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'06 700EFI 6 x 6 top end rebuild

3176 Views 12 Replies 5 Participants Last post by  scsmith42
I'm in the process of rebuilding the top end on my 06 Ranger 700 EFI 6 x 6. This project has actually been in the works for about 2 years; I've managed to keep postponing it until the engine finally quit working last month.

The cylinder walls wore extensively at the top of one of cylinders and blowby was causing extreme oil consumption and plug fouling on the other cylinder (presumably due to the blow-by from cylinder 1 pushing oil past the rings into the chamber on cylinder 2. The compression finally got so bad on the first cylinder that it would not run.

It is an unusual cylinder wear pattern that I have never seen before. Of the portion of the cylinder where the rings ride, the top 3/8" was extensively gouged and worn (about .030 - .040 of wear) over about 1/2 of the cylinder. The rings that corresponded with this portion of the cylinder were extremely worn as well. The resulted in a significant loss of compression only when the cylinder was at TDC and maximum pressure.

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The problem originally showed up when the first fuel pump failed when the Ranger was about a year old. Subsequently the plastic intake manifold cracked on the bottom (due to seat pressure from above - pre the metal bar fix that Polaris came out with). My original deduction was that the cracked intake caused the mixture to lean out and thus scoring the cylinder, but when it was disassembled the piston skirts and cylinder walls look fine - no scoring. The only abnormality is the wear in the cylinder at the top. Strange.....

Chris Ball helped me out a couple of years ago with obtaining replacement OEM pistons, gaskets and a cylinder kit, but when I tore it down yesterday I noticed that the valves have significant wear where they meet the seat and if I grind the original valves there will be sharp edges - not a good thing.

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I was really surprised by the amount of wear on the valves considering that the ranger only has 810 hours on it. Both intake valves are worn about the same; the exhaust valves are not worn as much as the intakes. The guides are tight (which is usually what wears before the valve seating surfaces). As I recall, typically wear on the valve face is due to either excessive spring pressure or low lubricity in the fuel.

There have probably been 50 times when the engine has been operated at redline for 4 - 5 minutes at at time (running 3 miles down the road to a local gas station), but other than that it encounters a lot of start - stop work for 1 -2 minutes running across the farm or back and forth from the house to the shop.

Has anybody else encountered valve wear like this? I also noticed that Polaris indicated that they had superseded the original valves with new ones so perhaps the original ones were too soft....

Thoughts appreciated. Thanks much.

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Yes, l agree with Carnivore, looks like some dirt has made its way in the engine. The plating is gone at the top of your cylinder. Once a little bit of debris gets into your engine, it acts like sandpaper to your cylinder walls and valves. If you have any questions, I will be glad to help.
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