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Major Neo Rb25det Engine Damage

drgnball34

By drgnball34,
in Engines & Forced Induction

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drgnball34 Rising Star

drgnball34

Posted
Posted

Please take the time to read as it is long but very important

As the mechanic proceded to bolt down the 2nd cam he heard a cracking sound. He took it off and checked to see if the cam had snaped but turned out it didnt. He placed it back down and continued bolting everything back 2getha. He then cranked the engine over to check if everything was ok but could hear snaping sounds. Thinking that he bent a valve he proceed to do a compression test. Thats when he heard a crunch sound. We took the head off and i nearly fainted. A valve snaped and with the cranking of the engine, must of dislodged itself and fell into the cylinder bore. As a result smashed head, damage piston and burred cylinder bore.

He can not explain what he did wrong but suggested that the head had a crack valve seat prior to the cams getting bolted on. And this has not allowed the valve to close properly thus not only hitting the pistion, but on a angle which contributed to the valve snapping. But if it was cracked in the 1st place, then i would have suffered from miss fire in that cylinder. Not to mention under heavy engine load and with the constant high rpm, that valve would of crack long ago. My car has only 50k kms of which ive only put 5k kms and was runnig perfect when i gave it to him. He suggested that the cause of a crack valve seat was because i was runing too lean. But its only ever been boosted (AVCR) the last 2k kms and been below factory boost cut.

My theory is that before placing down the cam, he either set the timing wrong or placed in dwn the wrng way. When he bolted it down the, the force would of pushed the valve onto the piston and snaped it. Could any tech people please give insight and feedback to what has actually happened to my engine? He is trying to shift the blame on me and wiggle himself out of any responsability. This has caused a great deal of stress upon myself.

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https://www.sau.com.au/forums/topic/136302-major-neo-rb25det-engine-damage/
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Craved Grand Master

Craved

Posted
Posted

i bent 2 valves on cyl 6 when i bolted mine in ..

i was later advised that the crank needs to be moved OFF TDC so that none of the pistons are at full extension, that way if the cams are not in the correct location the valves will not meet with the piston.

cant see how it would be able to be that off that the valve would snap though

GTRgeoff Grand Master

GTRgeoff

Posted
Posted

Which piston did the valve break in? 1 or 4?

As mentioned before bolting the cam down at top dead centre (#1) can cause the valves to contact a high piston and bend or break as the cam may not be perfectly aligned for that timing.

A valve seat would not do this at all unless dislodged. Was there part of a valve seat sitting loose in the cylinder?

He is clearly not a good mechanic. Viewers may have already worked that out. He should have cranked the engine off TDC and put the cams in then retimed and fitted the timing belt. Then he should have cranked it over a couple of times using a ratchet off the harmonic balancer bolt to ensure there was no confliction of the moving parts. He should have stopped immediately there was noise as well, not continued on with a compression test.

If he refuses to repair the damage he has caused take the head and valve piece to a place that does engineering materials analysis for a report on the cause of the failure. They will know if the seat or fatigue or sheer ham-fistedness caused the breakage. You can use the report in a small claims case for compensation.

blur Proficient

blur

Posted
Posted

maybe the cam was bolted down with no reference to tdc at all, and some of the valves opened and had piston contact which would be enough to bend/ crack a valve.. either way its not going to be nice, not exactly a common engine at the best of times.

RB30-POWER Mentor

RB30-POWER

Posted
Posted

Not to mention there could be hairline cracks or fractures in the pistons, valve guides are probably cactus and so on.

Not sure what work was done but maybe the cheaper option is to buy a another motor for $1500 and dump it straight in.

24V head work will add up real quick.

StockyMcStock Proficient

StockyMcStock

Posted
Posted

what an idiot.

1) put engine on TDC number 1

2) put exhaust cam in with cam gear dot lined up approximately towards where it will be when you put the rear timing cover on. torque it down.

3) do the same with inlet cam

4) fit timing belt and tension it up.

how goddam hard is it?

when your crank is at number 1 TDC, number 4 is there as well (i think it's number 4 anyway) so all you have to worry about is number 1 and number 4 valves hitting the pistons. visually check the lobes to see that they aren't at full extension when you install the cam. it is not a difficult concept.

make him fix it.

SLIMVLT Enthusiast

SLIMVLT

Posted
Posted

owch vcat any 1 take him to vcat to get the cash then get some 1 else to fix it.

ive seen plenty of this stuff recantly (im a tech/mechanic at a nissan/kia dealer) and ppl dont seam to think its worth changing timing belts, had about 7 instances in about 3 months all with major valve snapage and alot of busted cams,pistons heads ect, and usulay they break at highway speeds.

ive also seen various aprentaces stuff up valve timing with predictable results.

the best 1 was his own car (xf with ef motor, twin gt3070 ect) the work shop manual didnt have a crutial step in it for installing the timing gear (so he says anyway) resulting in the cam been about 40 degrees out.

it wouldnt turn over so he put a big snap on bar on it. it would turn but not verry good. so he put it in his car cranked it over and not much happened.

i gave his wolf 3d some tweaking thinking he hadnt set it corectly (it sounded suss at this stage. and when it cranked over and fired (well splutered) there where flames about 4 foot high out of the intake and the exhaust.

it smashed every inlet valve and bent/broke every second exhaust valve. broke every piston and masacred the head. prity funny after the event not at the time

http://i54.photobucket.com/albums/g81/slimvlt/Picture303.jpg

http://i54.photobucket.com/albums/g81/slimvlt/Picture305.jpg

http://i54.photobucket.com/albums/g81/slimvlt/Picture310.jpg

http://i54.photobucket.com/albums/g81/slimvlt/Picture315.jpg

http://i54.photobucket.com/albums/g81/slimvlt/Picture294.jpg

http://i54.photobucket.com/albums/g81/slimvlt/Picture317.jpg

pics of the mess

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