Uhh Ohh, lost compression and lots of valve rattle

[uh6077]

Last week I took the 41 Desoto to get inspected. Passed with flying colors but while out running some errands it died doing about 50 mph. Sounded like rocks in a can but the noise went away when I pushed in the clutch to coast. Soon as I released the clutch the noise would start again. Finally got around to checking compression today. 65, 0, 60, 35, 50, 65. NOT GOOD. It always smoked a bit so I figured the valves or rings were tired but not THAT bad. Looks like one or both of the #2 valves let loose. When I get a chance I will removed the inspection cover and see what is going on. Any ideas?

[Owen_Dyneto]

Broken valve spring? Or a lost valve spring keeper?

[c49er]

Not good!!

[Marty Roth]

Sounds like your timing chain or timing gerars may have jumped a sprocket or two, or more. In this case the camshaft is no longer in-synchronization with the crankshaft.

 

If that is the case, then the valve timing is out of phase with the cylinders and ignition. Valves will open and close , but not when they are supposed to, and compression by piston will be minimized since valves may be opening when they should be closed.

 

One way to check would be to remove the timing cover on the front of your engine, and to rotate the engine, hoping that the "Little Dot" on both the crankshaft and camshaft point DIRECTLY at one-another, and that will be where #1 cylinder should be at TOP-DEAD-CENTER. (Ignition timing can be adjusted from there per the marks on your flywheel). If the marks do not line-up, then it is time to replace your timing set

[uh6077]

I hope it isn't the chain. The car still starts pretty easy and drives (Drove it off the flat bead and into the garage). Hardly has any power (obvious with those compression numbers) but I think that if the timing was off that much it would be a bear to start and idle. That is my hope at least. A broken spring would explain the 0 compression. Maybe it is just time for a valve job. I wouldn't mind taking the engine out anyway so i can clean and repaint it. 

[ply33]

Had that same noise once with my '33: Turns out the upper land on a piston broke and the top ring also broke. A piece of the ring got between the piston and the head which cocked the piston enough that the piston skirt then broke. Fortunately the cylinder walls were not damaged and it was relatively easy to fix things.

 

It is my opinion that the reason why the piston and ring failed was that there was a ridge at the top of the cylinder due to wear and that my driving style was a bit more enthusiastic than the previous owners. With a little higher RPM that the engine was used to the piston/ring were probably impacting a little on the ridge on the top of the cylinder.

 

Cleaning up the ridge and bores on the cylinders and a new set of pistons and rings took care of it. Of course if you are going to do that you might as well do the bottom end too.

 

So don't be too surprised if you don't see anything amiss when you pull the valve covers. I'm guessing you will need to pull the oil pan and/or head to see what is really going on.

[Rusty_OToole]

Those engines are foolers. They will continue to run without complaint or excessive noise in an advanced state of wear. Compression test suggests you need an overhaul at least, and possibly a complete rebuild.

 

Fortunately parts are easy to get and not expensive, and they are a simple engine to work on.

[uh6077]

Well, rebuild it is. Not sure what happened. I don't see the missing pieces of the pistons so I assume they got swalloed by the valves. Amazing that it still ran. Drove it into the back garage this morning.