Saturday, 25 May 2013

Well thats the tricky bit done

Started replacing the timing chain and sprockets today, as expected the new sprockets have no marks and what with the timing being so far out it was best to start from first principles and set up the timing from scratch.

Firstly having taken the old sprockets and chain off the extent of the wear was really visible. The Crankshaft sprocket was unbelievably worn, I thought the teeth tips had broken off but having looked at the part they have just worn and bent. The camshaft sprocket was a bit worn but nowhere near as bad.

Crankshaft sprockets old and new, the teeth on the old one have worn and bent over severely.

Camshaft Sprocket nowhere near as worn although the teeth are a bit hooked.

Next it was time to measure TDC. A little tip from some videos on you tube from MOSS is that a BMW Mini wheel bolt is the same thread as a spark plug (14mm diameter x 1.25mm pitch). I bought one on ebay for £1.25!. This was screwed down the plug hole. A timing disc was printed off from the Internet and laminated and then fitted to the end of the crankshaft. I then made up a pointer out of a tent peg and a paper clip which was mounted on one of the timing cover studs. I then turned the engine over until the piston was stopped by the bolt down the plug hole and took a reading from the disc. I then turned the engine backwards until the piston was topped again and took another reading. TDC is then halfway between the two readings, this was marked off on the timing disc and a mark scribed on the crankshaft and the engine front plate to mark TDC.

BMW Mini wheel bolt screwed into the plug hole of No 1 cylinder.

Timing Disc and pointer arrangement to find TDC
It was then time to fit the crankshaft sprocket, This turned out to be pretty difficult to line up the woodrufe key with the slot in the sprocket and the new one was  a very tight fit and had to be carefully tapped into place with a hammer.

The camshaft sprocket was then fitted without a chain and the sprocket alignment checked with a straight edge, all was still in alignment.

The camshaft sprocket was then rotated until both valves of No 1 cylinder were just opening/closing with the same clearance, AKA the rocking point. This is how the valves should be at TDC for correct timing.

The sprocket was then carefully removed without altering the camshaft position and refitted with the chain. A bit of trial and error to align the camshaft bolt holes by trying different tooth positions and alternative bolt holes and all was aligned. Camshaft bolts were then fitted and a check that the crank was still at TDC and the valves at rocking point. Once confirmed that the timing was set I scribed some timing marks to make the job easier if  it ever has to come apart again.

New Sprockets and timing chain fitted, valves timed and new timing marks scribed.
 The rest of the job should be a bit more straight forward. Need to clean up the timing cover, fit a new oil seal and timing chain tensioner and then assemble with a new gasket. Tappet clarences adjusted. Ignition timing needs to be set approximately. Plugs need to be replaced. Water pump housing replaced with a new gasket, radiator replaced and exhaust put back on and then it should be ready to try and start the engine.

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