22 replies to this topic

[Ron Alan]

I think I know why a motor in one of my cars failed but I was surprised at what I found when I took it apart. Hoping to learn more from some of you guys with way more experience! 1.6 motor fyi...

 

Details...#4 rod out both sides of block. Can see oil pressure drop in video from 60 to 25 in about 20 seconds and then motor died within 10 more. 

 

Piston and rod were in pieces.  What surprised me was the amount of oil I found in the other 3 cylinders along with lots of metal. This was in the combustion chamber when i pulled the head off the block. My guess is the oil came in through the intake valves via the intake via the valve on top of the valve cover that vents crank case pressure. But how does a whole bunch of flat metal flakes get in there?

 

The top of each piston(outer) and the corresponding portion of the head is all dented/scored...as if this metal was in there for awhile. It doesnt seem all the metal is part of the the piston or head as some is magnetic. Can 2-3mm size pieces find a way out of the lower end? Can they get past the screen and filter?

 

I understand detonation but not sure what it looks like. I guess i anticipated lean looking plugs and combustion chambers but the oil and all the metal has got me scratching my head?

 

Leading up to this failure we had an electrical issue in which the car would stumble or die for up to 3 seconds above 6000 rpms. Turns out it was in a harness plug/wire under the dash that went back to the fuel pump. So the fuel pump would basically shut off for a period of time. In the video you can see the AFR gauge jump to 22.4 when the car basically died(no fuel)in these brief moments. 

 

Fire away...

[Lmcgrew79]

Not an expert on miata engines but a lean condition in any motor is bad and could blow it from over heating or detonation. If you had oil and metal in the intake track it seems it backfired/detonated/blowup occured while the intake ports was open.

[Dave D.]

Fairly typical of engine failures with a common plenum intake. Shrapnel gets pumped all over after the explosion. GM and many others had bulletins about cleaning intake manifolds after engine failure to prevent contaminating the new engine.

[chris haldeman]

Magnetic pieces are from the rings. 2nd ring is very brittle and shatters into 2-3 mm pieces.

[Ron Alan]

This is the first time more than just the rod broke for me. It now makes sense how much debris can get back into the intake with a wide open hole to the crank. But so much so fast is amazing. 

 

Can I attribute the damage on each piston and corresponding portion of head to the pieces metal or is this what a lean condition looks like? For my own sanity and future knowledge I'd like to understand why a new motor fails like this. It had conventional 10-30 with redline break in additive. As I mentioned, before the failure the fuel pump was losing power for short periods of time at high rpm and left hand turns. It ran perfectly normal below 6000 and in the pit(at the time we could not duplicate the stumble in the paddock). No rod knock could be heard prior to the loss of oil pressure and then the seizure of the motor.  I found this thread from  a few years back...the picture Keith posted is similar 

 

http://mazdaracers.c...stion-chambers/

[chris haldeman]

Keith's pictures show only signs of debris. Perfect example of what the ring chunks leave behind

[Steve Scheifler]

What Chris said. And once it blows, pieces can circulate between cylinders through the intake.

A new build? How many race hours?
If it was detonation I would expect visible piston damage that was obvious rather than bearing failure. Was the block decked to trymue it or for compression? How much did the pistons stick up above the block? Look very closely at the tops of the pistons and the bottom of the head where it hangs over the piston. If you had just enough stretch to make light contact, that can compress the bearing without breaking anything else, then the bearing wears quickly, pressure drops, bam. It may have simply been a pump failure or clogged passage but you really need to eliminate other possibilities so you can avoid a repeat.

[Ron Alan]

New motor...maybe 1.5 hours on test day? New pump. With head gasket on block still...pistons below by maybe the head gasket thickness...30 thou?

 

I guess if you had a bad oil passage how would you ever Know? What I do know is the motor kept losing fuel pressure(via the fuel pump losing power or signal). This was literally the first time i had ever had a AFM in my car. I know it would jump to 22.4 whenever the car died(again, never longer than 2-3seconds). I dont have the video in front of me so not sure if this also happens when you let off gas and brake? But i distinctly remember that when i watched the video at the track...as well as seeing the oil pressure go from 60 to 25 before ka-boom!

 

Yes Steve...I would not like to gloss over what may have also caused a problem though maybe less likely. Dont want to repeat mistakes if possible...although a bad wire/harness connection cant be expected!

 

 

 

Speaking of harness...another car with a different problem if it rings a bell for anyone.

 

95 car starts then turns off...from 1 to 20 seconds after starting. Will start again and turn off...3rd or 4th try will not start at all. Wait 1 hour and the process will repeat.

 

So far what I have figured out...  With a noid light it is losing injector pulse. Does not lose spark to plugs. Does not lose power to injector...just ground signal...which I believe comes from ecu? Different cam sensor does the same thing. So I'm losing signal either in the harness from the cam sensor to ecu or ecu to injectors. This was as far as I got before i stopped goofing with it...am i missing something simple or am I chasing another bad wire/connection?

[Diller]

 

Speaking of harness...another car with a different problem if it rings a bell for anyone.

 

95 car starts then turns off...from 1 to 20 seconds after starting. Will start again and turn off...3rd or 4th try will not start at all. Wait 1 hour and the process will repeat.

 

So far what I have figured out...  With a noid light it is losing injector pulse. Does not lose spark to plugs. Does not lose power to injector...just ground signal...which I believe comes from ecu? Different cam sensor does the same thing. So I'm losing signal either in the harness from the cam sensor to ecu or ecu to injectors. This was as far as I got before i stopped goofing with it...am i missing something simple or am I chasing another bad wire/connection?

 

I had this issue when it was cold on my 94. I replaced EVERYTHING in the ignition system with no success. I decided to try a friends ECU and boom, fixed my problem.

 

The ECU is responsible for taking the analog signal from the cam sensor and outputting digital pulses to the coil and injectors. Mine had water damage and rust on the board so that probably had something to do with it.

[Ron Alan]

I had this issue when it was cold on my 94. I replaced EVERYTHING in the ignition system with no success. I decided to try a friends ECU and boom, fixed my problem.

 

The ECU is responsible for taking the analog signal from the cam sensor and outputting digital pulses to the coil and injectors. Mine had water damage and rust on the board so that probably had something to do with it.

I should have said I did try another ecu...repeated the exact same problem. So I'm assuming mine is fine. Thanks!

[davew]

Check the grou.ds for the engine harness near the throttle body. Some are on the bottom side. Then replace the ecu and coil pa k with known good unitz. If fixed replace one piece to determine which one was damaged by the ad ground wire.

[RWP80000]

Ron,

Sorry for your loss!  I agree with all that it is typical after a catastrophic failure like you experienced to find debris distributed to most (if not all) of the cylinders. Once the intake valves are damaged or held open (bent) the other cylinders pull all the debris out of the bad cylinder into the intake.

 

As for detonation, it is easy to spot in that there will typically be a textured/pitted look to the base piston aluminum material generally around the outer piston top edge in a localized area with a soft radius'd trough where the aluminum material is eroded away.

 

In your case, I tend to think that what you experienced was not due to detonation for a couple of reasons; First from your description it sounded that the A/F gauge went very lean which, if this was happening ,quickly would result in not enough fuel being present in the cylinder to create adequate heat to generate detonation damage. Secondly, if detonation were to be the underlying cause it would probably not have manifest itself in the catastrophic failure you experienced as the detonation damage would result in piston erosion/damaged to ring and lands and thus generally a loss of cylinder pressure and accompanying power with no intake cross contamination. There is however always the "chicken or egg coming first" issue in that if the piston were to have expanded excessively to the point of very high friction/drag condition inducing a rod or rod bearing failure (but not on my high probability list).

 

My inclination is that you exhibited a basic rod bearing failure but the reason for it can be very elusive. I did not see any mention as to the condition of the rod journal or bearings.  I am presuming that they were probably totally wiped out and heavily "blued" on the failed cylinder. I noticed you mentioned the oil pressure dropping from 60 to 25 shortly before the failure.  I find it unlikely of you having a rod bearing failure with 25 psi of oil pressure. This leads me to question crank journal and rod bearings themselves.  It also raises my curiosity as to the oil pump relief valve.  A stuck open relief valve could regulate your pressure down to the 25 psi range at high rpm's but allow a much lower operating pressure to occur at lower rpm's. I would take a closer look to see if the pump relief piston is in the stuck open position.  Even if you find it is stuck open, that condition could also be from debris picked up in the pan from rod brg. material as it started to fail. You probably won't be able to figure out much from the failed journal but you may want to closely examine the other three to see how they appear and possibly verify clearances.  Then again, maybe it was just a QC issue and someone forgot to torque the rod nuts.

 

Good luck with your investigation.

Rich Powers

[Ron Alan]

Thanks Rich. We all know how often we see these motors in street form come in with rod knocks. Not nearly as often are they blown up as what happens in our race motors(which we rarely see rod knocks). I assume this is because we do not drive them around at 2500rpm

 

The oil system is a giant controlled leak correct? Lets assume at 60psi and 6500 rpm the system is doing its job. A loss in pressure(pretty sudden) at that same rpm could be the result of what? Stuck open relief valve? Pump itself? Something allowing much more oil to "leak"?

 

I has always been my understanding that an early explosion(detonation for lack of a better word), which could be as simple as timing, pounds on the top of the rod bearings. Eventually as they become egg shaped...oiling becomes a problem correct? I assume a bad injector may cause this same condition in one cylinder if it is delivering less than the proper amount of fuel(lean condition)?

 

Here is what I do know...

 

In 6 years I have had 5 motor failures in 3 different cars(90,95,99)...every time it is #4 cylinder. All these motors had been dynoed and AFR was set in a safe/conservative range. Here are details...

 

1. New build 95 motor. Lasted 30 minutes on track before it began to seize. Driver recognized no power or ability to accelerate and backed it down. Limped to the pit. Did not blow up. #4 rod bearing frozen when taken apart. New crank and rebuilt motor. Flowed injectors before reinstalling and found 1 to be off maybe 30% at full tilt. Couldnt verifiy which hole it was originally in.

 

2. 95 OEM motor. Worked head with 65k bottom end. Ran 5 years! Always used oil...much more towards the end of its life. Made better power every year. 117 when head was first put on...123 the weekend it died 3 years later. SAME failure...loss of power on track as it began to seize. Driver kept his foot in it trying to get back to the pit(didnt make it)...2 sided block vent holes in #4!  No idea after why this happened other than just age and abuse and maybe low oil...guess.

 

3.  99 motor. OEM bottom end with built head. 3rd weekend on track. SAME failure...loss of power. Driver backed it down and limped back to pit, Huge #4 rod knock when he got back. New crank and back to dyno...1st and 2nd pull AFR started lean and went leaner!! WTF?? Ahhh...why is the charge light on? Voltage check...11.4?? Learned the fuel pump apparently works less with less voltage! Ok...pretty confident this original failure was a no fuel lean condition at speed. Did not have an AFR in the car originally but on the dyno with the bad alternator it went to 18!! New alternator and the new motor is still running(I'm knocking on my thick skull right now )

 

4. Rebuilt #1 motor from above. 4th weekend. Finished P2 at both Majors races at Thunderhill 2015. On the in lap of the 2nd race the motor began to seize 3 turns form the pit. Driver putted and the car died the minute he pushed in the clutch coming off track. SAME failure...#4 rod bearing!  No idea on this one...new crank and back in service!

 

5. New 1,6 motor....as described in the beginning of this thread! Less than 2 hours on the motor. Still had conventional oil in with break in when it failed. SAME  #4 rod bearing

 

For sure many are going to read a description above and say..."that was my motor"!

 

So, i can conclude 2 things from my mishaps. PULL OFF track if you cant accelerate...this saves you money and time! #4 rod bearing likes to give up first! 

 

I DO NOT envy motor builders...it has to be a thankless job for the most part 

[MPR22]

Ron I have detonated a 1.6 to death.  The piston was chewed up pretty badly and it started to loose the rings, it went soft like i was loosing an alternator.  NO big rod explosion.  

I have burned a 99 from being too lean, valves went first and then it just started to lay down, no knock what so ever. 

 

Have seen several ventilations. A couple from improperly sized rods after a crank turning, not the builders fault, the machinist had a broken machine and didn't notice until several rods were mis-sized.  Catastrophic over revs will pull the rod apart and ventilate.  Not saying that is what happened but could be.  The oil pressure will drop when the rod starts to pull apart and soon thereafter blamo. 

[RWP80000]

Ron,

From what you have described it appears your failures are due to an inadequate supply of oil to the #4 rod bearing.  Probably the reason for this lack of oil supply was different in some/each situation.  The fact that it is always #4 indicates an oil supply issue as the #4 journal is the furthest from the pump supplied oil coming off the front of the engine.

 

As you mentioned, the engine operating oil pressure if a function of the system leaks (clearances) downstream of the pump output along with the speed (rpm) of the crankshaft turning the pump. Other than the the oil pressure relief valve, which can only act to bleed off pressure being delivered by the pump as a function of the spring tension behind plunger to hold it on its seat, the only other thing would be the viscosity of the oil being used. This also assumes the oil pump pickup is accessing a constant supply of minimally aerated oil.

 

Given the above, some reasons that the supply of oil may be in adequate at the #4 rod journal could be as follows;

-Engine oil level is inadequate to allow pump to provide adequate output resulting in aeration.

-Engine oil viscosity is to thin (or oil to hot) for pump to provide adequate output or an adequate oil film to be maintained at rod.

-Engine oil level is not adequate to allow pump to provide adequate output due to lateral forces keeping oil away from pickup tube.

-Engine oil pressure is inadequate to maintain an adequate film of oil between the rod bearing and crank journal.

-Engine bearing wear has increased operating clearances resulting in the operating pressure dropping below required minimum.

-Engine oil is excessively aerated resulting in oil film degradation at rod bearing/journal.

-Engine oil bypass plunger sticking open reducing supply pressure available.

-Engine clearances on average are excessive for the output of the oil pump being used.

-Combination of some of the above occurring.

 

Since you have not reported any engine failures while on the dyno, yet you have experienced very early bearing failures I would be focusing on how vehicle dynamics might be impacting your bearing life.  With your "long life" failures it may just be a case of clearances reaching the point where the oil pressure drops to the point that a failure occurs or it could just be the case of the engine oil level being allowed to get lower than usual resulting in the oil film being inadequate to sustain an adequate oil film.  

 

For the "short life" failures I would be looking at the build clearances, oil pump functionality (did you reuse the oil pump from a previous failure?), bearing quality, rod reconditioning quality.

 

We experienced rod bearing failures early on in our SM racing endeavors and now closely monitor our engine oil dipstick reading consistently before going out on the track.  We make it a point to never go out with the oil level below the full mark on the dipstick.  This means we frequently top off the oil level adding two to three ounces of oil at a time as required.  I have also found that it is very easy to get a bad reading due to oil in the tube getting transferred to the stick as it is inserted and removed.  This can easily result in a false "full" reading  I try to always get a cold "full" reading before starting the car each day as that is my reference point for tracking the rate of oil being used under race conditions. Since doing this it has been years since we have had a rod bearing failure with an SM.

 

Rich Powers

[Rob Burgoon]

 

 

In 6 years I have had 5 motor failures in 3 different cars(90,95,99)...every time it is #4 cylinder. All these motors had been dynoed and AFR was set in a safe/conservative range. Here are details...

 

 

 

Fire the driver, fire the mechanic, hire a witch doctor, order a new batch of mazda OEM filters and copy someone else's oil brand/viscosity.

 

 

[Steve Scheifler]

We have had one catastrophic failure with ventilated block, and it too was #4. That engine was fresh when installed but had multiple seasons and quite a few rental/loaner drivers along the way. No sign of contact between piston and head, or detonation.

[Bench Racer]

Thanks to all for the very informative experiences and knowledge.

 

We all know NA #4 cylinder runs hotter than the other 3 cylinders??? Partial cause of the #4 failure???

[Ron Alan]

Thanks Rich again! More questions and info...

 

 

 

If in fact running oil below 1/2 full is a potential problem...that could be an issue. I dont add until it is below 1/2 generally. Maybe a combination low oil and oil at the end of its life??? If in fact a real possibility...you may have just saved many future motors Rich by anyone reading this!! Pretty confident a motor will dyno better with low oil...but that may not translate to the track?????????

 

With few exceptions I've always run Mobil1 10-30(reasonable and available). 3-5hrs on average i think(2-3 events)

 

Not one failure was with the same driver.

 

Mazda bearings(first failure and known high amount of failures in country we went away from them). 2 other brands of bearings(One 2 metal, One 3 metal)

 

4 of the 5 motors were OEM oil pumps(2 original, 2 purchased from Mazdaspeed). 1 was OEM "cleaned and checked". Not from a blown motor.

 

Same machine shop and builder on all motors. I'm able to be involved in the whole process. Unless I'm clueless at what I'm looking at I see everything being checked meticulously. 

 

All motors had OEM(original/used)polished cranks...nothing machined(possible metal contamination in the hard to clean oil passages).

 

If in fact bad money shifts(3rd to 2nd instead of 4th or 2nd to 1st instead of 3rd)) can lead to bearing failure...a definite other possible cause! 

 

 

So, the 1.6 motor that started this thread was in one of my 2 entries in the 2015 25HR event this past month. As mentioned it was a fresh build and done at the same time as the motor for my other car(99 1.8). Same process, parts, oil, tuning everything leading up to the race. Only difference was the intermittent failure in the 1.6 harness that was causing the fuel pump to turn off briefly at high rpm and cornering. The 99 car ran like a champ for 25HRS and collected the win!

 

Before starting this thread i was getting mixed feed-back as to why the failure(as I have on past failures). It only seems logical all things being the same...the only difference may have been the root cause. BUT...it would seem even here there is a difference of opinion on this???

 

I dont know if I or others here can solve this but I for one always feel the need to learn and understand all possibilities, Any information is valuable and I'm sure will not only help me but others down the road. Keep your knowledge coming! Great stuff Rich! And Michael's comment on running lean with no adverse bearing effect is interesting...for sure I ran my 95(original OEM motor) for about 3 or 4 events very lean(opps!!). Found out when I dynoed and it was around 13.6 at the lowest...nice light tan plugs! This was after we were allowed FPR and I turned the regulator the wrong way thinking I new what i was doing...doh!!! That was 1.5 years before this motor failed!

[Steve Scheifler]

One thing I'm sure you can rule out is the oil being too old/degraded so quickly. But prove it yourself, are the other bearings showing clear signs of wear?
On the NB at the 25hr, how many times did you change the oil during the race? How do those bearings look?