I've got a 98 GTX RFI that lost compression in one cylinder. I tore it down and sure enough the piston was bad. The cylinder walls appear to be perfect. I ordered a top end rebuild kit but I'm wondering if I have to have the cylinder heads bored or can I just install the new piston and rings?
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Top End Rebuild
- Thread starter wvcorder
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AKnarrowback
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No experience with that particular machine or engine, but a standard practice would be to hone out the cylinders and remove any glazing, rub marks and put a good cross hatch on the walls and measure the bore where you are at before ordering any pistons. If you are close to max clearance then you might as well bore one size up and put in larger pistons, but don't do the bore job until you have the pistons in hand so the machine shop can measure the exact piston going in.
But my experience is with old steel sleeves. If it is a nicasil cylinder face that is different and the more experienced members on here can guide you.
When you say it had a bad piston what condition is it in? Do you know what caused the failure?
But my experience is with old steel sleeves. If it is a nicasil cylinder face that is different and the more experienced members on here can guide you.
When you say it had a bad piston what condition is it in? Do you know what caused the failure?
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Thanks for the info. I don't know what caused the failure. I just bought the ski and it had been sitting. It only has 70 hrs on it. Both cylinders were pretty rough on the tops and the front one had a piece broken off around the rings on the side. I'm assuming is was from just sitting for a long while and then being ran. Would that make sense?
Nope. You need to have the cylinders professionally measured with an actual bore gauge. It’s the only way you will know if it needs to be bored oversized or not.
Pistons typically seize from lack of oil or lack of fuel from dirty fuel system and/or injectors.
Pistons typically seize from lack of oil or lack of fuel from dirty fuel system and/or injectors.
Was the failed cylinder the PTO side? I bet your bore is gonna be fairly round with not much taper and will be the upper end of the size limit. You'll need to mic the bore in several places to verify. Using WSM pistons will probably get you dang close to the almost new spec. without boring as WSM recommends .0045" - .005" piston to bore. You'll need to hone but you'll likely have enough material. Check free play on the connecting rods.
Post pictures of the cylinder and pistons. Likely it was lean. Send the injectors out for cleaning and servicing. Check fuel pressure and verify the fuel regulator is holding pressure. Replace both filters in the tank. Watch for those needle bearings falling out under the piston when you go to remove it.
I'm on my 3rd RFI in the last 12 months. Currently putting one back together. Believe it or not, the engine with this piston actually started. Good luck !!
Post pictures of the cylinder and pistons. Likely it was lean. Send the injectors out for cleaning and servicing. Check fuel pressure and verify the fuel regulator is holding pressure. Replace both filters in the tank. Watch for those needle bearings falling out under the piston when you go to remove it.
I'm on my 3rd RFI in the last 12 months. Currently putting one back together. Believe it or not, the engine with this piston actually started. Good luck !!
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