new guy, couple M20 head questions

[paulkeith]

First tech post, been lurking for a while, just recently signed up. I've owned a pair of e36 M's, but am now looking at my first E30.

I found a local 188k mile 325is with a cracked head for a pretty decent price. He says he's got the head off. My gut reaction was to just yank the current motor, find a lower mileage replacement and swap it in. BUT, then I started thinking I could probably get the job done by just putting a new head on. This leads to my questions...

1) If my used replacement head came off a running (ie not blown/slipped tb/overheated) engine, do I need to tear it down and get it decked?

2) What causes cracked heads on the M20s? Overheating? Should I be concerned about the block's condition?

3) Do the blocks ever need resurfacing? ie, if i'm going to have to go through the trouble of pulling the block and tearing it down to get it to a machine shop, I'm just going to swap the whole engine.

4) If he's had the head off for a period of time long enough to call the project quits and put the car up for sale, I'm assuming I'll have some surface rust on the cylinder walls if he didn't properly protect them. What are my options for cleaning up the walls? pistons? is this another motivator for swapping the whole engine?

Just looking for thoughts on what you'd do in this situation.

Thanks,
Paul

[jlevie]

As to:

(1) Maybe, maybe not. That depends on how many miles are on the head

(2) Overheating

(3) Rarely

(4) If in decent condition you might not have to do anything. If lightly rusted, honing the cylinder bores and new rings may be required. If heavily rusted or pitted, a rebore, new pistons and rings would be needed.

[delphini]

Could possibly be that the heads off because the timing belt went "POOF". AND THEN if the belt maintenance has been neglected , chances are good it also needed a water pump . Along with the old "well i already pulled the head for 'ya" story could aldo be bent valves , nicked pistons or a whole slough of other problems going on in there.
I would pour some motor oil in the cylinders with the surface rust and perhaps some PB BLASTER or wd-40, hopefully the corrosion will easily come off with a good soaking and a little elbow grease. My 90 zinno was a situation like this and all is well with her now a little money and a few parts later another e30 is back on the road .

[paulkeith]

I'm not 100% that the cylinder walls are rusted. He says he pulled the head because it was cracked, but I've got no details on the length of time the head's been off, if he did any kind of preventive storage or coating on the cylinders when he pulled the head, etc.

Smart money says he neglected cooling maintenance, overheated her and cracked the head. If he's run too much coolant through the oil I'm leaning towards just swapping the whole motor. Don't wanna throw money at a new decked head if I'm going to spin a toasted crank bearing 500 miles later.

What's the time estimate on a first time e30 motor swap for a relatively well-equipped/experienced wrencher?

[germancarsonly]

I've bought a bunch of dead E30s over the last 12 or so years. I guess I've bought 3 that I was told the same thing, the head was cracked by the seller. All 3 time when I got to see the car, yup it was cracked alright.... shit it was broken when the rocker shafts tried to go through the hood because of a broken timing belt. These heads do crack from the engine being overheated, but it's not near as common as the broken timing belt. You need to look at it.

In most parts of the country a used M20B25 engine complete sells for the same or at the most $100 more than a used head from one. R & R time for a guy that knows cars is about the same - head swap or engine swap. You will spend about $100 less with the complete engine as you don't need the gasket set and head bolts, but on the used engine replace the T-Belt, tensioner, and WP just the same as the head swap.