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Discussion Starter #1
My 800xp had 3500 miles when I purchased, it now has just shy of 10,000 miles. Been a good machine, very few problems besides replacing IAC and TBAP harnesses, axles, and some bearings. I've kept the maintenance up and she used a little oil but not much. Checked the compression last winter and compression was even with both cylinders around 175psi. A few weeks ago I jumped on to check cows and thought I heard a whistling sound, intake boot was tore. I had actually replaced it not that long ago because other one had some cracks forming but had not created a hole yet.

Definitely had sucked some dust, I live on gravel, changed boot, cleaned intake components, and changed oil. I feel like she definitely lacks power now, starts easy still, slow acceleration, just doesn't feel like she has much pep. Will even die sometimes if I forget to take parking break off and give it gas. Checked compression and one cylinder is now like 120psi and other is still 170psi or so.

So what I'm wondering is, do I just do a whole top end, with 10,000 miles I'm sure it was due anyway, and just see how long it goes? I'm sure the bottom end cant be perfect, ill do the work myself but if i do the top end with new jugs from Wiseco I'm looking at $550 or what are the chances whole motor is bad? Or should I take top end off and see how the bottom is before ordering parts. If the bottom end is bad then I'm not sure if ill do it all myself. I use the machine daily and don't really want to be down longer than necessary, so I would rather have top end kit sitting here before tearing in. But if replacing the top end will more than likely get me a few more years then Im ok with that vs putting out cash for a new motor.

I don't hear noise coming from case, a little bit of ticking but figured that was just piston slap from top end getting dusted. What are signs of bad bottom end? Does weak power come from the top end being shot?

Thanks for any insight and direction.
 

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That sucks J but it does sound like you dusted the engine. With that many miles (10k) and after a good dusting, if I was going to hold on to it for many more years to come, I would be doing the bottom end as well. It won't take that much longer and not that much more money and you will know where you stand because if you don't.............that little voice will be second guessing you over and over and over............and over.....
 

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Your guys responses are kinda of what I was guessing you where going to say. Although looking at things tonight there does seem to be a lot of oil under the valve cover. I really don't notice much smoke, just knew I was going through oil.

Anyway, if going through a rebuild would you buy a kit that includes new valves since it's already going to be torn down?
 

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Unless you just want the challenge of rebuilding the engine, before I did anything else, I'd do a cylinder leak down test to determine whether the engine got dusted and the rings,cylinders, pistons are the casue of the compression loss or if a burned valve is the cause. This can be determined with a high degree of accuracy by a cylinder leak down test, but not by a simple compression test. All it takes is one leaky valve to knock compression in one cylinder down substantially. A dusted engine should have low compression in both cylinders rather than just one.

With regard to the bottom end, if you're going to tear it down far enough to inspect connecting rods, unless bearings are outrageously expensive, I'd just replace them. No being familiar with the specifics of the 800 engine, I don't know whether the rod bearings are a simple insert type or needle type that requires rod replacement as well. I did an overhaul of an old Polaris 400 2 stoke that had the needle type but the rod was still OK so only the bearing itself had to be replaced. That engine had a two piece pressed crankshaft which had to be pressed apart, the rod bearing replaced, aligned and pressed back together. I was able to adjust final alignment by putting the crankshaft between centers and checking runout with a dial indicator. In other words, some equipment not commonly found in a home shop may be necessary, which adds to cost if things must be taken piecemeal to a local shop for specific work to be performed.

With regard to a kit with new valves, that would depend upon the difference in price between a kit with and a kit without valves, the condition of my original valves and whether I had the equipment to regrind valves or a shop that would do it. When it comes to valves it isn't just a matter of slapping new ones in and moving on, valve seats have to be in good condition, or reconditioned, replaced if necessary and possible and lapping in the valves (even new ones). With 10k miles I'd plan on valve seat work as needed.

Another consideration is to compare the price of parts and labor, (valve seat resurfacing, replacement, for example) to having a rebuild done by a reputable rebuilder like nFlow. The choice of using a rebuilder may be more cost effective and efficient in the long term if much work must be done by a local engine building machine shop.

If I had made the choice to definitely perform the rebuild myself, I'd tear things apart, inspect and then order parts or a kit as necessary bearing in mind that additional parts or work may be found to be necessary as the rebuild progressed.
 

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Your guys responses are kinda of what I was guessing you where going to say. Although looking at things tonight there does seem to be a lot of oil under the valve cover. I really don't notice much smoke, just knew I was going through oil.

Anyway, if going through a rebuild would you buy a kit that includes new valves since it's already going to be torn down?
J, synthetic oil burns clean ....IOW's, you are not going to see alot of blue smoke like you would with conventional oil. 10k , burning alot of oil and a recent dusting.............. that equals top and bottom rebuild where I come from. I realize Ranger Nitwhit skipped it on his low mileage one lung two wheel drive 500 when he fried it up but common sense with that kind of mileage and circumstances big oil burn/dust, dictates top and bottom. Up to you of course.
 
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I was suggesting checking the rods for up/down play when the jug is off. If you only want a couple of years out of it and minimum down time, I would go the top end route. The oil filter likely did its job.
 

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Discussion Starter #9
Found a leak down tester to borrow, just got done doing that. One cylinder is about 25% and the other is 30%. All of the air seems to be coming out of the valve cover vent hose.

Checked compression numbers again, 120 and 150.
 

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Pretty serious numbers J. 10 -15 % on the leak is about max and about the same on the number spread on the compression test. It sounds like the crankcase is pressurizing and that explains the evacuation through the crankcase vent hose.
 
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Does everyone with the nikasil coated jugs just replace them? Or can they be reused if not scuffed to bad? Seems like a waste if you do.
 

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Discussion Starter #12
Pulled head, cylinders looked way better than I had pictured in my head. Anyway, haven't pulled jug, wanted to see head and cylinders. Top of both cylinders have some lines as seen in picture, but cannot feel them with fingers, only by sight. Pistons seem really tight when I pushed on them and rotated clutch. Valves didn't look bad to me either.
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When you get it apart remoe the top ring from each piston carefully and put it in the cylinder using an inverted piston to push it down about a half inch, then measure the ring end gap with a feeler gauge. Comparing that measurement to the OEM spec should give you and idea of how much ring wear there is.
 

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Do you just rough up the cylinder walls a little new rings and let it ride?
I've not rebuilt an engine with Nikasil coated cylinders so I can't say for certain. If it were me I'd mic the bores to insure they are round and if all is good break the glaze with something very fine like a ball hone but in fine grit and I wouldn't run it in and out but about twice with lots of light lubrication. The coating isn't that thick and you don't want to go through it or you have to get it re-plated or replace the cylinder.
Fact or Fiction? Engine Hones for Nikasil Cylinders
 

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Agree with rangerewhit, hone cylinder a little new rings, I'd run the head buy some where and revalve it, good to go
 

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Discussion Starter #17
pulled jug last night, pulled rings off, definitely to much gap in rings. I know some of this will be ring wear and new rings would have a smaller gap, but I think it's to much. Feel like best thing to do is replace jug and be done, can't see any cross hatching. I couldn't find my feeler gauges, but the ring gap was significant, I found tolerance is supposed to be .15mm-.35mm, business card is about .25mm, and I could have put a stack in the gap. I'll get a measurement tonight.

Good news is I couldn't get any up and down play in rod bearings when pulling/pushing on rods. So I'm hoping that means bottom end is good, I have yet to see any metal shavings or find play in bottom end.

Going to pour alcohol in head tonight to see about any leaks. What's best way to decarb head?

Wondered about taking head, valve cover, ect. into tractor dealer and have them run it through their parts washer, owner is friend of the family.
 

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Discussion Starter #19
Yes, ordered the Wiseco kit, should have Thursday. Hopefully have time to work on really cleaning head up tomorrow, worked a little bit and most of carbon came off head, valve faces are the worst, but I haven't been aggressive at all.

Pressed valves down, seats looked really good, trying to find a spring compressor so I can disassemble. Checked ring gap of used rings, 1.27mm easily slid in, so definitely wore, current gap is atleast 5x out of spec. Pistons looked way worse in daylight then they did last night with just shop lights.
 

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Get a spring compressor on loan from a big box store. Just don't buy the parts there!....:cool:
 
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