Evinrude - 40HP Powerhead Problems – help!

[Chris Wilson]

I have a powerhead for a 40 HP Oil Injected 1991 Evinrude, which has failed. I am in the process of ordering a rebuilt powerhead (I’ve contacted iboats, who seemed very knowledgeable, but have not ordered yet) but I know I’ve got to start trying to figure out what might be some possibilities for the root cause failure. I’m hoping some of you might be able to toss out some suggestions.<br /><br />Anyway, here is the info I can provide so far; I have attempted to tell everything I can to help with some ideas, (therefore you may want to get a cup of coffee before you start):<br /><br />Engine 1991 Evinrude, 40 HP, VRO Model No. VE40TLEIA, Serial No. G 02596825.<br />Boat: 16ft Lowe - bass type.<br /><br />Purchase used “as is” from a local Maine Store, spring of last year. Ran fine for a while and started to become unreliable (power fluctuations, hard starting, etc.) We had the carburetion system rebuilt by one of the local Evinrude Dist/Marinas later last summer and that helped some. Result, much better but still not where it should be – still temperamental. <br /><br />This spring, it seemed to be running the same, but through use, learned how to deal with it. However, it again deteriorated and we started to “diagnose” again. We have a manual and did a check on the oil injection using a clear tube to determine if the oil was being delivered to the engine. We did not get real scientific about it, but the oil was being delivered and we repeatedly had to refill the tube to keep a supply. It looked good to us and we started to look at other things. The short of it is we thought the engine seemed to be running cool and found the thermostat was stuck open. Bought a new one and the improvement was incredible. We could not imagine the unit operating any better. We had rock solid idle and excellent power through the whole range. We finally thought we had it under control. Four or five fishing trips without incident were renewing our confidence.<br /><br />Then, two of us took the boat out trolling for salmon on Lake Michigan. The 7 mile trip out was fine. Trolling was fine a couple of stalls, but we attributed that to operating at low idle for an extended periods (two fish by the way). After about three hours of trolling, the lake started to rough up so we headed back. Along the way, the engine sound suddenly changed and we started to rapidly lose power but the engine did not stop until we throttled back. Somewhere in the sequence of events, we noticed a rattle sound. We pulled the cover and saw the starter engaged even though the engine was off. We can’t remember if we saw the starter engaged immediately thereafter or after subsequent restarts. Anyway, we were able to get the engine restarted and verified the starter retracted and the rattle seemed to go away. The water flow seemed normal both the indicator and the cooling discharge. We could not actually touch the discharge due to the difficulty to reach in rough water. We could still plane, barely (probably more a credit to the flat bottom boat than available power), and at full throttle could only get about 3000 – 3300 RPM. Prior, we could get over 5000.<br /><br />We got in ok and, since we were camping, did not have a lot of tools to do much. Although the plugs were cleaned and gapped earlier this year they were still “not new”. As a result, we bought two new plugs, gapped them and tried the boat again, no improvement. The starter stuck again and the rattle sound was present.<br /><br />When we got home we found out this much more:<br /><br />1)It appears that the Starter Motor has failed mechanically and does not retract the starter gear when the engine actually starts (the starter has been electrically disconnected and removed from the engine and is still extended). However, it does function and seems to be spinning freely. This means that the flywheel would be driving the motor armature (could the inertia of the armature being constantly applied to the outside edge of the flywheel be a factor?) but other than that no other bad things are going on in that arena.<br /> <br />2)We have spark on both plugs but did not check timing.<br /><br />3)Removed the carbs and checked the reed valves. All look good (about 8 per carb if my recollection is correct – anyway, if not 8, a lot more than I expected).<br /><br />4)We found very poor compression on the top cylinder and less than one would expect for the lower cyl. We did not have a gauge so I can’t give figures. Just held our thumbs over the plug holes and cranked. Turns out compression numbers probably don’t matter, read on…<br /><br />5)Pulled the head and found the upper cylinder to have: Walls with excessive wear and gouging, the piston head to be light colored (more metallic hew in the middle and center and light brown/darker on the edges (compare to the lower cylinder below). The piston is very loose. Put it this way, I can move it side to side so easily that I can make it rattle. There is some of the piston material missing on the edge (I can start to see the first ring) on the left side, as you would view the piston looking into the cyl. The piston material missing is along the cyl wall between the intake opening on that side and the exhaust port just below it. This damage does not seem to be anywhere else on the piston including the intake port on the opposite side. The piston and cylinder look dry. Like no fuel or lubrication evidence.<br /><br />6)The lower cylinder. Much tighter tolerance and no missing piston material. The walls are rougher than I expected (still MUCH better than the upper) but this may be normal deposits of oil, carbon, whatever. I would have to do some testing to see if the surface deposits can be removed or actual wall scoring has occurred. But there is a night and day difference between this cylinder and the upper. The piston is more uniform in color but has much more black carbon deposits. There is evidence of wetness in the intake and overall. Except for the question on the cyl wall, this is what I might expect a piston and cylinder to look like for a 10-year-old engine with normal use.<br /><br />7)We pulled the flywheel and a physical examination of the coils, etc. underneath did not reveal anything obviously bad.<br /><br />Anyway, that is what we have so far. Again sorry about the long note but hope the info will help and some of you can provide some suggested areas to check out as we try to bring this unit back to life.<br /><br />Thanks for your time…

 

[12Footer]

Re: Evinrude - 40HP Powerhead Problems – help!

Causes of the failure can still only be speculative, but include an originally stuck ring(s) caused by heavy carbon buildup, water injestion from a leaking port plate or head gasket, water pump failure, or oil injection failure (I hate oil injection systems,as they can fail).<br />A plugged,or lean-running carb can provide inadaquate lube to the cylinders it serves too.<br />So you see, it's hard to say.<br /><br />Once you have her rebuilt, disconnect that pesky VRO,and mix your gas in the tank..The only way to mess that up, is to not add oil at the time of tank-filling---the ONLY time to add oil (so one doesn't forget this step).<br />Verify that the cooling system is functioning at all times by use of a water jacket pressure gauge (if possable), a temp gauge (if possable), or alarm,(if nothing else is available).<br /><br />Carbon builds-up rapidly in 2cycle engines, when they are idled extensively. It's the byproduct of burning the lubricating oil allong with the fuel.<br />Most manufacturers have intervals for "decarbing",but a good rule-of-thumb is every 80 hours, and after every 4 to 8 hours of steady idling. Decarbing is a process that cannot be done "too often". <br />However, if I had to guess at what caused your engine's failure, I would have to say "dangol oilers!!" <br />It is next to impossable to get any performance out of a fuel injected engine, if you mix the oil in the tank, as the injectors weren't designed to atomize the heavier mixture. But if you have carbs, it's THE way to go , In my opinion...I dont trust oilers and never will. I guess that means, I'll never own a FICHT engine, and would probably make the 'leap' to 4stroke,given no other option.<br />I only wish there were other ways to 'monitor' what is happening inside a 2stroker underway, than there allready is. There is just no way of knowing until it is too late.<br />From your description, (a great description,i might add), you did all you could do to 'monitor' you engine's performance, other than premixing and carbon removal. Other than that, you could not have prevented what has happened,as you would have no way of knowing....The drawbacks of 2strokers.<br />I hope you get her running again, top-notch, and under-budget.

 

[beeza]

Re: Evinrude - 40HP Powerhead Problems – help!

Hi prop head,had to reply to this as your problem was identical to the one i had a couple of years ago.The cause seemed to be 2 fold.Firstly the restrictors in the water jacket were past their best but still reasonably intact.Secondly the major problem seemed to be a blocked jet in the carby, plus a low float level.This to me obviously caused the detonation of the piston which allowed metal to bridge the spark gap causing the loss of power.Hope you're as lucky as i was in repairing this engine,only had to give bores a light hone and a good second hand piston,even used old rings.

 

[beeza]

Re: Evinrude - 40HP Powerhead Problems – help!

Forgot to add,did a lot of searching to the cause of this and found the link that when the carby is running lean on these twins it's nearly always the top cylinder that suffers worse.

 

[Chris Wilson]

Re: Evinrude - 40HP Powerhead Problems – help!

12 Footer and boady, thanks for your reply. Very interesting possibilites. We will have to walk through our symptoms and see which of what you suggested fits the problem. Maybe a little from both.<br /><br />I do have a question but I think I know the answer. There was a suggestion that "decarbing" was a necessary process after a time. Am I correct in assuming that "decarbing", is simply a long high speed run? Or is ther more to it?<br /><br />Also, we have been really paranoid about the VRO since we got it and relaized (too late) how complicated the system was that performed such an important function. In my opinion, the fuel/oil pump mechnism is way too compicated (too many ways to fail) for what it does and the consequences if it doesn't. We are seriously considering the advice to go to fuel/oil mix. However, for the problem at hand, I'm not sure how a failed oil injection system would affect only one cylinder and not the other.<br /><br />Anyway, great suggestions, we have much to think about while we wait for the powerhead to arrive. boady - Too much damage to clean up the cylinder. We are pretty sure they are both shot anyway - just that one is much worse than the other. However, I continue to come back to how one cylinder is so much worse than the other.<br /><br />In addition to the responses I received here, I've read a number of times in this forum about the negative effects of "lean" carboration. Can anyone explain why this causes damage to the piston?<br /><br />Thanks