Hi looking at buying an old engine which needs a rebuild. what should i look for. what can wear beyond repair anything which may cause any issues?

Thanks nick

What is the engine?
What type of tune are you aiming for after the rebuild?
What is the engine for? (a restoration or a replacement/upgrade)
It's hard to tell until the engine is apart. It may be reasonably good or everything may be flogged out. If you just want to pull it apart to make sure nothing is to bad then wack it back together as a stock runabout some people would leave pretty much everything. But if you going for a decent power horse then bearings, oil pump, bushes and shims, skim the block and head are just some things that should be on the list of things to replace (or checked) no matter what. Depending on the condition of the engine you may need new pistons, a re-bore, crank work, cam, push-rods, timing gear etc etc
This really can't be answered to accurately until the engine is striped down.
I think a standard rebuild on a decent condition engine with absolute minimal internal wear is $3000 at a ball park figure, but that can easily go up to $5000 or (much) more depending on what needs doing and what you want to get done.

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Respect mine and I'll respect yours.

Quotes I got today range from $700 to $1500 depending on the work needed.
And that's just machining Nd balancing now add new pistons rings bearings wesh plugs and then let's add head work... Carbies, exhaust, clutch, flywheel, and if you can't build it yourself add the price of the build at about $75 an hour and man you can't rush a good thing.
I'm allocating at least a week for assembly of my motor because I want to blueprint it after the balancing job. And I haven't built a motor in 15 years

I do have a good runner 998 but it does blow a little smoke so could be rings or valve stems. Is an EPIA engine from a 76 clubman.
No carb etc just a bare engine but I'm in Vic

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If its got tits or wheels its gonna cost you

1973 Solid side Leyland Mini Panelvan 1100 in Hairy Lime(Elma)
1976 Clubby project in progress
1966 Morris Mini Deluxe in need of a full resto
1971 Mini K Garden Art