924 head problem

[jonjchris]

Hi All,

A few days ago I stopped for gas on my way home. I was a bit low on oil so I added some. When to star out again the engine had a strange knock, would not idle properly, and seemed to have very little power. It did run but was a bit difficult. I was close to home, so I drove slow and nursed it home. This might have been a mistake.

Today, I started diagnosing the problem. I took off the valve cover and found that the oil feed tube that runs on top of the cam shaft had broken and was laying down by the valve springs.

I just wanted to get a few other opinions before I take it further. Is there any chance that this piece of tubing damaged any of the valves? I have recently done head gasket on this car, so I am not afraid to do it again, but if I don't have to, that would be better. A compression test is my next task.

Thanks for the help. If i did not mention, my vehicle is a 1978 Porsche 924.

[jonjchris]

Here is a photo of what I found.

[kdjones2000]

I don't see that loose piece causing any problems with your valves, unless it got caught between the cam and the follower.

I would be more concerned about lack of oiling of the cam/followers leading to wear of the hardened layers. You might find that your cam wear increases significantly, but you may also be lucky.

Find another one, make sure that the plastic piece that goes into the cam bearing boss is tight, and take a look at your oiling after putting things back together to make sure that your oiling is still working on all cam lobes/followers.

924board.org is a great source for this type of stuff.

Good luck, Keith

[jonjchris]

The piece of the oil pipe was down by the first cylinder valve springs. I am working on a compression test now.
#1 102lbs
#2 106lbs
#3 I have not been able to get a read
#4 not tested yet.

If it would have done any damage, it would have been to cylinder #1 or #2.

I think I am giving up for tonight...look at it tomorrow.

[redstrosekNic]

Wow. I'm amazed that the metal tube broke as opposed to the plastic elbow. (Although I just replaced the plastic elbow in my car and was amazed at how tough to install that little bugger was! It took lots of force to get it to pop into place, and it did not seem to hurt it)

[ideola]

That is a really bizarre failure. I have never seen anything like that. Did you perform the head gasket work yourself? Did you remove the cam oiling tube during that process? I can't imagine how the tube could have broken in that fashion while leaving the elbow intact.

How many pieces did the tube break into? Have you determined whether you've found all of the pieces or not?

There are two things I would worry about with loose metal fragments in top end of the head: damage to the cam and lifters as mentioned above; and damage to the lifter bores, which may occur if pieces got down into the lifter adjusting holes and dragged down into the bores.

I strongly recommend removing the cam bearing caps, then remove the cam, and then remove the lifters. Carefully inspect the cam for any signs of stuff getting caught between it and the lifters, as well as any signs of wear from lack of lubrication. Even though the engine only ran for a short period of time with the broken tube, it is highly likely that the tube was cracked before it broke, which would result in improper oiling of the lobes and lifters behind where it broke off. You should inspect these very carefully for flatness on the lobes, and pitting on the surfaces of the lifters.

Once you've inspected the cam and lifters, you should very carefully inspect each lifter bore to see if there is any scoring that might indicate something getting down into the valve train. If the lifter bores are OK, then it's unlikely that anything got down into the combustion chamber. I would also take great care to make sure all of the metal fragments from the broken tube have been found and removed. If it broke into many small pieces, I don't think I would take a chance of leaving the head on. The missing pieces could be floating around in the head and could cause future damage. You might use a magnet to help search for the bits, but if it were me, I think I would just remove the head entirely so it could be shaken and turned upside down. This will allow you to inspect the head surface, the piston crowns, and the cylinder walls just to be certain no further damage was done. Obviously, at this point, the head gasket will need to be replaced, as they are NOT reusuable.

Now, the other problem is that the cam oiler tubes are NLA from Porsche. I have a very small stash of good used units that I have been hoarding, so let me know if you need one.

Sorry to hear about the failure, and best of luck in the diagnosis and repair.

[jonjchris]

I did the head gasket replacement myself almost 2 years ago now. I did not remove the oil pipe or the cam shaft myself but I did take the entire head into a local shop to be machined. I assume they took the cam and the valves out to plane the head. When I got it back I adjusted the clearance on all the valves when I set the timing.

The broken piece of pipe appears to be in one piece, (it seems to fit perfectly into the missing section. There are a few scuffs in it where the cam or a valve spring may have hit it. There may be some small filings but I believe I there is only one piece.

I am most concerned that the piece of pipe may have caused a valve to not close properly causing it to bend. Or the reverse case causing a valve not to open properly.

Thanks for the advice. I will post updates as I get into it more. I did find a used part from Auto Atlanta, but a new one is almost impossible to find.

[emoore924]

Any problem with lack of oiling is going to be down at the other end of the head *where no oil was going*. At least with the broken off part, some oil would be spraying onto 1I and 1E, less so onto 2I and 2E, etc. The broken part would damage 1, the lack of oiling #4.

If you bent a valve you'll have no compression on that cylinder. An easy diag.

Not sure you need to take things apart to know you have a problem. Rotate the cam until the lobes are pointing up. Take your fingers and spin the followers in the bores and look for obvious damage. If you find it, turn the cam until the lobe is horizontal and mic it. If its in spec, and otherwise looking undamaged, I think you might be ok. If the follower is pitted or gouged or the lobe is flattened or worn, more investigation would be warranted.

Also never seen that failure before. I've seen breaks partway down the tube but never at the end like that.

[jonjchris]

Hey All. Just an update on this vehicle. Life got crazy busy and my car has now spent the last few months sitting in the garage. I decided to pull the cylinder head this week and I clearly found my problem. The head gasket burned through between #3 and #4. I now have the head in to a specialty shop for work and inspection. Hopefully I can get this car back out on the road some before the winter.

Is there anything special I should do to prep the cylinders before I re assemble with a new head gasket? I assume I should get it as clean as possible. I have one spot where the gasket burned through that I am not sure what to do with. #4 piston is cleaner than the others, I assume from some antifreeze steam cleaning. #1-3 have quite a bit of carbon build up.

Any thoughts would be appreciated

[emoore924]

The head should be checked for straightness and straightened if it does not meet spec. Also WYIT, the machine shop should check valves and guides, replace as necessary. Make sure you don't need repair between 3 and 4 where you had your burnout -- there should be no metal missing in the head -- the block is iron so should be fine.

Get a good head gasket. There are choices out there ranging from stock to fancy pants cometic (if you want to raise the compression a little you can buy a .027 cometic). I have cometic on my track car. Otherwise do the usual stuff when you do a head gasket.

[Slam]

My wife's 931 had this failure, so while it is uncommon it's not unique. How are your engine mounts?

Did you re torque the head at the specified interval after changing the gasket? Head bolts may have worked loose.

[jonjchris]

Hey all,

I got my head back from the shop yesterday, and I got it all back together. The shop did a very thorough job. They went through everything, replaced valve seals, cleaned and planed the head and valves. I am also happy that it started on the first try once everything was back together. I do think my timing may be a little off though.

Can someone point me to a detailed timing procedure? The last time I did head gasket, I had a very good explanation, but I can't seem to find that again. It was either from here, or 924.org, or Clark's Garage. I know I am close on the timing but I want it right.

Thanks for the help.

[emoore924]

To time the 924 you need to set marks on the crank (flywheel pulley if you want to do it the "official way"), the cam and the distributor. Then set ignition timing with a timing light.

There's a "O" on the flywheel and a pointer on the bell housing. Alternatively, use the crank pulley at the front of the engine. Turn the engine with a socket on the crank pulley.

There's a "o" on the backside of the cam gear that needs to align with the pointer on the valve cover.

There's a "|" on the edge of the distributor (remove the cap and you'll see it) to which the rotor would point to the #1 plug wire when the cap was on.

There are lots of writeups over at 924.org.