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BaitThrower
10-06-2010, 03:59 PM
While out fishing the other day I took off from the ramp with my tinny and Yamaha 30CV outboard...

About 100 metres from the ramp I get this high pitch sort of ticking/pinging sound... then a few seconds later the motor starts missing and cutting out like its running on one cylinder... Anyway I quickly head for the closest shore and make it before it cuts out altogether... No paddling needed :)

After sinking 40cm into the mud on the shore I pull the cowl off and look around... Doesnt seem to be any external damage or anything loose etc...

So I pull the spark plugs just to check those.. Top one looks fine... Pull the bottom one off and WTF! The ground pin or whatever that bent bit on top is called has been bent right over and almost touching the central electrode thingy (excuse the technical terms). There was virtually a hair's gap between the two.. Aha! this has to be the problem (the symptons were logical for that problem), although I had never seen anything like it... I did perhaps have the plugs torqued up a little too much and perhaps they were extending into the clyinder too much, but even so they should have suitable clearance. I was using the correct plugs with gap set correctly as per specs... but this bottom plug gap was virtually closed.

So I crack open a set of two new plugs (NGK BR8HS-10) and put them in, carefully checking not to overtighten too much... Fire her up and she is back running at full power. Decided this was definately the problem and kept going and no trouble all day...

So, has anyone else had this happen before? I had never seen it and though it was quite odd!

bigjimg
10-06-2010, 04:08 PM
Can't offer any suggestions as to what may have caused that to happen but they are the same plugs that the Merc/Mariner 30hp takes.I've had the plugs fail internally that make the motor fire intermittantly.Every thing looks fine on the outside and hard to trace until you replace the plugs and the motor runs as it should.Jim

FNQCairns
10-06-2010, 04:09 PM
While out fishing the other day I took off from the ramp with my tinny and Yamaha 30CV outboard...

About 100 metres from the ramp I get this high pitch sort of ticking/pinging sound... then a few seconds later the motor starts missing and cutting out like its running on one cylinder... Anyway I quickly head for the closest shore and make it before it cuts out altogether... No paddling needed :)

After sinking 40cm into the mud on the shore I pull the cowl off and look around... Doesnt seem to be any external damage or anything loose etc...

So I pull the spark plugs just to check those.. Top one looks fine... Pull the bottom one off and WTF! The ground pin or whatever that bent bit on top is called has been bent right over and almost touching the central electrode thingy (excuse the technical terms). There was virtually a hair's gap between the two.. Aha! this has to be the problem (the symptons were logical for that problem), although I had never seen anything like it... I did perhaps have the plugs torqued up a little too much and perhaps they were extending into the clyinder too much, but even so they should have suitable clearance. I was using the correct plugs with gap set correctly as per specs... but this bottom plug gap was virtually closed.

So I crack open a set of two new plugs (NGK BR8HS-10) and put them in, carefully checking not to overtighten too much... Fire her up and she is back running at full power. Decided this was definately the problem and kept going and no trouble all day...

So, has anyone else had this happen before? I had never seen it and though it was quite odd!

sorry mate she blew up, basic lean out or scored bore/coked ring lands trashed a ring on the exhaust port.

FNQCairns
10-06-2010, 04:37 PM
sorry mate she blew up, basic lean out or scored bore/coked ring lands trashed a ring on the exhaust port.

Oh, ok I just read the whole report, you may have spat a portion of a ring, otherwise i dunno strange things happen.

i would purchase a cheap compression tester from an auto store and see whats up, if nothing then forget about it unless simply interested and you pull the head you may find little dents...from that tinkle sound you heard...still the tinkle could have be pre combustion.

compression test.....

Noelm
11-06-2010, 09:32 AM
only a couple of things will cause that, if the motor is original and never been apart, then the things that can cause are not good things, first, a bearing has failed and the piston is able to come up a bit further and flatened the plug, or as mentioned, something has broken off a piston and when bouncing about (causing the funny noise in the process) and has hit the plug end and closed the gap, neither of these things is going to be fun or cheap, because the motor runs now, (without the noise) I would reckon that the piece of piston/ring is the culprit, and the offending bit has been burned to bits, or luckily shot out the exhaust, remove the bottom plug (the one that was closed up) and get a small torch and have a snoop inside to see if anything looks "bad" if you cannot see anything, then a head removal is in order, but do not continue to run the engine, you may turn an uncomfortable reapair bill into a new engine.

BaitThrower
11-06-2010, 09:57 AM
eeek ok thanks for the advice. I have a compression tester and will do a test and post results today. Will also peek into bottom cylinder and see if I can spot anything unusual.

If it was a bearing, wouldn't it have done the same to the new plug I installed after running it again all day?

Noelm
11-06-2010, 10:09 AM
yes, and also the noise would still be there, that's why I suggested the piece rattling around, mind you, it may have just been a small blockage causing it to run very lean, but you need to know, if the piston has a bit missing, or part of a ring has come off, it is only a matter of time before it just lets go altogether, a compression test MAY pick it up if the difference is big, but an inspection is a far better option if possible.

BaitThrower
11-06-2010, 10:36 AM
Ok I just took out the plugs (which were a new set with only an hour or so on them as per initial post) and they look ok... Normal tan colour on insulator and otherwise fine.

I shone a torch into each cylinder and I can't see anything abnormal... Each cylinder head does have a bit of carbon build-up on them however and are quite dark (its a 2002 model). But I couldn't see anything out of the ordinary and no bits cracked or loose etc (as far as I could see through the spark plug hole anyway).

I compression tested both cylinders are they both read pretty much identical at 120 PSI.

Thoughts?

BaitThrower
11-06-2010, 10:38 AM
yes, and also the noise would still be there, that's why I suggested the piece rattling around, mind you, it may have just been a small blockage causing it to run very lean, but you need to know, if the piston has a bit missing, or part of a ring has come off, it is only a matter of time before it just lets go altogether, a compression test MAY pick it up if the difference is big, but an inspection is a far better option if possible.

There wa sno further noise that is for sure... I did notice the trip before when it was making that noise that I did have a bit of an air leak in the fuel hose fitting which may have caused it to not get as much fuel as it should have been... would that make any difference?

Otherwise see my post above with results of quick inspection and compression... Thanks for the ongoing advice too!

Noelm
11-06-2010, 10:40 AM
it might be your lucky day then, whether you remove the head to have a good look or not is your decision, it may have just been bad luck (or good luck) and you had a bit of crap block a jet and run it lean for a bit, but the choice is yours really, run it and hope, or remove the head and investigate, being a 2002 model, it might be time to remove the head anyway to check for salt build up and a proper inspection. Running lean may explain the noise, but not the plug being closed!!

BaitThrower
11-06-2010, 10:59 AM
Yeah I will give it a bit of a run in the river next time where I am not far from any shore or the ramp and see how it goes. I rarely run the motor WOT so it doesn't get abused much :)

I might also run some Johnson/Evinrude Engine Tuner through it to clean up the pistons and hopefully the carby, or i'll investigate pulling th carby for a proper clean.

Will check for salt buildup too at some stage but no signs of engine overheating as yet or the like and the pump seems to work fine. I pulled and replaced the thermostat just as a standard sort of service item and when I did so, there was no sign of any salt build up or major corrosion in and around that part of the motor so I suspect the rest might be relatively clean too...

Anyway as mentioned, next trip I will take it easy and be on the lookout for problems and address as required.

finga
11-06-2010, 11:13 AM
It times like this is when a bore scope is handy.

Noel...do you reckon a big wod of carbon coming off the crown could have closed the spark plug gap??

Baitthower...was there an obvious mark on the leg of the spark plug where something hit it??

STUIE63
11-06-2010, 11:29 AM
The high pitched noise describes how a yammie I had once sounded when I didn't have the fuel line hooked up . the fuel pump really ticked loud .
I can't explain the plug though unless a piece of carbon came loose
Stuie

BaitThrower
11-06-2010, 11:54 AM
Finga, No real obvious sign of a hit on the spark plug, just kind of bent down like the gap had been narrowed... same shape and same oritentation etc etc.

Stuie, Hmm ok, yes it is like a high pitch tick and it was consistent, i.e. like it would tick at fast but regular interval, but it would not stay ticking, just tick for a few seconds and then go away when I increased throttle, so maybe it is the fuel pump ticking?? And come to think of it, the speed of ticking seemed relative to the throttle too, so if I throttled up, it would tick faster, throttle down and the tick was slower...

cormorant
11-06-2010, 11:58 AM
Look closely at that plug again - could be a piece of the porcelian that cracked away and jammed for a minute in the bore. That would be a bad one and you may have got lucky and it got spat out the exhaust. After a can of engine tuner have a good look at the top of the piston with a decent penlight torch and if you see any indentations I'd keep a close eye on the compressions and a set of decent oars in the boat. Gaps can close and it usually hapens with rough installation of plgs where they get banged against the plughole on teh way in.

Silly but check it is the correct plug for the motor as different plugs have different reach.

Running lean with air being sucked in a fuel line can generate huge combustion chamber heat and teh edges of pistons can come off along with piston skirts.. A borescope may help see it it is the piston but there would be indentations in the rest of the piston where it did a little dance

You sure there was oil in the fuel and fuel was fresh?

Look at your butterflys in the carbies and see if there is any difference. Some brands still use a screw to hold on the butterfly and it wouldn't be the first to come undone and get sucked through the motor of jam in a crank bearing before getting spat out. Same for a peice of a reed valve - torch down carby to check if obvious and screws that hold reeds in place.

Check inside the cowl. Have had similar noises from cowl insulation rubbing on flywheel and also wiring loom etc not placed back where it should have been and rubing or blocking teh advance

The other cause which is common for the noise is the pull starter ( squeal) where it doesn't release properly , rubs etc. Have a good look at it as on other brands they can drop a circip and they then rest on teh flywheel . Not sure on a yami how they are connected. Warning that there is a spring in there that will take your finger off or a eye out so if looking be very carefull and gave a look at the parts diagrams first. Check tension on bolts that old down pull starter and if it has a electric start option check the gear is sliding up and down the input shaft cleanly and has all teeth while also springing back to where it should.

Unknown noises can bring tears to the eyes but go looking for the cheapest and easiest options before pulling stuff apart to narrow it down and going to a shop and have a engineer look at aborescope is a cheap option after that.


PS

With plugs out turn it over by hand and see if it is smooth , back and forward to see if there is any slap , chatter, flywheel side to side in case it is a crank bearing. It would have to be bad to discover it this way but easy quick check anyway.

Ps ya sure it was from the powerhead not the gearbox? Check the oil down there for smell ( burnt) and too many metal flakes or water in there.

STUIE63
11-06-2010, 12:11 PM
Finga, No real obvious sign of a hit on the spark plug, just kind of bent down like the gap had been narrowed... same shape and same oritentation etc etc.

Stuie, Hmm ok, yes it is like a high pitch tick and it was consistent, i.e. like it would tick at fast but regular interval, but it would not stay ticking, just tick for a few seconds and then go away when I increased throttle, so maybe it is the fuel pump ticking?? And come to think of it, the speed of ticking seemed relative to the throttle too, so if I throttled up, it would tick faster, throttle down and the tick was slower...

Next time just disconnect the fuel line you will hear the pump click . see if it is the same sound
Stuie

BaitThrower
11-06-2010, 12:12 PM
Look closely at that plug again - could be a piece of the porcelian that cracked away and jammed for a minute in the bore. That would be a bad one and you may have got lucky and it got spat out the exhaust. After a can of engine tuner have a good look at the top of the piston with a decent penlight torch and if you see any indentations I'd keep a close eye on the compressions and a set of decent oars in the boat. Gaps can close and it usually hapens with rough installation of plgs where they get banged against the plughole on teh way in.

I'll do that... the noise has been there for a few trips, but it is only there every now and then and lasts for just a few seconds so its not a conitnuous noise...

Silly but check it is the correct plug for the motor as different plugs have different reach.

Definitely is the correct plug, verified by the manual and the sticker inside the cowl itself.

Running lean with air being sucked in a fuel line can generate huge combustion chamber heat and teh edges of pistons can come off along with piston skirts.. A borescope may help see it it is the piston but there would be indentations in the rest of the piston where it did a little dance

I suspect it was running lean for a trip or two because I discovered a air gap in one fo the fittings that probably got slowly worse...

You sure there was oil in the fuel and fuel was fresh?

Yes it was definitely fresh fuel and yes definitely oil... It is recommended to run at 100:1 and I rarely bring it to WOT (mostly cruise at 3/4 and nothing more. In the last few trips I have been added a bit of extra oil to the mix. so its more like 75:1 I run now... Being a single carby, I found running it at 50:1 caused quite a rough idle... and given I rarely stress the motor I decided to stick to the lower ratio.

Look at your butterflys in the carbies and see if there is any difference. Some brands still use a screw to hold on the butterfly and it wouldn't be the first to come undone and get sucked through the motor of jam in a crank bearing before getting spat out. Same for a peice of a reed valve - torch down carby to check if obvious and screws that hold reeds in place.

Will check this..

Check inside the cowl. Have had similar noises from cowl insulation rubbing on flywheel and also wiring loom etc not placed back where it should have been and rubing or blocking teh advance

Initially I thought this was the case, but I've looked and cant see anything obvious here...

The other cause which is common for the noise is the pull starter ( squeal) where it doesn't release properly , rubs etc. Have a good look at it as on other brands they can drop a circip and they then rest on teh flywheel . Not sure on a yami how they are connected. Warning that there is a spring in there that will take your finger off or a eye out so if looking be very carefull and gave a look at the parts diagrams first. Check tension on bolts that old down pull starter and if it has a electric start option check the gear is sliding up and down the input shaft cleanly and has all teeth while also springing back to where it should.

This is a possibility given the timing and occurrence of the noises I have observed in the past... I will look at that too..

Unknown noises can bring tears to the eyes but go looking for the cheapest and easiest options before pulling stuff apart to narrow it down and going to a shop and have a engineer look at aborescope is a cheap option after that.

Well I need to test a little more after resolving the above issues and see if it returns. I fish mostly estuary so never too far from land...


PS

With plugs out turn it over by hand and see if it is smooth , back and forward to see if there is any slap , chatter, flywheel side to side in case it is a crank bearing. It would have to be bad to discover it this way but easy quick check anyway.

I dont think it is this as it is smooth and chatter free and I think the flywheel runs pretty true. Again this only happens for a few seconds and only occassionally so it is harder to pin down.

Ps ya sure it was from the powerhead not the gearbox? Check the oil down there for smell ( burnt) and too many metal flakes or water in there.[/quote]

The motor is second hand and I've had it for almost 2 years. When I got it the upper shaft seals to the gearbox needed replacing so I did all that and got it all back together... Because of that I have been checking the gearbox oil regularly and there has been no signs of leaks and the gears function nice and smoothly.. The noise is definitely coming from under the cowl somewhere!

Thanks for the advice!

BaitThrower
11-06-2010, 12:14 PM
Next time just disconnect the fuel line you will hear the pump click . see if it is the same sound
Stuie

Ok good idea will try that :)

cormorant
11-06-2010, 12:36 PM
Last ones

have heard a noise similar with a faiing waterpump or incorrectly installed thermostat where the water in the head goes to steam and shoots out a squeal. Check motor temp next time with it off and back of hand on head ( should be warm but not stinling hot) and look for steam or inconsistant flow from pisser.

Check rest of fuel hose again and fittings for a vacume air leak.

Check breather on tank was open and is clear ( use your mouth through your hand and blow through the cap as sometime they get crapped up with something and when under enough vacume they "whistle "the air in. Same if cold fuel and tank then going into sun you can get a build up of pressure and vapour and a whistle out the breather.

Check the ank lift pipe in the tank is actually clear and the bottom of the tank hasn't got debri in it. low pressure conpressed air is quick check blowing back down fuel line

Ethanol fuels sometimes collapse some fuel hoses . they look perfect on the outside but collapse internally. Cause the motor to try and suck air into the fuel pipe.

Fuel filter , external or on motor can also cause a vacume / pressure situation if they are not seated right and clear.


If all the above doesn't get it you must have narowed it down somewhat.

Dave_H
11-06-2010, 01:17 PM
Awesome, easy to follow advice there cormorant. Top Stuff!

Noelm
11-06-2010, 01:32 PM
yep, agree with all that, but the major problem is, what flatened the spark plug! none of those things will do that, so there is only a couple of possibilities, the plug was never gapped properly when new (maybe) it was dropped before installation and closed the gap (maybe) or (wait for it) something sinister was bouncing about on top of the piston, banged the plug flat and shot out the exhaust port (probable) what the "something" is will be anyones guess without investigation. Take your pick what option you select.

BaitThrower
12-06-2010, 10:35 AM
The plug had been in for a few months and had 5-6 trips under its belt, so if it was this way on initial install, I'm sure I would have had the same problem from the beginning of that plug install.

I'm leaning toward something has hit it... because it was ok at the ramp and only just started to happen as I throttled it up a little about 100m from the ramp...

Just not sure what could have hit it... if it was a piece of ring, then I should have got poor compression readings on the bottom cylinder shouldn't have I?

Anyway I will try and do a cylinder clean with engine tuner and then see if I can get a better look at the piston heads.

Fed
12-06-2010, 11:54 AM
I don't know your motor BT but I'd think it would only take a few minutes to pull the head off and have a look. The last motor I blew up had needle rollers from the piston pin everywhere except where they were supposed to be. It showed no signs at all until it locked up when one got stuck in a port and locked the piston.

savagetin
12-06-2010, 04:01 PM
Sounds like water ingestion to me. Only takes a few drops to cause alot of damage in a small motor and there are no signs of what caused the damage when the motor is stripped down.

Tony

tunaticer
12-06-2010, 05:58 PM
Check the surface of the piston directly under the spark plug, If the plug was bent inside the firing chamber it will be marked, if not it was closed before it was set into the hole. It certainly is not hard to close a gap with a bump or drop and not notice it before putting a plug in.
The squeal could also be one finger of a reed valve getting a harmonic chatter happen. This usually only occurs after a long period of no use and some of the fingers get gummed with 2 stroke oil setting.

I run surface gap plugs because they never fail due to their design. My plug in my 15 yr old motor have done thousands of hours and were put in when the motor was new. I pulled them out a month ago and they are still like new. Carbonization does not occur with these plugs too.

BaitThrower
17-06-2010, 04:31 PM
Check the surface of the piston directly under the spark plug, If the plug was bent inside the firing chamber it will be marked, if not it was closed before it was set into the hole. It certainly is not hard to close a gap with a bump or drop and not notice it before putting a plug in.
The squeal could also be one finger of a reed valve getting a harmonic chatter happen. This usually only occurs after a long period of no use and some of the fingers get gummed with 2 stroke oil setting.

I run surface gap plugs because they never fail due to their design. My plug in my 15 yr old motor have done thousands of hours and were put in when the motor was new. I pulled them out a month ago and they are still like new. Carbonization does not occur with these plugs too.

I checked the surface of the suspect piston again today and can't see a thing. Did another warm compression test and pretty much 120 PSI on both cylinders...

Ran some engine tuner through it and it blew out a bit of the carbon and ran fine on the muffs otherwise.

I dont think there are surface gap plugs that corss reference to NGK BR8HS-10 plugs. I havent found any information yet anyway online.

BaitThrower
17-06-2010, 04:36 PM
Additionally, since I have an IR temp gun I decided to double check the head temperatures while it was running on the muffs at idle and slightly faster idle...

Reading on the cylinder cover plate (next to spark plugs) the area around top cylinder read a constant 120 degrees F and the bottom one was a fair bit lower around the 100 deg F (normal?).

I checked up the heads and this was around 125 degrees F...

The thermostat is rated to open at 118-126 degrees F so it seems its doing its job and the colling system is all in good working order... Never has been a problem... It was interesting to see the bottom cylinder runs a bit cooler though...

doctorbob
02-09-2012, 03:16 PM
Just noticed my merc 2 stroke 75 doesn't have pins on end of plugs. What the?. Yesterday at high revs kept losing revs, thought it may have been tank breather hoses but no. Drained water tap lots of crap and stuff, checked cylinders and no drop in revs when removed top plug lead. Could this be the reason for drop in revs bearing in mind ran ok at high revs for minute or two before drop in revs. Bit worried about plugs
Rob

nigelr
02-09-2012, 03:46 PM
Maybe a load of shite fuel BT? Water in it, diminished octane or something?

doctorbob
02-09-2012, 04:46 PM
Also just found motor only running on middle and bottom cylinder. Is it possible to be an easy fix or straight up very expensive.

nigelr
02-09-2012, 06:51 PM
I'd start with new plugs and a new lead for the top cylinder db.

doctorbob
18-09-2012, 02:57 PM
Thought engine problem was fixed, $500 new plugs service tune top seals on gearbox and thought good to go. Mechanic told me was lots of water in trap when he checked. Took boat out today for 1 hour and once again when running at 4500/5000 revs motor likes revs and power. Very frustrating, should I drain all fuel from u/f tank and refueling with conditioner, run motor at high revs with syd tank?. Can the coils play up when they heat up I'm wondering if one cylinder is not firing when gets hot.
Rob

nigelr
18-09-2012, 03:58 PM
db, don't know about outboards, but when I rode bikes yes, the coils could start to play up once hot.
Invariably, within a short period of time, they subsequently died. Same with the old Holdens we had too, from memory.....
Were the leads and plug caps replaced when the plugs were changed?
Good luck with it.