Broken pistonrings! what caused this?
10-09-2007, 02:16 AM
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Broken pistonrings! what caused this?
Hello.
This is my first post here but hoping for some help.
Iīm an Swedish enginetuner that has came into a problem with a customer.
The customer says itīs my fault.
I keep saying it might be my fault, but only when iīm 'proofed guilty'
The problem:
An 4cyl 2 litre 4 stroke engine broke itīs top pistonrings on all 4 cylinders when cranking.
My question for you guys who plays with engines in water all days is:
Is there any chance that an engine almost can hydrauliclock and when cranking the rings can brake?
The lock i talk about wasnīt enough to make the engine stop at crankning. but just about enough to break the rings.(guessing here)
He accuses me for having to high ignition on idle but i cant see how thats going to crack the rings as you get far more higher cylinderpressures att fullthrottle than on idle with closed throttle.
The ignition was 30 degree before tdc at idle, quite high, but not alarming high.
This was happening just when starting up an new engine as it didntīt run well on idle i just advanced it from ~15 degree to 30degree for a while.
Took a small calm run with the boat , it went really fine.
but we got splashed by an another boat and my engine was sucking in a lot of water so it stalled.
Then when cranking, no noise at first, then after a few turns the engine fires and makes an alarming noise from the rings.
Sorry for bad english.
Rgds
Momental
This is my first post here but hoping for some help.
Iīm an Swedish enginetuner that has came into a problem with a customer.
The customer says itīs my fault.
I keep saying it might be my fault, but only when iīm 'proofed guilty'
The problem:
An 4cyl 2 litre 4 stroke engine broke itīs top pistonrings on all 4 cylinders when cranking.
My question for you guys who plays with engines in water all days is:
Is there any chance that an engine almost can hydrauliclock and when cranking the rings can brake?
The lock i talk about wasnīt enough to make the engine stop at crankning. but just about enough to break the rings.(guessing here)
He accuses me for having to high ignition on idle but i cant see how thats going to crack the rings as you get far more higher cylinderpressures att fullthrottle than on idle with closed throttle.
The ignition was 30 degree before tdc at idle, quite high, but not alarming high.
This was happening just when starting up an new engine as it didntīt run well on idle i just advanced it from ~15 degree to 30degree for a while.
Took a small calm run with the boat , it went really fine.
but we got splashed by an another boat and my engine was sucking in a lot of water so it stalled.
Then when cranking, no noise at first, then after a few turns the engine fires and makes an alarming noise from the rings.
Sorry for bad english.
Rgds
Momental
10-09-2007, 06:57 AM
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your english and spelling are better than a lot who write here for whom english is their first language... so no worries.
on the 2 litre 4 cyl motors that i have done, when they would come apart with broken top rings it was almost always because the pistons had become worn and the ring grooves were no longer square. but that took some time to happen... 10 or 12 hours at full race speeds and conditions.
i have seen a million times guys rebuild motors and break the top rings by not sufficiently cleaning up the ridge at the top of the cylinder or using a different make of piston w/ a slightly different top ring placement...
im not sure i have ever seen a motor with ALL the top rings broken...
if they are just broken in two... that is just two pieces, i would wonder if the end gap was too small. if they were broken into many tiny little pieces, that usually meant interference issue... like the piston JUST touching the head...
it would be hard for me to believe that you could rattle ( detonate) the top rings out without some significant tell tale sign on the piston edges and i would not have expected it to do that and still run as well as you say... but its possible, i suppose altho if i understand you correctly, 30 deg at IDLE is going to be probably 55 or so at 5000 revs which will rattle the rings out of it in a heartbeat if thats really what you did and where the timing ended up. on my 2l i ran between 32 and 36 TOTAL advance depending on the weather and anything more than that just killed the power... and those were 10 :1 motors an 100 octane fuel.
i would think that if you got water in there and were able to turn it to get the water out then that wasn't true hydraulic lock ... but again... you were there, not me so only you know. you can know that for certain because IF that did it, a NEW ring will be very tight in the groove... and ill bet its not.
all guess work on my part, of course without seeeing the stuff but there you are.
on the 2 litre 4 cyl motors that i have done, when they would come apart with broken top rings it was almost always because the pistons had become worn and the ring grooves were no longer square. but that took some time to happen... 10 or 12 hours at full race speeds and conditions.
i have seen a million times guys rebuild motors and break the top rings by not sufficiently cleaning up the ridge at the top of the cylinder or using a different make of piston w/ a slightly different top ring placement...
im not sure i have ever seen a motor with ALL the top rings broken...
if they are just broken in two... that is just two pieces, i would wonder if the end gap was too small. if they were broken into many tiny little pieces, that usually meant interference issue... like the piston JUST touching the head...
it would be hard for me to believe that you could rattle ( detonate) the top rings out without some significant tell tale sign on the piston edges and i would not have expected it to do that and still run as well as you say... but its possible, i suppose altho if i understand you correctly, 30 deg at IDLE is going to be probably 55 or so at 5000 revs which will rattle the rings out of it in a heartbeat if thats really what you did and where the timing ended up. on my 2l i ran between 32 and 36 TOTAL advance depending on the weather and anything more than that just killed the power... and those were 10 :1 motors an 100 octane fuel.
i would think that if you got water in there and were able to turn it to get the water out then that wasn't true hydraulic lock ... but again... you were there, not me so only you know. you can know that for certain because IF that did it, a NEW ring will be very tight in the groove... and ill bet its not.
all guess work on my part, of course without seeeing the stuff but there you are.
10-09-2007, 07:01 AM
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I am almost sure that the rings were broken by hydrolock, some guys run with the timing all in and the distributors locked - no advance. 30 degrees of timing would not break rings.
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10-09-2007, 01:30 PM
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It is very unusual to break all rings with a hydrolock situation. All pistons would have to travel to the compression stroke to make that happen. You would probably physically lock the engine with 1 or 2 cylinders full of water. So...
My best guess is that there is some chance that fiddling with the timing or fuel settings may have leaned out the engine and caused it to detonate. Are you sure that there are broken rings?? If you or your customer are assuming you have broken rings just by the noise that the engine makes, then that may be a mistake. It could be the valvetrain or connecting rods.
Was the engine torn down? If so, and rings were definitely broken, the way they were broken will tell a lot.
Is there more info you can supply?
-Larry
-Larry
My best guess is that there is some chance that fiddling with the timing or fuel settings may have leaned out the engine and caused it to detonate. Are you sure that there are broken rings?? If you or your customer are assuming you have broken rings just by the noise that the engine makes, then that may be a mistake. It could be the valvetrain or connecting rods.
Was the engine torn down? If so, and rings were definitely broken, the way they were broken will tell a lot.
Is there more info you can supply?
-Larry
-Larry
Last edited by ljsmith1; 10-09-2007 at 01:35 PM.
10-10-2007, 03:23 AM
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Hello again fellas.
Very glad to read this much response from you.
First things first.
The engine is equipped with fully mappable ecu and the actual timing was lower at a little bit higher rpms
I just used 30 degree to make it idle,as i didnīt have any throttle adjustment for idling.
on slightly higher rpms ~1500rpm the advance was 16 degree and advancing up to 33 degree at 4000rpm then falled down to 30 degree at the top rpm (7000rpm)
The engine is turboequipped and had the boost at ~10psi(0.7bar) and when that boost was reached the ignition was 26degree before tdc at the same point the unboosted curve had 33degree, and the boost ignition also falled the same 3 degree to top rpm.(23 degree)
Compressionratio on engine is 8.8-1 and an 16 valve head modified to be less sensitive to ping.
I ran the engine at 98 octane fuel(i belive it equals to 93 octane is the states,Sweden messes up the ron/mon jungle)
When i dismounted the exhaustpipe i noted that 2 of the pipes had a lot of condence(heated water) inside it.
(I did start the engine after that crank just to shut it off at once when i heard that horrible noice)
Therefor iīm guessing it was water messing my customers rings up.
Rgds
Momental
Very glad to read this much response from you.
First things first.
The engine is equipped with fully mappable ecu and the actual timing was lower at a little bit higher rpms
I just used 30 degree to make it idle,as i didnīt have any throttle adjustment for idling.
on slightly higher rpms ~1500rpm the advance was 16 degree and advancing up to 33 degree at 4000rpm then falled down to 30 degree at the top rpm (7000rpm)
The engine is turboequipped and had the boost at ~10psi(0.7bar) and when that boost was reached the ignition was 26degree before tdc at the same point the unboosted curve had 33degree, and the boost ignition also falled the same 3 degree to top rpm.(23 degree)
Compressionratio on engine is 8.8-1 and an 16 valve head modified to be less sensitive to ping.
I ran the engine at 98 octane fuel(i belive it equals to 93 octane is the states,Sweden messes up the ron/mon jungle)
When i dismounted the exhaustpipe i noted that 2 of the pipes had a lot of condence(heated water) inside it.
(I did start the engine after that crank just to shut it off at once when i heard that horrible noice)
Therefor iīm guessing it was water messing my customers rings up.
Rgds
Momental
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10-12-2007, 06:00 PM
#8
10 psi boost is high
Like Ed says I would of thought burned holes in pistons before breaking rings, if its from detination and not water?????
or lifting ring lands, burning sparkplug eletrods off,blowing head gasket etc
Like Ed says I would of thought burned holes in pistons before breaking rings, if its from detination and not water?????or lifting ring lands, burning sparkplug eletrods off,blowing head gasket etc
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10-13-2007, 10:39 AM
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the boost is 0.7 bar (10.15266 psi)
Thats 1.7 bar ABSOLUTE pressure
And that not much at all on an 2 litre 16v engine. itīs hardly stressed at all.
The engine is now mapped and tuned at 2.0bar = 29.psi
And runs fine.
well well.
Engine broke itīs rings in unboosted mode at IDLE
How much boost there was isnīt important as it had a fine timingcurve at boost.
Have you two read my info at all?
Rgds.
Thats 1.7 bar ABSOLUTE pressure
And that not much at all on an 2 litre 16v engine. itīs hardly stressed at all.
The engine is now mapped and tuned at 2.0bar = 29.psi
And runs fine.
well well.
Engine broke itīs rings in unboosted mode at IDLE
How much boost there was isnīt important as it had a fine timingcurve at boost.
Have you two read my info at all?
Rgds.
