1993 88hp Evinrude E88MSLETE - Knocking Noise

[MrFishy]

Purchased this motor about 4 months ago and have done the following to it:

Changed water impeller
Changed lower unit oil
Changed starter and starter solenoid
Cleaned out gas tank - dumped old gas and started fresh 50:1 mixture
Changed primer solenoid

Compression 61, 58, 50, 53. They were taken a month ago.

I prime the gas, put it out of gear and push forward on the throttle then the engine roars and starts. It takes a few tries before I can put it in neutral and get it going. Yesterday took the boat out everything was fine. On the way back to the dock it started making a knocking noise (Please click on the youtube link to see what I am talking about). Before I take it down to a shop or with the help of you guys I might try to fix this. Im sure its something inside the motor now and not as simple as swapping out a part.

The boat still turns on and goes into gear but I know theres something wrong. Rather than using this way I want to fix whats going on before getting it out on the water again.


YOUTUBE LINK: https://youtu.be/UXXN010I7JU

https://youtu.be/WQwiaK8KhKI

Thanks in advance for your help.... P

 

[jakedaawg]

I cant hear it in the video but those comp numbers are suspect not just because of the low numbers, that is the guage as it would not run with those numbers, but because of the spread.

You want less than ten per cent difference from high to low. Might want to pop off the exhaust port covers and take a look.

 

[boobie]

Do a cylinder drop test on it.

 

[G_Hipster]

I cant hear it in the video but those comp numbers are suspect not just because of the low numbers, that is the guage as it would not run with those numbers, but because of the spread.

You want less than ten per cent difference from high to low. Might want to pop off the exhaust port covers and take a look.

Ditto, were the throttle plates open when it was done????

 

[flyingscott]

Throttle plates do not need to be open to do a compression test. But that test definitely needs to be redone with a different gauge. Does the knocking sound only in gear or all the time I can't hear it in the video.

 

[emdsapmgr]

That compression should be in the 95 range, so your is reading low. Agree, many of the compression gauges read incorrectly. Try another gauge. Hard to hear the knock which should be of concern. These V4 engines will have a "piston slap" noise when they get a lot of hours on them. The clearances in the rotating assembly will cause this "slap" noise. Sort of sounds like a knock, but is not a fatal problem. The engine has loosened up inside and you'll get the piston "slap." An overhaul is the only fix. But since you may have the slap- it is not fatal. Run the engine-you should get many hours of use from it still. Your compresson numbers are all fairly close and the engine sounds good in the video- which to me, makes the compression gauge suspect. If you do find the compression is correct, then I'd consider an overhaul with 4 new pistons/ringsets.

 

[Faztbullet]

Yesterday took the boat out everything was fine. On the way back to the dock it started making a knocking noise

Piston slap does not happen suddenly....Run another compression test as may have broke a ring.

 

[MrFishy]

Did another compression test with a new gauge as recommended, results were as followed:

Top left 100
Bottom left 100
Top right 100
Bottom right 90

Going to do a drop test next. Do you guys think its safe to take the boat out this weekend ? LOL

Im itching to fish:lol:

 

[MrFishy]

I asked about an overhaul and they wanted to charge me 2000$ for 4 new pistons/ringsets. i bought this engine and boat for 800$. How time consuming and knowledge do I need to get this done?

Thanks
P

 

[interalian]

Just for the parts, or parts, machining and labour?

 

[MrFishy]

Just for the parts, or parts, machining and labour?

Everything. Is that a reasonable price?

 

[interalian]

If it's Canadian dollars, a very, very good price. If US dollars it's probably in line. A tough decision on an $800 original rig, but it's your decision. I spent C$1500 or so to re-build my 90-140 project this spring - all labour except machining by me. I paid $1 for my boat, motor and trailer (and the 90hp original motor was OK, just a little weak).

 

[emdsapmgr]

The compression numbers you got on the block are not that far out of line. Within 10%-all. 100 was probably the norm when the block was new. That block has a lot of hours left in it. The fact that one piston is low would be a good reason to do a good "decarb" on the block. The compression may come up 4-5 Lbs afterward on the low cyl. Worth a decarb-considering the overhaul expense.

 

[MrFishy]

The compression numbers you got on the block are not that far out of line. Within 10%-all. 100 was probably the norm when the block was new. That block has a lot of hours left in it. The fact that one piston is low would be a good reason to do a good "decarb" on the block. The compression may come up 4-5 Lbs afterward on the low cyl. Worth a decarb-considering the overhaul expense.

Whats the best way you recommend decarbing the motor? I have heard mixed reviews on using SeaFoam and have used it myself once on a motor that made it run on high rpm and have a feeling it helped end its life. It was an older Johnson from the 80's

 

[jakedaawg]

No Title

This is the best, follow the instructions. A lot of folks swear by sea foam but I have not found it to produce the same results. I wish it did as its less ezpensive.

 

[emdsapmgr]

I use the same Bombardier product that Jaked uses. Seems like these crossflow engines are somewhat more susceptible to accumulating carbon around the pistons and rings that other 2-strokes. OMC's brand badging on their cans has been replaced with "Bombardier" and the can is now blue. Same stuff. The instructions on the can are perfect. I do subscribe to their request to warm the engine up fully prior to using the spray. Also, there is no reason you can't do one or two applications to start out with. This product will get a lot of carbon out of the ringsets and from around the pistons and can raise the compression slightly after an application. Good stuff. I like this product as it's a little more syrupy (thicker) than the Seafoam-which is more like water. In addition, I use the Bombardier XD50 2 stroke oil. That oil has this "engine tuner" liquid added to the oil. So, when you run the XD50 oil, the Carbon Guard feature burns through the carbon as you run the engine. That's why the XD50 oil is slightly more expensive.

 

[jakedaawg]

Yeah, it just dawned on me that the cans have probably changed. I have several cases of it due to an ordering snafu years ago when we were a dealer.

 

[MrFishy]

Im having second thoughts about decarbing this engine. The previous owner seems to have never decarbed it before and I feel like that if I start doing it now it will cause more damage than anything. Lets just say the seals are worn out cant the carbon be holding everything together or is that just a bad assumption? I have been reading threads that people say it destroyed the engine due to it never being decarbed and then doing it all a sudden puts to much pressure on the engine which causes it to stop working.

thoughts?

 

[interalian]

I'd say you can't really go wrong with a de-carb. Just don't feed it so much tuner at once that you risk hydrolocking the powerhead. Any carbon in there won't be holding anything together, and seals aren't in the combustion areas where the carbon builds up, just on the pistons, heads and exhaust ports/cover.

 

[jakedaawg]

Just do it, they are wrong on "so" many levels of thinking.