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Tue May 01, 2012 9:42 am

I pulled my 63 bus out for the season a couple weeks ago. This past Saturday I drove it to work and back, 70 mile round trip, around 50-60mph the whole way. Everything work great.

Sunday I do the same thing, but around 5 miles from home, bad noises from rear of bus. Pulled over, and the engine has stopped. I try to start it, but the starter just clunks. I figure the engine is siezed and call for a tow.

At home, I grab a wrench and try to crank engine by hand. It will turn in one direction, but not the other. I pull plugs, 3 come out easy, 1 is jammed tight.

Pulled engine and pulled the head with the stuck plug...

Here's what I found:

Piston removed:

I have a local welder who will weld the piston back together. He said he will try to weld the valve back to the stem, but wasn't 100% sure on that one.

Anyone have any ideas what caused this?

Here is a pic of the head:

Does it look like it's been running lean? The exhaust valves on the other head look the same. (the picture doesn't show the true color, they are a little more brown).

The engine was running hot last summer when the weather was hot. It was only in the 35-50 degree range this weekend when I was driving, so the engine oil temp was fine.

Tue May 01, 2012 9:53 am

whats the valve spring look like

Tue May 01, 2012 10:05 am

weld the piston together? you serious?

get someone proper working on this thing. Please. If you have the time and tools, just not the know how, please ask. Those are not parts that can be welded up and returned to service

Tue May 01, 2012 10:10 am

Erik G wrote: weld the piston together? you serious?
The valve too! :lol:

Tue May 01, 2012 10:41 am

I was just kidding about welding it up...

At this point I'm looking at replacing all the cylinder/pistons. The one head, possibly both. The cam looks good, but have some pitting in lifters, so they need replacement. I haven't had a chance to look at crank or connecting rods yet, but the one rod might have suffered some damage.

I just don't want to go through all this without identifying the root cause of the problem and have it happen again!

Visually the valve spring looks fine. What should I be looking for?

Tue May 01, 2012 12:25 pm

A dropped exhaust valve in cylinder 3 is the most common valve to go, this cylinder runs the hottest because of the oil cooler position.

The valve stem breaks and the valve generally goes through the top of the piston, the engine will need rebuilding because of all the small broken bits of metal inside.

Tue May 01, 2012 1:24 pm

amotomura wrote: What should I be looking for?

when your engine stopped, how hot was it?

If you spit on the case (aim for the base of the generator stand) did the spit just hang there?
kinda sizzle?
sizzle and bounce off immediately?

could you hold the dipstick....
as long as you wanted?
for a little bit?
heck no!!!!!

Tue May 01, 2012 1:26 pm

past posts by this user indicated overheating problems. could have done the damage a long time ago, and it just now decided to puke the valve into the piston

Tue May 01, 2012 5:56 pm

kevm wrote: A dropped exhaust valve in cylinder 3 is the most common valve to go, this cylinder runs the hottest because of the oil cooler position.

The valve stem breaks and the valve generally goes through the top of the piston, the engine will need rebuilding because of all the small broken bits of metal inside.

Nailed it.

Given your history of hot running, the weakness could have begun at any time and it just happened to snap when it did.

You will have no peace of mind unless you do a complete tear down for cleaning and inspection of internals for damage and debris--you know those little pieces of metal are in there somewhere.

Tue May 01, 2012 8:04 pm

Thanks for everyone's replies!

At the time of the break, the engine was running quite nicely, around 180, probably because it was cool out.

I had lots of temp problems last year, so it sounds like the damage might have been done then....

I have my engine completely torn down right now and am inspecting everything. The pieces of piston are everywhere!!

Trying to decide how to rebuild it. Any suggestions?

Tue May 01, 2012 8:11 pm

amotomura wrote: Thanks for everyone's replies!

At the time of the break, the engine was running quite nicely, around 180, probably because it was cool out.

I had lots of temp problems last year, so it sounds like the damage might have been done then....

I have my engine completely torn down right now and am inspecting everything. The pieces of piston are everywhere!!

Trying to decide how to rebuild it. Any suggestions?

with an experienced machinist and quality parts

Tue May 01, 2012 8:15 pm

Get the Bug Me video, buy parts and do it yourself. That's if your broke like me. If you can afford it, take to a good mechanic and have him rebuild.