Hello ausmini brains trust.
Just a quick question, I’m in the process of rebuilding a 1275 at the moment
And I have end up sourcing another block and today it arrived.
Well the bores look bloody great and in great condition.

I was told it was a 40 thou over bore but when me and a good friend (retired fitter and turner) measured it up... found it to be std bore.
Finally a small win, well sort of.

So I was thinking that I might get away with a quick hone and a re-ring
So the question is what’s the maximum tolerance I could get away with on the bore for a re-ring.

I’m more than happy to get rebore next size up, but funds are tight and if I could save money.
Plus this car is not a daily drive and I’m not chasing big horses....just wanting a bit more nippiness than my current 998 can give.

Cheers Neil

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I have a mini because I'm not allowed to play with small thermo nuclear weapons any more. (bloody neighbours you’d think they would be happy that they don’t have to turn a light on when they need to take a leak in the middle of the night)

Generally, if there is visible honing left in the bores and all over the bores, then a re-hone will be OK, however, if not, I'd suggest measuring the bores at the top, middle and bottom of the stroke and in thress axis at each level (so for 1 bore that's 9 measurements). The bores seldom wear even and so go out of round. Any more than about 5 - 6 thou (factory recommends 4 thou as the upper end clearance) piston to bore clearance or more than about 1 thou out of round and I'd be considering a re-bore.

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Re-ring jobs seldom last, pistons usually have upper ring land wear, and if you are then going to fit new pistons it's pointless fitting standard ones into oval, tapered bores. It will burn oil and lose power too.

A proper rebore and hone to the next oversize is only $100-$150; add a new piston & ring set for $200 and you then have nice round bores with the right piston clearance and correct honing pattern. Good for maximum power production.

[edit] However, I have built 2 engines using oversize S/H low mileage pistons, both gave good power and didn't burn oil.
My 1st one was a 1310 with Mahle forged flat top race pistons, the 2nd is the 1412 stroker in my car now (the Hypatec pistons had 4 hrs running in a 1360 Elder 8 porter, on GR's dyno). New ring sets were used in both cases.

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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.

As the Doc knows, I tried a similar thing on an engine I bought where the PO had done a similar thing. I too wanted to save a few $$$ so thought the re-hone and new rings the PO did would suffice. I regretted it the whole time I owned the car. It really is not worth the $$$ you MAY save.
KB

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Yep I’m inclined to rebore…….. but where is the fun it that.
Ok there is visible honing marks at the bottom of the bore and very faint to none at the top.
We did check top, bottom, front, back, and sides.
Bottom where spot on
Top.........three bores where all within one to two tho, manly on the thrust side.
Top on number one bore was closer to six….. but del said it was odd as it was more to the side and not on the thrust side, if that makes sense.
And the six tho part was at the very top of the stroke. They way del explained it to me was where the piston rolled over at the top of the stroke.

He got me to run my finger over it and I could fell the lip in the bore then as my finger slid down I could feel it go in and then come back out.
And yes I reckon it was only just the width of a ring.

I asked him what would cause and he felt that some thing was miss aliened and that’s why it was more to the side......

I might have to come down to south for a while just so I can get cheap rebore and mini parts.
The cheapest I have been quoted on a rebore here is three hundred dollars, I don’t think I’m going to be able to find one that does them one hundred to one fifty here doc.
If I could find cheap freight......... Sydney might be the go

I’ll ring around more places next week for rebores cost next week………if any body could recommend some where up here I would appreciate it if you could send me some details.
Also looking for some where to do a crack test and grind on a crank. The same place that quoted me on the rebore quoted me three hundred on the crank.

Just to mention the block was a bare block so I still have to buy new pistons even if I re-ring.

Thanks GT mowog, Doc and 1310/71 really appreciate the replies and the input
Cheers Neil

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I have a mini because I'm not allowed to play with small thermo nuclear weapons any more. (bloody neighbours you’d think they would be happy that they don’t have to turn a light on when they need to take a leak in the middle of the night)

Sounds like sending your block to Graham Russell and buying a set of hypatecs & rings from Adelaide might be the go then.

I recently sent a set of Escort rims to brisbane for someone off eBay. They organized the freight on either smart freight or smartsend (can't recall) for $60. Four boxes 15kg each. I've also bus freight can be good but pickup and delivery might be an issue there I guess.

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Didn't you tell me that the Block came from Sydney??

Do you have the caps with it?

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Bluey-1973 Clubby - 1330, high lift, big cam, 7 port madness in progress..

Gumby-1978 Minivan, British Racing Green - 1310, high lift, mild cam, enlarged porting and chamber shape with big valve head, supercharged build in ever slow progress!

Well, since you need to buy pistons anyway, you might as well go next over-size and re-bore it.

Best of luck with it

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I`d suggest that it`s more than likely caused by a bent con-rod

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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.

awwww... that can't be good..

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Bluey-1973 Clubby - 1330, high lift, big cam, 7 port madness in progress..

Gumby-1978 Minivan, British Racing Green - 1310, high lift, mild cam, enlarged porting and chamber shape with big valve head, supercharged build in ever slow progress!

however, it`s pretty typical for a 40-odd year old donk that`s been stuffed with by 500million people over the years

i`d bet there is more bent rods currently running around right now without thew owners even knowing it

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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.

Not to be picky here, but - and it maybe be classed as a fine line - I'd call it mis-alignment of the rod. It will (typically) be only slightly out. I'd class a bend as something that would (at the very least) lock up the engine.

As part of a proper over-haul, you'd close and hone the rods and check them for alignment (straightness) as sure as you'd torque down that 6th Main Bolt.......

Tobermary, it's a pity you don't have the old pistons, they can tell you a LOT about the history of the engine and it's general condition.

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