Boring Question!

[TravEX]

I've come across a jug for my R (spare one), it's already bored .040 and he says 'some' porting. How much can the jug be bored? Can I even use it? Will it have to be sleeved? Called a local shop and they said the jug can only be bored out 1mm (.039....).

I want a spare so I can rebuild it and just swap the jugs out when a rebuild is needed.

Thanks

Travis

[Somekindofjerk]

.50 is the biggest you can bore a jug. You could use it, just buy an oversized piston and rings.

[KASEY]

WHAT YEAR 250R??? most can go to .080 and some go to .120.... just depends what year your workin with

[TravEX]

Thanks for the reply. I've checked out ebay and can get Wisco sets up to 3.5mm over. Didn't know that.

This is gonna be my first experience with rebuilding a motor. I think I can handle it, and that's another reason I want a spare jug to practice the first time one.

[TravEX]

WHAT YEAR 250R??? most can go to .080 and some go to .120.... just depends what year your workin with

It's the 86 in my sig. How can I tell what compression the piston kit is? Ask the seller?

http://cgi.ebay.com/ebaymotors/Honda...spagenameZWDVW

Would that be what I need? I know I'll have to measure the diameter to get the right one, but is that the right parts.

Thanks

Travis

[Somekindofjerk]

Just know that when your reinstalling your piston it may not want to go in right away. You may have to woble it a bit to get it to slide up. DO NOT on it or try to force it.

Do they go .120 over? Holly hell, thats quiet a thin sleeve! lol

[TimSr]

WHAT YEAR 250R??? most can go to .080 and some go to .120.... just depends what year your workin with

Yep, the liquid cooled R's go to .120" which is 3.0mm. Most two stroke cylinders will go to .080" (2.0mm). You should only bore the minimum necessary to clean the bore out. Boring is not a performance modification. It is for cylinder wall restoration.

[TravEX]

Right, I'll measure with a micrometer the diameter at 2 perpendicular spots on the cylinder (per the manual) to check the roundness and wear and see if I need another bore or not, right?

[TimSr]

Right, I'll measure with a micrometer the diameter at 2 perpendicular spots on the cylinder (per the manual) to check the roundness and wear and see if I need another bore or not, right?

Correct, they wear egg shaped. The center wears faster than the top and bottom of the cylinder. The other thing besides wear that could require a bore job is deep scratches or other surface irregularites. Light scratches can be removed with a honing, which should be done whenever rings are replaced.

[Old 179]

.50 is the biggest you can bore a jug. You could use it, just buy an oversized piston and rings.

Did not Honda have a standard bore,25 over, then 50 over???? Had to go to say a Wiseco and went .10,,20 .30 ect!!!

[jason85atc250r]

i would recomend taking it to a shop and have them check it for what bore size you need. then they can order the rite piston and do the bore it out for you.

it would suck to not be checking it rite and order the wrong size piston.


the 85 and 86 250r's can go to .120 over. the 87-89's can only go to .080 over . you can bore them to the .120 over if you use the old style pistin and get a spacer plate. making a spacer plate motor make a noticable difference.

[TravEX]

Thanks for the info!

[TimSr]

Did not Honda have a standard bore,25 over, then 50 over???? Had to go to say a Wiseco and went .10,,20 .30 ect!!!

Lots of confusion on bores between the metric system and SAE. Im not picking on you, because I swear that 90% of the peopel out there get this wrong!!!

Honda did have a .25 and .50mm oversize which =.010" and .020".("= INCHES)

There is no such thing as .10 .20 etc. Its actually .010" .020" etc.
Metric, which is how about every piston I know is marked, goes .25, .50 etc.

.25mm = .010"
.50mm = .020"
.75mm = .030"
1.00mm = .040"
1.25mm = .050"
.
.
2.00mm = .080"

Certain numbers are very confusing to descipher when people dont say whether its mm or thousanths. Then to add to the confusion, they always seem to put the decimal in the wrong place.

For example, "its been bored 1 over". Does that mean .010" or 1.00mm?
The worst one is when somebody says, "it been bored 50 over". Again, .50mm or .050"?

To make it more confusing, seems everybody is always talking in inches ("Its been bored 80 over") while every bike piston I know of is always marked and measured in mm. People rarely say "its got a 2.00mm overbore", even though it may be stamped right on top of the piston they just installed.

[Old 179]

Lots of confusion on bores between the metric system and SAE. Im not picking on you, because I swear that 90% of the peopel out there get this wrong!!!

Honda did have a .25 and .50mm oversize which =.010" and .020".("= INCHES)

There is no such thing as .10 .20 etc. Its actually .010" .020" etc.
Metric, which is how about every piston I know is marked, goes .25, .50 etc.

.25mm = .010"
.50mm = .020"
.75mm = .030"
1.00mm = .040"
1.25mm = .050"
.
.
2.00mm = .080"

Certain numbers are very confusing to descipher when people dont say whether its mm or thousanths. Then to add to the confusion, they always seem to put the decimal in the wrong place.

For example, "its been bored 1 over". Does that mean .010" or 1.00mm?
The worst one is when somebody says, "it been bored 50 over". Again, .50mm or .050"?

To make it more confusing, seems everybody is always talking in inches ("Its been bored 80 over") while every bike piston I know of is always marked and measured in mm. People rarely say "its got a 2.00mm overbore", even though it may be stamped right on top of the piston they just installed.

After I post, I realize that I didn't point that out. Glad you caugth it. It's best to correct a miss quote then to leave it alone and others thinking it to be correct.

[TravEX]

So, let's say the bore diameter is 67mm, do I order a 67mm piston kit? What if it's a little over or a little under XXmm, do you round up or down when ordering or have it bored up to the next mm?

I didn't get that extra jug I was bidding on (I didn't realize they went so high!), but I plan on rebuilding this winter.

Thanks,

Travis