Cylinder Wall Inspection (Pictures)

[Sureshot]

Have a 50 HP 2-stroke with low compression on the lower cylinder. Took the head off and these were the results.

Lower Cylinder:



Upper Cylinder:



Cylinder Head (lower cylinder covering is the darker one on the right):



I'm trying to figure out what is causing the low compression. Having a hard to time figuring out if the lower cylinder is scored. The piston seems to look fine. Also not sure exactly what to look for as far as the head gasket condition. Any advice would be great! Thanks.

 

[blimp]

Re: Cylinder Wall Inspection (Pictures)

cylinders look ok, i bet you just had a bad head gasket. There is evidence of oil/gas mixture leaking in the picture of the head, but that may be just from removal.

 

[blimp]

Re: Cylinder Wall Inspection (Pictures)

you can also check the rings by removing the intake bypass cover and exhaust covers, you can push on the rings with a pick and see if they still have spring in em.

 

[1946Zephyr]

Re: Cylinder Wall Inspection (Pictures)

The head looks pretty clean on one cylinder, as if though there was water leaking in. Usually if water is leaking in, the carbon build up will get cleaned out. The lower cylinder looks like it has signs of pitting, due to rust in the cylinder. I can also see that the piston in that cylinder is pretty badly scored. If you remove the intake bypass covers and exhaust cover, you'll see the scoring on the cylinders. Bottom line is: Low compression due to a leaking head gasket. Water damage to lower cylinder and rust pitting. Scored piston. Looks like it's time for a rebuild. What are those small holes in the cylinders for?

 

[joewithaboat]

Re: Cylinder Wall Inspection (Pictures)

The two clyinders look very different. The lower looks like it has a gray metalic paste smeared on the walls. ?? Upper one looks clean??

 

[DealBrkr]

Re: Cylinder Wall Inspection (Pictures)

Lower looks like water leak for sure, upper seems to be okay. The small holes in the cylinder look factory. Banshee racers call them worm holes. They will have them machined into the cylinders on the intake side to allow more fuel mixture flow.

 

[joewithaboat]

Re: Cylinder Wall Inspection (Pictures)

I think you have poblems in the lower. Blow the picture up guys.
my .02

 

[Sureshot]

Re: Cylinder Wall Inspection (Pictures)

Thanks to everyone for the replies. Yeah not too worried about the upper cylinder. Compression test came in good and I don't see any vertical scratches. For the lower, what is the tell tale sign of water leakage? I sprayed some fogging oil into the cylinder a few weeks back but I don't know where the gray color is coming from. There's definitely some scratches although they don't seem very deep or severe.

Without jumping down the path of a rebuild quite yet, is it worth it to just replace the cylinder head gasket and check compression? If it stays low I guess I've got my work cut out for me.

 

[sschefer]

Re: Cylinder Wall Inspection (Pictures)

Looks like you overheated it to me. Looks like flame over on the piston edge. That stuff on the cylinder walls is aluminum from the piston. It's also on the head. The cylinder walls don't look too bad otherwise. You can clean up the aluminum deposits with Muriatic Acid and then run a bore gauge down it to get a true bore check. If the bore is within specs you can run a brush hone down it to break the glaze and put a cross hatch on it. I'd replace the pistons, rings, wristpins and bearings and you should be back in business. Doesn't look like it got hot enough to bother the rod journals but check them for blueing just in case. If you can't clean it off with a green scotch brite you may want to consider replacing them too. I almost never do unless they are way out of spec but I'll leave that up to you.

 

[Faztbullet]

Re: Cylinder Wall Inspection (Pictures)

That a ignition or carb problem, since you added oil to cylinder its hard to tell as you changed the color of piston dome and head. It has not been overheated as #1 shows no evidence of being hot also. The only cover you have for piston access is the exhaust cover as this is the foam cast block. Dont look like water intrusion as all the carbon is intact in the head and combustion chamber. The holes in ports are on the exhaust side of ports are are idle relief passages, they reduce the compression about 10psi, and worm holes are likely the same as finger ports used in a outboard. The gray color is aluminum being rubbed off in cylinder due to scuffing and a head gasket aint going to fix it it will need torn down......Sorry

 

[1946Zephyr]

Re: Cylinder Wall Inspection (Pictures)

I dont know Faztbullet, it looks an awful lot to me that water intrusion has hit that bottom cylinder and the water has cleaned the carbon away from the head. If you look closely at the lower cylinder pic you can see the pitting on the bottom, plus you can see some ugly score marks from the piston.

 

[Faztbullet]

Re: Cylinder Wall Inspection (Pictures)

The picture of the head, #2 cylinder is on the right with the bottom cowling brackets and it has a lot of carbon. Mostly likely a carb problem and went lean but have seen the packs with advanced timing on a cylinder. The pitted look may be trash in cylinder along with the oil as the exhaust port is dirty and not clean. Either way its going to have to be torn down...

 

[Sureshot]

Re: Cylinder Wall Inspection (Pictures)

Probably a little bit of history might be good. Had it out on the water and the boat cut out at full throttle. Couldn't get it to start back up. A week or so later it was really hard to start but I finally got it going. It had a real rough idle and then cut out again on me at full throttle. Never could start it again. Had a mechanic take a look and diagnosed it w/ bad compression on lower cylinder, leaky carbs and a bad voltage regulator (whatever that is).

 

[1946Zephyr]

Re: Cylinder Wall Inspection (Pictures)

Yep, bad compression, most likely due to a leaking cylinder head gasket. Water got in there from it and caused the scoring. If water gets into the cylinder in a running engine, the water leaking in will actually clean the carbon off the cumbustion chamber, as I can see in the picture of your cylinder head. I'm willing to bet my bottom dollar that there is pitting on the bottom of the cylinder, from water sitting in the cylinder, too. Of course, once you start the engine up, the rust is quickly scraped away and causing scoring on the piston.