Do you have to offset bore for 73.00mm pistons because i have had one reco shop say yes and one say No and another one say Good only knows.... GR arer you out there

So can anyone help.....

_________________
"Ex" is an unknown quantity and a S"pert" is a drip under pressure!

Hi, I'm anyone

I have been told that 73 mm (someone else might take it a little further) is the outer limit of what you can do without off setting, but I feel that it could be foolish not to off set...

You could also try Matt Read, he does heaps of big bores and has had load of experience with them.

hee hee , yeah i`ve Only done 500million of them,,,, it`s true , i counted every one of them Obviously Kidding

Ok,,, yes i would off-set it,,, it leaves nice "even" amount of meat between the bores

& in fact the head gaskets were changed (way way back in Noahs ark days) to accomodate said off-setting,,, so all the 1275 head gaskets you buy these days are allready set for an larger & offset bore----> go on,,, i know you`re all gonna check em now hey???


only hassel is that """MAYBE""" (Maybe not too) But maybe you can break into the oil galleries on the back end of the block,,, sometimes they do & sometimes they don`t

easy fix if it tho,,, locktite some 3/8th" steel rod & punched into them & then off-set drill em

Job-done, easy-peasy & far better off off off off off setting setting setting -stutter stutter than not not not... makes for a stronger bore for now... & maybe make life easier later if/when it needs to go bigger again later on,,, like my 74.7mm bores

_________________
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.

Neither of my 73,0mm bore motors are offset. No problems either.

_________________
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.

At 73.0mm bore you should be able to do it without off-setting...but.....it is dicey if you ever want or need to go any bigger from there...probably consider sleaving......When I do them this big, I off set, so you can usually go a few more times....

73.5 usually works fine with current gaskets, std offset.
The usual reason for offsetting used to be so you can go to 74.0mm, or bigger.
But 74mm pistons have been rocking horse for years (GR has had some made now) and not many people except MADMAT Read bore to 74.7 these days.

_________________
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.

Whether you offset bore or not,
Keep in mind that if the block has previously been bored the existing bore may not be small enough to accomadate the offset you require, so your choice could be easy!
If you think about it you will understand what I mean.

Dave

_________________

HI Mr Magoooo
To answer your question yes you can straight bore to 73mm /73.5mm and some times you have to if the bore is already out to .060 there is not enough metal to off set the bores, may be only .005 depending on how worn the bores are.
If i have a std bore or a .020 bore and take it to .060 over size i start to stager it at .060, if you move the bores out from the centre of the block .015 tho you wind up with an eaven amount between each cylinder on a 73.5 bore you will have .140tho between each cylinder.now in saying this with the a+ blocks i some times only stager the two centre bores because they have a bad habit of breaking through into oil and some times water in no4 cylinder,hope this helps.
Graham Russell

_________________
"It's better to be not informed than ill-informed"

Thanks Graham, The block is at 0.060 what would you suggest????

_________________
"Ex" is an unknown quantity and a S"pert" is a drip under pressure!

get whatever off-set you can,,, no biggy tho,,, if you can only get 15thou out each bore then cool

73mm is .094 thou oversize so from ;060 you should get maybe 12 or 14 thou offset each bore,,, depending on the current situation of any existing wear & scores,,,,
it all helps tho

_________________
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.

Hi Mr magoooo
I have just got a new shipment of 72.5 mm pistons that is .012tho bigger than your + .060 bore and you will not pick the difference in power by going bigger than that, so there's another bore size for your block,
but as matt said get as much off set as you can but you will not get much on a worn +.060 bore.
Graham Russell

_________________
"It's better to be not informed than ill-informed"