The crank should drop enough with the mains caps slackened to be able to slide the old upper shells out, and the new ones in. That's certainly the case on the V8, and I see no reason why the 6 pot should be any different.
My view on this type of procedure is that it is fraught with unseen consequences. It is your car though and if you need to be involved in a learning experience like this then the choice is ultimately yours. The Rover P5 IOE engine is an expensive and complexly assembled unit in comparison to the alloy V8.
Before leaping in where angels may fear to tread, first ask a few well considered questions.
Why do you want to change the main and big end bearings! Have you considered the camshaft bearings too! They're also an element in the lubrication system/galleries that maintain pressure to the crankshaft bearings.
If the bearings are marginal the crankshaft journals are highly unlikely to be pristine either. Nor is there any possibility to check the journals, or even at the very least linish them if a bearing has picked-up. Wedging main bearings around the crankshaft journal and into their respective housing whilst laying on your back under a car in my view smacks of a desperate repair method that has a high probably of going south. Allowing the crankshaft to hang off either the clutch shaft bush/bearing or the torque convertor input shaft doesn't sound like a well considered repair method!
Consider too that 'new' bearing shells aren't a perfect half circle designed to fall into place. They are designed to not only sit slightly proud of the bearing housing (requiring a firm fit to sit in place correctly) but also with a degree of spread between the bearing shell ends. There is a designed degree of bearing crush when the cap is torqued down. It would also be an advantage for the back of the shell to sit in a clean bearing seat.
The back face of a bearing (seat side) can reveal a lot of useful diagnostic info about that particular bearing and journal's relationship with regard to wear patterns.
Rear main seal. This will be disturbed. Consider that this is in all probability an old seal intimately mated to a surface over years of use. It is also a split seal I believe held at the rear of the engine by 2 half plates totally inaccessible with the repair method that you're considering. Disturbing this seal as it surely must, will with all probability and with the assistance of Murphy's law create a rear main bearing leak...but who know's you could be lucky.
Front timing cover seal and valve timing chain and tensioner. You'll need to remove all of this as you won't want to accidently drop a tooth or two and throw out the valve timing.
My advice for what it's worth (considering it's free), is to carefully think through your options before diving-in. If it were mine though I'd remove the engine. (Been there done that)
DJM16 a keen enthusiastic/ restorer may want to add to this as he is currently involved in a hands-on comprehensive repair to his engine and no doubt knows the pitfalls that you may encounter with this type of procedure.
Ive changed many main bearings with an engine in situ. I use the top of a large nail with the head suitably filed down flat inserted into the oil holes in the crank to remove the old top bearings and push in the new top by rotating the crank shaft. The main bearings need only to be slacked off very slightly if at all. I was shown the method by my father and still remember him telling me that when as a mechanic in the army,he drained the oil and ran the engines of trucks that had to be left (to stop the Germans using them) that they took a surprising long time to seize up.
Probably one of those featuring Dunkirk. I believe that was where my dad was referring to (wasn't there a film with John Mills). I think it was as much as slowing down the advance by blocking the roads with seized up lorries and tanks as stopping the germans from using them.
I have changed both big ends and main journal bearings in situ (although with the benefit of a four poster hoist). Why? I took them down to check the state of them and found one worn through to the copper. Given that I was not ready to do a full engine re-build 6 years ago, it was a reasonable compromise that kept me running.
Bear in mind that you cannot get to the rear main journal without taking the gear box off. So if you do not mind that not every main journal is replaced then go ahead. This is what the garage used by a previous owner *may* have done.
I had to do something about the oil leak from the rear main seal, and elected to do this by taking out the DG box (yes it is just possible!) for access rather than pull the engine. While I was there, I checked the mains and big ends for wear. Since I was already there, and there was *some* wear, and my friend with the hoist was not cool about his hoist being occupied for another month or two while I rebuilt the engine properly, I just put in new mains bearings and big ends and put it all back together again.
Of course you will not drop all the main bearing caps at once, or something drastic will happen. But you can drop them one at a time with impunity. I found the the upper bearing shell was pretty easy to remove,and replace with new, even with all the others still done up tight. I started each off with a little tap from a mallet on the end of a screwdriver. The shell could then be rotated 90 degrees by placing a flexible prodder (cut-off plastic cable tie?) between the crank journal and the upper bearing carrier and pushing. You can soon get a grip on the other end coming out, and continue to rotate it around the crank journal.
The biggest argument for NOT doing your journal bearings in-situ is that the rear journal is the one that may be the most worn, as it carries the flywheel / torque converter, and this is precisely the one you cannot get to without taking out the gearbox. This was the case with my engine.
The main argument FOR doing this is that I was able to keep my 3 litre running for another few years before I really had to rebuild the engine. We could certainly argue about whether that was a good thing in the light of the extreme wear I found elsewhere on stripping the engine!
(As has already been mentioned, the sump will come off in-situ. There are two difficulties, first the tie rod needs to be removed from at least one end. I forget if the sway bar also needs to come off. Second, the sump tends to hang up on the bronze mesh filter on the bottom of the oil pump.)
With regard to the camshaft bearings, these are likely to be more worn than the big ends and mains, but unlike those, excess wear is unlikely to lead to a major failure until they are so worn that oil pressure is really low. You can actually take the cam shaft out with the engine in-situ too (provide you remove the radiator and make an access hole in the firewall. But doing this is a real pig of a job. You can also change the timing chain, since you now have the radiator out. And while you have the camshaft out you may as well fix the oil pump with new gears and shaft.
Of course by this time, you have done 50% of the work needed to remove the engine.
Hi does anybody know if big bearings and mains can be got at by removing the sump with the engine still in the car on a 3litre auto many thanks
Hi, I have done it, 2 years ago when my big ends went, its not easy, but can be done.
The 3 main problems are;
Supporting the engine as the bellhousing/engine to gearbox adapter has to come off and it has the rear mounting attached to it. I put a scissor jack under it to support the engine.
Getting the crank out past the crossmember and the aforementioned scissor jack, it is a heavy crank. Getting the crank back in for the same reasons, without damaging the crank. It also not so easy to check the bearing clearance with the crank in position, I used plasti gauge in the end. We used to use it in the Army and it gives a good indication of correct clearance. My crank had been reground on a previous rebuild and I wanted to check this time, as 2 years and 7000 miles down the line big ends went. Was all good.
The biggest problem is getting the rear main with the side seals in correctly and correctly mounting the rear crank seal its is a real pain. If I had to do it again I would get the engine out if at all possible. The car has run fine since. Land rover s2/3 parts and bearings fit, and most parts are available from LR. Don't grind to .010 as they don't have that size.