Mystery repeated engine failure that disappears! (1 Viewer)

[dorcom]

Yes you read it right!
"Mystery repeated engine failure that disappears!"
You got to read this whole true story! It is so unreal at the same totally the facts! I'm completely puzzled!

We all know a 2F is rigid but certainly cannot heal itself.

I have encountered most bizarre fatal sounding engine failures in the last 9 months that disappeared again. Yes, you read it right again "disappear.."

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December 18 2012 ~ 4pm
A normal day, all is fine, coasting slowly to a stop at an intersection the engine starts knocking nasty as if I whack a hammer at the block; tack, tack, tack.... The engine shakes, vacuum is ~ 4-5in/Hg lower from the normal ~ 20in/Hg I have. Cylinder 5 shows no change response with simple spark plug wire on/off test.
@#$%%^&*! I verbalized loudly...
My guess was, her time has come at 330k miles...

I stop, shut off ignition and think. Maybe I make it home driving slow on the freeway in 5th gear. Otherwise it's AAA flatbed.

After a few minutes I start her up, the 2F starts up and shakes tack, tack, tack... I noticed that during cranking you hear no knock.
I rev her up a little and the nasty sound fades little by little.

Slowly I crawl with 40mph home on the freeway. While driving I notice the knock has faded more and more and the vacuum returns to normal. (I have permanent a gauge installed)

Arriving at home all sounds hunky dory like nothing ever happened and she purrs!
WTF?
I rev her up take her for a spin, all is well and perfect! Hmm..
Compression check is acceptable on all with variance 150 - 160 psi. No blue smoke.

...12,000 miles later... ..and three oil/filter changes:

July 19th 2013
Smog check, pass all stellar. Tech guy says "Wow she runs really nice and clean..., the engine runs smooth too".
Yes.

-------------------------------
July 21, 2013 ~ 3pm
I roll into a parking lot, engine idling suddenly a tack, tack, tack engine sound fades in! The 2F shakes. Cylinder 6 fails the simple spark plug wire on/off test.
Ohh FTSA! Ohh MF'r, this is it I think.
I rev'd her up twice gently to about and no more than 1,500rpm...
...and then...

Yup!
Sound gone! Engine runs normal again!
Vacuum good, exhaust steady. A classic S.N.A.F.U?
Ah WTF, I'll keep going.

Driving her home I noticed she runs actually damn well, responsive powerful and all.
At home compression check, all acceptable! WTFF is going on?

So I go, keep driving around. I notice she runs really runs exceptionally well, better than ever. Reasonable good mileage (16mpg), very good power and responsiveness, 1qt oil per ~1.5k, no blue smoke, no nasty sound, etc. SNAFU again?

Yesterday Aug. 09 2013 I came home from 1 1/2 hour freeway trip going average 55 - 65 mph, all well and humming.

Before I turned her off I mildly rev'd her a couple of times to listen how smooth and solid she sounded. Great. I listen to her idle purr. Perfect. ignition off.
Good night, sleep well.

---------------------------------
August 10, 2013 343,4xx miles
(~14,000 miles later since December '12)

This morning, less than 12 hours ago from my previous arrival, I go at 7:30am and started her up...

Tack, tack, tack.... MF, WTF now?
Rev'd her up twice....

Guess what?

Sound almost gone! Runs almost fine again!

WHAT IS GOING ON? Please, you tell me! I'm lost!

The only thing I can conclude is a random stuck open intake or more likely exhaust valve getting hit by the upcoming cylinder top until the latter knocks it back into action. Is this a know issue?
Or what else could it be?

 

[Lead Head]

My bet would be valves getting stuck partially open. I doubt the F engines are interference, so piston-valve contact is pretty unlikely. The terrible knocking sound is probably from gigantic valve lash you'd get with a stuck valve. Ever heard a collapsed hydraulic lifter before? Terrible knocking sound. The rear cylinders on most older inline-6 engines run the hottest, so the rear valve stems probably have a lot of burnt oil/grease/carbon on them, and with 345,000 miles, the profile cut into the rockers to rotate the valves probably isn't doing much anymore.

 

[lehiguy]

The next time this presents itself, get the valve cover off ASAP and check for proper valve actuation. Have a good look at the rockers and push rods. I have seen some bent push rods and some seized rockers.

 

[60Works]

Stuck valve or lifter. The lifters aren't hydraulic (unfortunately) so they haven't collapsed.

Due for an oil change? See if any metal is in the pan.

Maybe pull the valve cover and try adjusting the valves. See if any stick.

 

[dorcom]

My bet would be valves getting stuck partially open. I doubt the F engines are interference, so piston-valve contact is pretty unlikely. The terrible knocking sound is probably from gigantic valve lash you'd get with a stuck valve. Ever heard a collapsed hydraulic lifter before? Terrible knocking sound. The rear cylinders on most older inline-6 engines run the hottest, so the rear valve stems probably have a lot of burnt oil/grease/carbon on them, and with 345,000 miles, the profile cut into the rockers to rotate the valves probably isn't doing much anymore.

Hey thanks for your reply!
That's a sensible thought. A rocker with a lash clearance of a 1/4 inch will sound rather nasty!
I agree with you, the 2F is a non interference engine I looked up a cross section drawing.
the knock, now gone, does sound more "lighter" like a "tack tack" than a deep "tock tock"!

I just took her for a drive and the sound is pretty much gone. She runs quiet alright again.
I'm going to attached in a followup post an audio file how she sounds now, after she "self healed" her wounds....

Any thoughts on an special oil flush or additive or gas supplement that really works and could effectively aid a "loosening/cleaning" of valves and/or deposits etc?l

 

[dorcom]

The next time this presents itself, get the valve cover off ASAP and check for proper valve actuation. Have a good look at the rockers and push rods. I have seen some bent push rods and some seized rockers.

That's the plan although I hope much it well never do it again!

 

[dorcom]

Stuck valve or lifter. The lifters aren't hydraulic (unfortunately) so they haven't collapsed.

Due for an oil change? See if any metal is in the pan.

Maybe pull the valve cover and try adjusting the valves. See if any stick.

Fresh oil 500 miles old. I'm almost tempted so say it seems to tend to happen so far AFTER an oil change.

A valve clearance job will be next.

 

[rcmccars]

you could always put a bottle of sea foam in the gas and oil run through a tank and change the oil again. have heard of that cleaning things up but don't know of the ill side affects. maybe others can comment. personally im a fan of lucas injector cleaner. I run it through every motor I have (12 vehicles, dirt bikes 2stroke and 4, garden and construction equipment) and it seems to keep the oil cleaner when it time for a change. idk maybe its just me.

 

[inkpot]

Buy a cheap stethoscope. The next time it makes the noise, jump under the hood and start isolating the source. John

 

[ntsqd]

I'm agreeing with the sticking valves diagnosis.

Don't need a stethoscope per se. I use a really long screw driver or piece of steel bar stock. With bar stock I put my thumb over the near end and rest the thumbnail inside my ear; with the screw driver I put the end of the handle in my ear (those rounded end Craftsman's are the most comfortable). Place the other end where ever you're wanting to listen to.