Sometimes stuff just breaks,

[FrankZ]

I went wheeling about a week ago with some friends and heading back down on our last trail my XJ sounded and ran a little rough. We got down tot he trail head and started siring up our rigs with my OBA system when I heard a nasty mechanical POP. The engine died and I was about 2 hours west of home. I called a friend and he drove 2 hours to get me, my busted junk and my family.It took a couple of days before I could remove the valve cover and start poking around and this is what I found.



The red arrow is pointing to the #6 intake valve, or to be more exact, where the valve should be.

I pulled the cylinder head hoping to find minimal damge, but ended up with a little more than that.

Here's a shot of the #6 combustion chamber.


Heres' what the intake valve looks like.


The area indicated by the red arrow is the damage to the guide. You can also see the damage to the edge of the intake port.


The piston took a beating as well.


The good news is that there wasn't any coolant in the crankcase, the #6 sparkplug wasn't damaged, and the block appears to be fine.

Today I took the head, #6 piston, #6 intake valve, and 3 pieces of valve spring to the shop that did my machining for me. I was prepared to hear "You need a new cylineder head." Instead I was told that the damage was actually fairly minor and it would cost about $50 to repair the damage!

The root cause of the failure was single break in the valve spring. The spring broke a second time while we were airing up and that allowed the rocker arm to pound the valve enough that the retainers finally popped out and allowed the valve to drop into the cylinder.

The new parts are on order and I should be back on the road in a week to 10 days.

Moral of the story...even new-ish parts can fail.

[dwg86]

What brand valve spring?

[FrankZ]

I knew someone was going to ask me that. I can't remeber but I'll find out and post up the name. My machine shop is going to take a really close look at the remaining 11 springs and see if anyof them are showing signs of fatique or stress fractures.

[Alex22]

We're lucky the valve is so close to vertical in the I6 engines. I've seen the damage this exact thing will do to a typical 23* V style engine. Broken pistons, broken off valve heads busting the cylinder wall open, destroying valve seats and such.

It doesn't take much for a valve spring to break. That is why inspecting every component of your engine. A small scratch from something like a file or a sharp edge somewhere in the shop and when the spring starts flexing the stress is no longer spread out across the entire spring. The forces build up in one spot causing metal fatigue, and eventually a crack.

~Alex

[gradon]

So they'll ream out the guide and and insert another? Same with removing and installing another seat? What're the green arrows for?

[FrankZ]

Just to highlight what it should look like. Yes the guide will be bored out and a new guide pressed in, same for the valve seat.

[FrankZ]

What brand valve spring?

Elgin, they make alot of springs sold under a variety of names.

http://www.elginind.com/engineproducts.html

[Alex22]

Fun Fact of the Day: There are two companies that manufacture all of the wire used in valve springs, both are owned by Japanese companies. The budget brands buy the low grade stuff while the top names ($) get the best stuff.

[SilverXJ]

And who are the best brands? Or, whom should we avoid?

[Alex22]

Most of the high performance engines we build use ISKY, Ferrea or Comp and a few with Crane springs. Its best to stay away from the parts that look too good to be true or from a company you have never heard of before with a very low price. But, as the thread title says.. Sometimes stuff just breaks.

~Alex