Yea.. A bent rod. And I didn’t even know it…... It bent way back , about 20k miles before I installed my turbo. When I “Mysteriously” lost some compression in that cylinder. I now believe it was caused by hydro locking it from fuel.. Which would make sense because at the time I was having lots of injector problems in that cylinder. Shortly after which I check the compression on and it was down to about 135psi, where the others were at 170 ish. I figure it hydro locked because there is absolutely no signs of damage to the valve or the piston. I still cannot believe I drove for that long on a bent rod. Even more amazing is that I Boosted as much as 13 psi on it and it never broke. These things, as mtcookson found, MUST be forged. I was at the drag strip 2 weeks before I pulled my engine apart and found it. That is when I uped the boost to 13 psi and the compression , was actually better after the dragstrip that it was before. That means that even though I went 16 passes at 13 psi it did not bend anymore. A testament to the strength of Nissan V6s especially VGs.

Well. So that is the first part of my story. Now hear is the tear down and rebuild half.

So I decide that my low compression has to be caused by a bad valve. And I decide to pull the head off and have it fixed. I had done a leak down test and found that air was always coming out of the exhaust valve no matter where the position of the engine. This makes sense now because with the low compression of the cylinder (85 psi warm) The fuel was not burning clean and the exhaust valve was getting rather fouled up. Causing it not to seal as well. Also a in the leak down I found no more air coming out of the crankcase when testing that cylinder than when testing any of the other cylinders, so I declare the rings good.

So I get the head off (front head luckly) and find.. Yes, the valve is leaking more than the others , but I doesn’t seem like its leaking enough to cause the compression to get that low…. So I start to think Something is fishy.. But I go on with the plan. Later that night I’m cleaning the block off and looking at the other cylinders thinking .. Hmm.. wow the pistons come right up flat with the block… so I turn over the crank.. And about went In shock from what I saw… The Bad cylinder was 3/16 of an inch short of the deck!!! I could not believe it. I kept thinking , what could it be.. Everything I though kept leading back to it being a bent rod.. Yet I still was in denial. Off with the oil pan, down with the jaws… sure enough bent as can be.

Second to the rod never breaking was how unbelievable all of the clearances where. One would assume that with a bent rod you would be wearing out everything that has to do with that certain cylinder let alone not punching a hole in the block. The rod to crank bearing…. Plastiguaged it.. PERFECT.. The piston.. Perfect… The piston rings .. Perfect… The Cylinder wall.. Perfect.. You could even still see the cross hatching clearly (amazing for 184k miles, 75k of which it was driven very hard.) so I decided to use the piston over, the piston pin over, and even the rod bearing over. I pulled a rod out of a bad VG I have laying around check the clearances and installed it. All when well with that. I even changed my mind on getting the head redone.. I figure .. That piston coming up 3/16 of an inch short was probably 95% to blame for the low compression. So the head , untouched , went right back on. And she runs good and smooth again for the first time in a LONG time.

There is more to my reinstall.. But I will touch on that in another thread. This is enough for now.

WOW.....just WOW

Looking back....you never noticed a vibration or sound?

I must say that is amazing...

that the new style yo.

Awesome man... I'm really surprised that rod didn't break and do some major damage! definitely a testament to Nissan.

Just an FYI as well.. the VE rods are the same as used in the VG30DE and VG30DETT, and are good for ~400wheel hp reliably. probably cna go more than that, but at that point you're looking at rebuilding the engine on a somewhat reqular basis anyway, so the rods are almost always replaced.

nonetheless, it's pretty amazing that it didn't do any more damage.

Before you put the head back on, did you at least re-lap that valve into place? should have gotten it to seal pretty good that way.. either way, once you get the engine broken in again, you might want to run a couple cans of seafoam through it to clean up the deposits from the rich fueling.

That's an amazing story. My 87 max threw a rod and it was all over at that point.

Makes me wonder what is going on under my hood! Glad you got it figured out before any real damage was done.

amazing it didn't break at that boost level. Really good engineering on nissans part, and partially luck on your part.

That's incredible... but makes me wonder if my engine is possibly the same way. My engine hydrolocked before due to an injector issue (luckily not while running or anything) but I'd still be interested in seeing if something similar was done.

Definitely some awesome Nissan engineering though.

Nice pics! That definitely says something about the durability of the engine components.

That is too cool!

You should have beat it back str8 with a dead blow. It would have been fine. Thats good stuff.
Choray

Thats awsome. Did you pull the engine or leave it in the car?

~Alex

who needs low compression piston when a bent rod does the same thing. Once again, what internal components are forged from the factory? Piston, rod, crank? Does anyone know what material the rings are made from?

geeeze -- how did that not fubar other things inside the engine?? simply unbelievable!

My thoughts Exactly