If you blow a head gasket, must you have the block honed before fitting a new'un?

not really, but............ Usually when you blow a head gasket, you've reved it too hard, or too much compression. I'd give the block and head a visual inspection then if it all looks honky dory then wack a new head gasket on it, and go a little easier, but if you want to be sure then go right ahead and hone it. But this is my opinion, I'm sure other people on here would have more experience with this
cheers
Damo

yes i agree..you might have just rev the hell out it..either that or the gasket needs to be replace anyways...

Often the head gasket blows because the engine overheated.

By "hone" you are talking about the cylinder bores, right? You can feel with your fingers to see how smooth the bores are. Even if the valves are burnt, this probably doesn't need doing. Sometimes even when the piston gets a melted spot the bore is still OK, but be sure to give it a good visual inspection.

Or if you mean mill/machine/deck the block for straightness ... very unlikely this would need to be done. The aluminum head is more likely to warp, but can be .1 mm out of straightness and still be acceptable for street use, meaning that rarely needs to be done (see head gasket discussion for the exact specification).

From my experience on this topic it is more likely that the head will warp than any troubles occuring with the block when ur car over-heats this happened to me recently and i tryed a new gasket without having the head checked (idiot), i only had it for a day after that and the heat caused the oil rings to weld to the pistons ( you should have seen the smoke when that hapened!!!). since then ive had the head reco'd ($300) new pistions ($250) and i have to have the block honed tommorow

that my 2 cents

K, I should explain something, this is not for my 1200, but my "runabout" Mazda Cappela 1600, 1.6 OHC. The radiator blew, and it overheated, so I took it to a radiator shop, they fixed it, it started fine, but when they went to move it in the morning, wouldnt start. Verdict was a blown gasket. They want $700AUD to fix it. The damn car only cost me $200, so after shelling ot $300 for a new radiator, I really dont want to let them do it. I was thinking just replace the gasket but my dad said the block could be warped. How do I find out if it is or not? Can I find out myself, and if its not warped replace the gasket, or do I need to shell out to get it proffesionally done?

easy way to tell if u dont mind a mm out get some thing that is flat like a 2-3 mm thick sheat of metal and plave it on the tope when its all take off cus even if you get it honed they will end up taking it all off or is my idea not a good one the reason i said2-3 mm cus if its like 1.5 mm or smaller its bound to have flex in it and might not be dead flat all over

Mazda piston engine runabout....
Why did you bother as Mazda piston engines would have to be as good as triumph ones.

i had overheating probs for a while

gasket went

head needed machining

i also heard you need to wait around 48 hours b4 taking head off to let it cool properly as if you take it off hot it will definately warp!

Yeah, you need to wait for it to cool down, but cool to the touch is good enough, maybe a few hours. Make sure you unbolt in the right pattern.

$700, no way Jay! as you said this is more than the whole car. The parts (head gasket set) is maybe $50?

Take it off and check the warp of the head. Don't worry about the block. '70s Mazdas have a reputation for warping the head. You can measure with a good straight edge. Check with an old mechanic if you don't have a precision straightedge, that's the only equipment needed (straightedge and feeler gauge). Oh, and get a book that lists the Mazda specifications.