Allowable "slop" in pistons??

[ScottinAZ]

OK, first off, the engine in question is a 1982 Evinrude 115, (E115TLCNB) that has had an idling issue since purchase. I pulled the plugs, and had evidence of what I thought was water on the plugs, (beaded up liquid on the surface) so I pulled the heads today. Also, I did a compression test on it about a month or so ago, and got 115-120 on all holes. I dont remember the exact values, but they were above 110, and even on all holes (within 10% at least)

What I found was one head gasket that was obviously poorly sealing (scorched fire ring) but no obvious damage to either heads or block. Just for giggles, I worked the engine through a full revolution and checked the pistons for looseness. I can wiggle all of them a bit, but to my eyes (4 stroke automotive) it seems excessive. Are 2 smokers built with looser tolerances to compensate for the lower operating temperature?

The cylinder walls are good, no signs of metal transfer or scoring, the crosshatch is still there, and there is no appreciable ridge in the bores. There is signs that there has been a bit of water in the cylinders above the top ring, but nothing more than a light water discoloration of the metal, no active rust or pitting.

My take for now is that I need new gaskets, the heads need to be surfaced, and the heads properly torqued, the engine run, and then retorqued. Im just not sure how much play is acceptable in the pistons. Keep in mind that the engine just wouldnt idle worth beans when warm, and that there were no funny, "i'm gonna blow up in 5 seconds" noises coming from the motor.

What is the group consensus here??

 

[wilde1j]

Re: Allowable "slop" in pistons??

"Wiggle" means exactly what? Can you rock the pistons or do they have up/down slop in the bore, or what? Not clear what you mean.

From your other observations, it appears you have a healthy motor.

 

[ScottinAZ]

Re: Allowable "slop" in pistons??

I can rock the pistons side to side, there is no movement or slop in the direction of the bore. Wiggle means about a 32nd to a 16th of an inch of "wiggle" when grabbing the deflector and moving side to side

 

[emdsapmgr]

Re: Allowable "slop" in pistons??

Two stroke pistons do have some slop. This is normal. A new engine will run quietly. An powerhead with many hours on it will be noisier than a new engine. You can actually hear the piston slap at idle in a worn engine. This does not mean the engine will fail imminently. An engine which has high hours can have a lot of carbon accumulation around the rings. It can inhibit the sealing capability of the ringset, affecting idle. A good idea to put some Bombardier Engine Tuner through the engine when you get everything back together.

 

[robert graham]

Re: Allowable "slop" in pistons??

piston/cylinder clearance should be in the .002" to .004" range, but with 25+ years of wear, yours is probably a good bit more due to wear. It doesn't mean the engine is going to die soon but may rattle some at lower RPM's. you could have those pistons knurled about an inch around the skirts which will expand the diameter a bit to take up the slack and helps with oil retention on skirt area. a local machine shop could do it for you and probably a lot cheaper than new pistons and you would be set to go and your motor would be quieter. of course, getting the pistons out of the block could be a real job though. Good Luck!

 

[iwombat]

Re: Allowable "slop" in pistons??

My total number of 'rude motors viewed is limited, but I have yet to seen a motor that just plain wore out. I'm guessing they're very few and far between. Most often something happens to cause catastrophic failure. If you can still see the cross-hatches and there's no ridging I'd bet dollars-to-donuts you're still in spec. Although, donuts are getting more expensive by the day.

 

[jonesg]

Re: Allowable "slop" in pistons??

http://www.youtube.com/watch?v=SgavzDPDAy0&feature=channel_page

Loose pistons sounds like this.

 

[F_R]

Re: Allowable "slop" in pistons??

You can't measure the piston clearance without tearing it down. The top end of the piston is loose as a goose even when new. The clearance is measured at the skirt, which is much tighter.

That gasket certainly does show leakage at the fire ring. I strongly suggest you also pull the exhaust covers (between the cylinder V) and check for leaks in there. When they leak it squirts water in through the exhaust ports. Very destructive!!! I'd say you are lucky to have caught it early. I've seen many motors wind up in the bone pile from water intrusion.

 

[ScottinAZ]

Re: Allowable "slop" in pistons??

I can certainly pull the exhaust cover, but the gasketing is tripping me up a bit. IN the exploded views, it shows two gaskets, one under the cover for the exhaust, and another for the water jacket cover. On the non BubbleBack motors, are these the same part number? It does not give a separate part number for this application, so I want to make sure to get the correct parts.

 

[gazza2007au]

Re: Allowable "slop" in pistons??

salt water entering the cylinders thru the exhaust manifold looks like this

 

[F_R]

Re: Allowable "slop" in pistons??

I can certainly pull the exhaust cover, but the gasketing is tripping me up a bit. IN the exploded views, it shows two gaskets, one under the cover for the exhaust, and another for the water jacket cover. On the non BubbleBack motors, are these the same part number? It does not give a separate part number for this application, so I want to make sure to get the correct parts.

Yes, I can see where the confusion comes in. They combined the 90, 115 and 140 into one picture. The BRP website shows that the 115 takes two #317914 gaskets

 

[lowkee]

Re: Allowable "slop" in pistons??

I'm interested in this piston 'slap' discussion in a completely unrelated engine (the 2.0 in my Dodge Neon). I was told by a dealer that it was a non-issue and would live a long and happy life. As much as I'd love to trust his fortune tale, that slap is quite discomforting to say the least. An identical 2.0 in another Neon I owned had no slap and was noticably more powerful, especially in the low RPM ranges. The non-slap engine also burned no oil where the 'slapping' engine burns about 1 quart every few thousand miles.

No real 'help' in this post, but that is my experience with piston slap and how different a non-slapping engine performs. IMO, piston slap is far from a non-issue if you want a well-performing engine.

Let us know how this turns out and if you get rid of the slapping.

 

[F_R]

Re: Allowable "slop" in pistons??

I'm interested in this piston 'slap' discussion in a completely unrelated engine (the 2.0 in my Dodge Neon). I was told by a dealer that it was a non-issue and would live a long and happy life. As much as I'd love to trust his fortune tale, that slap is quite discomforting to say the least. An identical 2.0 in another Neon I owned had no slap and was noticably more powerful, especially in the low RPM ranges. The non-slap engine also burned no oil where the 'slapping' engine burns about 1 quart every few thousand miles.

No real 'help' in this post, but that is my experience with piston slap and how different a non-slapping engine performs. IMO, piston slap is far from a non-issue if you want a well-performing engine.

Let us know how this turns out and if you get rid of the slapping.

All I can say is that I've owned a couple of Chrysler 4 cyl cars and they were a tad noisy to the trained ear.

However, comparing that to these outboards is comparing apples with oranges.

 

[lowkee]

Re: Allowable "slop" in pistons??

All I can say is that I've owned a couple of Chrysler 4 cyl cars and they were a tad noisy to the trained ear.

However, comparing that to these outboards is comparing apples with oranges.

Thanks, but you may want to read my post before replying. There is no 'orange' present in my comparison. I compared two identical engines, one with and one without piston slapping present and compared performance.

 

[F_R]

Re: Allowable "slop" in pistons??

Thanks, but you may want to read my post before replying. There is no 'orange' present in my comparison. I compared two identical engines, one with and one without piston slapping present and compared performance.

And you might want to read my post before replying. I said that comparing a Chrysler car engine to an Evinrude two-stroke outboard is the same as apples and oranges. In other words, they are worlds apart in every way except they both have spark plugs.

 

[ScottinAZ]

Re: Allowable "slop" in pistons??

ok, I got the head gaskets re-installed today. Engine is running noticeably smoother at idle on muffs (will get it to the lake in the next few days hopefully) Engine has no sign of piston slap noise, nor any other, other than a healthy motor. I guess my worry about the slop that I observed was nothing. WOOOOO HOOOO time to go boating again

 

[wilde1j]

Re: Allowable "slop" in pistons??

Enjoy!