18 replies to this topic

[Milo1997]

Just recently bought a 1275 engine and noticed the bores are badly scored anyone reccomend what size to bore out to also what piston and ring I will need . What does it cost ? Cheers

[Steve220]

Depends how deep the scoring is.

[sonikk4]

1293 is the first overbore so start there. Your engine machine shop should be able to tell you what is required.

[mk1leg]

show us pics...and try the finger nail test....if you feel the score with the nail then it need either a hone or at worst a rebore...............

[Milo1997]

I can definitely feel then well with my fingernail
If bored out to 1293 what size pistons would I need ?

[gazza82]

+020" ... but get them to overbore first .. incase 20 thou isn't enough. As well as the marks, they will check that the bores aren't worn oval, etc. Or you may find honing will remove them, but the machine shop will be able to advise.

 

The sizes are .020", .040" and .060": that's 1293cc, 1301cc and 1330cc approx

[Fast Ivan]

it may be one those suck it and see jobs - bore to the next size (+020) and see if it removes the marks, if not go to the next size and so on.

That said an experienced machinist may be able to give a more informed opinion before metal is cut.

difficult to see from pics but can you post any up?

[Craig89]

The trouble is you really need the pistons before the block is bored so that the bores can be matched to the pistons. Unless really bad I suspect +20 will be enough

[Milo1997]

Ok I will get some pictures on here Friday cheers

[nicklouse]

just take it to your engine builder/machinist and get then to sort it.

 

IE supply and fit pistons etc. also the crank would do with a grind and new bearings etc etc.

 

if you are having some head work done again discuss with engine builder re compression camber sizes etc..

[Milo1997]

What will boring leave compression ratio as ,will I have to change anything to compensate or it ?

[Dusky]

What will boring leave compression ratio as ,will I have to change anything to compensate or it ?

(from my CR calculator excel file) : With a standard 1275 with 8 cc dished pistons, a 20 thou overbore would take the compression from 10.62:1 to 10.75:1 .

No real difference really

Edited by Dusky, 20 January 2015 - 02:36 PM.

[nicklouse]

but then I bet the block will be skimmed. and......

[racingenglishcars]

Please measure the bore first. It may already be bored, If you then order +20 pistons expecting a +20 bore, you will be stuck with pistons that don't fit the new +40 bores. 

[Milo1997]

What size will the bore be if already bored out to 1293?