Rebuild needs after a broken timing chain


#1

The timing chain on my rebuilt Datsun 280Z broke and I’m not sure of the best way to rebuild the engine. When the chain let loose the exhaust spit out a combination of oil and coolant so obviously there are many issues to resolve. I tore the engine down and I currently have the head off and the block still mounted. So my question is really about the best way to approach rebuilding the engine. I’m guessing the head might be cracked but I don’t know if the block may have also been damaged. Can anyone help give typical repercussions of losing a timing chain and the best course of action to start rebuilding the engine? I’d like to avoid spending a lot of time and money figuring out what needs to be replaced so any information would be great.

Thanks,
Tim


#2

I don’t know if you want to hear this or not but when the timing chain of my '73 240Z broke…there wasn’t much left in the way of salvageable parts except the block and intake/exhaust manifolds. The overhead cam head, camshaft and valves were trashed along with the pistons, connecting rods and crank. I was passing a truck when it happened so I’m estimating the speed at about 60mph. If your engine was idling when it broke then you are probably better off than I was. You need to have a mechanic who is very knowledgeable about these engines to take a good look at it. Good luck.


#3

@missileman

So we’re talking about an interference engine, correct?


#4

Yes…a very severe case of interference.


#5

If the cylinder head is off, a simple visual inspection will tell you a lot. If you see valve imprints on the piston surface, the valves are probably damaged. Cracks in the imprints tells you the pistons are trashed. You can rotate the crankshaft to lower the pistons and expose the cylinder walls and check for gouges, nicks, and cracks. If the walls are smooth as glass and the piston tops are damage free, a replacement cylinder head may be all you need. But, since the last 280Z rolled off the assembly lines in 1978, and the ZX in 1983, I wonder the age of the engine could dictate an overhaul instead. With an overhaul, you replace the piston rings, rod bushings and crank bushings, but instead of machining the block, you just hone the cylinders.


#6

You now have a parts car…


#7

@Timmer1 - what are the cylinders like? Any gouges/scratches/etc? How many miles on the block? What happens when you turn over the engine with a wrench?

You really need to give us LOTS more info.


#8

If all you need is a replacement cylinder head, that doesn’t seem like such a bad problem to me. I mean, you are driving a pretty old car. Some problems are to be expected. And a cool car. I’m envious! There must be heads for this car available in junk yards all across the USA, it might need some new valves and a valve seat job on the junkyard head is all to get you back on the road. If the block is toast too, well, get a junkyard block and have that rebuilt too if necessary. This is a classic car and a fun car to own a drive. Good on you for preserving it.


#9

Take the heads to a machine shop and have it inspected an a magnaflux test run to check for cracks.

As for the block…you might be able to get a way with just a cylinder wall inspection. But there could be hairline cracks in the pistons after they collided with the valves.


#10

Thanks for the feedback. I’ll do a good visual inspection and post an update. The engine was a rebuild with about 30K miles on it so I’d like to replace just the head if possible. Thanks


#11

Great looking car @Timmer1. My 240Z was a different color of red but your 280Z sure brings back memories. Best of luck with your engine. I would put it back on the road even if I had to install a newer V6 engine and transmission.


#12

What should be done as a first step is to determine why that chain broke. If the rebuild did not include a new chain/tensioner; mistake.

If this was a 30k miles chain/tensioner that broke then the reason for the failure cause really should be sorted out before doing anything else.
The nose of the crankshaft should be examined to make sure that any keyways are undamaged.

Good looking car by the way. :slight_smile:


#13

The newer Chevy V8s are pretty small dimensionally.


#14

I installed a “Scarab” kit (small block Chevy) in my 240Z after my engine was trashed. I liked the power but the handling was terrible. That’s why my suggestion was for a V6 engine. I love “more power” but the extra weight in the front end made it hard to keep the little fellow on the road.