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-85-86-ATC-TRX-250R-Wiseco-Piston-Kit-040-over_W0QQcmdZViewItemQQcategoryZ43977QQitemZ460951 9185QQrdZ1QQsspagenameZWDVW

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 hammer 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

[Somekindofjerk]

Usually you would buy the piston first and have the machine shop bore the jug to match the piston. In your case, find a piston thta offers .0002 inchs of clearance. That will give you the clearance you need.

[TimSr]

I always bore to the minimum necessary to clean it up. What that means it having it bored first an then getting the matching piston because you really dont know where it will end up. Most of mine have required .020" taken off which would give you a 67.50mm bore, but Ive had a couple bad ones that required .040" to be taken off. Id been sending mine to Wiseco with instructions to bore the minumum necessary, and they would sent me back the correct piston kit. Ive been told Wiseco isnt boring any more, but if you call them they refer you to someone who does it for them. Bore jobs vary greatly, and since your piston kit and gaskest are the most expensive part of a top end job, its wise to not skimp on a qulaity bore job by somebody who knows these type motors well, to make your components last and run like it should. Sub qulaity bore jobs are the most frequent cause of premature top end failures, as people tend to give it little consideration, and usually blame it on their premix or someting not nearly as critical.

[TravEX]

Thanks again for the help. There is a company not too far away that does motor work that I would trust. Is it common to just get the company to bore it, then them order the piston kit, then I pick up the freshly bored jug and piston kit and do the rest myself? Or should I just take them the whole trike and let them do all the work and it be ready to go when I pick it up? I'm trying to save as much $ as possible, but don't wanna skimp if it hurts me in the long run.

Thanks again

Travis

[Dammit!]

Is it common to just get the company to bore it, then them order the piston kit, then I pick up the freshly bored jug and piston kit and do the rest myself?

Travis

That's how I do it. Having a shop rebuild a two-stroke top end is a waste of money. If you're even just remotely mechanically inclined, you can do it yourself easily and you don't need a second jug to practice on. It's very simple. No special tools required other than your typical socket set/screwdrivers and needle nose pliers for the piston circlip (edited: and a torque wrench! And always remember to re-torque after it's been run up to operating temp and cooled back down again or it will very likely leak coolant at the head gasket). Like was already mentioned, use OEM gaskets, make sure the gasket surfaces are cleaned up and don't force anything. Make sure the piston is installed with the arrow facing in the direction of the exhaust flow. I like to use Copper Spray on the head gasket.

When in doubt, don't be afraid to ask questions obviously. This board must have 20,000 top end rebuilds under it's belt (collectievly of course). You can get a shop manual to download from deepa. I don't have the URL handy.

[TravEX]

Thanks Dammit. I've got a Clymer and the desire to do it myself. I'll do it the way you and TimSR do, that's sounds like the right way, and the best way in the long run. I can't thank ya'll enough for the help, it's invaluable! I'll probably fire this thread back up when I do the rebuild.

Thanks again,

Travis

[Kintore]

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.


Tim i just wanted to say, you have saved me having a heart attack. My piston says 50 on it, so thats only 0.020, that means I can run a yamaha OEM pison 2nd oversize. Thanks!!!!!:w00t:

[daputz]

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?


When you measure it, do it 6 times, like you said perpendicular up to down the cyl. This will allow you to see if the cyl is barrel shaped. 2x 90 degress from each other at the top, middle and bottom of the jug.