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1G what could have cause this?

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goonie

15+ Year Contributor
251
4
Mar 2, 2004
soutomaior/spain, Europe
hi there
this engine comes out of a 1994 gsx (7bolt)
the previous owner had it repaird
they put in a new set of pistons and rods the mechanic said the car idled for 10 sec started reving on its own and exploded (strange)
if you look at the pics piston 1&2 are oke but 3&4 are ruined including the rods never seen something like that before
let me know what you guys think

thnx in advance
 

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That's a mess. Motors just don't "start revving on its own" though. Looks like it hit redline unloaded and grenaded.
Lots of people call themselves "mechanics" but really a true mechanic would have just shut it down during the initial start up if things started to go horribly wrong.
 
yeah thats what they told me it hit redline
but wouldnt they all be ruined? (the pistons)
previous owner told me he ordered the piston set and rods on ebay for a 6bolt engine
but this engine is 7 bolt
could that be the cause of this?
 
EDIT: I posted right after your own reply. So he ordered 6 bolt rods AND pistons for his 7 bolt block?! Without proper machining, that cannot work. The 6 bolt rod has bigger diameter on the big ends of the rods, and the wrist pin diameter is 21mm, compared to 7 bolt piston pin which is 22mm. I'm pretty sure they would have noticed that the rods would feel extremely loose coupled to the 7 bolt crank.
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Agreed with Marty. Unless it was an old diesel which some how 'ran away', but gasolines don't do that... On the first picture, you could see a fresh looking liquid just under the knock sensor. Might just be oil or coolant, but maybe the sensor had the typical failure where they 'spill their goo' out which looks like that. With a broken knock sensor your engine wouldn't really have any idea what's going on. Couple that with other factors (bad tune, improper timing, improperly torqued parts) and catastrophic engine failure like this could happen.

Also I see that you're from Europe. If we have to be honest, almost nobody around here specializes in these cars or has any real experience with them. Most shops either just go brand new German-spec cars or Italian. When it comes to Japanese or American tech, they just have no clue what's going on, and the chances of the shop f***ing things up is much higher. It's just how it is. At least based on my personal experiences...
 
yeah i think thats what happened the mechanic didnt had a clue what he was doing
and to think that the car went to the shop for a broken valve
the owner wanted do do things right and ordered a brand new set of pistons and rods
and these are the results
can you tell by the look of the rods and pistons if ite 7 or 6 bolt?
 

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This looks like to me is rod caps/bolts failure caused by too tight rod side clearance.
i think you have a point there i dont know how mucht the side clearance must be
but its a pretty tight fit i just checked no side clearance at all

also the bearings where all looking ok minus the one where the rod got ripped of the crank
 
Here is a 6 bolt stock rod with ARP bolts and NPR stock replacement pistons.
The second picture is what I check when building ANY engine. Ford, Chevy, Dodge, Mitsubishi, Saturn etc...they are just nuts and bolts to me.
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I don't have the rods and pistons in this motor yet or the side clearance and rod bearing specs would be on it too.

Easy way to tell is measure the wrist pin.
If its 22mm that is a 7 bolt if it is 21mm its 6 bolt.
 
Last edited:
Easy way to tell is measure the wrist pin.
If its 22mm that is a 7 bolt if it is 21mm its 6 bolt.
Yes, but just in case should check the rod bolt size, too. If it has 7 bolt M8 or 6 bolt M9. because if this is 6 bolt rod + 2g piston combo, it would have 22mm pin on 6 bolt rod.
 
yeah i think thats what happened the mechanic didnt had a clue what he was doing
and to think that the car went to the shop for a broken valve
the owner wanted do do things right and ordered a brand new set of pistons and rods
and these are the results
can you tell by the look of the rods and pistons if ite 7 or 6 bolt?
7 bolt Stock piston by looking at them will have an F1 at the end like the ones in the picture. Stock 6 bolts will not have the F1 on top.
 
Yes, but just in case should check the rod bolt size, too. If it has 7 bolt M8 or 6 bolt M9. because if this is 6 bolt rod + 2g piston combo, it would have 22mm pin on 6 bolt rod.
True!
 
so after checking everything wrist pins 22mm rod bolts m8
i think its save to say that it is a 7 bolt combo
i messured the rod on the end it ie 21,5 mm (for side clearance)
the crankshaft was
cil 1 - 21,5 mm
cli 2 - 21,7 mm
cil 3 -21,7 mm
cil 4 - 21,9 mm
so for sure that crankshaft is bend

next question
can a broken valve bend a crankshaft ?
because the car went to the shop due to a broken valve
i think the mecanic didnt check the crankshaft? and just put on the parts?
look at the pic of the damage head head (cil 1)
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Good lord, that cylinder would get real hot with all the damage that wasn't smoothed out in the head. Every pointed place will glow orange. I would have removed the valves, smoothed out all the pits from what ever bounced around in it, THEN proceeded to do a valve job.
I have never had a valve bend a crank or a rod, I guess anything is possible, but over the years I have never seen it hurt more than a piston, head and sometimes the cylinder wall. Usually the valve will bend or go thru the piston. I can see why they bought new pistons now tho. The one that was in that hole would be all buggered up just like the head is, if not worse.
My .02 cents.
 
from what i think the damage in the head is from when the valve broke the first time
they put in new pistons and put the head back without smooting it out
because the piston on that cilinder looks fine no damage what so ever
the damage was on cil 3&4

thank you guys for all the input
 
If you were in the States, I am sure everyone would would tell you to source a new setup. Head is marginally salvageable to me and the rest is scrap.
Is it hard to find a 4g63 motor in Europe?
 
yeah parts are hard to find overhere i bought this carjust because its a gsx i already
owned a gst (1990) i am pulling that engine to put it in the gsx
this engine is built by darren king (ffwd connection) red tag stroker
the one in my avatar
 
I stick with my original diagnosis, I have seen it hundreds of times being a tech, lots of windowed motors over the years, stock ecus, grandma owned cars that get handed down to the grandkids and they run the balls off of them until a rod lets loose or a piston collapses, every thing has a last operating cycle, and thats what the corporations has us explain to the customer in a case like this, there is simply a limit to what old used parts can take and revving them is disastrous in some cases, why did my perfectly fine push mower put a rod through the block one day out of the blue? it had a stock rev limiter and plenty of oil?
 
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