finally got my old engine from gps, took it home and opened it up to find the reason for the huge smoke trails it was leaving behind,

 

oh! yes! what a beauty piston number 6 had melted through,

due to detonation,

 

took some pics for you but the damn camera wont download, when i get it sorted will send a few pics as a warning to us all!!

 

dewi ap

How come you were just detting on one cylinder then? Partially blocked injector - creating a lean mix?

hi simon,

 

hmmm!! a very good question, i have checked the other pistons,

and there is no visible damage to pistons or bore!!

 

it looks like there was tremendous heat in cylinder 6 as it has melted the corner of the piston away and holed the corner too!!

 

could a lean mix have done this??

 

when i drove it full bore i was getting the stones in a baked bean tin noise if you know what i mean LOL!!!

Originally posted by FASTREDZ

it has melted the corner of the piston away and holed the corner too!!

 

You may have other problems if your pistons have corners !

Isn't no. 6 at the back right side..?

 

Anyhow - that cylinder alwasy tends to run hotter and get problems first.

...due to the casting flashings in the waterways for that cylinder....

Originally posted by FASTREDZ

hi simon,

 

hmmm!! a very good question, i have checked the other pistons,

and there is no visible damage to pistons or bore!!

 

it looks like there was tremendous heat in cylinder 6 as it has melted the corner of the piston away and holed the corner too!!

 

could a lean mix have done this??

 

Engine damage of this nature is usually caused by the following:

1. High compression resulting in pre-ignition

2. Bad ignition timing resulting in detonation

3. Lean Mix resulting in detonation

 

Lets try to analyse these factors:

Number 1 - Can be caused by an incorrect piston - can't be that I guess, so perhaps Exhaust valves aren't opening fully?? This would be leaving superheated gases in the chamber - a possibility.

 

Number 2 - We can rule out because the other cylinders are ok. (The sixth chamber does get a bit hotter due to the coolant flow, but this wouldn't be enough to hole a piston. I would expect slight pitting of the piston crown on a highly tuned engine which is running very close to det on piston 6 but not a hole)

 

Number 3 - Again we're isolated to one chamber here so its either an injector not squirting enough fuel in. Or its receiving more boost than the other chambers, which is highly unlikely.

 

(Now, I'm no engine expert by any means so don't take the above as gospel. Hopefully somebody will correct me on the above if they know oherwise.)

 

Other factors to consider are:

- Incorrect sparkplug - putting the flame expansion in the wrong place would be undesirable, and could lead to an eroded piston crown, or head erosion.

 

- Too much oil getting in the cylinder (I nearly overlooked this) - when oil mixes with petrol it burns a lot slower causing carbon deposits to build on the piston much quicker and thicker than normal. This when driving around normally wouldn't initially be detrimental to the operation of the engine, but the problem is two-fold:

1. These carbon deposits effectively lower the available space in the chamber causing higher compression (a contributory factor in pre-ignition).

2. When you come to put your foot down for any length of time - these carbon deposits will super heat and cause pre-ignition.

 

The combination of these could over time destory the piston

 

Anyway - none of this is gonna get your motor fixed, so apologies for the lengthy waffle.

Unforunately cylinder 6 in our engines is the "weakest link" and most likely to suffer from detonation.

I've seen 2 VG30DETT's with a hole in piston nr. 6 myself and heard it is the cylinder that fails most.

 

main reasons:

1. As Andy already pointed out: cast flashings in the water channels around cylinder 6 cause that it gets less cooling then the other cylinders.

 

2. since the injector for cylinder 6 is the last in line on the rail, it gets a lower fuelpressure and it also gets slightly warmer fuel as the fuel has to move a longer distance in the warm part of the rail (see your point nr. 3)

 

-Eric

hi there willy ed & lymon,

 

after reading your reply a few pieces started to fall into place!!

 

no 1 i was using a copy'd chip for se-nissan which ran alright till the engine blew up!!

 

no 2 there was a slight water leak on the engine so i added radweld to the mixture, now im sure someone told me the waterways in the casting are very fine, so when bumb ass ( me )

added the radweld it probably seriously reduced the cooling efficiency of the no 6 cylinder!! resulting in a very hight temp in the cylinder!!

 

no 3 i was running 13.5 psi boost! ok so its a little higher than stock and raises the temp a bit but im sure the zed can cope with it!!

 

ok then this is how the story went!! new turbo's fitted 13.5psi,

new chip fitted, everything running fine for about 6 months,

 

on way home one day on a private test track!! 140mph and a puff of smoke, shit i thought , dipstick blow out of hole!!,

everytime i lift off throttle i got a puff of smoke!!,

 

so i spoke to a few fellas and i fitted the turbo technics breather kit!!

 

this solved the problem no more smoke!!

 

so one day again on the test track about a month later, bout 70mph, kicked down lunged forward and all of a sudden a huge plume of smoke at every speed!!

 

it was interesting what willy ed said about the oil in the bore,

now then with my first experience of smoke it was probably a piston ring looking back and the breather only masked the problem but when i carried on driving more and more oil was pushed into the bore, burning away this coupled with the radweld probable finished my engine off!!

 

sorry for the long post but i think this is what happend to my doomed engine!!