Guys, have an a15 in a 1200 ute with a Celica 5 speed & have snapped the flywheel bolts. Ripped out the gearbox, replaced the flywheel, bolts etc & also the harmonic balancer which basically shattered as a result, slightly damaging the keyway. Tried to start the car and then discovered it had no compression and had bent the exhaust valves. Spoke to Jeff Taylor @ JTS and he said he had seen this happen many times and that I should check the camshaft bolt as it has probably come loose because of the harmonics created after the flywheel bolts snapped. He was right, but it has also damaged the hole in the camshaft that the dowel pin sits in meaning that the pin is loose. I am worried that this may cause problems. Any ideas ? do I have to replace the cam or not?

holy crap! How did you do that? I've abused the living bejesus out of my engines, and I've never managed to do that!

Well accoding to Jeff, if you are driving hard (I was) and you miss second gear (must have) then this is a fairly common occurence.

ive never seen the dowel pins in these before, but it could be possible to have a new larger dowel pin instaled and inlarge the old hole to suit?? just take both the cam and sprocket to a machine shop and see what they say..

I'd replace the cam
A loose pin can lead to a snapped pin and allows the timing to have slop... thus putting the valves in the wrong spot when you don't want them (hence bendy stems)

I've spun the flywheel off my A15 before
I now use grade 12.9 cap head bolts , loctite and lockwired in place
And a spigot bearing mounted in the flywheel itself (not relying on a crank bush/brg)

I'd also get everything balanced again just to be sure.... what clutch and flywheel you running ?

I've split the font pulley before, and had the flywheel come loose. But never had the cam bolt come loose.
I'd just get a new sproket, set your valves gear up where it need to be, (With the new cam sproket 1/2 a turn out) and drill a new dowel hole in the end of the cam. (Thats the easy way of dialing in a reprofiled cam too.)

As well as using loctite and 12.9 capscrews, I'd chase the treads with a tap, and clean them out with brakeclean (or loctite primer)and compresed air. I've doweled my flywheel to the crank as well. Thing is the end of the crank is very hard, so getting the dowel holes drilled takes a bit of doing.
If you use lots of loctite that helps too. As it oozes out, it takes up the space between the treads on the shank of the capscrew and the hole in the flywheel.
it'd also pay to inspect the mating face on your flywheel. If it gets badly fretted, it wont seat nicely and may keep coming loose forever. the same goes for the end of your crank (Although harder to fix, without changing the crank) in extreme caases where it's come loose many times.

So basically it overrived (missed a gearshift). This is when flywheel bolts let go.

Be sure to torque the bolts to spec. Too loose and they can snap. Too tight and they can snap.

Thanks for the advice gents, decided to play it safe and have now removed the engine and cam. Off to the machine shop tomorrow to see if they can do something or maybe get a new cam if needed.