Big end shells

[57traveller]

Having only ever changed big end bearing shells on an engine out of the vehicle I have a question re doing this job with the engine insitu.
Is there sufficient access, with the sump removed, to change the shells, particularly the conrod half, without removing the cyl. cover and then the pistons? I don't relish too much of a tight squeeze in the crankcase when lying under the car when it may be easier and possibly quicker to remove the head and pistons.

[turbominor]

Done the big ends a few times on the drive lying on my back.

Take of the bigend caps and you should be able to push the conrod of the crank as the pistons should move up the bores easily (take the plugs out first)

To do the mainbearings you would need to get the crank out

[57traveller]

Thanks for that Iain, you've confirmed what I was hoping and it wasn't too bad doing the change from underneath, and as you say, just a matter of pushing the pistons up the bore clear of the crankpin.
Fortunately I'll be in a warm dry garage and not on a cold, hard driveway.

[turbominor]

last time i did that was when i converted my v8 rangerover to a v7 in a deep gully in Wales..

It went bang and a rod came through the block

off came the sump,
out came the piston,
off came the big end.
remains of rod cut off and reinstalled.

Injector disconnected and of i went with a lump v7 for 3 more days of off roading and a long drive home...


I would make sure the crank is in good condition while you are in there as there is no point fitting new bearings if the crank needs a grind..

Pay loads of attention to refitting the sump or your oil consumption will increase allong with rust protection

[57traveller]

The bottom end rattles are not too bad at the moment - but detectable. Just hoping that a new set of shells will delay the inevitable a while longer!!

Yes, got to get those cork strips right for a good seal.

[rayofleamington]

57traveller,
My first Minor was suffering from general 'high mileage' noise and poor oil pressure.
I change the big ends from under the car as per Iain's method - the old ones had started to break up and had large chunks missing. I also changed the timing chain and finished the job with a new rocker assembly, and the engine was completely transformed and gave many more years hard service.
The mains should really have been done at the same time, which probably explains the oil in the bellhousing and problematic clutch which came about 3 years later, so if your big end shells look in poor condition, consider doing the mains too (although it makes the job 20 times bigger)

Good luck - I'd recommend some good goggles when under the engine as it likes to drip oil on your face / eyes when you least expect it and with the big ends off you never know where the next drip is going to come from

[57traveller]

I don't want to remove the engine yet Ray, it's still in very good all round condition, good compression, acceptable oil pressure, nil oil consumption between changes, no other rattles, except for this very minor big end noise. Trying the simplest option first. I suspect the earlier 17 deg. BTDC ignition timing episode hasn't helped much. I'm sure it would soldier on for a good few more miles yet but wish to renew the shells hopefully before the crank shaft is affected.

[Alec]

Hello 57,
as the many replies above confirm it is possible and relatively easy to change the big end shells, especially if you use sockets. (The sump bolts will be time consuming using spanners.)
I would definitely look at the mains at the same time, and a little trick in changing them in situ is to (do one bearing at a time, i.e don't take all three mains caps off together) remove the cap, then put a split pin into the oil drilling in the crank and rotate the crank so that the head of the split pin pushes the upper shell round and it can then be removed. Obviously the engine must be turned in the right direction so the locating tab end of the bearing comes out and the pin should not project too far out.
good luck,
Alec

[57traveller]

Thanks Alec. The end main bearing cap can't be removed without first taking out the two bolts through the front plate attached to the engine block. Not without removing the timing cover, etc. It will get to the stage where it's just as easy to remove the engine which I don't want to do yet! The centre cap should be o.k. to remove, that's the bearing that wears the most anyway, so it may be worth inspecting. I will not renew just one or two sets of main shells either, the new shells will be taking more load than the worn bearing(s) then. The cap (lower) shells will be the most worn due to it being an underslung crankshaft. Larger engines have a special tool (similar to the bent split pin method) supplied to fit in the oil hole for turning out the top or bottom main shells depending on crankshaft configuration.
Couple of thousand miles to next service so I plan to attack it then after the oil is dropped from the sump.

[Alec]

Hello 57,
oops, forgot about those. To expand slightly, there is not a lot of point changing the big ends if the mains are bad, which is why I suggested checking them.
It's a long time since I learnt that trick, and it doesn't seem that well known hence my posting. As you point out, it doesn't always work on all engines.

Alec

[57traveller]

You're right Alec but if the sump is off, the bottom end shells removed and for the sake of about £12, I might as well fit a new set anyway.
Don't know if you've seen it, there's a recommendation in the Haynes Manual that bottom ends are changed at 30000 miles and mains at 50000 miles, to prolong the life of the engine to around 150000 miles. As the engine has to be removed to change the mains it would surely then make sense for a complete overhaul, so I don't see the logic behind that second recommendation.

[Alec]

Hello 57,
Yes, there is a similar recommendation for my other car, a Triumph 2000. However if the main bearings are bad, even with the crank journals being good (unlikely in my experience) then the new big ends, even at £12 is a waste of money unless you really need to postpone the inevitable overhaul. A lot of oil pressure will be lost with worn main bearings and reasonable big ends.

regards,
alec

[lowedb]

The weak point on a triumph 2000 engine is the thrust bearings, which drop into the sump rather too easily. I'd never do a partial rebuild on the bottom end of one of those.

Actually, that was my first ever engine rebuild. Trolley jack and axle stands for my birthday so I could fix my dad's car!

[Willie]

I changed the big end shells on my car when i discovered I had
very low oil pressure (no noises, just low oil pressure) and it was
a complete waste of time because the crank had raised metal in line
with the oil holes right round each big end. Should have known
better but the new shells lasted about twenty miles before the oil
pressure reverted to very low again! If you can feel irregularity
on the crank then don't waste your time.