Skuffed Piston WHY?

[JohnBoy]

Have 1995 ProMax 2.5 I re-ringed and cut the heads 14 hours ago. Never had any problems with it for last 200 hours before rering. Today I set the timing to 0 deg idle (use to be 8 deg BTDC and 25deg max (Use to be 23deg BTDC no advance module) Timing was rechecked again after melt down to be sure. I noticed that the EGT gauges were reading lower than usual by 100 degrees(1050) on one side and the other stayed normal at 1150 at WOT idle was around 750deg and crusing up to 5000 rpm stayed aroung 900 degs.. The boat ran great for 2 hours today then I made a pass at WOT for at least 2 miles while running a friend. As I let off I heard a slight slapping noise so i shut down. I started it back up and noticed it was not firing on all cylinders so I shut it back down and got towed in. A quick compression test showed a perfect 135psi on 1,2,5,6 with #4 at 122 and #3 at 5 psi. Took the heads off and all looks great but there is alot of piston skirt aluminum on the intake port side of the piston wall on #3. I have a bullet proof fuel system and pressure was at 37psi at all times and all else seems ok but number #3 and #4. Is there a possiblity that 3 and 4 are batch fired as a pair and thats it or injectors are going bad or clogged. Also noticed that all cylinders looked wet with oil except #3 which was very dry and the piston top was clean with lite pitting on the top #4 piston had some oil film but piston top was clean where all the other cylinders are dark brown. I will take pictures in the am if this will help. I plan to repair this next week and need any input on possible causes so this doent happen again. Any ideas are greatly appreaciated.

Thank You, John Smith

[Simon]

What spark plugs did you have in it? buz8h, or buzhw ? If you cut the heads and set the timing at 25 with buz8h plugs they are to hot.

[JohnBoy]

Simon the plugs are BUHW

[ImbadBob]

Injector fouling/ clogging killed my 260 last year. 3 & 4 are triggered together from the outboard powerpack . Lost # 2 on modified 2.5 200 from water coming from exaust divider gasket once. Have you injectors tested . If bad have cleaned and flowed merc is real proud of them. Bob

[JohnBoy]

I think I found the problem. I took the fuel rail with all injectors still installed and ran two hoses of #3 and #4. The I fired them with the fuel system at 37 psi. and collected the fuel in measuring cups. The #4 produced exactly 3/4 cup and #3 produced only 2/3 cup during the test peroid. I then measured different injectors against others and found that all are the same flow in cups except #4 which is very close to the rest and #3 that flows way slower than the rest. I believe this is what caused my skuffed piston. Now where do I send all 6 and get them cleaned and flowed??

John Smith

[XS4U7566]

Jay Smith posted this info the other day here is were you send your injectors for service Kinsler Fuel Injection Company, 1834 Thunderbird Troy Michigan 48084 Phone# is 1-248-362-1145 jay said the cost was $ 95.00 for six injectors hope this helps Greg.

[Propman]

Send them to Richard at Speciality Services 1-650 348 1106

[us1]

Look for water leaks. The low EGT on one side at WOT and a clean piston is screaming water leak to me. What did you set the ring gap at when you did the rings? Are you running a popet and thermostats?

[QUICKSILVER]

Jay can give you a NAPA # for the same injector that merc sells. NAPA around $60 merc $160.

[sosmerc]

A pressure drop test can also be performed before any dis-assembly to find a "major" fuel delivery problem. To further narrow it down to a particular injector you would have to perform a similar pressure drop test with the manifold removed so that you can access each injector for disconnect.
Needless to say, sending the injectors out for flow testing is a good practice before re-assembling after any major project. Using Merc's DDT tool makes doing a pressure drop test very easy on the laser style EFI systems and I do it as part of any routine tune up. It can also be done on high performance systems as well, but the return line must be closed off and all but one injector plugged in at a time for the test.
The EGT readings you gave might indicate that an ignition problem was occuring, and if it was lack of proper ignition voltage at either cylinder 1, 3, or 5 then two injectors would not be firing properly. No ignition or no fuel delivery would certainly cause low EGT readings.
The possibility of water entry is interesting. I'm not sure how that would effect EGT. Water is not compressible and thus compression would go up dramatically...would this not create more heat? Could this cause detonation-like damage? Or would it wash away all lubrication and cause scoring? I'm interested in what others think about water leaks and how they might effect EGT readings.

[sosmerc]

Just got through re-reading the initial post and a thought came to mind. I've heard many times about how failures seem to occur just as one "backs off" on the power after a sustained high speed run. I've read about this enough that I have been very concious to back off very slowly from a sustained high speed blast. If you watch your EGT carefully you may even notice that temps may go up slightly higher as you back off slowly...on my particular laser EFI 2.5 I run slightly warmer at 5500 RPM than at 6000 RPM. I pretty much stay away from 5500..either I run slower or I run higher, but for my particular setup I stay away from 5500.
My point being that you may have been running near the edge of leaness during your run and then as you backed off things got momentarily hotter due to the reduced cooling effect of less fuel as you backed off.
Maybe we should be rigging some type of switch that we could toggle after a sustained run to feed in a richer mixture for a short period as we back off...like opening the head temp circuit causing things to go 40% richer.

[sho305]

Did that on sleds all the time. Put in smaller jets to go faster, then if you were wot on a lake or road for a distance, you could flip the choke on since it was an enrichener jet. You needed this when it got real cold and it ran leaner. The button sounds like a good idea to me if you want to be safe.

Sounds like you found the problem here, but I have had that with intake air leaks too(not on an OB yet). You let off and it gets lean from the leak. Wonder how Merc efi syncs the throttle with the injector flow when you let off fast.

[JohnBoy]

Well tore it down today and it doesnt look too bad. All 5 cylinder walls and pistons look brand new. #3 is scuffed on both sides where the wrist pin goes through but the sleeve looks like it just needs a hone or possibally bore. I found a smakk peice of rubber hose stuck in the inlet of #3 injector. I just replaced the pressure line from my fuel filter with a stainless braided one. The small piece of hose probally came from the inside of the new hose as I didnt think to flush it out after cutting to lenght before installing it. All the injector will be sent out tomorrow for cleaning and flow testing. Anybody heard of leaving the injector screens out? Why would you do this? US1 I had my machine shop hang the pistons on the rods and check ring gap. I run a poppet valve and temp usuall stays around 120-130 degs. I will check for a water leak. Im posting a few pictures of the pistons and sleeve.

Thanks, John Smith

[JohnBoy]

Cylinder Wall

[JohnBoy]

Scuffed piston

[JohnBoy]

Picture of #2 piston top. This was the cleanest one on the top side.

[JohnBoy]

Another shot of piston. OUCH!!

[us1]

Yes, lets see a picture of the top of the #3 piston. If the top of the piston is not melted and the sides are seized it is not lean detonation. Although I do agree it sounds like you do have an injector problem on that cylinder. An over heated piston from water washing the oil off the cylinder or just bad cooling on that cylinder will cause a seizing situation with out detonation. The only reason I am harping on this is to get you to full check everything before reassembly. Many times in the past I thought I have found the problem when I was really over looking a more serious problem.

[us1]

Notice there is no detonation in the combustion chamber.

[JohnBoy]

US1 the top of #3 has small pieces of melted aluminum all over it so does the spark plug and the exhaust port only on that cylinder. The top of the piston has a melted portion missing down to the top ring only where the exhaust port is. I will still check for water leaks. I just installed new head gaskets before running maybe there is a water leak.

John Smith

[JohnBoy]

US1 The picture you see is #2 I will take pictures of #3 and post later tonight. I must go and eat at Moms house for Sunday dinner now.

John Smith

[JohnBoy]

Heres a shot of #3

[us1]

I still looks like piston expansion or lack of lubrication to me.

[Burke Kilgour]

If it was a lean burn-down, wouldn't the piston edge be melted away (or at very least rounded off) where the exhaust port is?
I agree with US-1, this does not look like a lean condition problem.

[JohnBoy]

More pictures. Look at all the metal on the top of the piston.

[JohnBoy]

Piston top

[JohnBoy]

Inside of exhaust chest #3

[sho305]

I agree, everyone I seen melted the top edge too from lean.

[JohnBoy]

I still think it detonated, but I'm open to any ideas. I have checked the cooling system around #3 and don't see anything clogged. The water pressure is around 17- 20 psi WOT and head temp has never gone over 130 degs in the middle of the summer. The small piece of rubber hose that jammed in #3 injector inlet had to of made that cylinder run lean. I tested #3 against #4 with separate measuring cups. Before disassembily I fired both 3 and 4 as a batch firing with a 9volt battery and measured the volume of fuel. #4 = 3/4 cup and #3 = 2/3 cup. This would make the #3 cylinder run lean on fuel and oil. I still want to make absolutly sure of the problem before I put it back together. US1 please look at new pictures and tell me what you think. If you still think it wasnt detonation then tell me what I need to start looking for

Thanks, John Smith

[JohnBoy]

Something esle I left out. I installed water diverter hoses 14 hours ago on #5 & 6. Would this cause #3 to run hotter or screw up the cooling system since I run a poppet valve and 1/8 washers instead ot t-stats?

John Smith

[us1]

That is a classic seized piston. I see no detonation. All the metal on top of the piston and in the exhaust port came from the side of the piston. Notice how it seized big time on the intake side too. I wish I had a detonated piston picture to show you but I just through out the piston from the last melted motor. I will look and see if I can find something. I’m not trying to give you a hard time, just don’t want to see it burn up again. I love steel sleeve motors, that’s what I specialize in.

[us1]

Here is a good detonation melt down. Look how you can see the whole ring from the top of the piston at the exhaust port. Also combustion chamber was so hot all carbon has been burnt off and replaced with aluminum.

[us1]

Just for fun here is what happens when a locator pin fall out of a stock 200.

[JohnBoy]

US1 your not giving me a hard time just valable information to solve a problem. What caused the piston to seize. Ring end gap which I trusted to someone else and didnt measure myself or heat from lack of cooling water.

John Smith

[sho305]

Maybe lean condition got it warm, then lack of oil trashed the piston before the top melted? Maybe not running wot enough to melt top?

[us1]

It could be a combination of things like extra heat from the injector blockage combined with a tight ring gap or tight piston clearance or even water. The cool EGT with reading down two or three hundred degrees at WOT usually means water but the piston does not look clean on top like water can do. What oil do you use at what ratio and what RPM do you run it at.

[JohnBoy]

sho305 this was the first real hard and long WOT run I did since a rebuild 14.5 hours ago. It was at least two miles and probally 45sec of 8000 rpm. It ran great until I let off all of the sudden. Then the engine stalled. Upon trying to restart the battery seemed low but it fired right up and ran on 5 cylinders so I shut it back down and got towed in. There seemed to be a light knocking noise from 3800 - 4800 rpm that sounded like detonation. I didnt pay any attention to it since everone says you can never hear them knock if you hear it it's already too late.

John Smith

[us1]

Now we are getting some where. You are turning 8000 RPM with a popet, not good. Is the 130 temp the water temp? Does this probe go into the water jacket? What is the type of oil and ratio? What size out the outlets on your drystack.

[JohnBoy]

US1, I use Pensoil 100% syn. at 40:1 and add a little extra so it is is probally around 35:1. I have turn this motor up to 8500 rpm never had any problems in three years. I decided to replace the rings 2 months ago due to a bad leakdown on #5 .Since the rering I have been very easy and never turned it up for 14 hours. I ran it hard and long at 8000 the last run that caused the seize. Thats another thing I reringed it and loose max rpm whats up with that.

John Smith

[us1]

Is the 130 temp the water temp? Does this probe go into the water jacket? What size out the outlets on your drystack. You were luck before.

[JohnBoy]

US1 the water runs single 5/16 hoses off t-stat housings and 1/8 fender washers. The poppet valve has a 5/16 hose off of it. There are diverters in 5 & 6. Water presure is very low under 5 pounds but 17-20 at WOT. The temp sender is in the head where the over heat alarm sender would be so its not in water but close. I can take my hand and hold it in the water leaving all water dumps. The poppet water dump is always the hottest. The water temp is unconfortable but feels like 110-115 degs since I can hold my hand in it. My unit is not drystacked. The one piece plate has four dump holes with no resrictors.

John Smith

[sho305]

I had a sled that did the exact same thing from a bad intake gasket. I ran it for a while-no problem(after fresh bore job, pistons, rings, all new). Then week later was doing WOT runs on road and it would kill when I let off. Then start and run fine. I was thinking sieze maybe, so I pulled exhaust and there were lines in the piston. I was able to sand it, and clean the ring land of the tiny bit in there. Was ok between the lines and cylinder was clean. Investigated and found tiny leak in underside of intake gasket. Figured for sure it was WOT hot, then lack of oil/fuel when I let off (at high vacuum in the intake so it sucked air good) that did it. It was just enough to barely sieze it. Your lean injector could do the same. Many motors will knock at lower rpm torque range, then not at high rpm so it might not have detonated at 8000rpm.

Also if you where at 8000rpm and let off and the injector stopped(may not hardly work at all at idle if restricted), then you had the motor coasting down hot from 8000rpm with that cylinder dry! That could do it by itself.

Would check out water temp thing just the same, seems like it woud show though on gauge. Lower EGT could be from weak fire in that cylinder.

If that injector was bad from the git, then it might go faster when fixed:)

A ring could have been tight, but in 14 hrs....shoulda been ok. the new rings still are tight, that could be rpm loss, as well as your problem here. That injector could have been weak the whole time.

[us1]

It this were mine I would run .007 piston clearance for Mercury pistons, .022 ring clearance, no popet, Mercury oil for steel sleeve motors and never go less than 32 to1. I have learned the hard way form any deviation from this.

[us1]

How tight are the heads.

[JohnBoy]

That perticular bank the gauge usually read higher than the other side by 100-200 degs. The exhaust temps where alway the same 1150 at WOT except this time it they where different, The left side was lower. Hell I was running almost 100mph I tend to only look down for a 1/10 of a second. The EGT gauge could have been at 1400 and I wouldnt have seen it. I do know as soon as it acted funny and stalled I looked at the water temp and it was 110 deg. I am starting to think I need to check ring gap next time and I plan on sending the injectors out for cleaning and flow testing. Then I need to make the correct mods to the cooling system. US1 poppet at 8000 rpm bad thing? should I remove it and plug the weep hole? I ran the poppet valve for three years was I just lucky? I know no 260 horn motors have poppets is there a reason for this?I will send you full pictures of my mid section, exhaust plate, block and heads and you can tell me what I need to do to the cooling system for the intended RPM. This motor has turned 8500 with a small prop but I run a larger prop now and would like to keep it lower than 8100.

John Smith

[JohnBoy]

US1 the heads are stock I think. I have 135 psi compression with thin gaskets, but thats on my gauge and I don't know how accurate it is. My friends 260 horn is about 140 psi on my gauge he has 34cc heads.

John Smith

[us1]

I’m not sure I understand. In you first post you said you cut the heads 14 hours ago how could they be stock. No race motor Mercury produces runs a popet because over 7000 RPM it restricts water flow and the pistons will start to seize.

[JohnBoy]

The cut heads was 5 or 10 thousands I believe but not sure. It only gave me 7 pounds of compression from previous readings and then some thin gaskets. Thats my mistake I ment around stock compression 135psi. Also #4 is down on compression 123psi compaired to 1,2,5,6 at 135 +/- 1.

John Smith

[us1]

Did you get the ECU richened for the thin gaskets and cut heads. Those laser ECUs run on the edge of detonation already.

[JohnBoy]

No the ECU was not touched. It is analog and has an adjustmant screw on the back side. I don't mess with it. It is the ECU from Project Laser and was sold to me by Mark when he parted out his motor. I remember in that article he lost a couple pistons from fuel delivery problems. Hold on we where talking about the piston did not detonate it seized from cooling problems or lack of clearance or ??.

John Smith

[us1]

Originally posted by us1
It could be a combination of things like extra heat from the injector blockage combined with a tight ring gap or tight piston clearance or even water.

[JohnBoy]

OK I just got back from the machine shop and it is a combination of things. After looking at the block and piston heres what they say. The #3 cylinder was very lean it is pitted all over the top of the piston and the spark plug is much whiter than the rest. The block has a cooling problem. It is running too cool. the clearances that they set it up for needs a minimum of 125 degs water temp and should be around 140-150deg WOT. I was at 110 when the problem happened and I usually run under 110 which is way to cold. The combination of a lean condition on #3 made the piston swell and the sleeve was too cold which caused clearence problems and it to seize. Also there is a small amount of damage to #4 from a cold seize that happened sometime during the 14 hour breakin it will need honing and replace the rings. #3 will get a new sleeve and piston. the shop is going to lend me thier ECU tester so I can set the rich/lean when I get it back together. I was told that the washers I have in the t-stats are too big and that both t-stat housings need to go to the same hose then out instead of two separate dumps from each t-stat. The poppet valve needs to be removed. It has a dump hose on it that would normally go to the top of the block but was routed out the cowl. they also told me that this was not a stock block. the port heights are higher and someone has done some porting work. So now I need to figure out how to make more heat in the cooling system. The injectors where sent out today to Kinsler for clean and flow test.

Thanks, John Smith

[us1]

Just have them set all the bores at .007 for Mercury pistons and you will be all set for 110 water temps.

[sosmerc]

Anyone have any experience or thoughts about lead substitutes with regards that it might provide some extra cushion to prevent scuffing such as in the case we have been discussing?
Does anyone think that piston engines are more sensitive now that we are stuck with unleaded fuel? Or am I all wet in that 2 strokes have oil in the gas that should meet all lubrication demands.

[JohnBoy]

US1 I want to thank you for posting most of last night to solve this problem and thanks to all that replied. I will ask the shop to set the clearance to .007. Also Kinsler will test #3 injector before cleaning for a couple extra bucks and let me know if it was clogged or it was just the piece of rubber hose caught in the inlet. It all makes sense now. On a laser motor #3 and #4 injectors are aimed at their respective reed cage but the fuel can cross over between the two. Being that #3 injector was not flowing correctly it leaned out #3 bad and leaned out #4 a little too since #3 clyinder was stealing a little of #4's fuel charge(man that was a mouth full). Thats why the EGT gauges had slightly different readings and why both #3 and #4 cylinders got scuffed. I guess if the clearance was .007 then it would not have seized but would have eaten the top of the piston with a little more time. Thanks to all that replied and I will post the results of the injectors and should have it back together and running in 8 days.

John Smith

[myron]

also if you are going to turn that motor 8000 I would put some SPS rod bolts and replace the plastic caged bearings with ones from the Hi-Perf motors. I would also go to a digital ECU. You probably have an A-18 and they have a bad lean spot in the mid-range.

[us1]

Myron has some excellent advice there. I would consider running Mercury oil because of the steel sleeve at 32:1 also.

[H2Onut]

That was a great read !

[sho305]

I have read a thousand times that 2 strokes do not care about lead. They only care about octane being enough to stop the detonation(of couse lead will raise octane). The lead only lubes valves, and I think it does little of that or every old car motor would have blew all the valves out long ago!

I think us1 is right, in that you have a clearance problem. Need to clearance for the temps you run. Not knowing what temp works best for your Beastly Merc motor....guessing us1 knows these things. Aluminum piston grows a lot in there at WOT with the HP you are at. Obviously the lack of fuel/oil caused that one to puke; unless somehow that cylinder had a different clearance. Most builders check/set them all the same unless a particular cylinder runs way hot/cold due to design/cooling setup. If the rest are good, than it was pretty close. Never takes much to puke a motor making way more power than it was supposed to....dammit! Anything lean always makes a grenade out of a 2 stroke in my experience. My uncle ran rc planes, and they had to set the motors rich as they would seize when they ran out fo fuel otherwise.

[Mark75H]

Think about this: Deisels never had any lead and have tremendous pressure loads on the pistons/rings/bearings. Also great heat loads on the exhaust valves and seats.

Guess what? Most of the lead stories are just that: stories, urban myths.

Tetraeythl lead was just there to increase octane, so they didn't have to make the gas as good (ie: mo' money, mo' money, mo' money).

[GGAARR]

Originally posted by QUICKSILVER
Jay can give you a NAPA # for the same injector that merc sells. NAPA around $60 merc $160.

Jay,

Do you or anyone else in the forum have the NAPA # for fuel injectors to fit a 1994 Merc 200 XRI.

[steve]

If you have the ECU with the rich lean pot on the back , then its the Mod VP box. Thats the only analog I know of with the pot. Thats a race box and it is much more prone to being lean in the midrange. Compared to say a ProMax 225 box, the curve is similar but the midrange is much leaner for acceleration. According to Sean at Rapair here is the order of leanest to richest in the mid----ModVP, A17 ProMax 225 original ( was recalled for blowing motors), A32( ProMax 225 later), A23 ( this is the ProMax225 OS/SS box). Your own post mentioned that the previous owner of the box had blown a few pistons. You are lean at some point on the curve. An stock A32 or A 23 with the rev moved would be a good move. Plus its Digital. My 2 cents

[Markus]

The additional lubrication you get from metal in the fuel is extremely small compared to the lubrication from the oil. However, some people believe in it; I believe the Yamalube TCW-3 sold in the US has molybdenum in it to the same effect, although stronger. In addition, I found some other company making TCW-3 with moly a long time ago. There is a link on my links page if anyone is interested. However, as I said before the "dry" from the metal is insignificant compared to the "wet" lubrication from the oil.

To build on what Mark75H said: The stories you hear about gasoline being worse than it used to be because it does not contain lead any more is pure bs by people who do not know much about fuels. (I never hear them in Europe, by the way, only in the US). Today's gasolines are cleaner and better than ever.

[sho305]

I thought the lead thing was bs too. After seeing old cars and old small engines run on it for years with no problems except the spark plugs and exhaust lasted way longer. Then they said the valves would go bad, right. Valves went bad anyway on old stuff. But I shut up while people kept on about that.