16 replies to this topic

[minimotion]

looking to have my 1275 bored to 1310

can anyone tell me the best place to get pistons from quality for money wise?

 

and am I doing the right thing going to 1310?

[Cooperman]

It is normally considered best to always go to the next size up when re-boring, so in this case it's +0.020" which gives 1293 cc.

Pistons should be 21253-020 from Mini Spares and always take the pistons to the machine shop so that the bores can match.

[MrBounce]

It's always worth chatting to the guy who's doing the machining. He suggested that I got the pistons as his supplier was likely to be more expensive! Don't forget if you use TMF+ discount (7.5%) at Minispares, that's a decent chunk of cash off!

[Jordie]

As stated above, always take the pistons with you!

[minimotion]

Will I get much more out of the engine if I just got to 1293? Thanks for letting me know about the discount!!!

[HarrysMini]

No noticeable gain in power, no. But then, even with 1380, you wouldn't notice much difference. The power in an A Series engine comes from the head, not by increasing the bore size.

1293 is generally considered a repair rebore.

[HarrysMini]

Also, a rebore alone will make almost no power difference at all, as other components have to be modified to fill the larger capacity!

[RedRuby]

If you go to 1275 +0.20 giving 1293 the standard +0.20 pistons at mini spares are 44.99 each inclusive of vat with 7.5% off you will save a total of about £13.50 (3.37 per piston). Before you are eligible for discount you need to pay £5 to become a TMF member and then contact Simon at mini spares to lodge the discount on your Mini Spares account.

[minimotion]

Lovely thanks for the help guys and girls looks like il go 1293 and spend the extra I would have on a futher rebore getting the head sorted

[ACDodd]

Hang on your missing the point a straight rebore and fresh pistons add power regardless of size. This is because you restore the original piston ring/bore finish and can now hold the ring squarely in the bore. This means an increase in seal compared to the worn original. So a rebore adds power. The mistake you making is assuming that the original old bore and rings is as good as new. Which of course it is not. The old setup is costing you power.

Ac

Edited by ACDodd, 18 February 2014 - 05:44 PM.

[HarrysMini]

Hang on your missing the point a straight rebore and fresh pistons add power regardless of size. This is because you restore the original piston ring/bore finish and can now hold the ring squarely in the bore. This means an increase in seal compared to the worn original. So a rebore adds power. The mistake you making is assuming that the original old bore and rings is as good as new. Which of course it is not. The old setup is costing you power.

Ac

What I was saying is, it doesn't increase power output - it just restores what might have been lost if the current setup is extremely worn.

[ACDodd]

Interestingly it does not have to be extremely worn, easy for an engine suffering bore wash to be 25% down on bhp with less than 100 miles on it. I have seen rebores add an easy 14hp to an engine that has good valve seal. Ie don't underestimate wear. This is the biggest single cause of low power outputs.

Ac

[HarrysMini]

That's true actually, extremely was probably the wrong word.

[3ltrmini]

Great topic guys and all very good advice BUT please dont forget to let this guy know that the more you bore it out ie 1380/1400 he will have to upgrade the rad because it will run hotter due to the bore walls being thinner,many a big bore have been totaled because a standard rad has been used..

[wile e coyote]

If shopping for 21253 pistons try your local motor factors - 21253 is the old ref for them  - but an accepted norm - but a bit of research and  you'll get the right reference they're Nural now - (as a starter mine at +60 are parts ref 87-524114-00)  local place got me the set in for  £130.....