In 1990 I made a long journey, aiming to attend a meeting in Coventry. Whilst caught in traffic on a motorway I noticed an uneven idle, but the car seemed to rev fine and the uneveness wasnt noticeable above 1200 rpm. After about another 1.5 Hours of high speed motoring (whilst I was overtaking a truck at ~85 mph) something big gave way! As I stopped, the engine was still idling but making an enormous mechanical bang once a revolution. This required a tow home and further investigation. I initially assumed a big end cap had come away, but there were no holes in the block, and apart from the noise, the engine appearedf to be running on 4 cylinders. Removing the sump, expecting to be greeted by obvious signs of damage, I was surprised to find nothing appearing to be wrong. Only when turning the engine by hand could I see the crank had split between No4 Big End bearing and the final Main Bearing--so the pistons weren't physically connected to the flywheel any more! Crank failures are known on the TR's 4 cyl engine, and this is normally blamed upon resonance in the crank around 3000 rpm (I certainly spent many hours cruising at 3200 rpm, which equated to 75mph, on motorways). People often state that removing the original fan assemby excacerbates this problem, as the fan provides some damping action for the crank. This may be so, but my car has always had the original fan fitted (as far as know) so a more likely cause is failed propshaft UJ's (see elsehwere). A spare crank was obtained (thanks Max!) and fitted during a full rebuild of the bottom end.

The exact form of the fracture was from the inner edge of No4 big end (initiated by the sharp angle between the web of the crank and the bearing surface). The surface shows the slow progression of the crack, followed by final brittle fracture. I guess it was cracked part-way when I noted the uneven idle. The end of the crank (No3 Main Bearing, Flywheel flange and that's all) is now a chrome plated objet d'art...

As an aside, when I initially guessed that a big end cap giving way was the cause of the problem, a friend and I decided that since the engine was most probably entirely wrecked, starting it would cause no further damage....Therefore, in order to get the car into a suitable place to strip out the sump, we decided to drive it up a steep slope into a garage. It drove surprisingly well (in hindsight), OK there was a lot of noise, but the car pulled up the slope fine, with no evidence of slipping drive in any way. I now guess that the 2 sections of the crank must have been in contact with one another to transmit drive.