150 XP running on four, mostly

[hidolr]

Looking for fresh ideas: I have a 1987 Evinrude 150 XP (STXCUR) Crossflow with top two cylinders (1 and 2?) misbehaving. When I try to rev the motor by actuating the carburetor linkage for the top carb only the motor will rev until about 1/4 throttle (top carb only -- other two carbs at idle) then spit (sometimes) and die on top two cylinders above 1/4 throttle. The other two carbs (middle and bottom) will rev independently up to full throttle. Compression is same on all six cylinders (90 psi). When top carb is slowly actuated to the point where the top two cylinder die there is still an ignition spark -- rather my timing light says there is (I cannot locate my spark tester). With the motor running, when I open the throttle valve on the top carburetor I can see the primary then secondary jets working even after the top two cylinders quit working.

Things I have tried: swapped bottom carburetor with top carburetor, swapped #1 and #2 coils with #3 and #4 coils, swapped spark plugs, and cleaned recirculation fittings. Even though they appeared OK when viewed through the intake manifold with the carbs removed, I pulled the intake and checked the reed valves (leaf plates) -- they are OK.

Any ideas?

 

[o/b tech]

Re: 150 XP running on four, mostly

There is a possability that you may have a broken sealing ring between cyl's 1&2 on the crankshaft. These rings keep the cylinders seperate from each other so they don't bleed fuel/air back and forth. With the motor running, breifly put your hand over the opening of the top carb, to richen it up, be carefull, and see if it picks up either cylinder. If there is a problem with the sealing ring than the motor has to come apart. Hope the info helps.

 

[emdsapmgr]

Re: 150 XP running on four, mostly

Stop the engine when the top cyls start to misfire. Are the plugs wet or dry? How do they compare to the other 4?

 

[hidolr]

Re: 150 XP running on four, mostly

The plugs for the top two cylinders are dryer than for the other four even after carbs/plugs/coils were switched. And, as I said, the reed valves are OK. The crankshaft sealing ring has to be one of the rarer problems an outboard can have and one of the most expensive to repair, thus, it makes perfect sense to me. Wonder where I can obtain the special connecting rod cap alignment/installation tools?

 

[Fl_Richard]

Re: 150 XP running on four, mostly

You dont need those stinking tools. Lead pencil's and fingernails work every bit as good.

Have you ruled out power pack? The spark can still be firing but at the wrong time.

 

[hidolr]

Re: 150 XP running on four, mostly

Regarding Power Packs: Timing light shows a stable spark and it's the top cylinder on eack bank that are not making power or taking more than a little throttle. Would not a Power Pack affect all three cylinders on a bank? I am an old motorcycle mechanic and fully certified auto mechanic and former part-time outboard mechanic. I know my way around two strokes (e.g., older Japanese singles, twins, and triples and older outboards) but this has me perplexed.

Besides trying carbs swap, coils swap, plugs swapAlso replaced fuel pump/VRO unit (fuel pump diaphragm was bad and I had a spare). Also tried manually pumping fuel primer bulb with no luck. Just finished pulling reed valves to thoroughly check condition and they are OK. I don't know of a way to check the crankshaft seal ring except by disassembly.

 

[o/b tech]

Re: 150 XP running on four, mostly

You are correct, there is a pack for each bank, and if there is a problem it will not usualy take out only one cylinder. Even less likely considering both packs involved. Cylinders 1 & 2 don't share the same trigger winding in the trigger base. Chances are that it is not the trigger. Since you have swapped carbs with a known good one that is fueling on the bottom cylinders, chances are that it is not a fuel problem. Coil swap changed nothing. Problem still points to a bad sealing ring. Unfortunately, the block has to come apart to visualy diagnose.

Have seen this problem once before on an omc v6. Ring broke allowing the two cylinders to affect each other. When the plugs were pulled, they were also dry. Hope the info helps.

 

[hidolr]

Re: 150 XP running on four, mostly

Thanks to all for the information/help. I was only verifying that my luck has not changed, i.e., my $9 problem is several hundred dollars deep inside the motor. Alas, the risk of buying used with only a garden hose test. I will update my findings after teardown.

 

[emdsapmgr]

Re: 150 XP running on four, mostly

Some thoughts about your problem and the broken seal ring. While possible to break, a single fracture may not mean much to the overall performance, as you would still have significant sealing surfaces between 1 and 2. If the ring disintegrated, you would have metal pcs all through the #1, #2 crankcase and head area. You should be able to see something through the plug hole or the side intake cover. Assuming the ring is mostly intact, but broken, it may make little difference to the running of the engine. Here's a couple of things to check: 1. Pull all 6 plugs out. The engine powerhead with heads/reeds makes a specific breathing sound when rotated. Put a wrench on the flywheel nut and rotate the engine by hand (no starter noise.) Your ear may be able to detect minor differences in the way #1 and #2 sounds vs the other 4. If all six sound the same, I'd continue investigating 2. #1 and #2 cylinders just happen to be indexed on the flywheel. Run the starter and check the idle timing on both #1 and #2. They should be in the 5-7 degree range. 3. If the ring is broken, it will affect idle the most, when crankcase compressions are low. When operating at high rpm's the seal ring loss becomes negligible when at 5000, and the compression is significantly higher. 4. Any OMC engine will idle fine with one or two cyls not firing on the hose. At normal rest in the water is another thing. How does it idle in the water? After all this, you may well have a cracked seal ring as the others have indicated. I'm hoping that you don't. Good luck and keep us posted.

 

[o/b tech]

Re: 150 XP running on four, mostly

Food for thought, when I saw this problem in the past, indexing the flywheel didn't show a problem as the ignition system was working fine. Although the sealing ring was broken, in one spot, it didn't create any shrapnal and could not see any problems visualy. Could see the normal operation of the reeds when the engine was running, airbox removed, except that the motor was not running on two cylinders, that also happened to be 1 & 2 as well. Same frustration in trying to diagnose problem. How we discovered the problem was by pulling the spark plug lead on cylinder number 1 and sprayed in extra fuel to that same cylinder. Nothing should have happened but number 2 cylinder started running. The only way that could have happened was that number 2 started pulling the extra fuel required to lite. Otherwise there was no way we could get either cylinder to fire at any operating range. When we pulled the motor apart found the cracked ring and replaced. put back together and motor ran on all 6 cylinders. Because the description of the problem and steps taken are the same, this leads me to think that the problems are the same. Hope this extra info helps in the diagnostic process. Good luck.

Let us know what you find and would be a good time to freshen motor up as well. Hope your deal is a good deal for years to come.

 

[emdsapmgr]

Re: 150 XP running on four, mostly

I think you have done some nice work on this. Upon reconsideration, once the ring breaks, it is likely to become quite loose and may pass more air than I originally considered. Also, if this did occur, any additional running could damage the crank groove, so best to get it apart.

 

[hidolr]

Re: 150 XP running on four, mostly

Pulled the ehaust cover off today: port side of block is relatively clean and dry, starboard side is carboned up and wet top to bottom. Through the ehast ports the pistons look great. Twisting flywheel back and forth results in a clicking sound (like timing gear if it had timing gears) and a muted squawking sound in both directions of rotation. Sounds much like a dry car-door hinge. Powerhead is loose and will be lifted out tomorrow for teardown; my fingers (and toes) are crossed.

 

[o/b tech]

Re: 150 XP running on four, mostly

Sound like the number one cylinder has carboned up rings and is allowing blowby anyway. don't know what the clicking sound is but sqwauking sound is the air being drawn past the reeds and is a normal sound.

With number 1 being as carboned up as it is, it's a good idea for the tear down anyway. Good luck. Curious to see what you find.

 

[o/b tech]

Re: 150 XP running on four, mostly

Thanks emdsapmgr, Hope the Blackhawks do well.

 

[hidolr]

Re: 150 XP running on four, mostly

Well, I split the crankcase and the crank seal rings are all unbroken and best I can tell, OK. Upon further inspection (which translates as "the inspection that I should have done from the beginning") I noticed that all of the pistons on the port side are clean (no carbon) and the pistons on the starboard side are carboned up past the rings. The rings on the top cylinder on the starboard bank are carbon-siezed. This formerly 'really good' mechanic is feeling pretty dumb right now. I think I will orient the pwrhd until the starboard cylinders are vertical and pour in Seafoam and see if the rings on #1 will free up. If not -- re-ring it. Argh!

 

[emdsapmgr]

Re: 150 XP running on four, mostly

Sounds like the starboard side may have been running cold for a long time. A cold side will promote carbon accumulation around the rings. Check to see if the thermostat is stuck open and whether the pressure relief valve is functioning properly. If you have the exhaust cover and intake covers off, you can use this access to apply more seafoam.

 

[hidolr]

Re: 150 XP running on four, mostly

In response to the last comment, the carboned-up starboard bank was running noticably hotter (by touch) than the port bank. Upon disassembly I didcovered that ALL of the pistons on the starboard bank were carboned up with the top piston ring sticky and the bottom ring completely seized. No way to free those guys except by prying them out; two days in heated heavy-duty carb cleaner wouldn't touch them. The pistons on the port bank look great. In fact, the x-hatched honing marks are still visible in the cylinders and the rolled-in ridges on the piston skirts are barely worn. Rings, thermostats, gaskets and seals are already delivered, new solvent is in the tank and I am ready to get going. Still have to locate an anaerobic sealer for the cases or get a tube of case sealant (Hondabond or Yamabond) from one of the motorcycle shops.