Snapped Camshaft

The message from "Ali Day" contains these words:

Provided you haven't turned the engine over with it broken, the valves should be OK. Any idea why it broke?

The only thing I can think is I got a bit too keen and and tightened the third bearing just a tad too much. I'd had the whole block off to replace the cylinder head gasket, looks like it had gone before and who ever did it just didn't replace the old stretch bolts, and as they were torquing them up the left near corner had started to shear (was only finger tight and held together by a couple of threads when I got in there so was lucky to get it out) So I replaced the two belts, bearings tensioner, etc, was just putting it back together when the cam just went. Is it as simple as just going to the garage and getting a new camshaft or does it have to be matched in anyway....

Cheers

Hang on here. Unless I'm mistaken, you mean the bearing caps are matched to the head, surely not to the cam? That's how it is with the Vauxhall I did recently anyway. Otherwise it would imply that you can't replace the cam without replacing the entire head. Which would be unreasonable (though I wouldn't put it past modern manufacturers!).

If that is the case you'd be better looking for a used engine, it will cost you less.

But if I'm right, you should just be able to drop in a new camshaft. And be very careful to tighten it progressively, in rotation (in the case of the Vauxhall, there is a recommended relative position of cam and crank that reduces the stress on the camshaft while tightening).

I thought the whole lot was matched up, but if what you say is true then maybe it is just as simple as dropping a new cam in? God that would be nice!

I you haven't got the caps mixed up or back to front then that should be the case. It depends on why it snapped, if the heads warped then another cams more money down the plughole, a scrappys head will be cheapest.

Gone across the whole thing with a straight edge and looks fine, and all the caps are conveniently numbered. I'll try putting the other one in tomorrow and see how that goes.

Thanks

Could just be sods law, make sure there's some oil under the caps & tighten them evenly.

There's no problems about replacing a camshaft. A new camshaft will be the same as the old one. Use some cam lube when you fit it just to give it the best chance of wearing in well. Mike.

You lucky bastard. Just get a new camshaft.

Is there anything to worry about with regards to wear on the tappets?

thanks again

Ideally it's better if new camshafts are fitted with new or resurfaced cam followers, so they can run in together, but I wouldn't worry about it. Fitting new camshafts with worn followers shouldn't give any problems. I'd still advise your use of special camshaft lubricant though, and you'll probably need to reset the valve clearances on the new camshaft. I'm not familiar with the Zetec 1.6i DOHC engine, but I assume the cam followers are buckets with shims on top or underneath. Which can be sods to set without a nice range of shims to hand. Mike.

Fitting a new camshaft and using the old followers will knock out the camshaft in a very short time. And,IINM, the Zetec range (and virtually every other modern engine) use hydraulic followers.

Why would you use a lube other than normal engine oil? Surely the camshaft bearings are normally pressurised with engine oil?

You don't have to use it, but IMO it's advisable. The pressure of cams on followers is quite high, and until a new camshaft has rotated a few times the cam lobes and bearings are relatively rough. It could be said that how well a camshaft is installed, and initially lubricated, is a critical stage in it's life. You can give a camshaft a good coating of engine oil, but by the time the engine is started most of that oil wil have drained away, risking a pickup until the surfaces smooth off a bit, and generate less heat. The short time between starting, and full lubrication from the oil pump, is a period where good lubrication is needed Cam lube is a sticky high pressure lubricant that when put on the camshaft, stays there and lubricates during that critical period, until the oil pump takes over. Being an EP oil it is ideal for that initial startup. Personally I would never fit a new camshaft without using it. Many suppliers include some when you buy a new camshaft. In any case it's cheap enough. A couple of quid will buy more than enough for a new camshaft. Mike.