Engine Rebuild

Mini 1275GT Resto-Mod, Jan-2013

Although the engine started and ran well, it produced loads of blue smoke on startup and the oil pressure seemed very low as it took a bit of revving to put the oil pressure warning light out and it came back on at slow idle.

I firstly thought the oil burning was due to worn valve guides causing oil to leak into the cylinders so whipped the head off and took it to the engine specialist Blackburn Bros in Preston.

They cleaned up the head, lapped the valves and replaced the valve oil seals but confirmed that the guides were fine:

They also said that the A-series head very rarely gave oil issues – the oil burning more likely was due to piston rings.

So I stripped the engine completely and found some badly worn components:

The oil pump was completely wrecked:

The oil pump rotor was very badly scored and pitted – clearly a major contributor to low oil pressure. The damage was most probably caused by a gearbox/diff failure (see gearbox repair article) and since the engine shares lubricating oil with the gearbox, the oil pump will draw through any debris from damaged gears. This shows how important the oil filter is on a Mini engine.

The main and big end bearings were in generally good condition, except for one of the centre mains that had started to break up:

There was about 30 thou end float on the primary gear when there should be about 3 thou. This was due to the “C” washer that holds the gear on the crankshaft which was badly worn:

With a new “c” washer, the end float was about 12 thou but should be less than 6. The thrust washer was 0.112”, so I needed a new one at 0.118. I opted for a .118″ to .120″ primary gear thrust washer, to give 4-6 thou float.

There was some pitting on the cam followers, so decided to replace these:

The crank thrust washers were worn on one side only:

The pair on the left were still at the original thickness of 90 thou. Whereas the pair on the right were at 86 thou, i.e. 4 thou undersize. I measured crankshaft end float at 5 thou, so a new std size thrust washer set would do.

The crankshaft and camshaft were in good condition – no scoring or pitting – so I opted to reuse these as standard. There was no sign of wear or scoring to the bores so I opted to keep the standard bore and just replace the piston rings. The bare block was cleaned with a strong detergent solution and the oil and waterways were flushed through at high pressure:

Here’s the rebuild parts list:

FW Thornton:

Piston rings and bearings from the various mainstream suppliers – Minisport Minispares, etc – vary greatly in price, rings from about £50 to £150, so I wasn’t sure what I would get. Instead, I went to FW Thornton, as I thought they may know a bit more about engines than the “ordinary” parts suppliers. Thorntons supplied:

  • Goetze rings (3 compression rings + 1 oil control)
  • Glyco main and b/e bearings
  • Plus crankshaft thrust washers


  • Oil Pump Spider 2 Bolt (GLP141)
  • Flywheel Keyway – Pre Verto (88G508)
  • Primary Gear C Ring On Crank Genuine (22A319)
  • By Pass Hose Kevlar “S” 1275cc Only (AEG484)
  • By Pass Hose Clip (3H2963)
  • Performance Cam Follower (2A13EVO)
  • Camshaft Gear Locktab (2A759)
  • Head Gasket Set With Std Copper Head Gasket 1275cc (AJM1140MS)
  • Primary Gear Thrust Washer 1275cc .118″ To .120″ (DAM6488)
  • Crank Pulley Lock Tab (12A398)
  • Timing Cover Oil Seal All Pre 1992 (88G561)
  • Clutch Oil Seal Upto 1992 (13H2934)
  • Block Gasket Set All 1300 Except S (AJM206MS)
  • Duplex Timing Gear Kit (C-AJJ3323)
  • Flywheel Bolt Locktab Pre Verto (22A1155)

Plus a set of ARP big end bolts from ebay at £75!

The rebuild was pretty much drama free, just followed the Haynes manual plus the excellent engine build thread on the The Mini Forum.

I used Redline assembly lube on all bearing surfaces plus cam lobes.

I cleaned out the crankshaft oil passages with carb cleaner then with the new bearings fitted and lubed with Redline I refitted it and torqued up the bolts. Also fitted the camshaft, oil pump and temporarily fitted the timing gear. Just needed to make sure that crank turned freely by hand with no sticking points before continuing:

Although its not a performance build, I opted for the duplex timing gear as they are so cheap (about £28). I’ve not fitted the tensioner, though some people do:

Note that you have to fit countersunk screws underneath the crank sprocket where there were bolts previously. I used thread lock on these and also “staked” the head (whack it with a centre punch near the edge to dent it and prevent it turning).

Pistons with new rings refitted and big ends torqued-up:

The engine & gearbox were now mated and a nice new copper head gasket was fitted. Not sure about these yet – some good stories on the forums about these, some bad.

Head re-fitted and torqued-down. The engine is mostly re-assembled and nearly ready to fit back in the car:

Before re-fitting the engine to the car I set the valve clearances and static ignition timing as you can turn the engine on the flywheel or crank pulley bolt. A lot easier to do now than when in the car.

I used cheapo oil (£9.99 – Wilkos) for the first 100 miles running-in. Then I changed the oil filter and oil for some Comma 20/50 classic. After 500 miles I’ll do another oil & filter change then re-torque the head and reset the valve clearances.

I’ve done about 200 miles and so far the motor seems to be running strong and smooth. Oil pressure comes on instantly, it runs cool, the plugs are about the right colour and there’s no smoke from the exhaust.

NB I’ve been using one of these digital torque guages from Machine Mart:

It works to a far wider range of torque settings than a normal torque wrench and I can use it with a wrench to suit the size of the nut/bolt being torqued. i.e. A large breaker bar for high torque (150 ft-lb+) and a normal-size ratchet for small bolts at lower torque settings, making it a lot easier to set the torque accurately and less likely to stretch a bolt or strip threads.