Broken pistons and rings

[Rusty O'Toole]

Broken pistons and rings seem to be a common failure point on Chrysler flathead engines. Does anyone know why? Is there a way to prevent this happening?

[Niel Hoback]

Over revving a worn engine will do it every time.

[greg g]

When things loosen up higher than normal revs can whack the rings into the cylinder ridge. The second theory is uncorrected chronic spark knock or pre ignition caused by carbon build up hotspots.

[Don Coatney]

Overheating a high mileage engine can and will lead to this failure. My theory is the excess heat causes metal to expand and grow thus allowing the piston to contact the ridge at the top of the cylinder breaking the top ring. Once the top ring is broken the piston will look as pictured after a few more miles.

[wallytoo]

or this

[james curl]

I had rebuilt my engine with new .040 oversize pistons and rings. after a 4800 mile trip I pulled it apart for a extruded piston pin bushing and discovered two pistons with the top rings broken. After checking the vacuum at a steady 70 mph fount that I still had 14 inches if vacuum. I had the initial advance set at 10 degrees advance. Have since gone back to 4 degrees without anymore problems, the head was milled .090 and the top of the block had .010 removed increasing the compression which I assumed would allow more advance.

Edited December 15, 2012 by james curl
correction

[1941Rick]

Pre-ignition was probably the most common cause of Don's piston failure.

[Tom Skinner]

Gents,

And that is the crux of flat head ownership. Run em by the book and their slugging along in traffic, run em a tad "hot" and they keep up in modern traffic.

When worn or carbon build up bites them boomyow a ring comes flying out the tailpipe. I have owned a few 1948 Chrysler Royals since 1973 with the 250.6 engine and that's the gig. It is what it is as they say in NYC. It is the attraction, the challenge, the lifetime of fun keeping these behemoths on the road.

Heck, I can't think of a better hobby that has taken me 40 years down the road.

I hope everyone is as grateful as I am, and that we can continue our hobbies in good health, in the coming year.

Merry Christmas and Happy New Year!

Tom Skinner

Huntersville, NC.