L16 blew up

[71Ratsunguy]

So i was driving to work Thursday morning, and soon as I let off the gas on the freeway off ramp, i hear a loud knocking. I come to a stop at the red light and it's barely running, still knocking, then dies. I managed to push it into the parking lot of a restaurant. Long story short we'll skip to the goods. I tore into it today and here is what I found. This is the engine that was in the car when I bought it out of a barn ten years ago. No idea how many miles are on this engine. First thing I did was pull the valve cover, here is what I saw

Next I did a compression test #1 150psi #2 150psi #3 125psi #4 0psi. The picture above is the intake valve of cylinder 4, no compression.

That is #3 cylinder

I have not dropped the pan I had enough for today, doing the work at my dads shop. #3 cylinder obviously hurt a piston which makes sense that it made noise when I let off the gas and there was no load on it. Why the #4 intake valve is catywompus I don't know.

Ironically the worst looking spark plug was #2 which seems to be fine. It did have bad detonation under full throttle but I would always back off if I heard it.

[metalmonkey47]

Just a rough guess, looks like it may have been detonating. running lean, perhaps too much timing? That really sucks man.

[datzenmike]

By the time you hear it, it's almost too late. If you heard it at full throttle why didn't you back the timing off long ago. It was probably detonating without you hearing it. Well too bad, lesson learned.

[racerx]

Its all good probably time for a rebuild anyway, lesson learned

[71Ratsunguy]

It ran like a top, idled so quiet you thought it was a Prius, never heard detonation driving it everyday, unless I smashed the throttle, then I'd back off. I have been driving it everyday to work and back, about 15 miles up the freeway, I have a 4 spd and stock gears which I think are 3.90s I'd rev this thing out, no tach but I assume 4K plus at 70 to 75mph but it obviously had a problem. I have heard a tapping noise come and go when I'm on the freeway for a long time..I think it was that piston. When I drop the pan and pull that rod and piston out I'll bet the piston is cracked to shit and sloppy wrist pin maybe... Hence the knocking.

[71Ratsunguy]

Timing could have been too far advanced, my old man is a Motörhead been into blown gas, alcohol, and top fuel engines in the 80s running drag boats. And he still is in the drag boat racing scene now, that his business. He likes to put as much advance as possible.... Very knowledgeable engine guy, But he's not a Datsun guy. I replaced the timing chain a couple years ago and we timed it, maybe it fucked it up because of that? In the long run? Again if I heard pre det I would let off, never heard it it otherwise, and I've never heard of detonation happening without hearing it. Wtf is up with the valve in #4 cylinder though?

[71Ratsunguy]

Had my Webber rebuilt by a friend of his, carbs is his business, it was rich at idle when I sent it to him. He went through it and it was still rich when I got it back, what helped is when I replaced my coil, and battery and re established my ground wires. It ran way better. The wiring has been hacked up by somebody before me, I've been having to fix that shit, I hate wiring

[71Ratsunguy]

I want to know wtf happened here, but I'm not going to rebuild this engine I have an L20b I started building years ago, then I moved, bunch of stuff went into storage... Block is ready for assembly I have and A87 peanut head that was fully redone too, just have to check my Pistons (get the shit out of storage) and make sure it will all work. So I will have questions about that as well.

[flatcat19]

Maybe the valves needed adjusting.

[racerx]

Or it was slowly sinking, like what happened to mine.

[datzenmike]

 

Rocker has jumped the lash ad. Possibly something jammed between the valve seat and valve face and it closed on it. Have a look. As stated maybe too much lash clearance.

 

The short stroke L16 is good to over 8K so no worries below this.

 

Here's a good read on detonation and it's causes and effects... http://www.contactmagazine.com/Issue54/EngineBasics.html

[racerx]

When u did compression check, 1) did u warm up car to operating temp. 2) use screw in type 3) open throttle wide open. More accurate this way.

Also was a valve adjust ever done?

[banzai510(hainz)]

Looks like a valve lash pad got caught up or jammed if its on the same cylinder thats fucked up.

 

if noisey alwasy cheak!!!!!!!!!!

 

I would do the L20, fuck the L16 unless you really need a spare(SAVE IT)

 

DETONATION ISNT THE PROPLEM.your  to ck the timming every now and then. PIngin will be heard if driving a weber DGV for sure

 

would be notice over all the cylinders if detonation issues

[Stoffregen Motorsports]

If Pops the motorhead was tinkering with your timing, it's likely that it was advanced-to-the-point-of-detonation which is never the right thing to do. Sure, having the most timing your engine can handle is better for just about everything except emissions, but you need to have the right curve for that timing to come in at the proper moment.

 

Most old timers don't ever think about adjusting the springs or restricting the mechanical advance, and a lot of them think vacuum is a good idea. Not if the curve isn't set properly.

 

There's an old saying in our industry; "never let your neighbor touch your carburetor." Maybe we should add "never let your dad touch your timing."

[Stoffregen Motorsports]

One other thing that nobody has mentioned, the lash pad could be the result of a sticking valve. In which case, the engine failure could have been a lot worse.

[scooter]

you got lucky with that lash pad.. like stroff said I bet that valve stuck, and got beat back up by the piston. lucky the rocker didn't decide to eat your cam for lunch