broken camshaft - replacement procedure?
 

Hello folks,

Well ,a terrible thing happened today. The engine was in the car and ready to fire. I turned it by hand, out of superstition, to double check. I cleaned everything ...and well I just forgot to take out the sprocket and its wrench. I still dont understand how I could do that. It went into the blade of the fan, undid the 27 bolt : broken camshaft. I almost cried. All this work. looks like some kind of freudian slip. Or maybe I am the reincarnation of Sysiphus. I dont know.

Tomorrow I will take the compressions. There is no mark on the push button beneath the cams, I can feel a good compression by hand (although I dont expect no miracle!!)

It turned out I have another head (from a very tired engine)So I took of the camshaft and try to put in on the head , but I cannot put the cam bearings, looks like I need to press the shaft... ...is it even doable?

Even if I know that i will surely have to remove the head :(
Im so angry at me...

:(:(:(

So sorry to hear that, what a bummer.

The good news is that at least it happened at low engine speed. So I think you can expect that it will not be too bad to repair.

I had a timing belt failure about 5 years ago in my 740 (belt that had relatively few miles on it but was OLD). It happened around idle speed and it broke the cam into three pieces! So I know how you feel.

But the good news is, on my car, there was no damage whatsoever to the bottom half of the engine. Pistons, rods, etc, were all fine. I replaced the cylinder head with a good used spare I had, and the car was back on the road the same weekend. So don't despair too much........ It happens. :o

The fact that the camshaft tends to break when timing slips on the D24 engine is actually a good thing in many ways, when you think about it. It turns the camshaft into a kind of sacrificial part, a safety valve that gets destroyed but saves other parts of the engine from more serious harm. You would rather be dealing with a broken camshaft than have to worry about bent rods, broken pistons, bent crankshaft, etc. Fortunately the cam breaks so fast that those other parts tend to not suffer.

All that said, I think the safest point of view is to figure the entire cylinder head needs to be checked out. I would not want to just replace the camshaft if it were me. I would assume any part in the head that took impact force should be considered compromised and replaced. That means all the valves and guides, all the lifters, and of course the camshaft itself. Probably also should get the cylinder head aluminum main casting carefully looked at by a machine shop. It is rare but not unheard of for the cam bearing towers to get physically damaged or torn off when the cam breaks so you want to be sure there are no signs of that or other harm.

The reason for this concern is that if you leave impact-affected parts in the engine that "look fine" but have unseen damage, you might get it running and on the road and seeming healthy, but then something could fail later on during operation that could cause much more severe harm. The common story of this is with a damaged valve that later drops its head into the engine and wreaks havoc. That is why you want to get all of those parts that could fail in this way after impact out of the engine.

Yet still, the good news is that with the D24 (due to shared parts with the extremely common 4cyl VW diesel), items such as valves, guides, and lifters are easily purchased and cheap. So the whole exercise shouldn't be too costly or difficult.

Goes without saying you should also do a careful inspection of the front of the crankshaft and the timing gear, and replace anything that suffered damage there. Probably at least the timing gear will need to be replaced assuming its "key" got torn off. Hopefully the nose of the crank is not damaged, although even if it does have more wallow in it you should still be able to use it no problem. Probably want to look at that before making any other decisions though.

Good luck and keep spirits up, it won't be too difficult to get it back to where you had it before, and who knows, maybe you'll get some more new parts out of the deal. :cool:

Hello V8, thank you very much for the detailed and above all compassionate answer, it warms my heart!

I understand. Now, replaceing the valves, shims etc is, even if the material is cheap, is not a DIY job, if I understood well.

I unfortunatly do not have the means to pay for the whole repair of the head (which already cost me 600€ ) . Well , to put it bluntly, I'm kind of broke!

My only solution to make the engine run again for the moment would be to put the head of the car I took part from recently (86 GL, with refurbished VE pump)

It is from an engine that had 600 000km. Now it really is a shame to put back a head from a tired engine when I could have make my motor working with a head that had 110 000km and 600€ of refreshment.

But when I think about it, at the moment I drove the donor car home (which I was illegal but it was such a long time without having head the sound of the D24) to tear it apart, it ran pretty well! Cold start was absolutly impossible, I had to go for 2nd gear with some speed, towed by a friend, otherwise it would just not start. I gave the bottom of the motor to a friend, and it happened the pistons were scratched, drilled (it is not the good word. I mean there was holes sometimes. piston rings dead...that explains low compression)


But if I understand correctly , a tired bottom affects compression, but a tired head...just do his job normally? the car had no HG issues...

the only thing that bothers me is that i dont remember the number of marks of te HG...I think it was 3....but i m not 100% sure...is there a measure to ensure I take the good thickness?

thank you again :)

Personally I would basically agree with you on all of that.

I don't really see anything too wrong with running the 600k KM head IF the engine it came off of was known to run well and didn't have any known issues with using oil or coolant, etc.

You would want to check that head to ensure it is straight with no warpage (straight edge), and probably want to check for any signs of valve face or seat pitting and valve guide wear. Look for severe cracks as well of course, although as you probably know, small cracks between the valve seats are normal and no concern.

Some people would also want to replace the valve stem seals although that is a more involved process. New camshaft seals could be wise and those are fairly easy to change. You can check valve guide condition by measuring lateral movement of the valves -- severe wear is easy to spot. You can also check valve sealing using water in the ports, and look for any signs of oil intrusion in the ports that would suggest leakage past the valve guides or stem seals. Or if you really wanted to take it all the way you could hand-lap or replace and lap the valves.

But if the engine made it to 600k and ran well it may be just fine to drop that head on with no work done to it, assuming it checks out. Valve guide wear used to be a problem on these engines but with good synthetic oils it is not much of an issue from what I understand now. And an engine that put on 600k km and still runs well probably has to be one that was maintained well and mostly saw highway usage. Apart from wear to the valves/guides/seats/seals, you're correct that there's really not much to wear out in a "tired" head and it would probably run with zero issues, as long as it's bolted on top of a healthy bottom end with good compression (and timed correctly, etc, etc). :)

On HG thickness, yes you can take measurements to select it based on piston protrusion from the block. The greenbook shows the method. But changing to a different head doesn't affect the thickness of gasket needed. So you can just use the same thickness that it has now.

Hello V8,
Yes you re right, I just thought about what I wrote soon after I sent the message, and of course changing the head has nothing to do with the gasket!
I put the head and there is apparently no problem with the fuilds. but now I kind of understand why the car that the head comes from could barely start (30km + second gear!). Ok, the bottom was very worn , but I have a tremendous valve adjustment issue!! I checked the maintenance of the car, the papers show that the oil change etc were OK, and for sure the car barely run in town ... but I cannot see any valve clearance job . So I will do it during the following day, and maybe I will use the shims from the head I broke?

valve clearance results : 0.15 on four out 6 exhaust (0.35) then 0.05 and 0.30

Nice, that doesn't sound so bad other than one that's pretty tight.

Shims are pretty easy to get since they were used on many very common VW/Audi diesel and gas models.

Sounds like you are almost back in action, good news!

Yeah :cool: I put back the rights shims (3.40 instead of 3.65 originally) and I m good for all the valves clearances now !

I started the motor : it went on very high revs for one second , tremendous black smoke and then died. I checked the timing before but i did another check : almost 3 teeth off the mark on the crank. Last time I was lucky.. but I now understand that working without the proper tools is a pain in the ass. For example , when I put the lock pin into the pump housing, when I tie/untie the cam sprocket, the pump / crank still can move a bit and I have to do the job 4 times before a perfect alignment. Now I have to do the "boring" jobs : stuck caliper piston (compressed air does nothing, I dont know how I will get it done) , vehicule alignment...some cleaning :p

i'm so happy!! I started the motor for real (like 30minutes)in the car, it's been two years now! so happy to hear this noise without problematic things, it strated right off almost without pre heating (warm weather today)

That's great news! Congratulations! I'm sure that is a great feeling of relief and accomplishment.