you an awful lot more power. Head modifications, a different cam, and correct compression ratio will give you more power.

 

What exhaust have you got?

[Blatherskite]

Extra power in a SPi, I recommend a Stage 1, 2 or 3 head as a good start. We fitted stage 3 to otherwise standsrd SPi and went from about 55hp to 73 measured on rolling road. Easier than rebore, and you can undo it all if you want.

[Corey96Williams]

You don't necessarily need a rebore, you need to measure to see if you need a rebore.
 
As has been suggested, a rebore won't give you an awful lot more power. Head modifications, a different cam, and correct compression ratio will give you more power.
 
What exhaust have you got?

I've got a stainless steel exhaust, with a cooper manifold.
I was looking at getting a 1.75" RC4O/Maniflow soon instead.

[Cooperman]

Just boring to 1330 cc (no such thing as 1340) will gain you 3 to 4 bhp.

The key to improving the old A-series engine is gas-flowing the cylinder head. Until you do that little can be gained in a meaningful way.

You have a classic car. it won't ever be fast, so why not go for nice driveability combined with smoothness. You can improve an SPI to some extent, but it is limited unless you want to spend thousands on a complete engine re-build. A friend of mine rebuilt an SPI into a 1330 with twin HS4 SU carbs, a much better head, better cam, etc. It cost him over £1900 including a precautionary gearbox rebuild.

You can leave your classic standard and buy a very quick modern everyday car for that sort of money!

[Corey96Williams]

Just boring to 1330 cc (no such thing as 1340) will gain you 3 to 4 bhp.

The key to improving the old A-series engine is gas-flowing the cylinder head. Until you do that little can be gained in a meaningful way.

You have a classic car. it won't ever be fast, so why not go for nice driveability combined with smoothness. You can improve an SPI to some extent, but it is limited unless you want to spend thousands on a complete engine re-build. A friend of mine rebuilt an SPI into a 1330 with twin HS4 SU carbs, a much better head, better cam, etc. It cost him over £1900 including a precautionary gearbox rebuild.

You can leave your classic standard and buy a very quick modern everyday car for that sort of money!

Sound advice!

But no such thing as a 1340? All I seem to see is 1340cc engines when browsing the internet. (Although as I've said multiple times, I'm a complete novice)

[Carlos W]

 

Just boring to 1330 cc (no such thing as 1340) will gain you 3 to 4 bhp.

The key to improving the old A-series engine is gas-flowing the cylinder head. Until you do that little can be gained in a meaningful way.

You have a classic car. it won't ever be fast, so why not go for nice driveability combined with smoothness. You can improve an SPI to some extent, but it is limited unless you want to spend thousands on a complete engine re-build. A friend of mine rebuilt an SPI into a 1330 with twin HS4 SU carbs, a much better head, better cam, etc. It cost him over £1900 including a precautionary gearbox rebuild.

You can leave your classic standard and buy a very quick modern everyday car for that sort of money!

Sound advice!

But no such thing as a 1340? All I seem to see is 1340cc engines when browsing the internet. (Although as I've said multiple times, I'm a complete novice)

 

The problem is, the internet and mainly Facebook is full of idiots who talk rubbish.

[Corey96Williams]

 

 

Just boring to 1330 cc (no such thing as 1340) will gain you 3 to 4 bhp.

The key to improving the old A-series engine is gas-flowing the cylinder head. Until you do that little can be gained in a meaningful way.

You have a classic car. it won't ever be fast, so why not go for nice driveability combined with smoothness. You can improve an SPI to some extent, but it is limited unless you want to spend thousands on a complete engine re-build. A friend of mine rebuilt an SPI into a 1330 with twin HS4 SU carbs, a much better head, better cam, etc. It cost him over £1900 including a precautionary gearbox rebuild.

You can leave your classic standard and buy a very quick modern everyday car for that sort of money!

Sound advice!

But no such thing as a 1340? All I seem to see is 1340cc engines when browsing the internet. (Although as I've said multiple times, I'm a complete novice)

 

The problem is, the internet and mainly Facebook is full of idiots who talk rubbish.

 

This is what sprung to mind

[Cooperman]

The only way to get a 1340 would be to grind a crank down offsetting the big-end journals and changing from 1.75" dia big ends to 1.625" dia, then using the Cooper 'S' con-rods to run the smaller diameter. This would increase the stroke.

A straightforward +0.060" overbore gives 1330 cc.

Not a lot of point in doing either unless it is for historic competition where couple of extra bhp might knock a few tenths of a second off the lap time. Otherwise it's pretty pointless. If an engine needs a rebore & new pistons it is always best to go to the next size up, unless it's already at 1330 cc in which case it needs to be sleeved back to 1275.

[peter-b]

I concur with the others. The biggest problem you have with the mini is its 1950"s technology and you want 2015 performance. You can build a firecracker engine but reliability goes right out the window. Someone mentioned its an SPI, if you convert it to carbs won't you have rego problems?
Why not just get engine done by someone with mini experience, that can put the right combination of parts together to get the best performance AND drivable reliability.