No.4 Piston Gone Again, Cause Anyone???

K

KevShek

Guest
Im posting up this on behalf of a friend who has a highly tuned R of unknown origin. The car was imported crashed damaged, then fixed. Its laced with a bunch of apexi and HKS goodies including a Mines ECU. Anyways, the problems is this.

When he first got the car, it ran about 1.2 bar of boost, no problems, pulled like a frieght train, even then they suspected the car had been seriouosly messed with, but due to the lack of knowledge, they didnt know what had been done. Not long after, they lost compression in No4 piston, upon removal of the head/pistons, they discovered this fracture in No4 piston. (original spec)





As you can see, theres a considerable size chunk missing from between the rings.

So after this, they replace the piston with another factory unit.

Now a few thousand miles on, they have again suffered loss of compression in No4 Piston. The car has recently been to DP for a SAFC2 fitting and mapping, running about 1.4 bar of boost with a good solid 350 BHP. It was running great when they got it back, but again, removing No4 has shown the exact same signs of fatigue.





Upon closer inspection, weve noticed that the frature is in the exact location as the first time, in the exact same rotation around the piston. First they put it down to a dud piston, but to have it happen a second time in the exact spot is very strange.

Can anyone offer any explanations, answers or solutions? Any help will be greatly appriciated.
Thanks
 
J

jasegould

Guest
Too much boost on standard pistons? No 4 piston is the furthest from the waterpump so will run a bit hotter therefore more prone to det, maybe this has caused it.........only a wild guess :?
 
E

ex-gtir

Member
that seems to be where they always fail i have 6 pistons in total at my workshop which i though were alright but on closer inspection they all had cracks about 1.5> 2 apart :( nissan make a hardened crown piston)
mike
 
zia

zia

Active Member
was the cylindars bored out? honed? also was the crank? main seat? checked for distortion? looks more like if the piston is scrapping the wall.
if it had been det surely they would have checked it when it was mapped?

zia
 
K

KevShek

Guest
when he first changed the piston, he just glaze busted it, that was all. The head was removed in situ so he couldnt get the block profesionally checked for straightness. Hes even thought about the rods being bent, but wouldnt that cause piston slap or extensive skirt damage? rather than a fracture between the rings?

The cars been running fine with no det detected......

I will pass on your comments so far and see what hes gonna do. I will be putting in a new set of forged pistons this time rouind, so the block will be bored, horned etc.
 
A

Anonymous

Guest
Yeah well, 20PSI on standard internals and you're asking why the piston keeps shitting itself???
 
A

Anonymous

Guest
P11GT said:
[...] I will be putting in a new set of forged pistons this time rouind, so the block will be bored, horned etc.
Click to expand...
That's what you should be doing, hehe...
 
K

KevShek

Guest
he just wants to check if theres any other possible causes before putting in an £XXXX amount worth of forged to only find the same thing happen again.
 
K

KevShek

Guest
Heres some pics i dug up of his car. The engine bay remain relatively the same. This T3T04E was fitted here by them prior to the first piston incident. If your in the Newcastle/Gateshead area, maybe you have seen the R before.




 
A

Anonymous

Guest
well you know, what causes can there be? If you're getting forgies I'm sure you're doing all the right things to the block and balancing the bottom end... so that should fix any possible other cause as well!
 
K

KevShek

Guest
cheers zilla, will tell him to take all steps and stop cutting corners.

The manifold is a Protech Fabrications item, log style, for the SR20DE/T It has a T3 flange and Tial 35mm or 40mm actuator flange. They can be built to spec, and there is also a 2.5 or 3 inch downpipe available, but not sure about clearance against the engine cradle.

For more info see http://www.protech-fabrication.com/ you can buy from their distributor at http://www.powertechimports.com who can also supply the Garretts at very competitive prices.
 
K

KevShek

Guest
also, powertech can supply 4 bolt flanges, bends, pipes and coupling for you to build your own downpipe, which is what we did with our T3T04E setups.
 
Fast Guy

Fast Guy

Moderators
Staff member
I'd say it's been tuned to close to the limit for the standard spec and blown as a result. Probably suffering from a little det.

Make sure the block is bored to the correct size for the pistons and when it's in bits get the rest of the bottom end checked out too. No point doing half a job to have a problem 2 months down the line.

When it has the forged pistons put in, I'd get a power run done to abtain a fuel curve to make sure it's got enough fuel at the top end.
 
K

KevShek

Guest
the funny thing was, he took it to DP as a result of over fueling, he had fitted 550cc injectors and found the car to be far too rich during idle or low revs, and bogged down. There was some sort of HKS fuel computer fitted, similar to the AFC, but even turning that down wasnt enough. Now with the SAFC2 it runs, or did run perfect.

Nevertheless, it looks like a full rebuild is needed, just gotta find someone capable to do it in Newcastle or surrounding area.
 
G

GINGA

Active Member
Its quite likely the piston failed due to det on that cylinder maybe get the injectors cleaned and flow checked, just because the mixture ratio is ok doesn't mean its ok for each cylinder as all your measuring is the mixture of each cylinder added together :wink:
I would also check the wiring etc to the injectors as any problems could cause a slight lack of fuel on one injector that wouldn't show up with a afr gauge :(
I've had this problem on my car even with forged pistons but the forged ones didn't break the ring lands they just melted lol but it was on No1 cylinder (furthest from the gearbox) both times than sustained the most damage I put this down to possibly the fuel pressure/flow dropping in the rail by the time is gets to that injector :?:
So i've fitted a exhaust gas temp gauge into No1 exhaust runner so as to monitor the situation as in theory if its running weak or on the edge of det the temp should be high so I should be able to increase fuelling to compensate even if it does shows its running rich for all the cylinders it should be perfect for the one thats must likely to fail.
With that boost on that turbo your reaching the limits of the standard pistons anyway and should really be on larger injectors mines on 700cc ones with s-afc and I get no over fuelling at low rpm/ crusie as the closed loop lambda of the standard ecu adjusts the fuelling to suite on its own in those settings unless the lambda sensor is faulty but even then the fuel controller should have been able to be adjusted to compensate for those injectors :?
though why on earth you'd go to the trouble of replace pistons and not fit forged one's is beyond me in the first place :?
 
K

KevShek

Guest
GINGA said:
though why on earth you'd go to the trouble of replace pistons and not fit forged one's is beyond me in the first place :?
Click to expand...
I know the answer to this one LOL. The car had not long been repaired, back end shunt when he bought it, and he was eager to drive it. He'll learn!

The first piston went with the 444cc injectors, the second with the 550cc, so he thought it couldnt be the injector running lean, but now youve mentioned it, checking the wiring wasnt something we consider, thanks for the tip on that.

We did however consider he may have a dodgy fpr, and with No4 being closest to the fpr, it may have caused any leaness, but hes now got himself a Nismo item to sort that out.

Will 86mm forged pistons be oversized enough for him to install? there is a member selling a set at a good price. He doesnt want to make the mistake of buying them to learn that the bore will ultimately end up bigger when he get the block machined. Any advice on this is welcome.

Thanks for the help guys.
 
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