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Suzuki DF250 Engine Problem. Possibly Blown?

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Suzuki DF250 Engine Problem. Possibly Blown?

Old 06-17-2019, 06:57 AM
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Default Suzuki DF250 Engine Problem. Possibly Blown?

Hey guys, I need your help in diagnosing and making repair decisions on my DF250.

I have twin 2006 DF250's on a 28WA ProKat. I was headed 50mi offshore from Fort Myers to go catch some limits of red snapper, grouper and a couple other species.

At about 35mi the port motor lost power for a split second, rpm dropped, but then it bounced right back. I figured maybe it was a fuel issue since I recently changed the filters? At 41mi out the motor lost power and started to vibrate pretty strong. I immediately pulled the throttle back and shut that motor down. When I restarted the motor it had a loud tapping/knocking noise, shut it back down. I checked the oil, it was slightly below the low mark on the dipstick. This is very unusual because I've owned this boat for 7 years and they've never burned oil between service. Limped back in on one motor. Any ideas?

I'm not sure about the hours on the motors. I bought them with 550hr on them. Owned it seven years and I'm thinking 100-150hr a year have been added since then?

So far I've drained the oil and strained it for shavings, not a spec of metal in the oil. I've also pulled all the plugs and looked at the top of the pistons. All plugs and pistons look black and dry with no gouges except for the piston on the bottom starboard side of the motor. The bottom starboard piston doesn't look scratched, but it is wet and black, and the spark plug gap has been pushed closed.

Spun bearing? Debris went through the cylinder? Timing issue?

Let me know what you think and what I should check next. Also, any of you do it yourself mechanics ever rebuild your own powerhead before?
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Old 06-17-2019, 07:56 AM
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Take a wood dowel or plastic straw and stick it in the plug hole on the affected cylinder. Let it rest on piston top. Rotate flywheel slightly back and forth and see if piston follows crank travel. Should be no detectable play.

If ok, try a compression test.

A closed gap means something got loose in there. Maybe a dropped valve. I don't think piston can hit the plug even if rod came loose, but not certain.
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Old 06-17-2019, 08:03 AM
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Sounds like a dropped valve
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Old 06-17-2019, 08:13 AM
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Did you happen to notice the temperature of the engine? Any alarm or codes?

Since you had just replaced the fuel filters, I would consider looking at the fuel injector for the bottom cylinder. If it is clogged, the cylinder can overheat and close the gap on a plug. Being it is the bottom cylinder makes it more suspect as that is where debris is more likely to collect in the fuel delivery. Suggest you try to steal a good fuel injector off the "good engine" and try it on the problem cylinder on the "bad" engine.
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Old 06-17-2019, 08:59 AM
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Unfortunately sounds like an internally damaged engine, either valve or bearing failure causing the closed spark plug. I would check compression and go from there. Either way the motor must be torn down to figure out what happened and how to proceed but more then likely going to be a full rebuild, block and heads will need to be decked in order to true them up for reassembly.
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Old 06-17-2019, 02:11 PM
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I really appreciate the feedback guys.

I really like the idea of putting a straw or rod in the plug hole and checking for play at the piston rod/crankshaft. Iím going to give it a shot. If there is no play I will do a compression test.

Seems like this is the safest order to test the motor.

There were no alarms. I donít know if there are any codes, I havenít taken it in yet.

What would cause a valve to drop?
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Old 06-17-2019, 04:18 PM
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Lots of ifs and maybes, only option is investigation, starting with the easy stuff, like the rod through the plug hole to see if the piston is moving, then compression, there was a "feature" on another model that the screws on the throttle butterflies came out and went through the engine, but not that particular HP, but, you never know, remove valve cover and see if any valves are "odd"
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Old 06-17-2019, 04:29 PM
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Yep, check the throttle plate screws.
Serious porblem- Suzuki 250 4Strokes
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Old 06-17-2019, 04:36 PM
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Originally Posted by Outboard Specialties View Post
Unfortunately sounds like an internally damaged engine, either valve or bearing failure causing the closed spark plug. I would check compression and go from there. Either way the motor must be torn down to figure out what happened and how to proceed but more then likely going to be a full rebuild, block and heads will need to be decked in order to true them up for reassembly.
This is more than likely the issue seeing who it comes from. Buy a used one and have a spare or do the down and dirty.
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Old 06-17-2019, 05:07 PM
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Take it to a mechanic.....
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Old 06-17-2019, 05:25 PM
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Call kit down in Naples at Sawers marine. They are honest and fair. They do good work too.
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Old 06-18-2019, 03:16 PM
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Tried to test the rod bearing by placing a tube through the spark plug hole and resting it on top of the piston, then turning the crank back and forth to check for play. Didnít seem different compared to the starboard motor.

Compression is 30% less in the two lower cylinders on the starboard side of the motor.

Any ideas?
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Old 06-18-2019, 04:08 PM
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Lots of ideas, but, you will need to do some further investigating, do a leak down test to see what is reducing compression, could be a valve, could be lots of things.
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Old 06-18-2019, 06:27 PM
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I had a similar experience on one of mine. Was a rod bearing making the knock. Complete rebuild. Good luck. Talk to Jack at Superior.
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Old 06-19-2019, 05:01 AM
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Thanks guys I agree there are a lot of theories, I just want to narrow it down as much as possible and try to determine the extent of the damage on my own before I take it in.

New development! Retested the compression and only the lower starboard cylinder shows low compression. I pulled the valve cover and examined the cams and springs, they look fine. Iím unable to see the exhaust valves, but I can see the intake valves through the intake, they seem to be in tact. I rotated the crank until each cylinder one by one was at top dead center. Then pressurized each cylinder one by one with compressed air through the plug hole. The top two cylinders achieved compression and pushed the piston down until a set of valves opened and released the pressure. The bottom cylinder did not, it leaked air through the exhaust as soon as compressed air was applied. Does this mean I ďdroppedĒ an exhaust valve? Can the head be removed for inspection without removing the entire powerhead?

Did the valve drop in and beat around? Could it just be hanging and not have damaged the cylinder?
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Old 06-19-2019, 05:26 AM
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One last stop before disassembly. Get a cell phone borescope and take a look inside.
Were any of the throttle plate screws missing? They can get lodged and interfere with valve closing.
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Old 06-19-2019, 05:35 AM
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Iím missing one butterfly valve complete, but on a different cylinder.
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Old 06-19-2019, 05:38 AM
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I also found this in the bottom of the intake. Could it be a beat up butterfly valve? Maybe it was shot back into the air box by one cylinder and sucked into another?
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Old 06-19-2019, 06:13 AM
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Missing butterfly and screw is the piece of metal you found, at least part of it. The rest went into cylinder and did the damage. Unfortunately its a full tear down and rebuild at this point and getting a new intake with butterflys. The new ones are locktited and screws are peened over to never come loose again. My suggestion is all new bearings, rings and then pistons if needed. Replace oil pump while you're in there and make sure the block and both heads get decked for flatness so no future issues occur from warping. If cylinder/s are scored you may need oversize pistons. Take it to a shop that has done suzuki and has experience with them.
Sorry to hear about it.
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Old 06-19-2019, 07:41 AM
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For want of a screw a motor was lost.
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