Engine Knock

[athawk11]

 

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� �

[Ryan_M]

HOLY COW!!! That's unbelievable. Do you suspect any permanent damage from this (aside from one thoroughly destroyed screw?).

I was wondering what you'd been up to as things have been seemingly quiet out there in Arvada.  I must say it's a pretty funny thought picturing you slithering around under an open motor yelling directions to the Mrs...... "Hit it again...no, wait...OK, hit it again....!!"   

Glad you found the culprit. Nothing worse than gearing up for a big event and discovering what could be a complete catastrophe.

[1955CJ-5]

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

[bretto]

Wow Tim, if there was a book of oddities happening to engines, that would have to be in there.  Good ear and sleuth work, glad you found the problem and I hope nothing else is screwed.  Pun intended.

[scoutpilot]

[size=12]Tim, you have just brought to life one my greatest fears as a carb rebuilder.[/size][/b]

[p3ferris]

Would not thought of a screw.  The knock was not familiar.  As scrolling down I saw the pic of the piston and stopped,  That looks like a smashed screw.  I scrolled down and you confirmed what I saw.  Any indents on the piston.  If so I would be changing a piston.  Might want to look at the valve seat too for damage

[aboyandhisdog]

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]

Hello All,
Thanks for taking a look.� The only damage that I could find was a slight screw shaped indent in the piston face.� Amazingly, there was no damage to the valve.� The little screw must be related to Houdini.

Everything is back together now, and the engine seems to be running very nicely.� With the head having to be pulled, it gave me a chance to clean everything up and really inspect the engine.

This GPW is 70 years old.� It has never gone through a major rebuild.� While everything was apart, I was able to measure the crank journals.� All still original spec.� The pistons are stamped STD...standard.� It probably had a valve job at some point.� Compression test revealed that it probably needs a ring job.� I have mid to low 70s on all cylinders.

With all things considered, I feel very lucky to have this little engine, and lucky that nothing really bad happened.

Ryan, I knew you would find humor in some parts of this.� It gets better.� While flopping around under the Willys, and as you predicted, I kept asking Rachel to turn the key.� The testing ended when we broke the starter Bendix.� �:-[� It is a 6volt starter in a 12volt conversion.� I knew we were putting pressure on it, but I just kept asking for more key turns.� That just made my day even better. �

While doing the write up, I tried to be as concise as I could.� Truth be told, this went on for a solid 2 weeks.� Night after night...day after day, I was out in the shop.� While away at work, it's all I could think of.� I actually tore parts of the engine down numerous times while trying to avoid pulling the head.

Scoutpilot, I thought about you when I figured out where the screw came from.� Joe Friday at the 2A page mentioned a tool that is designed to peen these little screws.� I said to myself..."I bet ScoutPilot has that tool."� In the absence of this tool, I guess it's recommended to use red Loctite when setting these screws.� Ya live, Ya learn.

Tom, I had no idea the piston came that close to the head either.� On the high side of the piston stroke, it is nearly even with the engine deck.� And in this area of the head, it's on the same plain as the sealing surface, so it must come within mili-fractions of an inch.

Once again, thanks for having a look.� Hopefully this never happens to ya'll.� I wonder how many of you are going to add some red Loctite your screws?? :-/

Tim



� �

[1955CJ-5]

and the engine seems to be running very nicely

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

[Ryan_M]

Night after night...day after day, I was out in the shop.� While away at work, it's all I could think of.

I can relate to this whole-heartedly. I'd hate to also add up all the hours of sleep lost to obsessing over whatever the latest Jeep crisis is.

I'm curious - how did you clean the top of the block, pistons, and valves once you had the head off? I'm thinking you have to be careful once you start dislodging any of that built up crud.

[athawk11]

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

[bretto]

I wonder if loctite is affected by petrol at all.  Maybe there is a dif between the red and blue type in those regards.  Glad all is working out for ya though.

[athawk11]

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   

[Jeff_M]

I'm amazed that (1) the screw survived, (2) you actually found it, and (3) it apparently didn't do any damage.  Excellent post.

[F Bill]

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...