Engine teardown - 300+ hp with highish miles
 

Just pulled apart my old engine that I just replaced .

Why i pulled it out :

*was hardish to start and was running low vacuum at idle
*Every now and then under boost I would hear this knocking sound . After hearing this - it would cease running on one rotor altogether and run like shit . I would let it cool down and then restart it and it would run fine again. We dubbed it the "healermotor" because of this weird behaviour .

Conditions of use :
*Had 60,000 kms of hard running with an upgraded Greddy turbo at 11 psi of boost 320whp peak power and around 260lb/ft torque.
*Ran on 5w40 synth oil changed every 8000kms or sooner
*Set OMP to 1/2 normal useage
*Ran Castrol 2T premix at the rate of 250-300mls every 50Litres (200:1 minimum)

A little bit about the engine :
*This was a rebuilt engine with mostly second hand parts used .
*We installed Esmeril apex seals - which are softer than stock . They seem to be unscathed.
*We did some mild porting of the exhaust ports and a bit of a cleanup of the runners.

Pics and failure analysis to come ...........

Housing 1 : note cracks around spark plug holes
https://www.rx8club.com/attachment.p...1&d=1362968480

https://www.rx8club.com/attachment.p...1&d=1362968480
Housing 2 : cracks starting to appear
https://www.rx8club.com/attachment.p...1&d=1362968480

https://www.rx8club.com/attachment.p...1&d=1362968480

Rotors in good shape with minimal carbon buildup
https://www.rx8club.com/attachment.p...1&d=1362968480

Front iron - note gouge at side of exhaust port . This was by far the worst damage - 1mm deep at it's deepest point.

https://www.rx8club.com/attachment.p...1&d=1362968766


Rear iron- same gouge , not quite as bad
https://www.rx8club.com/attachment.p...1&d=1362968766


Centre Iron - same gouge , just started to form .
https://www.rx8club.com/attachment.p...1&d=1362968766

Front Bearing - down to copper in one spot
https://www.rx8club.com/attachment.p...1&d=1362968766


Rear bearing - even worse.
https://www.rx8club.com/attachment.p...1&d=1362968766

Can't wait to see! Always love to see failure modes.

This one might surprise you :)

Failure and wear points and points of interest:
*No signs of any overheating
*Cracks around sparkplug holes
*small grooves around circumference of housings in centre
*Wear at point where split apex runs
*Gouges in all but one exhaust port (rear centre) as shown
*Chaffing of irons where housings have been moving during compression cycle
*Front and rear bearing wear
*Esmeril Apex seals seem unscathed apart from some wear on the side where it slides on the rotor.

Main failure mode is the gouging of the exhaust ports . This could have been the knocking noise I was hearing as the corner seals were knocking in and out of the gouge.

I think I know why the gouges happened but would welcome any theories .

My first guess was apex corner piece, but it's a common mode failure on all the housings. Dunno how it was ported, but maybe the side seal was dropping in the port. Eventually it shattered and was carried around in the grove gouging the housing the whole way. Your right this one is interesting!

I'd like to hear some more educated guesses.

There is no mechanical damage to any of the seals -although there is wear evident in the corner seals corresponding to the gouge in the front housing .

Here is my theory :
There was minor port work done on the two outer exhaust ports and both of these are badly worn . There was no porting done on the centre exhaust port . One centre port is damaged but not anywhere near as bad as the outers. The other is unscathed.

I think the slight reduction in land width (on the outer ports) at the point the corner seal is over the port had a huge influence on the occurrence of this damage .

Wow... Ok, completely stumped. Something had to carry around to cause those wear marks. Doesn't follow the path of any of the seals. The eye shaped pastern has me the most confused. Still a great brain teaser.

The gouges follow the path of the corner seals exactly .... and so does the eye pattern

as documented on the Pettit site, the exhaust ports expand/flair when subjected to turbo thermal loading and then the corner/side seals take the brunt of it

porting it is a double edged sword

No sign of overheating around the ports - which is what Pettit were saying was the cause.....

The fact that the ported ports fared far worse than the unported , points more towards the land size being the issue to me . That and perhaps the increased loading from higher combustion pressures.

Unless your seeing a different eye pattern I don't see how a corner seal could have cause it. Corner seals always follow the outside of the housing they never cross over. The eye pattern does correspond to the approximate center of the side seal though, or maybe part of the scraper ring.

brain fade - yes of course . I was thrown off by the way the pattern follows on from the gouges .

you aren't boosting to 370 whp, so the effects are less

that's what I was saying about porting the exhaust being a double edged sword, you can try and reduce/compensate for the flairing, but then that's more thermal loading on less material plus the issue with porting increasing side seal abuse

also not sure why you would cut the OMP rate in half with only 200:1 premix ratio

also forgot to mention that IMO the bearing where to me indicates detonation issues

Learn something new every day. Thanks for sharing!

Housing wear does not seem that bad actually . I cut it in half for upper load areas (where lots of fuel is pouring through) but by about 1/3 under low load/cruise .

I was leaning toward insufficient (stock) oil pressures as the wear looks similar to high mileage NA engines . what makes you say detonation was a cause ?

because it will pound the bearings down to the copper

if you say so, but I would run more pre-mix with the OMP maxed out for upper load areas

Admittedly there was some bad detonation early in the engines life but certainly there were only a few events. Maybe two or three times max.

that you knew of, or anyone else including NA engines ...