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Discussion Starter #1 (Edited)
So this is probably the third question I've asked over the past two days but y'all are extramly helpful. What does it mean to bore your engine. Just saw two for sale post. "Bore .50 over" and another that said "Bore .40 over" so how many cc's would that end up being.
 

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boring a cylinder up/out/over means to drill the cylinder out to a larger size piston. it won't increase the cc's enough to amount to a hill of beans.
 
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to give you an idea .025 on a 350 cylinder increased the cc's by 5 , then .050 another 5 CC's , so the 350 was really 317 to start , .025 over 322cc , .050 over =327cc
 

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Just service over bores, they were probably worn out one way or another and had to be bored oversize with a new piston installed. cc would depend on the stroke of the engine so I can't say what cc without knowing what machine.


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to give you an idea .025 on a 350 cylinder increased the cc's by 5 , then .050 another 5 CC's , so the 350 was really 317 to start , .025 over 322cc , .050 over =327cc
did you think of the starting size bore ?, because if you look on the cylinder at the bottom, almost on every cylinder, they never read the true cylinder size in cc's ?, they are always under the size of the atv/motor. most trx300's for example, normally ran around 289 cc's I think they were ?. soooooo..you must start there when you increase the bore, not what they claim it is.
 

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I think so , a 300 Fourtrax is 281cc , 350 Rancher is 317cc , so my 300 engine is 322cc right now , it has a 350 sleeve bored .025 over
 

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rancher 350 is 329cc, the 350's piston on a 300 engine is only 317cc because of the shorter stroke. Most ATV's are within about 25cc of their official name. The 300 was 282cc, the 350D was 350.4cc, the 350 Rancher was 329, the 400 Foreman was 395, the 400 Rancher was 397, the 420 is 420cc, the 450 Foreman was 432cc, the 500 Foreman is 475cc, the 500 4 valve rubicon was 499cc, the 650 Rincon was 649cc and the 680 Rincon is 675cc.
 

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Nice spec list Mac , here is another one , the old 250A is 246cc , and the 300 has 281 embossed on it , maybe Canadian models are 282 .LOL ---
 

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And the 250A cylinder and 300 cylinders are the same, but the 300 has a longer stroke on the crank so more CC's using the same cylinder.

I got back 4 cylinders yesterday from Fishfiles buddy.

A 500 Foreman that was already bored .75 over and had a circlip pop out and dig a nice deep gouge in the cylinder wall. This one had to have the cylinder pressed out and a new sleeve installed, because 1.00MM over is as big as you can go oversized before the cylinder walls get too thin, and in order to machine enough metal out to bring the cylinder walls perfectly smooth (get that circlip damage/ groove polished out) would have required removing too much metal. So this one had a new sleeve pressed in and started over with a Std size piston.

The 2nd was another 500 Foreman cylinder that came with a project I bought. It had to be bored .75 over which means it had either been bored before or someone really ran it a long time after it was smoking/ rattling.

The 3rd was a 250A cylinder that I am going to use on a 300. It had to be bored .75 over so I'm guessing same as the 500 above. The Connecting rods on the 250A and 300 are not the same, so the pistons are different at the wrist pin, but they are the same size, so they cylinders are the same size as well. I just got a 300 piston and had the cylinder bored to match that piston.

The 4th was a 350 Rancher cylinder that was bored .50 over. That one probably hadn't been bored before, but was run for awhile after it started smoking so it had to go 2 sizes over.
 

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Jeep , I am curious on how that 250 jug is going to work out , I am sitting on at least 6 of them , what really throws me off on that one is the jug is embossed 246 and the 300 281 -----trips me out they would have two different cc's on the same exact part , I guess that is why they are different part numbers
 

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Nice spec list Mac , here is another one , the old 250A is 246cc , and the 300 has 281 embossed on it , maybe Canadian models are 282 .LOL ---
I am only going by memory, but I know that if you actually calc out the cc's on a 300, 74mm bore and 65.5mm stroke it works out to 281.7cc which rounds to 282cc.
 

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Jeep , I am curious on how that 250 jug is going to work out , I am sitting on at least 6 of them , what really throws me off on that one is the jug is embossed 246 and the 300 281 -----trips me out they would have two different cc's on the same exact part , I guess that is why they are different part numbers
OEM cylinders that came on the bikes would have the cc's on them, I suspect that if you were to order a new OEM replacement from Honda you would see no cc's written on the cylinder at all. They are absolutely the same and have been used interchangeably over the years without issue. IRRC the heads may be different, I don't know if that was to accommodate the stroke or if there was another reason.
 

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Jeep , I am curious on how that 250 jug is going to work out , I am sitting on at least 6 of them , what really throws me off on that one is the jug is embossed 246 and the 300 281 -----trips me out they would have two different cc's on the same exact part , I guess that is why they are different part numbers
Jugs will swap fine between the Trx250/Trx300/Atc250es. The only thing is the timing chain tensioners are different. You can use the 250 tensioner in the 300 jug but cant use the 300 tensioner in the 250 jug.
 

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Jeep , I am curious on how that 250 jug is going to work out , I am sitting on at least 6 of them , what really throws me off on that one is the jug is embossed 246 and the 300 281 -----trips me out they would have two different cc's on the same exact part , I guess that is why they are different part numbers
Jugs will swap fine between the Trx250/Trx300/Atc250es. The only thing is the timing chain tensioners are different. You can use the 250 tensioner in the 300 jug but cant use the 300 tensioner in the 250 jug.
If that's the case how does Honda (Partzilla for example) sell one jug for both models?

I wonder if they made a minor change to the new production jugs to allow both to work?

I'm going to run a 250A cam, sprocket, and chain with the 250A jug, but planned on using all of that on a 300. That mean I need to use the 250A tensioner as well?
 

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I have seen some adjusters that looked different and think they would also work , just made different and has a different part number
 

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Discussion Starter #19
Sorry forgot to specify it was two 300's. also if it doesn't really increase the amount of cc's why go through the trouble of boring out a sleeve. Like does it do enough to help the small 300 engines to turn bigger tires or what's the main purpose?
 

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Sorry forgot to specify it was two 300's. also if it doesn't really increase the amount of cc's why go through the trouble of boring out a sleeve. Like does it do enough to help the small 300 engines to turn bigger tires or what's the main purpose?
there is no reason, other than to be able to get the motor to run !..lol. when your cylinder wears out, or piston, or connecting rod..or all of the above ?, then most times it requires you to bore the cylinder out in order to fit a newer size piston back in the cylinder, which means, you have to bore the cylinder out/over. has nothing to do with tire size or turning bigger tires. yes, you have to bore the sleeve/cylinder in order to fit a larger piston in there.
 
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