Finally started getting my grey 185 ready for the road. Had all the symptoms of ringlands. No.3 very low compression and No.4 slightly down.

Both pistons had broken ringlands, but no signs of Det. on the piston top with the eye (although the camera plays some funny tricks with the flash).

Both this failure and the previous one occurred on events involving loose surface / low speed and a lot of time sat on the rev. limiter with wheels spinning.

Wondering if the failures could be heat related rather than det. related as the ignition map is pretty conservative at the top end as I run 95ron on the road / Vpower for events.

_________________
If at first you don't suck seed, try drier grain.

any signs of pickup on the bores?

Not that I noticed

_________________
If at first you don't suck seed, try drier grain.

High rev sudden grip and loading could be the cause. Also prolonged bouncing of rev limiter causes very high stress to piston rings and lands...

Well, the plot thickens.

Failure once again, pretty major this time in under 1000 miles from replacing No. 3&4.

Compressions now 160/165/0/160

I have confirmed that the ecu DOES NOT cut fuel during rev limiting (checked with sillyscope).

No competitions during this time.
No hitting the rev limiter.
I tweaked the 7000RPM cells very rich to cut power/cool things down and used this as max RPM (self limit)
Running max 1.15 bar boost

To summarise:

secondhand 205 engine fitted, and given hard use before failure after a year or so.

Failure 1: - no oil smoke from breather, just 3 cylindering on idle & low throttle. Compressions all normal. cylinder 4 appears to be faulty cylinder (by removing plug leads)
Stripdown reveals broken ringland on No.3 only.
Light hone on all 4 cylinders. Replaced pistons 3 & 4 with secondhand ones of same size. Used original rings on all 4.

Ran well for quite a time, including swiss trip where overheated a few times. Finally started 3 cylindering after a competition where it was on the rev limiter a lot.

Failure 2:
3 cylindering, hard to start, some oil vapour from breather but not massive. Compression very low on 3, slightly down on 4 (~10psi down).
Ringlands gone on 3 and 4.
Honed bores 3 and 4 and fitted secondhand pistons & rings. 1 & 2 left untouched.
Bore 3 had a patch next to bore 2 where the honing didn't touch intitially (warped bore I presume). Ended up honed a fair bit more than No. 4 .

Engine ran very well for a few 100 miles. Started to smell of manky oil whenever on boost. Made 307BHP on the rolling road. Then noticed low compression on 1 cylinder when starting cold (starter speed not even)

Failure 3:
Very quick deterioration over last 50 miles or so, from a stream of oil vapour from the breather on boost to steady stream of vapour when cruising and bonnet looking like it had a bucket of oil thrown over it. Compressions 160/165/0/160 so it's good ol No. 3 again.


So the question is, what could be causing it ?

The rolling road confirmed that mixture was plenty rich enough.
http://www.gt4dc.co.uk/forum/viewtopic.php?t=4993

Not stripped the engine yet from the 3rd failure, but the past 2 times showed no signs of det. on the piston top, plus (and I think the torque curve confirms) the timing is fairly conservative especially at the top end. It was mapped on 95 RON for road use using vpower for events for safety margin.

Could the problem be that the mapping is too retarded causing overheating ? but then if it were a mapping issue, why is it always No.3 (and 4)

It had a different head fitted after failure 1, with 800cc injectors so I doubt it's an injector issue.
No misfires / rough running which would indicate an issue with injector drives.

Other thing I'm wondering if it could be related to the cylinder warpage in No.3 causing extra blow by / local overheating.

Looking for ideas really, as I need to decide whether to chuck another secondhand piston in (quick & easy) or whether I should drop the engine & box and swap to a good 185 bottom end I have.
Alternative is that I have a forged engine (+.5mm) with cracked block and a spare block, but at the moment money is tight for spending out on machining etc.

_________________
If at first you don't suck seed, try drier grain.

Another point that may be relevant, ever since the 205 engine was fitted, I've found it very hard to get consistent AFR readings while mapping. Also on the RR day, it appeared my AFR gauge was in error as it was mapped on my gauge at 11.5-12 and showed on the dyno probe as 10.5-11. Could this indicate a problem of unevenness within the engine ?
Although the head,cams & injectors have been exchanged, the manifolds and block/conrods/crank haven't.

_________________
If at first you don't suck seed, try drier grain.

How retarded is it?
I was running 10 degrees of advance at the top as there were some disturbing noises coming down the det monitor (Subsequently partly diagnosed as worn big and little ends)
I wouldn't want to run much less than that for fear of cooking something with high EGTs

I suggest whatever you do fit an egt in #3 when you rebuild. JP found a cheap option (ciirca 70 IIRC including sensor) that has a nice little display and datalogging outputs

Inconsistent AFRs sounds a bit like a misfire issue to me

sounds like issues with blowby in bores to me causing localised heating that combined with 205 pistons is killing ringlands...

n.b dont seem to see many 185 pistons with broken ringlands ???

I have heard of ringland failure on 185's. Bear in mind a much smaller number of 185's run 1.2 bar boost as it requires many mods to do so, plus most of those that do won't be running the same power at the top end due to cam/turbo/injector issues.

I have added screenshots of ign & fuel maps to my dyno thread.

http://www.gt4dc.co.uk/forum/viewtopic.php?t=4993

I have subsequently taken a bit of fuel out of the top end (now reads 12-12.5 on my AFR) and added a couple of degrees more ignition at the top end. This may have killed it, although I'm pretty sure the damage was done prior to the RR.

_________________
If at first you don't suck seed, try drier grain.

Orf with it's head. Looks like I'm lucky to still have a working turbo.

No signs of det. damage on the piston.

Area of failure is 90 degrees round from the area of bore that's warped so I suspect not related.

Looks more like a brittle fracture than melting, but difficult to tell until I take the piston out.

_________________
If at first you don't suck seed, try drier grain.

Just 1 word - ouch.

The bits of ringland are nowhere to be found, although I haven't dredged the oil yet.

Looks to me like cracked ringlands led to blowby and overheating / melting of piston.

Note the thin slivers of piston metal stuck in the oil ring.












No. 2 and No. 4 were both in the early stages of ringland failure. No. 1 looks ok.





Interestingly, I re-jigged the injector drive just before surrey RR (after I noted the smell of rancid oil). Previously, I have run 1&2 from drive 1 and 3&4 from drive 2 and run 1 injector cycle per engine cycle. I changed it to run 1&4 together from drive 1 & 2&3 together, and changed to 1 injector cycle per crank rev. A problem with drive 2 would be consistent with the piston No.s failed. It would also be consistent with my strange AFR readings.

Thanks to Steve & JP, I have hopefully now found a cheap enough source of thermocouples to measure EGT on each runner, so I can look for signs of mixture problems in individual cylinders.

_________________
If at first you don't suck seed, try drier grain.

My bet is pre-ignition triggered off the tip of the plug given the location of the damage. Probable cause either weak mix or oil laden load. If it were purely hot burn related I'd expect those wussy little valve cutout bits to let go first. I'd also be expecting signs of det that caused the high burn temps

Don has one the same (I think) that I believe is caused by fuel pump failure (again pure conjecture) but he's too busy mucking about with old fords to take it apart

I have stepped away from my 'old Ford' to say the only reason we havent pulled my blown 3S-GTE apart is because I dont expect many uself parts to be left inside after it pumped most of the contents of the sump into my WTA and turbo compressor!

Regarding the suggestion to fit EGT's to monitor temps the race engine guys reckon that this wouldn't give enough time to save the engine. IMO you really need to monitor individual cylinder AFR's if you want to prevent this type of failure. This would allow individual cylinder trim and is what a lot of race teams do. Its probably expensive and tricky to set up quite apart from being overkill in an autotest spec ST185.

_________________
Don
GT4DC Chairman
1994 Toyota Celica GT-Four ST205WRC JDM 269bhp @ 0.9bar
1994 Toyota Celica GT-Four Special GT 590bhp @ 1.8bar
1989 Van Diemen RF88/89 Formula Ford 1600
2008 Nissan Patrol GU 3.0L ZD30DDTi 154bhp

Agree the EGT would be too slow to react in a 'fuel failure' scenario. I was thinking more in terms of diagnosing fueling inconsistencies between cylinders.

There was no shortage of fuel in the car, and no misfire. It was a steady, although fairly rapid at the end, worsening of the ringland symptoms.

_________________
If at first you don't suck seed, try drier grain.

After much discussion, I'm still not much wiser. Several people have looked at the pistons and agreed there is no sign of det. The failure was progressive over a few hundred miles, although the last 50 or so saw rapid deterioration so I'm not suspecting a single pre-ignition event. The only other thing I can think of is excessive heating of the pistons, which in view of AFR's I can only see hapening if some cylinders are running rich while others are running lean.

Now put the bottom end back together with 185 pistons and a light hone. Bores are looking pretty war-torn now The block's already scrap but would like to try to diagnose the problem before fitting a good engine, especially if it's a forged one.

To that end, I have invested a HUGE (:lol:) sum of money on 4 EGT sensors which will hopefully give me a clue as to whether 1 or 2 cylinders are running much hotter than the others.

Thanks Steve for the tip-off for cheap sensors:

http://www.auberins.com/index.php?main_ ... 1ac37cfefd

Not the perfect sensor for the job, but I'm on a limited budget at the moment. Just need to build 4 thermocouple amplifiers now.

_________________
If at first you don't suck seed, try drier grain.