Looking at the cylinder diagram, there is also 2 options for the cylinder. I am going to guess they have to match. So looks like I'll be calling the dealer Tuesday to get the right pistons.

I thought so, but good to have a second opinion. I'll put it back in with the mark facing the intake, as it was. I just wish I could find something regarding the IB and IIB markings. I haven't been able to find any explantions of differences. OEM parts diagrams show 2 options, but no reason for the options. I did order these from a dealer, so they had my machine info.

That is the page I saw. Cylinder 1 is at the rear of the machine, correct? In that case the arrow points at the intake, as mine was. But it states front and rear would be reversed and my piston was in backwards. I have yet to take apart the front (#2) cylinder as I wanted to tackle only one at a time with zero chance of mixing up parts.

Finally got around to rebuilding this beast. I have a couple questions tho. My current piston is marked II-B, and my new one is marked I-B. What are the differences and do I need to return these for the other type?

Also, the manual states the arrow should face the rear of the engine. This one was facing toward the front. Could that have caused the wear on the middle ring? It is pretty considerable.

NWK, after the time I have spent combing this forum I trust your opinion fully,  haha!!

So I see you highly recommend nFlow for reman engines. Do you know what their turn around typically is? Do they actually reman MY engine and ship it back? Or do I get one they have done and ship mine in as a "Core"? This is looking more tempting as I go, just for piece of mind and simplicity. Just don't want to be sidelined for months if I can avoid it.

Cleaned useless prefilter. Can't wait to get the Uni on it.

Whole lotta air coming from the crankcase tube. Am I correct in thinking that is a sure sign of bad rings? Or possibly piston failure?

Will check valve settings when I get more time. Headed to Vermont in the morn to look at a zforce 1000.

Here's something, I have oil on the crank sensor. That shouldn't be there, should it?

So tested again. Had the kids putt around to get good and warm.

Front cylinder has 135psi compression, holds 40psi at 50psi with leak down tester.

Rear cylinder has 120psi compression, holds about 30psi at 50psi with leak down tester.

Using a stethoscope. Hear a little air on the exhaust side of things. But would that allow oil to reach the airbox?

1400 miles on it.

Thinking about it overnight, I ran the engine to warm it up, but likely cooled down too much while removing panels and belt cover. Needed to check belt and clutch anyway. Going to try again later, removing what I can ahead of time.

Going to check out a 2018 zforce 1000 this weekend. 1900 miles. What should I watch for on these ones?

Thanks for the quick reply. Don't think it was heat, more likely the STOCK AIR FILTER that is still on this thing, haha! Obviously the prior owner was not a member here.... I just bought it last week. Just now ordered the Uni filter, oil, and an outerwear pre-filter. At least I'll be set once I figure out what I want to do with this thing.

The thing that gets me is it runs like a top. Starts quick, idles fine, plenty of power. If it wasn't for this site, I'd never know there was an issue to be resolved. Did an oil change, just because I am unsure when it was last done. Now I just need to get this oil in airbox issue figured out.

The compression being so low on one cylinder yet still running smoothly has got me scratching my head. Both plugs looked decent, light tan color.

I am tossing together a parts list to see where I might be price wise. I would love to just go the NFlow route, but not sure if  I want to drop $3k on an engine. Dealer quoted $1500 to rebuild top end when the PO brought it in.

I'll have to see if I can locate a bore scope and take a look in the cylinders. Maybe I'll see something that helps swing my decision one way or the other.

One thing I want to add - As I did the leak down test, I sprayed a soapy water all over everything I could get to. Figured if I had a bad head gasket or a crack I would see some bubbles. Nothing found. Also, with 90psi on the cylinder, I rotated the engine by hand slowly. I was able to hear when different valves opened and I could feel the air coming from the exhaust. Not real sure, but I think it may have still been blowing out of the exhaust a little on the compression stroke. I need to redo this test tomorrow and see if I can pin point what is going on.

Hi all, just did some testing on my 2015 800EX. Have a lot of oil in the air box. Compression on cylinder 1 was about 60psi, cylinder 2 was 120psi. So got a leak down tester. At 90 psi I can't build more than 20psi in either cylinder. I can hear air escaping, but can't find it. No bubbles in radiator, used a stethoscope to try to locate the culprit area, but I just could not find anything.

Motor starts and runs fine. No power issues, goes good. I have been up to 60mph with it and ran out of room before running out of throttle. Looking for any help I can get on this, because I am stumped at this point.

I bought this thing for cheap money last week. Prior owner was going to trade it in but dealer said it needed top end rebuild due to exhaust smoke. I have not seen any smoke. It does get quite a bit of oil in the airbox quickly, so I assume this is what they were talking about.

How hard are these things to rebuild? I am mechanically inclined, but don't want to fight with it if I need a bunch of special tools and such. For the price I gave, I can pay the shop to do it and still be happy with the investment. But it's always nice to DIY and put that labor $$ towards other toys!



Chris