9 replies to this topic

[Jae]

Hi,

I'm looking for some general advice.. I've just started to strip the engine I have for my Clubby Estate however, I've found the pistons are 21251 +030, this makes the engine a 1301.. ok, so originaly I was just intending to put new rings on the pistons (I thought the engine was a 1312), but now I've been told that the pistons I have are C**p.. ulrgh.

The engine will be primarily a road build and the odd castle combe day - running a SW5 cam, duplex timing, ported 12g940 head, Twin 1¼ SU's, and LCB (this is what I currently have). i'd like to lighten the fly wheel as well, and get eveything balanced..

So as I see it my options are:

a. Try and find a ring set for 21251 +030's (having trouble with this) £70? keep with a 1301 and try to keep the compression ratio low (to be safe)

b. rebore a 1275 block I have to +060 and fit new pistons (21250's £100 from morspeed + £100 rebore?)

c. sod it save up and buy one of those kits that are available from people, but try to reduce the price by getting them to leave out the camshaft & timing gears


My budget is limited (my daughter is only 7weeks old, I'm just buying a house and the gf thinks I spend too much on my mini)

What would everyone recomend? Will running a 1301 at low compression make that much diffrence for a road car than running a 1330 with higher compression?

Any help would be appreciated.

Thanks

Jae

[The Matt]

Firstly it depends what you call low compression I guess. A higher CR will run better (as long as it's not too high). The 1330s are a good size engine, with still the optin if another rebore later if it needs it.

I wouldn't know what a 1301 drives like (didn't know you could even get + 30s for a mini to be honest).

I guess the main questions are:

'what sort of power output are you looking for?'

'what is your budget?'

You can run a 1330 with a reasonably high CR and it will be reliable enough for everyday use too.

[Guess-Works.com]

you will realy struggle to find a set of +30 rings, I don't think they've been used for 20/30 years. The +30 was the original recommened maximum bore for the A series (by the book).

Basically a new set of 21251's will cost less than the rings, so If I were you Id be looking at a re-bore, and probably to +060, as a +40 may not get rid of any ridge at the top of the bore...

There's nothing wrong with 21251 pistons, they are good for a budget build but if you can afford the extra 70 odd notes, go to 21253's which are high compression cooper pistons. If not, take the block upto Simon, Morspeed, or some other establishment, and ask for a rebore +060, 21251's and the block decking for a 10:1 cr... I ran a 1330 block (which Simon did when he was at MED) like that for 3 years before I blew it up ( was not the pistons - was the head gasket ). That was doing sub 17 sec 1/4 miles.

PS if you want a lightened flywheel... should be able to do something for you after christmas...

Edited by GuessWorks, 22 December 2005 - 09:41 AM.

[Sprocket]

Keep an eye on ebay, old stock +30 rings seem to pop up regularly in small bore and large bore

[Jae]

That sounds great - I'll go with the rebore and save up for the pistons.

[tommy]

Basically a new set of 21251's will cost less than the rings, so If I were you Id be looking at a re-bore, and probably to +060, as a +40 may not get rid of any ridge at the top of the bore...

I don't understand how a +40 would fail to clear the ridge at the top of the bore? Surely the ridge is made up of material that hasn't been worn down by the rings thus is extra metal, not a lack of metal?

I'm probably wrong, just want to clear stuff up inside my head.

Cheers.

[Guess-Works.com]

what I'm mean is...

Those bores were taken out to +30 thou, if you went to +40 thou you would only be taking an extra 10 thou of metal off the bore in total, and effectively only 5 thou of metal off bore face. This is not a lot of metal, and would probably mean the ridge which can be felt at the top of the bore at the moment, would not get completely removed... A +60 rebore would take an extra 15 thou of the bore face which is plenty to get rid of the ridge..

[minidaves]

u can get a ring set for +30 21251 pistons no problems they still make the piston however they are not the best ones in the world, do better with 21253's if your going to rev the nuts off it, as for rebore costs look around my local shop charges nowhere near £100 quid for a rebore, but depending u might only need a hone and a set of rings or differant pistons

dave

[Sprocket]

I was quoted £75 for a 74mm offset bore from standatrd 70.5mm bore from a guy who specialises in Aston Martins, Ferraris and Rolls royces

[wolfie]

why not go for a +40 and use minispares mega range of pistons these are very high quality pressure cast and superb for the money