If, and I strongly suspect it is, it is the timing chain/guides, stop using the car NOW. If the top guide breaks or the chain snaps/jump you are heading into replacement engine territory or bent valves at least. Remove the rocker cover and inspect the chain and top guide. Hopefully you have stopped using it in time. I really mean it, do not even turn that engine over again!!! Sounds like the top rail plastic is gone. That means plastic in the sump and oil pump filter.
There are many guides, excellent ones online/youtube and manuals (Haynes/Bently) that will guide you through a DIY. The cost of tools and parts will make it much cheaper than a garage/dealer.
If you have access to your own space to work on the car it would take you a full day tops.
Basic necessities are:-
Mini timing tool kit. £35-40
Timing chain, lower sprocket, guide rails, uprated tensioner. Guide rail bolt o-rings. £80-180 depending on quality
New cam shaft bolts (for an S there are two lengths, for a justa both are the same length) £14
New crankshaft bolt. £8
Front crankshaft hub seal. £25
4 equal length sticks (BBQ skewers are good).
Torque wrench. £35-40
Socket set with E type sockets included. £50 - 80
Socket angle adaptor. £10
Shifting spanner that will do 27mm for belt tensioner. £20
Various screw drivers.
Crankshaft holding tool (to get the crankshaft bolt out and torqued back up). Make your own or buy.
Cam/rocker cover gasket and gasket sealant. £10-14
If you can borrow or already have some of the tools, great.
If it is very high mileage you might consider replacing the oil pump chain and sprocket too.
Get yourself some replacement plastic wheel liner expanding clips (these will break when removed).
Cooper 2009, R57.
Last edited by Scudder; Oct 22nd, 2018 at 08:23 AM.