Thread: 3.9 complete rebuild any tips, tricks, things to look out for?

Don't bother re-boring a Rover V8. I learnt the hard way that that they need to be re-sleeved with top-hat liners, otherwise the liners come loose.

I also learnt the hard way that the new camshaft needs to be run-in at 2500rpm for at least 20 minutes, so that the lobes don't wear off

Cheers Charlie

Quick hint: don't DIY a 3.9. Buy a top-hat linered reco short motor (3.9, 4.6, whatever floats your boat) from a reputable engine shop, then possibly it will last. 2 out of 3 3.9 engines that have come to me for repairs have had cracked blocks.

Originally Posted by bee utey

...... 2 out of 3 3.9 engines that have come to me for repairs have had cracked blocks.

Overheating ? or inherently fragile design ?

Originally Posted by superquag

Overheating ? or inherently fragile design ?

Reached their fatigue failure limit, poor design means that very little overheating is needed to set off the cracking. Around 250-300K it's a lucky dip to get a crack free one even if well maintained.

are the 4.4's a more reliable option?

Well, get a top-hatted block and then build it up. Anything other than the 3.5 V8s just seem to have that much less material around the liners that many wind up cracking.

Other than that, engine rebuilds tend to be rather straightforward. The heads go off to be at least serviced. The crank goes off to be checked and at least polished if not reground. The timing cover may need to be reconditioned since they corrode behind the water pump. You get to spend lots of time at machine shops asking them to do things.

If you get the block top-hatted, then you'd get new pistons as well, which would need to be fitted onto the conrods for you. You would then spend a lot of time checking the piston ring gaps in the bores, assembling, and then putting the pistons in.

Nothing is really that hard, just tedious and picky. You don't take short cuts or you pay for it later on.

It is quite nice when the thing is finally fired up and actually works, and even better when it's got several thousand k's on it and you know that you put it together. And you'll know what was done on the motor. I've got one here in bits, and it would appear that the big company over East who put the engine together years ago didn't worry about the marked crankshaft, or the odd piston ring that scratched a liner and ruined it.

I'm just about to do up an engine and I'm looking forward to getting the whole thing just right.

you doing up a 3.9 davo?

Originally Posted by Vanderz

are the 4.4's a more reliable option?

Not really, and there are a number of fitting issues too, they aren't a drop-in fit. Crankshaft rear end, block width, oil passages, emissions specs, all make it difficult.