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Can someone provide me with the piston daimeter for a 250F, I have a new piston, ring set, and timing chain coming hopefully by Friday and want to make sure I have the right tools to do the top end. K&D makes some nice ring compresors but the sizes vary and I only need one to cover me with my light bike. Also does the cylinder require honing. There no mention in the owners manual.

Thanks

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:banghead: Thanks, that simple, I'm going to go for the 3'' ring compressor; either way I'm going top have to spend money cause I don't have an adjustable that big. :banghead: Do you normally hone cycliders on 4-strokes when you re-ring them.

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Yes--ball hone. I paid $5.00 to have mine done at a local shop.

I did not use a ring tool. Just line up the rings as shown in the manual and put them in dry. The put a bit of oil on the top and work it a bit. If the rings are not slippery, you can put them in no problem.

Dirt Rider mag had an article where they showed how to use a Dremel tool and grind out some half-moon notches in the bottom of your cylinder skirt to allow you to put the wrist pin in after inserting a pistion with rings into your cylinder. This is not necessary to do and I didn't.

Keep things simple and clean. Take your time.

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Actually you may not need to get your cylinder honed, but if you can get it done for $5 you might as well. When I pulled my 250f apart last winter the cylinder still had the cross hatching from the factory. Then again, I didn't pound the heck out of my bike.

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Regarding the piston, the bore is listed as 77mm (3.03"). Refer to the bottom of page 2-6 for the details on the piston and cylinder clearance.

The cylinder should definitely be honed using a 3 1/2" spring ball, or "Bottle Brush" hone. Spin the hone with a 1/2" low speed (400-600 rpm) drill. As the hone rotates, run it rapidly up and down in the bore (about one pass down and back up each second, or more) to create the cross hatch pattern you need. Make only as many passes as you need to resurface the entire cylinder wall (it should only take about three to four trips up and down the bore) and pull it completely free of the cylinder on the last pass. These hones remove virtually no metal, do not change the shape of the cylinder, and will absolutely seat your rings in under 3 hours.

The fact that the cross hatch is still visible to the eye does not mean you shouldn't refinish the cylinder. And please don't start with the reports about how you didn't do it and your bike is fine. Sometimes you can leave the cylinder as is and get away with it, but if you want to get guaranteed results, the way a pro has to, then hone it. Works every time. Also, don't assemble the rings dry. They will desperately need lubrication in their first few seconds of operation.

The compression rings will wiggle into the bore with relative ease. It's the triplex oil ring that will give you trouble, and if you don't have a considerable bit of experience or technical skill, and a lot of patience, I do recommend a ring compressor.

If you have a later model ('02 or '03 and later), the cylinder skirt has two notches at 3:00 and 9:00 o'clock. If yours is like that, use the ring compressor, and put the piston into the cylinder on the bench, installing it from the top. Then, put the assembled piston and cylinder onto the rod as one. (please stuff rags in the crankcase so you don't drop a circlip in there, OK?)

If it's an '01, with no notches in the skirt, install the piston on the rod, use a ring compressor and carefully run the cylinder down.

Don't rock the cylinder as you go. That will allow a ring to bounce free of the compressor or the bore, and you'll have to start over.

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i'm going to be rebiulding mine this winter, i was told i need a 12mm torque wrench capable of 25 foot pounds, and another caple of 25 pounds for the bolts under the cams. i guess i'll just use a box end wrench for the bolts going from the cycinder to the head.

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i'm going to be rebiulding mine this winter, i was told i need a 12mm torque wrench capable of 25 foot pounds, and another caple of 25 pounds for the bolts under the cams. i guess i'll just use a box end wrench for the bolts going from the cycinder to the head.

You need a 1/4" drive inch lb torque wrench for the cam cao bolts. You also need a 3/8" ft lb torque wrench for the head bolts. There is no such thing as a 12mm torque wrench.

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i'm going to be rebiulding mine this winter, i was told i need a 12mm torque wrench capable of 25 foot pounds, and another caple of 25 pounds for the bolts under the cams. i guess i'll just use a box end wrench for the bolts going from the cycinder to the head.
You were told this:

https://thumpertalk.com/forum/showthread.php?p=2566238#post2566238

Sorry to have omitted the 1/4" torque wrench from the list, but you told us you adjusted your valves once, I believe, or did you just check them?

(psst: spell checker)

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I've never adjusted my valves either. I checked them a few times but thats it. How about a 3/8 drive torque wrench (inch pounds) using a 3/8 to 1/4 inch adapter and the required 1/4 inch socket?

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:banghead: Thank you for the great input, this is a great resource. I truely appreciate your comments. :banghead:

I just rebuilt a 250F engine. You don't need any ring compressor. The 250F rings are extremely thin and very easy to compress with your fingers, while working the cyl down over the rings. The bottom of the cylinder has a bevel on it to also aid the rings starting up into the bore. As far as honeing the cyl., all I have ever done is a light cross hatch with some fine emery and oil. All you want to do is lightly break the old glaze.

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I've never adjusted my valves either. I checked them a few times but thats it. How about a 3/8 drive torque wrench (inch pounds) using a 3/8 to 1/4 inch adapter and the required 1/4 inch socket?

The problem with using a 3/8" drive torque wrench is that usually the torque required (especially for the cam caps) is too near the low end of the torque wrench's range. A 3/8" isn't accurate down there, and you can easily wind up stripping a bolt, or end up with varying torques on the cam caps. I feel this is the source of a lot of trouble for people who end up with ruined cam journals.

You want the torques to be absolutely accurate, so it's best to go ahead and buy a quality 1/4" drive torque wrench, keep it out of the cold, and store it on zero to maintain its calibration. Probably set you back $150-200 (Craftsman, Snap-On, Proto, Matco), but It's cheaper in the long run.

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The problem with using a 3/8" drive torque wrench is that usually the torque required (especially for the cam caps) is too near the low end of the torque wrench's range.
That's a valid point. The other one is simpler; it doesn't fit under the frame very well to get at the rear center bolt on the intake cap. I also recommend reducing the torque spec on the cap bolts from 7.2 ft/lb (87 in/lb) to 6.2 ft/lb (75 in/lb). The called for spec is too high, IMO, and I understand that Yamaha has reduced it in later manuals, as well.
As far as honeing the cyl., all I have ever done is a light cross hatch with some fine emery and oil. All you want to do is lightly break the old glaze.
Remember I said,
please don't start with the reports about how you didn't do it and your bike is fine.
...hmm? I knew someone would. Like I said, if you want to go with the "Microsoft Approach" (works most of the time), fine. If you want to spend a little extra time and money to do it right, and get the rings seated almost immediately, hone it.

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The problem with using a 3/8" drive torque wrench is that usually the torque required (especially for the cam caps) is too near the low end of the torque wrench's range. A 3/8" isn't accurate down there, and you can easily wind up stripping a bolt, or end up with varying torques on the cam caps. I feel this is the source of a lot of trouble for people who end up with ruined cam journals.

You want the torques to be absolutely accurate, so it's best to go ahead and buy a quality 1/4" drive torque wrench, keep it out of the cold, and store it on zero to maintain its calibration. Probably set you back $150-200 (Craftsman, Snap-On, Proto, Matco), but It's cheaper in the long run.

That's a valid point. The other one is simpler; it doesn't fit under the frame very well to get at the rear center bolt on the intake cap. I also recommend reducing the torque spec on the cap bolts from 7.2 ft/lb (87 in/lb) to 6.2 ft/lb (75 in/lb). The called for spec is too high, IMO, and I understand that Yamaha has reduced it in later manuals, as well.

OK hold everything. I have a 3/8 micrometer type torque graduated from 0 - 100 inch pounds it's about 6 inches long. I also have a 3/8 micrometer type torque wrench graduated from 100 to 750 inch lbs. Last but not least I have a snap on micrometer type torque wrench graduated from 25 (or 30 it's been a long time since I used it) to 250 ft/lbs. Are the low end on these tools no good?

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If you can fit it onto the bolt in question, the 0-100 in/lb is perfect. If it won't, you can get an offset torque adapter (5/16" and 8mm are functionally identical). Try to avoid using a u-joint, though, as it will tweak your torque readout.

Use the 750 in/lb wrench for the cylinder head (27 ft/lb=325 in/lb) :banghead:

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I also have a 3/8" torque wrench that goes from 25 to 250" pounds. The mid-point of that is 137.5, half of that is 68.75. (25% of the wrench) I feel this is accurate for the cam caps.

Also remember that a torque wrench is most accurate from about 20%-80% (if I remember correctly, gray can probably chime in here). Work slowly so you do not go past the torque. Also, go in steps. Do not torque down the caps to 87" pounds the first time. Cut it down into 4 or 5 steps.

Jet blue, do you have the top end gaskets as well? Here's a general idea for the top end (my list of what I did:

Piston

Piston rings

Piston Pin

Piston clips

Head gasket

cylender gasket

tensioner gasket

timing chain

Ball hone the cylinder

I recomend ball honing it as well. The rings will set and give you good compression and years of trouble free use. When working on things, you'll learn this lesson quickly; since you have it apart, replace it. And not to mention; do it once, do it right.

I learned my lesson changing the timing belt on my Yota Tacoma. Changed the belt, idler pully, water pump, tstat, hoses, belts, even used fipg sealant from toyota. One thing I did not replace is the tensioner pully. Needless to say, 10 miles later, the pully failed, and I had to do my work all over again.

-Phill

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OK hold everything. I have a 3/8 micrometer type torque graduated from 0 - 100 inch pounds it's about 6 inches long. I also have a 3/8 micrometer type torque wrench graduated from 100 to 750 inch lbs. Last but not least I have a snap on micrometer type torque wrench graduated from 25 (or 30 it's been a long time since I used it) to 250 ft/lbs. Are the low end on these tools no good?

I was assuming you just had a standard 3/8 drive torque wrench. That's what I get for assuming. If you can fit it in there, your 0-100 in-lb will work fine. :banghead:

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Hey Phil thanks for the input. I ordered everything on your list. As I mentioned to Greyracer I did a leak down test on the bike last night and walked away with nice results. So now I'm a little torn about tearing it apart other than to maybe check the valve clearances. I've owned my 04 250F since late August last year. My concern is the bike has been ridden on average 8 hours a week since April. I'm not hard on the bike but it sees a lot of time especially when my sons bike is down which has been kind of frequent this season. I like greyracers comments as well and I am going to hold off until the bike needs to be reshimmed.

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