Interesting observation after rebuild!

MBradbury · 06-20-2004, 06:54 PM

Hi everyone,

Hadn't really thought of this, but observed this during the third oil change after a rebuild. I removed the oil screen to examine for any debris (thankfully there was none) and when looking inside, I noticed I could see the bottom oil control ring of one of the pistons at the bottom of its stroke. You can see the ring in the upper left of the attached picture. I just didn't expect the piston to travel that far down the barrel i.e. to actually expose the ring. I know it is only say 10% of the ring, but it clearly emerges from the bore allowing oil to get between the oil and compression rings. This is a tested set-up i.e. Max Moritz 98mm pistions and barrels on a '83 SC crankcase, and so far the rebuild is fine (100 miles). Just didn't expect to see such a thing.

Any comments?

Regards
Mark
1983 SC 3.2 Short Stroke
1988 soon to be '73 RS clone

Shuie · 06-20-2004, 06:57 PM

Sorry, I cant help much. What are your opinions of the 3.2 short stroke so far?

cstreit · cstreit's Garage

I wonder if that was an "oversight" or an additional way for the ring to dump oil scraped off the sides back into the case (since it is not submerged)? I know the "drain holes" in the piston do the majority of the work...

Good observation!

Wayne 962 · Wayne 962's Garage

That is pretty wacko. Where did you get the pistons and cylinders? Are they genuine Mahle sets, did you get them from Andial?

This *should not* be happening. I just had a long conversation on the phone where I showed someone this picture. We both agree on the following:

- You shouldn't run the engine until you figure out what is going on
- This should not be happening - the oil ring gap will eventually come around and pop out at this point, resulting in one or more broken rings (assuming the others might be the same way)

We're confused at what we're looking at. Clearly, the thick boss in the picture is not a cylinder wall, but some part of the case. In the picture, I cannot see where the cylinder wall would be. Are you sure that's a ring, and not a marking on the bottom of the piston? Where is the cylinder? Can you take more pics as you rotate the crankshaft, pushing the cylinder back into the bore?

If you look at a normal, used cylinder, it has almost a full centimeter of margin at the bottom of the cylinder - the oil ring should not go anywhere near the bottom lip of the cylinder...

-Wayne

Groesbeck Hurricane · 07-01-2004, 04:09 AM

Bump.

Any more information?

MBradbury · 07-03-2004, 06:32 AM

Wayne,

Just returned from a week and a half business trip and read your reply. I don't like the sound of this. I took the photos just before I went away, after the 3rd oil change. I did take it for a run of about 10 miles or so. I haven't started it since then.

The pistons and cylinders are original 98mm Mahle, sourced through Andial Racing. I have some photos of them that I can post. It's over a week since I took the photo, so I am not going to categorically say it is a ring. I need to take another look. I will post some more photos later.

Mark

MBradbury · 07-03-2004, 07:41 AM

Wayne,

I found another picture I took at the same time. It shows the thing under question in relation to the cylinder. I also attached a picture of the piston and cylinder before they where installed. Whatever it is, it doesn't look like the piston skirt shape. The alternative picture also shows what looks like the edge of the piston skirt, which is way too close to what looks like the ring when you refer back to the piston when outside the engine.

Could it be the chamfered edge of the cylinder and the very bottom of the skirt?

Only one way to find out for sure. Drain the oil as Wayne suggests, take the inspection plate off, take out the spark plugs and turn the engine over to see what happens. I will post more photos later.

Mark

Henry Schmidt · Henry Schmidt's Garage

What you are seeing is the bottom of the cylinder and the piston coming out of it. The rings are not in views. The picture seems deceptive but that is what we are looking at.
Because the cylinder bottom is flat at this location, if you could see the oil ring it would have popped out of the cylinder. If you remember putting the rings into the cylinders when assembled you know that the ring won't go into the cylinder without compressing them.

MBradbury · 07-03-2004, 12:33 PM

Everyone.

Panic is over. What looked like a ring was actually the base of the cylinder poking through the crankcase. I took the inspection plate off again and took some more photos (attached) that show the piston fully up the bore clearly showing the chamfer of the cylinder base on its lonesome. In the original photo it really looked like a ring. I need glasses. The other photo is similar to the earlier ones, where the piston skirt emerges from the base of the cylinder. The rings must be several centimeters away from this edge.

I am going back in the garage now to put it back together again. I need a dose of pleasure this evening. Think I'll go for a ride.

Thanks everyone.
Mark