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 ...

The whole thing looks like lack of oil. Think about millions of turns with little oil. It will slowly machine the materials away.

No premix gets down to the side seals that's why Mazda
pointed those oil squirters to the side seals.

I think team is referring to micro pings. The ones that still occur. Small enough that you can't detect it but big enough to cause wear issues.

That would be plausible if ALL the ports were gouged - but they aren't .

not trying to argue with you, we all have ideas and opinions, when it comes to turbo Renesis most of mine come from builders a lot more smarter and experienced than me

Thanks for sharing. Would be interesting to see future breakdowns from other ported engines.

The housing seems to have a lot of wear which is interesting seeing you used a milder seal. the use of second hand parts may skew some of the results.

Running a heavier lubricating oil without increasing the oil pressure bypass limits, will cause a reduction in oil flow (compared to stock). Flow increases directly with rpm until the bypass opens, and from then on is constant. Since increasing the viscosity increases the oil pressure at a given rpm, it results in the stock bypass opening at a lower rpm, giving lower flow than stock above that rpm.

The Mazmart/RX-7 mod allows the volume to increase with rpm pretty much all the way to redline. :rock:

^+1 Just having the same discussion with someone else.

that's all fine & dandy, until you get into the discussion of what the issue is; too little flow or too little viscosity?

further, even if you have extra flow do you really know where it's going? It doesn't necessarily mean it's flowing more everywhere.

the subject is more complex than the typical forum member seems to realize, comparatively speaking a 2-rotor engine doesn't have that many bearings to keep afloat

Brett...

What viscosity of oil did you use?

IMO...a lot of the bearing issues have to do with the shaft balance of the stock motors....If yours was anything like mine before I had it balanced I'm surprised it didn't shake itself to oblivion ;) I noticed a huge difference in the way the engine spun up after it was balanced

0W40 was posted earlier

I didn't consider the balance issue, good catch

Thanks for sharing man.

Yeah that is quite a bit a bearing wear for those miles. Was it balanced when it was put together last time? It really is important, I don't know why some do not think so. Also what type of 5W40 was used? This is why I am leaning towards all new stuff on my next engine rebuild. If I rebuild a Renesis anyway.

so whats for the future?
have you ever conidered putting an rx7 13b with the renesis outer housings?

Stop it. Just stop.

just saying; i know it seems hard but its been pulled off.
The exhaust ports are ideal for boost.

Shady says those exhaust ports were opened up a bit much. We are experimenting with opening the inside a bit more and smoothing that out and leaving the overall size relatively stock.

Anyways I've seen that same wear pattern on the bearings in 4 renesis engines now.

I am sold, factory balancing is not up to par. There is a good chance this is whats been causing engine failures when all seals are intact. Could be a good amount of factors involved though.

As these engines start dropping out of warranty more and more we will start seeing companies and shops jumping in with theories and solutions. Should get interesting here in a few years.

Just stop dude, you don't have a clue what you are talking about.


Yeah and I think team is right about the detonation issues, we have no real way of identifying pinging unless we hear it.

No that engine was not balanced and neither was the one i just put in :( . Think I'll do the oil pressure mod though - on the off chance that may help the situation .
The latest engine had no porting done plus it had practically new parts installed so should last a bit longer .

i see that bearing near pattern on all the non-Rx8 engine's i've torn down, the bearings don't wear evenly, especially on the rear main.

detonation WILL cause extra wear, and it'll be out of round too

Interesting, were those assemblies all balanced at a facility or just weight matched from the factory?

its a mix, most were probably factory assemblies, some are rebuilds, some are just stat gears in a box of stat gears.... we've got lots and lots of torn down engines @ the man cave.

the pic is from the competition prep book from 1979, the Renesis actually has all of the comp specs already, except the oil pressure, but you see that they took steps to keep the rear of the rear main from wearing 34 years ago....

competition book is here, http://foxed.ca/index.php?page=rx7manual#firstgen

I believe the coolant passages don't line up with the newer 13b housings. Unless you go with first gen RX-7 housings. Again, this is if I recall correctly.

sub

Another factor in the bearing wear is that I don't believe the bearings were replaced at the rebuild so they will have a lot more than 60000 kms on them. They may even be the original bearings from the original engine which means 180,000 kms . I assume the builder did inspect them and deem they were serviceable though.

Yeah using parts of varying stages of wear and then not balancing it will just insure that you will be doing this every couple of years :) More time to experiment, :lol:

yeah , I'm regretting not getting this last one balanced now . My engine builder wanted to do it but I actually talked him out of it ...... doh !