andika
15.05.2021 8:43:57
Anyone wanna buy (3) standard size pistons and rings for a 94' Mercury Sport Jet 90HP? haha more
See full version: How do you know when you need to get bigger pistons when honing
Anyone wanna buy (3) standard size pistons and rings for a 94' Mercury Sport Jet 90HP? haha more
Anways, I took it to a guy who knows engines, and he thinks its getting pretty close to the point where I'd have to go buy new pistons and have the engine honed / bored to match
Mike the bore just above the exhaust ports and near the top. Mike each at vertical (direction of piston pin) and across the ports. If the cylinder is out of round or tapered by more than .002 inch (two thousands) then factory recommends boring over. You have the option of .020, .030. and .040. (WISECO used to sell pistons .010 over but no longer does. I don't know if Merc does.) At any rate, overbore the smallest amount needed to clean up the cylinder if scored or to bring it back into round. [links]
Re: How do you know when you need to get bigger pistons when honing? here
take it to the machine shop and see what they would recommend.
False, unless you royally screw up the cylinder walls and can't hone it out .001" that should be the only time you switch to 100mm. Stress fractures are a very common problem at the cut-out's for the block half bolts. Whether you can see them or not, they are usually there until it breaks the sleeve. Example below: here
if a hone is needed, go that route.
You'll just need new rings
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The best way to bore a cylinder is to use a boring machine and not a hone. If you do use a hone you must use a high quality one like a Sunnen or an Ammco hone. Hones come in several sizes to fit different cylinder bores. Some of the Ammco hones have several sizes of stones so you can use a standard size hone in a large cylinder bore. The Ammco hones also come in several grit sizes. Coarse (60), fine (220) and super fine (320) for aluminum and plated cylinders. Some top-of-the-line hones use diamond impregnated stones but those are priced a bit out of my price range. here
Take the piston measurement and subtract it from the biggest cylinder measurement. Compare the result with the piston clearance given by the manufacturer of the piston. In other words if the cylinder measures 2.6114" and you subtract the pistons diameter of 2.609" you get .0024". Compare that to the piston manufacturers suggested minimum/maximum clearance. In this case that would be .0016"-.003" with a limit of .004". If it is within that specification you could hone the cylinder and put in a new set of rings. If it is OVER that specification you will need to bore the cylinder out to the next biggest oversize and buy a new piston and rings.
This is not to say I haven't bored out some wild and crazy holes. In my wayward youth, for a friend, I once bored out a Briggs and Stratton cylinder, to the next oversize, with a ball hone. It actually worked too! Unfortunately, a motorcycle cylinder requires a bit more precision. Boring with a hone takes a long time. Like several hours. I once honed a cylinder .040" oversize. I held it to the right taper and out of roundness but it took a long, long time. You need a quality hone, I used an Ammco hone. Then you hone a bit and then you measure. Hone a bit and then measure. It takes hours and is very, well, boring! When you are finished you want a nice 45 degree angle cross hatch pattern in the bore. Never hone a cylinder dry. Use lots of oil when honing. Buy the special honing oil. It works much better then plain oil. Honing oil cools the cylinder and hone. It also enhances the cutting effect of the stones. Use a lot of honing oil! more
The reason you take so many measurements is because cylinders can wear at different rates at different spots in the cylinder. The most wear occurs at the top of the cylinder and in the front and back portion of the cylinder. The least wear is at the bottom of the cylinder. Sometimes, you can even see slight hone marks at the bottom of the cylinder, even after many miles. The cylinder wears in a taper and out of round from the top down.
Resist the urge to put the hone in a drill press, kick her on high and have at it. Been there, done that. Didn't work so good. Slow, steady, and lots and lots of measurements. That is the way to go. here