Jump to content

Photo

O.K. - So I Blew My Motor...

- - - - -

  • Please log in to reply
5 replies to this topic

#1
bmarshall1

bmarshall1

    Member

  • Members
  • PipPipPip
  • 230 posts
  • Location:United States
  • Region:SW Florida
  • Car Year:1999
  • Car Number:23

Not sure I mentioned this yet, but last time at Sebring my motor let go, no bang, just an immediate loss of power and a LOT of smoke, I got off the track OK and the weekend was over.  Upon initial look, no oil leaks, no hole in block, it looked like a catastrophic head gasket failure with oil in the radiator and spewed around the motor compartment.

 

I removed the motor yesterday and WOW, in the intake tube and airbox were small chunks of aluminum and part of a piston ring!  These parts made it backwards through the manifold (and butterflies), through the MAF, and into the intake tube (with lots of oily radiator fluid).

 

Cylinders 1 and 2 are holding water in the intake tracts, cyl 3 has aluminum chunks in the intake track, and cyl 4 has 1 intake valve to piston contact and missing 1 head.

 

Short of physical damage from the metal parts coming back through, would the MAF and other parts be OK to use considering being exposed to the oil/water mix?

 

Not sure of the cause at this time but will be installing a spare motor.  Perhaps this weekend I'll tear the motor down and see the rest of the damage.

 

Thoughts on cause.  I know hard to say w/o seeing but I am leaning toward overheating or a lean cylinder, maybe injector issue.  Any clues to look for?

 



#2
chris haldeman

chris haldeman

    Veteran Member

  • Members
  • PipPipPipPipPip
  • 890 posts
  • Location:Mckinney
  • Region:texas
  • Car Year:1999
  • Car Number:73
1.6 car? Edit never mind I saw your other post stating 99.
X-factorracing.com
3 podium finishes
2 2013 NASA nats
1 2013 Scca runoffs
Donor - Made PayPal donation Bona fide - A bonafide Spec Miata driver BFG Supertour Winner - Circuit of the Americas Winner - Majors Winner - Make it Rain - Made Paypal donation of $100+ We have a Winnah! - Won their 1st race... Congratulations!

#3
Steve Scheifler

Steve Scheifler

    member

  • Members
  • PipPipPipPipPip
  • 2,617 posts
  • Location:St. Louis
You may never know with any certainty but from what you have stated so far I’d put most my chips on a dropped valve, probably snapped at the retainer (which you would find on disassembly but wouldn’t necessarily be the initial event), or a bent valve that then stuck open and then got the head snapped off next revolution, pieces circulating from there.
Bona fide - A bonafide Spec Miata driver

#4
bmarshall1

bmarshall1

    Member

  • Members
  • PipPipPip
  • 230 posts
  • Location:United States
  • Region:SW Florida
  • Car Year:1999
  • Car Number:23

Someone mentioned jumping the timing; since the motor is locked, there is no way to align the timing marks on the cam pully/gear.  Is there a away to check this from a purely random crank position?  Once again, not that all this matters...

 

How about a possible overrev on downshift, sending the intake valve into the piston (is this a thing?), possible holing the piston and breaking off the valve head?



#5
Steve Scheifler

Steve Scheifler

    member

  • Members
  • PipPipPipPipPip
  • 2,617 posts
  • Location:St. Louis
To the first question, no, but I seriously doubt the belt jumped any teeth prior to other events unless it was already exceedingly loose. Perhaps Jim, Chris or others will correct me on NBs but it certainly wasn’t a thing on the 1.6.

On the second, yes, possibly, and what I described in the second half of my post above. First contact in a mechanical over-rev probably doesn’t hole a piston on these engines but does bend a valve. Remember that what’s happening is the valve exceeds normal travel due to high velocity then hangs open a bit rather than following the backside of the cam lobe. Hence the common term of “floating” the valves. When the piston catches it hanging there and makes contact there is little resistance from the valve because the cam lobe is already gone, so it gets slammed shut and relatively little damage is done. That can cause it to stop seating properly, but nothing breaks, at least for now. But if it’s hard enough to bend the shaft further up and/or break the guide, then the spring can’t pull the valve back closed so the piston gives it a mighty whack the next time and something has to give. Another variation is that the valves don’t float but the connecting rod literally stretches enough that the piston taps a valve that isn’t floating (and therefore puts up more resistance). I do not know if that’s a risk on the 1.8. On the 1.6 the risk of rod stretch during over-rev is that the piston makes direct contact with the head itself (outside the combustion chamber bowl). This occurs when the block has been resurfaced to increase compression and/or to correct for core shift during casting. It’s why for years Sunbelt used pistons with a lower compression height (wrist pin located higher in the piston), allowing them to true the deck, optimize compression and increase quench without shaving the head surface. It also lead to serious issues for anyone later trying to rebuild those engines, which was common because they made some serious reliability compromises as well. All against the rules of course. But I digress. :)
Bona fide - A bonafide Spec Miata driver

#6
bmarshall1

bmarshall1

    Member

  • Members
  • PipPipPip
  • 230 posts
  • Location:United States
  • Region:SW Florida
  • Car Year:1999
  • Car Number:23

Thanks Steve - All go info.  The timing belt is tensioned what seems to be the right amount to my calibrated finger.  I am always interested in information and appreciate the help this forum offers. 

 

The engine had a good run, it's what came with the car back in 2012, was of unknown heritage, and was losing compression in a few cylinders already.  Considering the car's other faults, I'm surprised it lasted this long and it was ready to come out anyway.






0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users