I was preparing my Willys for the Fall Colors Tour.  I removed the driver side fender, replaced the fuel pump and adjusted the valves.  I put the fender back on and took the Willys for a test run.

About a mile into the run the engine suddenly started to knock.  I shut it down immediately.  A knock is never a good thing.  Here is a video of the knock…

http://youtu.be/Z4QOr8Lc88M


There are a number of things that can cause a knock.  Just to name a few… 

-Damaged or worn rod and or main bearings.
-Warn out crank or cam shafts.
-Excessive end play at the crank or cam.
-Bent piston rods.
-Piston wrist pins are loose and making contact with the cylinder walls.
-Damaged piston.
-Loose flywheel.

I invite the 3A page to add to this list.

I started my troubleshooting by concentrating on the things I had just changed…Fuel Pump, and valve adjustment.    The valves were all very tight.  I had adjusted them looser  to .16 as described in more recent manuals and memos.  I tightened the valves all back up, and changed back to the fuel pump that I had installed originally.  I still had a knock.  It was hard to determine where the knock was coming from.  I used a long rod as a listening device.  The knock was resonating throughout the engine.  This made it hard to narrow down my search.  It sounded more ‘metallic’ on the top, but most knocks come from the lower part of the engine.

Time to pull the oil pan.

I inspected every bearing, rod, piston wrist pin. They all looked fine.  I made sure the crank was not making contact with the oil pick up or any oil plugs. All good.

I have a GPW engine that has a timing chain.  These can be noisy, and the knock sounded louder at the front of the engine, so I decided to pull the timing cover.  On inspection, everything was tight.  No loose nuts on the sprockets.  No loose timing chain.  Pulling the front off also eliminated a bad belt, generator and water pump. 

With the bottom and front exposed, I had my wife crank the engine while I laid underneath.  I could hear a faint knock at the front, so I removed the fuel pump and checked the cam lobe.  It was fine.

There was only one more thing to do…pull the head.  But what could cause a knock on the top?  A broken piston, or maybe a chunk of carbon?  I was about to find out another possibility…

After pulling the head, here is a view of the engine deck.  #1 cylinder is on the left…




A close up of the #1 piston…



And some photos of the head…



And a close up of the #1 combustion chamber…



A definitive discovery.  This was the cause of my knock.

A few weeks prior to this event, I had removed the Carter WO to clean it.  I was missing a screw that holds the throttle plate to the throttle shaft.  I didn’t think much of it.  I just replaced the missing screw.  Note:  I had rebuilt the Carter about two years ago.  Maybe I didn’t tighten down the screw. 

So, a screw managed to fall into the intake manifold.  It sat patiently for…I don’t know how long.  Eventually, it was sucked in…through the valve…then into the combustion chamber on the #1 cylinder.  It finally moved to a point between the piston and head where it was smashed into the piston…causing a knock on every compression stroke.

There you have it.  One possible reason for a knock at the top of an L-134.

Tim   

Tim,

I hope there is no lasting damage..

A screw in the intake manifold is believable...

That it could get past that valve is really not believable...but it happened....Amazing...


Randy

Tim, you have just brought to life one my greatest fears as a carb rebuilder.

Sherlock Hawkridge, indeed!  Nice work.  I didn't realize that the piston actually got that close to the head such that a 1/8-1/4 inch screw would make contact...I learned something today.

athawk11 wrote on 09/10/14 at 21:53:13:


Well, that is a good thing! Glad to hear it.. you will make the FCT after all!

If that screw falls out of my carb I'm hoping the throttle plate will then fall off and it will quit.....

but, it's never been loosened that I'm aware of....but I'll probably check it anyway next time the air horn is off...

Randy

Randy, I would agree.  If you've never loosened them you're probably good to go.

Ryan, I was a little nervous about that too.  I'm not entirely sure how others have done it, but I had a scraper in one hand and my shop vac in the other. I worked carefully, so it probably took twice as long as it should.   I cleaned the top of the pistons when each was at the top.  I finished with a combination of of light duty wire brushes while constantly running the vacuum. 

I then used some mineral spirits, then brake cleaner.

Tim

Good question Brett.  I have no idea if the Loctite products are fuel resistant.  We use the Blue in my industry.  It holds, but is not impossible to break free if needed.  Red supposedly is permanent, and requires heat to break it free.

Tim

Remind me someday to tell you about the VW engine that suddenly developed rod knock the day I bought it because of a similar screw... Talk about a noisy engine...