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Discussion Starter · #1 ·
Bought a 2008 summit 800r with low compression for a good deal. Doing top end and would like to know what you guys think caused the piston to go. Checked out a few charts and can’t tell if it’s lack of lubrications or overheating. Would be nice to know to prevent new pistons and newly plated cylinders to go again. Previous owner didn’t mention anything about a fresh rebuild but the pistons don’t look all that old so wondering if something is going on
 

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At this point i would pull the crank out and have a really good look.

Check water pump drive gear.

Install new oil pump. as well as one way valves on cases.

Fresh seals.
 
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It may not be helpful in determining the cause of failure, but the picture of the bottom side of the pistons looks like the pistons are not matching? The top one in the image has extra features near the dome.

I'm not familiar with this engine, but can you tell if either piston is an OEM one and then relate that to which one is failed. It may serve as a clue to what's been changed in the past
 

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The the color/tint of the piston in the first picture has me question a complete loss of oil. I see one or maybe two of these each season, as most piston failures don't show this. It is the dark color, dryness and scoring that reaches all around the piston that gives it away.

Now look at the bottom piston in the third picture. Note how the underside of the piston looks dark and dry compared to the upper piston. This has me question a number of things in the oil system. While disassembling the engine, keep the crankcase, crankshaft, oil pump and all small oil lines as a unit for testing. With this unit on a work bench, remove the oil pump still connected to the small oil lines, to turn it around and use an impact driver to turn the oil pump at high speeds. Look for any leaks in the oil check valves, tiny tube fitting on the valves, small oil lines that runs from the oil pump to the check valve, and the fitting from the pump to the tiny oil lines.

Do this right and you will know if it was a lack of oil. Skip a step or cheat for wiggling things around prior to the test, and you will have lost the most important portion of the diagnoses. Do not move or play with any of the hoses or fittings until the test has been completed.

The use of a cordless impact driver is to get the oil pump spinning fast enough. A regular drill does not turn fast enough and take forever to a drop of oil.
 

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Next thing to check is the oil pool at the bottom of the crankcase. If the failed side has little to no oil pooled, then it's a no brainer, but still test the oil system.

Make sure to empty all the coolant prior to disassembly. Siphon out what you can and disconnect the lower coolant hose at the pump, or just remove the coolant hose with a large catch pan. Leave no coolant flowing in the crankcase. It is the PITA portion of the teardown, but it needs to be done. Also, always - ALWAYS - mark each head, cylinder and crankcase bolt with a sharpie prior to removal. If there is a loose bolt, this is the only way you will ever know.
 

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It may not be helpful in determining the cause of failure, but the picture of the bottom side of the pistons looks like the pistons are not matching? The top one in the image has extra features near the dome.

I'm not familiar with this engine, but can you tell if either piston is an OEM one and then relate that to which one is failed. It may serve as a clue to what's been changed in the past
The top one is a forged piston from Kelsey @ RK Tek.
 

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Thanks for the input, some helpful information
I can only hope that you pay it back with more pictures and results from you testing. No one does it alone.
 

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Check the bore size on the pistons or cylinder. Should be around 82mm. You might have a big bore cylinder on that rig. The big bore cylinder or pistons measure around 85mm.
 

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Are those pistons from the same engine !? They are VERY different designs (other than both being forgings).

The top is an Italian forging (78-26) and the bottom is also but using the Lt wt die (2115).

WIll need more pics to help here but as one poster has already pointed out...very dry.

- Scott @ MCB
 
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Discussion Starter · #13 ·
Both pistons are definitely different but stock size. Couldn’t really test the oil pump as I had already pretty much stripped everything but I think I’m just gonna get a new one. Also decided to split the case and check out the crank in case it did run dry and found my Center bearings shot, going to call cvtech I think and get a reman on Monday. Only other thing I’m having an issue with is the oil check valves not sure where these are? Small piece where the smaller oil lines go to the case?
 

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Yes that is them. If you go with a new short block? It will come with new check valves installed.
 
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Yes that is them. If you go with a new short block? It will come with new check valves installed.
Short block probably would of been the way to go but a little too late for that, everything is already paid for and cylinders re plated. So rebuild it is, thanks though I'll look into those checks
 

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Both pistons are definitely different but stock size. Couldn't really test the oil pump as I had already pretty much stripped everything but I think I'm just gonna get a new one. Also decided to split the case and check out the crank in case it did run dry and found my Center bearings shot, going to call cvtech I think and get a reman on Monday. Only other thing I'm having an issue with is the oil check valves not sure where these are? Small piece where the smaller oil lines go to the case?
Never too late to test the valves. Those are the pieces where the smaller oil lines go to the case. MCB sends out new ones with their rebuild kits.

When you split the cases, the failed side had no oil pooling at the bottom?
 

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Discussion Starter · #17 ·
Never too late to test the valves. Those are the pieces where the smaller oil lines go to the case. MCB sends out new ones with their rebuild kits.

When you split the cases, the failed side had no oil pooling at the bottom?
I think I'll call for a price for new ones if not expensive I'll just replace them and be done with it and also both sides had a little oil at the bottom,
 

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I think I'll call for a price for new ones if not expensive I'll just replace them and be done with it and also both sides had a little oil at the bottom,
Having somewhat equal oil on both side, it becomes even more important to reconnect the oil pump and two small lines to see if there was any leaks. It is dry from no oil, but the reason needs to be found. Could this be too much snow/water ingestion? The engine can drink a fair amount of snow without much problem, but there is always a condition when it stops working. My guess is the engine wasn't getting enough oil injection. Since it is a 2008 800R that could very well be.

How much oil would it go for a 10 gal tank of gas? 1/4 tank or oil?
 

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Discussion Starter · #19 ·
Having somewhat equal oil on both side, it becomes even more important to reconnect the oil pump and two small lines to see if there was any leaks. It is dry from no oil, but the reason needs to be found. Could this be too much snow/water ingestion? The engine can drink a fair amount of snow without much problem, but there is always a condition when it stops working. My guess is the engine wasn't getting enough oil injection. Since it is a 2008 800R that could very well be.

How much oil would it go for a 10 gal tank of gas? 1/4 tank or oil?
I'm not sure I just bought this sled never actually rode it beside loading it in my trailer and into my garage, it still ran just had low compression so decided was gonna do a top end and now here I am lol. If I were to just get a new oil pump and replace check valves should I not be good?
 

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I don't do those types of repairs, so I don't know. I personally hate walking home or being towed, which I had my share of both.
 
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