Fried Cylinder - inside view with high 10x magnification

[Imjus4u2nv]

I was driving my boat when day when it my Mercury 90 HP Inline six "tower of power" started smoking, got towed in and took the spark plugs out - found one plug from the #3 cylinder had melted aluminum, a sure sign of an overheat. I still am not sure what caused the overheat and that is what I am trying to figure out.
The cylinder is not firing but can be fired with a little work (likely just need a new ignition coil).
Compression good in all six cylinders and all at or around 130 psi (cold engine).
I took some internal video of the #3 cylinder, as well as the #4 cylinder (as it runs on the same carb and I was hoping to see if maybe I was running to lean). I also have video of #2 cylinder to compare them to.
I have no clue what I am looking at in these videos so any input would be helpful. I am hoping to get that #3 cylinder up and running but don't want to risk it ceasing up, it has been running pretty good on 5 cylinders. I figured I would try the video before taking the transfer ports off for a better view of the side of the cylinders.

The #3 cylinder can be seen here and is the worst of the cylinders (3 videos):
http://www.youtube.com/watch?feature=player_embedded&v=PHdcoSGTx5U
http://www.youtube.com/watch?feature=player_embedded&v=PHdcoSGTx5U
http://www.youtube.com/watch?feature=player_embedded&v=tJmZPx0Cz40

The #4 cylinder runs on the same carb and can be seen here (1 video):
http://www.youtube.com/watch?feature=player_embedded&v=oVvNW6cavqE

The #2 cylinder runs on a different carb then the #3 and #4 cylinders and can be seen here (2 videos):
http://www.youtube.com/watch?feature=player_embedded&v=BKj6bCMqxzo
http://www.youtube.com/watch?feature=player_embedded&v=oVvNW6cavqE

 

[CharlieB]

Re: Fried Cylinder - inside view with high 10x magnification

Lean combustion was beginning to melt the piston.

When two cyls share a carb the lower cyl tends to run 'slightly' richer while the upper tends to run 'slightly' leaner due to fuel 'fall out' in the air stream, which is why Merc jetting is 'slightly'' overly rich, so as to prevent those upper cyls from getting so lean as to melt pistons.

This tells me you may have a problem with that middle carb. Carb rebuild kits are cheap enough, get three and go thru the carbs meticulously. Making double sure the floats are adjusted perfectly. If you still have the old cork floats replace them with the newer style plastic floats.

While dealing with the fuel system, rebuild the fuel pump(s). Some 6's had two.

You were very lucky to have caught it before a serious melt down.

Edit; Most of those style carbs have an inlet fuel screen, be sure it is clean, or remove it and install a water separating filter on the boat.

 

[Imjus4u2nv]

Re: Fried Cylinder - inside view with high 10x magnification

CHARLIE- thank you that is some great advice. In your opininion, since compression is still good and engine still running, do you think if I get the bad cylinder up and running and keep it cool (by rebuilding carb and new impeller) it will be alright. Wondering whether better to run on 5 cylinders or to attempt to get it back on six.
Thanks again and any other input is welcome!

JAred

 

[Faztbullet]

Re: Fried Cylinder - inside view with high 10x magnification

A defective trigger will take out #3 also..

 

[CharlieB]

Re: Fried Cylinder - inside view with high 10x magnification

A defective trigger will take out #3 also..

So it may be a good idea to mark the flywheel and check timing on each individual cyl to ensure each is firing at near perfect time, i.e., one pair is not overly different from the other pairs.

If it was an over-heat from a lack of cooling generally the sides of the piston would be smeared onto the cyl walls more so than the top of the piston burned. The alum on the cyll would impare the ring seal and show a compression loss.

Your damage was from excessive combustion temp from a lean mixture, or as Fazt noted, possibly incorrect cyl timing. Which should also endanger the counterpart cyl on that trigger, #4. I didn't look at #4, it is blackened same as 1, 2, 5, and 6?

 

[Imjus4u2nv]

Re: Fried Cylinder - inside view with high 10x magnification

Yes 4 is blackened also but not as bad (in my opinion).
WHERE IS BEST PLACE TO FIND CARB REBUILD KITS?
Right now engine is running really rough. Think first step is to get all cylinders up and firing (need a new ignition coil I believe as no spark to #3 cylinder). Was also gonna rebuild carb's but did not know best place to get a rebuild kit- Any advise? It is a MERCURY - ( 90 H.P. (1986 ))
Serial No: 0A968445 Model No: 1090726.
I think I will get all cylinders firing, rebuild the carb's and then if still no good check the trigger and timing (because this seems the toughest and don't know how to mess with timing/flywheel removal and will have to get mechanic for that).
Sound like a good approach?

 

[CharlieB]

Re: Fried Cylinder - inside view with high 10x magnification

I like to look up fractory part #'s at Merc parts, then I am free to search all the aftermarket cross references from the factory #.

Compare part price plus freight. iBoats has a pretty decent selection available.

The #1 web site for genuine Mercury Mercruiser engines, parts and propellers

 

[quicktach]

Re: Fried Cylinder - inside view with high 10x magnification

I'm curious - how did you get the pix inside the cylinders ? What camera and device ?
Thanks

 

[Imjus4u2nv]

Re: Fried Cylinder - inside view with high 10x magnification

I like to look up fractory part #'s at Merc parts, then I am free to search all the aftermarket cross references from the factory #.

Compare part price plus freight. iBoats has a pretty decent selection available.

The #1 web site for genuine Mercury Mercruiser engines, parts and propellers

I honestly did not know iboats sold parts, always just use the forum. I just purchased to ignition coils from Iboats (with shipping was pretty close to the cheapest and I know it will be the right parts). Thanks for the response.

 

[Imjus4u2nv]

Re: Fried Cylinder - inside view with high 10x magnification

Lean combustion was beginning to melt the piston.

When two cyls share a carb the lower cyl tends to run 'slightly' richer while the upper tends to run 'slightly' leaner due to fuel 'fall out' in the air stream, which is why Merc jetting is 'slightly'' overly rich, so as to prevent those upper cyls from getting so lean as to melt pistons.

This tells me you may have a problem with that middle carb. Carb rebuild kits are cheap enough, get three and go thru the carbs meticulously. Making double sure the floats are adjusted perfectly. If you still have the old cork floats replace them with the newer style plastic floats.

While dealing with the fuel system, rebuild the fuel pump(s). Some 6's had two.

You were very lucky to have caught it before a serious melt down.

Edit; Most of those style carbs have an inlet fuel screen, be sure it is clean, or remove it and install a water separating filter on the boat.

Gonna have all three carb's rebuilt by a backyard mechanic at my marina, he is only gonna charge me 100 buck in labor to rebuild all three, the kits I will get from him also ($50 bucks each), I know I can get them cheaper but seems like my carb's are not factory (can tell they don't line up perfect) so easier to let him get the rights parts even if I could save a few bucks.
Uncertain how to rebuild the fuel pump (is this difficult, if so how much you think it would cost to get rebuilt including parts).
If these fixes don't work, will then move to the trigger as faztbullet suggested, although since two coils were no good I am hoping this was the issue.
The ignition coils will be put in Saturday morning, and the carb's right afterwards- will post update afterwards, thanks again guys!

 

[Imjus4u2nv]

Re: Fried Cylinder - inside view with high 10x magnification

I'm curious - how did you get the pix inside the cylinders ? What camera and device ?
Thanks

Bought it off ebay from china for 15 bucks, the instructions were in foreign Chinese but was able to figure out how to use it- really good quality for the price
10mm Mini USB Endoscope Inspection Camera TMP Waterproof Borescope Scope 2M | eBay

 

[CharlieB]

Re: Fried Cylinder - inside view with high 10x magnification

Does this look like your carb?

http://www.mercruiserparts.com/Show...N/38416.png&inbr=278&bnbr=10&bdesc=CARBURETOR

It is possible that the carbs have been replaced by a later model, and/or from a larger HP motor in attempt to boost HP a bit.

The jet size should be a good indicator.

Notice near the bottom of the page between items 32 and 33 you will see
Gasket and
Repair Parts Kit
These are your parts, notice prices.

Also, if the floats are still cork, replace them with the current floats made of plastic.

$50 X 3 for parts plus $100 labor, he's definitely pushing it.

iBoat carb kits 16.33 ea

Mercury Carburetor Kits - iboats

Check your motor here, see the carb #'s listed, then check your carbs to see the casting #'s.

These carbs are not hard to clean/rebuild/adjust.

 

[Imjus4u2nv]

Re: Fried Cylinder - inside view with high 10x magnification

CharlieB-
The picture you showed looks like the one I have but have to take a better look, it does not match the carb in the seloc manual (I know I need to get a mercury manual) as it does not have the carb filter on the top portion.
He is removing them, rebuilding, reinstalling and then will tune them for me. He is also replacing the float and all the other parts as opposed to just the gaskets so not sure if that would justify the price of the kits. I know I had priced them for about $30 bucks a piece, but he was able to rebuild them this week so I figured for a few extra bucks I may be able to get out fishing this week (not to mention ordering the right rebuild kits). Still seems like I am getting taking? Either way he already has them off so no going back now.
I know adjusting the carb's is not that difficult, but with a near fry-out of one of my cylinders because it was running to lien, I would prefer to let someone who knows what they are doing tune it (he also said he would show me out to tune it and how to winterize). If the carbs need to be rebuilt again (how often should they be rebuilt/cleaned?) I will be back for some advise (I was worried about correct float adjustments etc).
Will know more on Saturday- wish me luck! trying to hit the backend of the striped bass run in NY.

 

[CharlieB]

Re: Fried Cylinder - inside view with high 10x magnification

Sometimes we pay for convenience. If it enablbes you to get after the stipers this weekend, well, you can't really put a price on that.

Install a water seperating filter between the fuel tank and motor, it extends time between cleanings years.

When the motor will not accelerate near as well yet idles fine, and seems to run fine once on plane, then it may be time to clean the carbs again. Religious use of fuel stabilizer, and SeaFoam at the maintenance mixture, plus that water separating filter, I've seem some motors will over ten years without failure other than annual gear oil, and an impeller every other year.

Be religious about fuel quality and cleanliness, this is one of the most important factors. If the fuel gets much over 90 days, drain it and use it in your truck or lawn mower.

 

[Imjus4u2nv]

Re: Fried Cylinder - inside view with high 10x magnification

Responded earlier but never posted for some reason.
CHARLIE- thank you for all your help.
Already got the water separator installed, changed filter earlier in the season. When winterizing, should I change filter in fall or the spring?
I did a decarb with seafoam twice, but never used stabilizer, I will start to use that also (I am usually out a few times a week, sacrifice sleep for fishing lol). Do you fill the tank up to winterize? Seems to be two school of thought, some have told me leave it near empty and refill at beginning of the season while others say fill it up and use stabilizer. I had an issue prior trying to dispose of bad gas (two stroke pre mix so no use for it).
I am also planning on draining gear oil to winterize and refilling. Was going to change the impeller at the beginning of next season (would you do it now or in the spring?. Was also wondering if gear oil was self contained (can take lower unit off to replace impeller without draining lower unit oil).
Sorry for more questions!

 

[Imjus4u2nv]

Re: Fried Cylinder - inside view with high 10x magnification

Maybe I am just paranoid, but went down to the boat today to check on the carb work that was getting done - and up uncertain if he actually rebuilt them.
Looks like the carbs were never took off, although all the fuel pipes and other stuff was disconnected. Also was some orange rubber substance placed in a few spots, and an empty can of carb cleaner. Called the mechanic, he said he had removed them and rebuilt them at the boat. Told me the bottom carb float was gunked up but top two were pretty clean.
Is there anyway of telling if he actually rebuilt them. Prob just being paranoid here but want to make sure before paying him. Will try a bolt on one of the carb's and see if loose, but was wondering if any other way of telling if work was done.
Thanks again all!

 

[CharlieB]

Re: Fried Cylinder - inside view with high 10x magnification

Most all outboard gearcases are self-contained, there is no other gear oil. Changing oil in the fall to be sure any water contamination is removed before freezing weather.

Fuel tanks, empty is good, even if there is a small amount of water condensation the water separating filter should handle it.

Impeller change in the spring so it doesn't set all winter with half the vanes cramped.

2 stroke fuel will still burn just fine in a lawn mower and in most vehicles. The oil will burn, you won't notice the smoke as any oil fumes unburnt will be burnt in the cat. No problem.

 

[Imjus4u2nv]

Re: Fried Cylinder - inside view with high 10x magnification

Great info.
Checked the carbs this morning before I replaced two ignition coils. Going to meet the "mechanic" Sunday to have finish connecting fuel line and throttle , and tune the engine.
Was unable to confimr if he removed them but bolts holding carb on were hard to "crack" which makes me suspicious. Wanted to open up and check for new float but no room to open unless I pull the carb off (should have done this myself as Charlie said, doesn't seem hard and now I don't know what was done.
I could tell the idle screw was not replaced (not that it prob needs to but if he had the parts why not replace). Also, the yellow tube in the carb (the Jet?) Was not replaced, is this something that is/shoulod have been changed?
I assumed with $50 in parts I should have mostly new parts.
Will wait till he gets it running Sunday, then try to see if I can get some answers (don't want to accuse him, but want what I paid for).

 

[CharlieB]

Re: Fried Cylinder - inside view with high 10x magnification

Idle mixture needle/screw is re-used, jets are cleaned and re-used unless damaged, and are not included in carb kit which mostly contains gaskets, fuel feed needle and seat.

Floats sold separately. No external obvious parts unless you can see the edge of the gaskets.

 

[Imjus4u2nv]

Re: Fried Cylinder - inside view with high 10x magnification

Thanks again Charlie- was down at the baot with the mechanic, it appear he did the work as promised and att his point just going to have to assume he did.
PROBLEM- replaced ignition coils, the replaced coils are still not firing (#1 and #3). As mentioned earlier, is the trigger the next thing to check? Figure it can only be the switch box, the stator, or the trigger. My crappy seloc manual has instruction for testing the trigger and stator (if I can figure out how to use my voltmeter/ohms meter, but not sure how to test the switch box. Is there a way of testing the switchbox, or what would you recommend as my next step. I check the coil grounds and have a good ground, also appears to be about 12 volts (if I remember correctly) getting to the positive on the ignition coil (should this voltage be higher)?
As always any help is greatly appreciated. Worst part is, can't tune the carbs until I get it firing on at least 5, but aiming for all 6.
THANKS ALL!