Just a question about boring out a 1275 past 60thou.

It's my understanding that if you just bore the block out 90thou i think it is (what size is 1380cc?) that with the use of a competition head gasket then there shouldnt really be a problem of blowing the gasket between cylinder 2 and 3.

But i'm being told that it would still just keep blowing the gasket, and that you have to bore the block from a standard size off centre etc. so there is a larger gap between the cylinders.

So whats the go, does the head gasket really blow that easily? I could handle changing it every now and again, but not regularly.

I was also wondering, seeing as my source of information isnt really up to date with all the recent developments, has any mob made a gasket to suit the bigger bores? so your not getting gasket overhanging?

off-set boring is an ancient age old technque & yes is very common to do with very large over bores,,, & yes it`s meant to help deal with trying to keep as much meat between each bore as possible

even the gaskets were changed & had their bore centres changed & the diameter of each bore hole enlarged (back in 1970-ish) to accomodate for both the off-setting & the lager bores that became quite prominent

There is a companie (or 2) here in Aus who make larger bore gaskets with a good off-set but their name illudes me at the moment, & there are also other gasket companies in England who do a similar item

Beware tho,,, """Sometimes""" when you go for the offset--enlarged bore design you can break into one or 2 of the oil gallerys at the back end of the block,,, don`t worry tooo much if it happens tho because they can be plugged up & re-drlled off-set rearwards to repair the situation

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

For a 1360 (+.094", 73.0mm) there is no need to offset bore.
But... it is a good idea, if you are going to bore it further (73.5mm, 1380cc) or 74.0mm, 1400cc.

Good 74.0mm pistons are now available again for 1400cc, see Graham Russell.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thx for the responses. It's not really a dilema, its that block i bought off you Matt. Murray was telling me if you wanted to run anything over 60thou you had to offset bore from a standard block, but then i read in a vizard book that you only had to offset bore for 74.7mm i think it was, so i was just curious as to how big i could get away with seeing as its already at 60thou without breaking my bank

1380 works too without offset boring but as I said, it's a good idea. If you are going to do it, offset it well before you get to 1380cc- preferably, when boring upwards from 1330 size.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

i have mate who told he used to drive a mini that its engine was 127thou oversize - fella boring it didnt want to do it incase hit waterjacket or something. He told me that wasnt offset. It used to go like clappers he told me

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