Crankshaft bolts and how to Loosen them.

Swearing, so much swearing.

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Despite costing only £200 and having sills you could see through, Ermy passed her MOT first time. Well done her, all that time studying the Haynes manual must have paid off.

One thing that was noted though was a slight oil leak. Being an MOT you don’t get a lot of information, just that it’s an issue. We removed the sump guard and shone a big light in and got searching. Then removed the radiator, then all of the plastic covers and tried again. Then swore, removed the alternator, power steering pump and belts then finally found a crankshaft seal at the front that had not been fitted flush. This was creating a slight leak. Not enough to kill the engine but certainly enough to write off an 18 year old car. £3 seal, £300 bill for labour, coolant and replacement belts etc.

IMG 20161023 113620

The worst part about this seal was that to get to it involved removing the crankshaft bolt, a very specific 21mm bolt sitting at the front and centre of the engine which holds the timing plate in place. It is attached to the crankshaft and once all of the belts are off, rotates freely unless the engine is in gear. At this point it turns until the gears engage, torques up the rear differential and eventually transfers energy into the rear wheels.

If the car is not chocked down or the handbrake is a bit loose the car starts to roll forwards, running over the person turning the handle. Which totally didnt happen to us. Honest. Did we mention we are incompetent twits?

On a serious note, if the belts are not on at this point and you turn the crank bolt, obviously the timing at the crankshaft will no longer match the camshafts.

In our case this bolt was thoroughly rusted in place and needed a bit of work. Guidance online suggests a couple of ways to undo the sticky crankshaft bolt:

  • Camshaft tools that lock the cam shafts in place. This stops the timing from going out of alignment but the belt is designed to keep everything in time, not to lock the crankshaft. If the bolt is tight enough, the crankshaft simply turns shredding the teeth on the belt as it does so. IMG 20161026 172728
  • Putting the car in gear and a foot on the brake. This winds up the gearbox and transfers the force you apply into drive. The brake should stop that drive causing the car to move resulting in the force being applied to the bolt. This means that you turn the bolt a turn or more before it “locks”, though this is not a solid lock. It has a sort of spongy feel and the car will creak and rock on its suspension etc. This likely works when the bolt is not entirely seized.

  • Use the power of the car starter. In this case you brace a spanner between the bolt and the body of the car, then start the vehicle. Thus uses the start motor to turn the engine over applying massive torque. Since the bolt is locked in place by the spanner and is turning counter to the bolt, it should crack the bolt off. We had most of the engine in pieces, so it wouldn’t turn over, but this method would work if you knew you needed to undo this bolt and started with it before you stopped the rest from working.

  • A specific crankshaft locking tool. This uses the existing bolts to lock the camshaft to the body of the engine or something else solid. Some guides suggest that you can make something yourself to do this, using bracing steel or something to lock it all down, possibly by bracing it against the floor. We tried this and bent several screws and a couple of lengths of 5mm steel. IMG 20161023 160802

We gave up eventually and brought a very specific tool, shaped for the job which did it first time.

S l1000

Final conclusion, there are a lot of options for removing those bolts, and a quick search seems to suggest that such tools are available for most vehicles. Im sure if you are a garage with air tools this is easier to do, but if you plan on keeping the car for a while, the tool seems to be worth a go, especially as it was sub £20.


Welcome to Twits with Spanner. A blog following two chaps as they attempt to build an Exocet kit car with bits from a donor MX5, spanners and lots of hope. Read more about us