Piston meltdown... again

[jumjum01]

Blew left piston again on my RD350 ypvs EFI bike. Seems I cant get get it right. Piston burned on exhaust side at 8 o'clock seen from exhaust side. Keeping EGT below 550 deg. celcius, but still blown on freeway. LH cylinder, piston og plug is gray, while RH is brown/tan.

If LH crankseal was leaking air causing a lean condition, would this affect EGT?
Anyways I have blown the motor apart and changing all seals incl.crank seals. Crank is straight and good, but out of balance by 5 grams (measured with simple rotation setup using the crank bearings. Balance is now corrected at the flywheel and I am looking forward to see if the bike has less vibrations once its back on the road.

[kpke]

That really sucks. Sorry to see this. Seems the EFI is a different art than carbs.

[RZtuner]

That sucks! Looks like an air leak caused that. Do you pressure test the engine after assembly? What's all that black stuff smeared around the gasket? Are you using black RTV sealant on the head gasket? Much better to spray the gasket with a thin coat of high temp copper coat and let it go tacky before assembly.
With all that debris damaging the head, be concerned about damage to the crank.
550 deg on the EGT should be quite safe.

Tip: I set my EGT gauge to read in F deg. The larger numbers compared to degrees C gives you a more accurate reading, especially at speed.

[kobra]

What spark plugs are you running?

Definitely seems like an air leak.

[(F5)]

That's some real ugly detonation that has eaten the piston like that.

Ok assuming something queer isn't happening. Like an airleak, so test. Or one combustion chamber isn't smaller than the other, measure, or the crank is twisted to advance that side, measure with dial and gauge; then you are going to have to accept that cylinder needs more gas poured into it in those conditions.

You could buy a knock guage and compare cylinders. You can even feed into an Ignitech ignition the output and automatically back ignition off a few degrees if it registers knock.

Actually, check how aggressive your curve is at that point.

So we are talking 5000rpm at 1/2 throttle on the freeway (think about exactly where)? What happens when you back off? Powervalve down, closed throttle but mid revs and not much gas going in? Bikes often seize on closed if pilot is too small. EFI has to play the same game.

I bought what I thought was a decent EGT way back. It only sort of made sense at full throttle, full revs.

Apparently you need certain probes on a 2 stroke to get effective reading quick enough to see a sudden change. Mine weren't good enough. I also don't know how well they will tell you about cruising. I was never interested on race bikes.

After your measurement I'd try more gas, less timing, slightly opened pv; all at trouble revs and throttle opening as a starting point.

[kenny]

Look at water ingress too as that eats the front edge of the pistons along sudden lean fueling. Did it go onto reserve? If not then look at water. I cant see any detonation on the pistons I see marks from a ring that has broken up as the upper groove has been eroded away, causing the ring to snag and break up. Check is the head is perfectly flat on that side. EGT only works from a know datum. You need a perfect setup first then fit an EGT and thats the figure you look for for future readings.

[jumjum01]

I must admit that I did not pressure test engine after first melt down. The head gasket was a 3-layer with 1 layer removed to set proper squish and I applyed Treebond just in case since a had this in stock. The crankshaft is fine but have not checked for twist yet, but I will measure with dial. I am running BR9ES plugs. Combustion chamber volume is (was) equal, I checked with syringe and water before assembly.
Meltdown happend after accelerating in 2,3 gear a couple of times and then resuming crusing at 90km/h in 6 gear at 20-30% throttle. Then it lost power and started making rattele noises (pistion ring fragment playing ping-pong against cylinder head). EGT temp dropped on Left cylinder and Right went up. Fuel tank was close to full. When accelerating through gears and EGT got close to 550 degrees I have always pulled clutch and mild reved the engine to lubricate engine (tip from dyno guy) and it seems to lower EGT quickly.
After looking at the crankshaft seals, the left seal seems on the sloppy size. New ones are on the way, but I might do a pressure test on old seal to find the culprit.
Ignition timing is controlled by the microsquirt EFI ecu and run same ignition map as Zeeltronic PCDI module, but sligtly retarded

[RZtuner]

The 2 layer gasket compromises the gasket sealing ability a lot... and 3 bond is a no no for head gaskets. You are much better off using the stock 3 layer head gasket and machine your head for required squish and volume accordingly.... Or just accept a slightly larger squish clearance and live with it. It's not a race bike! Stock gasket is super reliable and used on all my race bikes.

The crank could be twisted after the first seizure and make short work of new crank seals if you use the crank again. Program your map to the OEM ignition map to rule out too much advance issues until you get it fully sorted.
Pressure testing is essential after every build.
Hope this helps!

[kobra]

I must admit that I did not pressure test engine after first melt down. The head gasket was a 3-layer with 1 layer removed to set proper squish and I applyed Treebond just in case since a had this in stock. The crankshaft is fine but have not checked for twist yet, but I will measure with dial. I am running BR9ES plugs. Combustion chamber volume is (was) equal, I checked with syringe and water before assembly.
Meltdown happend after accelerating in 2,3 gear a couple of times and then resuming crusing at 90km/h in 6 gear at 20-30% throttle. Then it lost power and started making rattele noises (pistion ring fragment playing ping-pong against cylinder head). EGT temp dropped on Left cylinder and Right went up. Fuel tank was close to full. When accelerating through gears and EGT got close to 550 degrees I have always pulled clutch and mild reved the engine to lubricate engine (tip from dyno guy) and it seems to lower EGT quickly.
After looking at the crankshaft seals, the left seal seems on the sloppy size. New ones are on the way, but I might do a pressure test on old seal to find the culprit.
Ignition timing is controlled by the microsquirt EFI ecu and run same ignition map as Zeeltronic PCDI module, but sligtly retarded

Always always pressure test. And if you're being really particular, vacuum test too.

One other thing to check is fuel tank venting. My cap was plugged by design (and the charcoal canister vent was also plugged) so I think that contributed to my meltdown.

[silverstrom]

On April 18th I told you that your plug chop looked very lean. Your engine failure shouldn't be a surprise if you seized it without addressing the very lean plug indication.

viewtopic.php?f=1&t=17212

[MK]

As we run pretty comparable setups I could point to one significant difference.
Your stinger diameter is MUCH smaller than mine. This leaves a lot more heat in the pipe and increases the risc of temperature related problems like deto or melting things.
I rather sacrifice some HP for reliability.

And the part of being on WOT, having it closed and then continue on medium rpm with low'is throttle position is kinda problematic condition for an EFI without load indication. Remember alpha N is always using the same amount of fuel for the same rpm and TPS.

What may have happened:
EGT sensors are rather slow when they're of the thicker sort. So 550 may not have been your real equilibrium temperature. It could have been higher.
I have 3 mm and 1 mm K type sensors and the latter ones react much quicker to changes (and are faster on equilibrium temp).

WOT cleans out residual oil and fuel that usually collects in the crankcase. As a consequence it runs somewhat leaner than usual after a WOT period.
Plus WOT puts a lot of heat in your engine and closing the throttle shuts up fuel supply which significantly reduces inner cooling.
And then you already try to get pretty lean in that range because the engine runs good & saves fuel with an AFR of some 14 - 15 in the low TPS range.

My guess would be that a combination of these things lead to a piston not knowing where to get rid of his heat temporarily and voila - you got your meltdown.

Unfortunately your pics are a bit too small, but the other side looks like it'd have some slightly visible detonation marks. This may have happened at partial load triggered by lean mix.
For example the Aprilia 250 race bikes had a burnout ban from the teams side, because they'd seize in an instant due to detos when being on high rpm and not WOT.

[Questo vecchio rz]

The 2 layer gasket compromises the gasket sealing ability a lot... and 3 bond is a no no for head gaskets. You are much better off using the stock 3 layer head gasket and machine your head for required squish and volume accordingly.... Or just accept a slightly larger squish clearance and live with it. It's not a race bike! Stock gasket is super reliable and used on all my race bikes.

The crank could be twisted after the first seizure and make short work of new crank seals if you use the crank again. Program your map to the OEM ignition map to rule out too much advance issues until you get it fully sorted.
Pressure testing is essential after every build.
Hope this helps!

Amen.. Plain & simple. So So many if not most RZs here and other venues have died here over the years when guys start adding programmable ignitions and or advanced timing with compression increases....
For anyone other than hardcore racers, I just don't recommend it.

I'm not familiar w your setup, sounds as if your using a alternate ignition system.

RZs perform reliable and quite well at stock or close to stock. The risk vs reward ( for most average people) just isn't worth it vs the FRANKLEY minimal power increases.
But I get it if you don't classify yourself as "average".

Also regarding plug chops, While still practical .Many of today's fuels don't give a traditional reading , do your research and proceed carefully .
If your programming your own alternate fuel and ignition systems .then you likely know this already...but just adding to what some here have mentioned

[MK]

Not every ignition with more advance is devil's work.
Some of them are TPS controlled and retard at lower throttle positions like described in the very first post.
Tech guys call that an ignition map.

[JanBros]

So So many if not most RZs here and other venues have died here over the years when guys start adding programmable ignitions and or advanced timing with compression increases....

you want the burn-time to be as short as possible. original ignition is not going to help you doing that. so if you've set up/tuned your engine in a good way, it should run best with less advance, not more. more advance is for 4-strokes who need it because they rev higher.

so don't blame the programmable ignition for human faults.

[jumjum01]

Thanks for all your inputs..
Both my intake boots where warped and had leaks guess that would be the main culprit. Today I have fabricated new intake using R6 boots, guess I shuold have dont this from day one All though the plug chop test fails to show the brown ring at the ceramic, i am fairly confident that the afr is decent. My wideband afr reading sensor, the dyno shop wideband afr reading and the spark plug color (new plug for WOT only) looks good.
I cleaned up the RH side piston and add a pics. New seals, new powervalves and bushings are in transit from UK to Denmark. This time I will pressure test the motor, how many psi?