'82 YZ125 bore over?

N

Nice Guy Eddie

Uhhh...

Jun 30, 2004

140

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• Jul 20, 2004

• #1

I have an '82 YZ125 that is being a real pain in the u know what...

first it was running crazy lean... the slide needle was not clipped so it would not open with the slide... got that fixed (still muttering with a faulty needle and seat).... but we can't seem to get any low end out of her.... so we finally took the jug and head off.... it is a steel sleeved cylinder, no noticable plating, and it is scored pretty bad... the piston is trash and has lots of little pock marks in the top and it has substantial scoring along the sides....

The head is littered with little pock marks.. some of them quite jagged.... (I think it blew a ring at one time and was never properly repaired)

We checked with Dennis Kirk and they carry oversized pistons for this bike.... 5 different ones!!!...

knowing this please answer these questions to the best of your ability

should I even consider just honinig and replacing with stock?

how much does boring over cost? (this is a biggie, as the bike is an '82 and I won't dump tons of cash into it)

will they mill the head with the bore (as a matter of course)?

are there usually local shops that do this kind of work/ where should I look for a qualified shop to oversize it?

Will the shop be able to determine what bore to go to if I just tell them the piston I choose to use?

will boring it pretty big be a good idea for a mostly trail bike... or should I stick with what DK (Wiseco) calls a 'standard' overbore? (I really want more low end than the typical 125 2-stroker has)

 

R

Rider 007

Member

Feb 10, 2000

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• Jul 20, 2004

• #2

If there is the kind of damage you describe, honing will not repair it and will just be a waste of money.

The 82 came with a boreable steel liner. If you look over to the left side of the screen you will see a link for Eric Gorr's Forward Motion business. I believe he charges $40 to bore and about $30 for head work.

Send him the top end assembly and he can check the damage and tell you what size overbore you will need to go to in order to remove the damage from the cylinder. The depth of the groooves will be the driving force to determine this.
He can provide the Wiseco piston required for the overbore.
He can also clean up the damage to the head if it is repairable.

If you don't know a competent local shop then I would recommend Eric for the work.

And on a 125 you aren't going to drastically affect the displacement by going to an overbore from cylinder wear.
The biggest difference you'll notice is that it actually runs properly since the rings will be sealing and you'll have the compression that you currently do not. This will be very noticeable on the low-end response.
You don't want to bore it any larger than necessary, since you want to have the ability to bore it again when needed.

Good luck. :cool:

 

N

Nice Guy Eddie

Uhhh...

Jun 30, 2004

140

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• Jul 20, 2004

• Thread starter
• #3

yeah, I kinda thought just honing would be a waste, I just needed someone to knock my head straight... thanks.... lol

The reason I ask about going extra large on the overbore is that I want to get more low end out of the bike... are you saying that going that much bigger will not result in a real noticeable torque change?

I tried to call Eric twice today.... no answer at all, not even a machine... :( ... I'll try again later

thanks for the input..... anyone else with some ideas

 

R

Rider 007

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Feb 10, 2000

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• Jul 20, 2004

• #4

Nice Guy Eddie said:

are you saying that going that much bigger will not result in a real noticeable torque change?

I tried to call Eric twice today.... no answer at all, not even a machine... :( ... I'll try again later

thanks for the input..... anyone else with some ideas

Click to expand...

Correct.

You'll notice more improvement from the increased compression of the fresh top end then you would by increasing the displacement a few cc's.

You can have Eric port it for more low-end if that's what you want.

I'm told the best time to reach him is very early in the AM (7:00 ish)

 

N

Nice Guy Eddie

Uhhh...

Jun 30, 2004

140

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• Jul 20, 2004

• Thread starter
• #5

thanks for the input.... I will get ahold of him and see what he has to say....

what about a local shop that usualy does cars?.... is there a reason they would not be a good choice?

 

R

Rider 007

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Feb 10, 2000

224

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• Jul 20, 2004

• #6

There may be some sharp guys there, but unless I know them personally, they aren't touching my stuff. That's why I send my stuff to people like Eric when I can't do it myself. They know what I want and expect and are experienced at it.
They don't "think" they can do it, they "know" they can.
Your local automotive machine shop probably doesn't have the experience you're looking for.
The price can be lot higher in the long run if it gets screwed up from the jump.
That's experience talking...

Good luck and let us know how it turns out.

 

J

JasonWho

Member

Apr 10, 2002

2,109

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• Jul 20, 2004

• #7

Nice Guy Eddie: What's the hold up on that carb work?! :-) If it were mine, I would just send it to Eric Gorr. Like 007 said, he has worked on about a jillion of them, so he is extremey experinced. He will know how far to bore it. Don't bore it more than that because it will need to be bored out again in the future. They can only be bored out so far before needing to be replaced. Again, like 007 said, the correctly working engine will give you more HP and torque.

smile - If you want more torque than what a 125 has, then you may need something bigger than a 125. :-) Most 125 MX bikes are designed for high RPM, screamin' demon style.

I know he might be able to get more low end torque out of it with porting, but that is $150 or so, I believe. If it was my bike, it should be thankful to get the cylinder fixed. :-)

 

N

Nice Guy Eddie

Uhhh...

Jun 30, 2004

140

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• Jul 21, 2004

• Thread starter
• #8

LOL... the hold up on the carb work is that the darn thing barely runs with the compression this low (120psi on an unknown accuracy gauge)... I can't hardly get her jetted right when she's in that kind of shape....

I haven't come to a real conclusion on the needle and seat yet... so the thing is running PRETTY DARN rich at slow speeds.... I'm kinda being a sloucher on this one because I have the sweet (newly jetted... thanks for the tips!!) KDX200 to ride.... and quite frankly this one is just a buddies bike that he needs help on, but more or less really just wants me to fix it for him because he won't put any real time into it... if that's the case, it comes after MINE.... and he keeps wrecking mine.... so it's an endless cycle... LOL

we'll get her up on her toes again..... just needs some patience I don't particularly have right now

 

J

JasonWho

Member

Apr 10, 2002

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• Jul 21, 2004

• #9

I hear you on EVERYthing! I generally like working on my friend's bikes, computers, etc. Last year, I helped out a riding buddy. I trued his front wheel some. It took us about an hour of tinkering to get it real straight. What does he do? Cranks it up, goes less than .1 mile, putting around, hits a stump hidden by brush and gets dumped over the handlebars. He and the wheel were fine, though. :-)

Carb fixed or not, it isn't going to run right until the cylinder and piston is running properly. Keep on him about it. Dirt bikes ain't cheap! :-(

Have fun with your KDX.

 

N

Nice Guy Eddie

Uhhh...

Jun 30, 2004

140

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• Jul 21, 2004

• Thread starter
• #10

yeah, I got no problem helping, but when they aren't helping, my helping comes to a grinding halt... He really wants to get it going, but he really doesn't have the time right now, so I'm doing some research for him to help put him in the right direction....

when we pulled the jug last night I told him right off that this was a big part of the problem and that we couldn't go any further untill he decided what he was gonna do (fix it or junk it).... I came here to find out what people pay for bore jobs because that is a big factor in a 20 year old bike... so far I'm inclined to tell him to fix it...

He found a shop nearby that will do the bore for $22.... is that insanely low?.... what would be the advantage of a Gorr job? (assuming they both know what they are doing, which I understand is a big assumption).... is there anything tricky about a 2-stroke bore that a car mod shop wouldn't know about?

for $22 (+$80 in parts from my nearby Dennis Kirk store... :) ) it is definately worth it

 

R

Rider 007

Member

Feb 10, 2000

224

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• Jul 21, 2004

• #11

For the $22 will they properly chamfer the ports? Do they know how? Will they determine what size overbore you need, get that piston in hand, measure that piston to verify its true dimensions and then set up the bore size to assure the proper clearance?
Can they properly service the head? Do they have a clue as to what a squish band is?

For an $18 difference it seems like a big gamble to me.

This is the experience part I mentioned.

These lessons are offered for free by people that have been there but, unfortunately, most insist on paying their own way...

:ride:

 

J

JasonWho

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Apr 10, 2002

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• Jul 21, 2004

• #12

I would tell your friend to send it to Eric Gorr. The money saved wouldn't be worth it, to me.

 

N

Nice Guy Eddie

Uhhh...

Jun 30, 2004

140

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• Jul 21, 2004

• Thread starter
• #13

well, it turns out that the shop for $22 a cylinder is quite reputable.... I know this because they will not do the work.... they said to take it to someone who knows what they're doinig with 2-strokes.... lol... (my buddy had talked to a bozo at the front desk... the technician was more in the know... imagine that!)

my buddy got ahold of Eric today... I'll let you know how it turns out... (no Jason, I'm not just saying that.... I will fill in the needle and seat thread as soon as we get it fixed.... lol)

 

M

mule418

Member

Jul 21, 2004

2

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• Jul 21, 2004

• #14

I'm curius, check the piston top to see if that thing has been rebult before. The remark you made earlier about the head and piston having ding marks in them may be due to a crank bearing going out. I'd check that out before putting a top end on it. I made that mistake once! just my 2 cents.

 

J

JasonWho

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Apr 10, 2002

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• Jul 21, 2004

• #15

I hope it makes it's way to Eric Gorr. I like keeping an old bike running.

HA! I will kepp an eye on it. Let us know how it all turns out.

 

N

Nice Guy Eddie

Uhhh...

Jun 30, 2004

140

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• Jul 21, 2004

• Thread starter
• #16

mule418 said:

I'm curius, check the piston top to see if that thing has been rebult before. The remark you made earlier about the head and piston having ding marks in them may be due to a crank bearing going out. I'd check that out before putting a top end on it. I made that mistake once! just my 2 cents.

Click to expand...

any quick notes on how to check the crank bearings?

hopefully before we send the cylinder to Eric.... which is supposed to be tommorow.... but I will wait and see how the crank is... I would hate to dump a pile of cash on this thing to have it fall apart again....

 

J

JasonWho

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Apr 10, 2002

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• Jul 21, 2004

• #17

I think you can check thr gap between the bearing and rod, or something like that. You would need the precise factory service limit on the measurement, though.

 

N

Nice Guy Eddie

Uhhh...

Jun 30, 2004

140

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• Jul 21, 2004

• Thread starter
• #18

HE'S GOT THE SERVICE MANUAL!!!!

small joys can be found everywhere eh Jason?

I'll tell him to find that info and go from that.... I assume too much gap indicates worn/broken bearings?... there is some noticeable movement, side to side on the lower connecting rod end... I hope were not in even deeper here.... :bang:

 

J

JasonWho

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Apr 10, 2002

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• Jul 22, 2004

• #19

How do you spell hallaleujah, anyway? :-) It should show in there what to check and how to check it. You may want to read up on the ericgorr.com website. There is some bottom end engine information in there.

I hope it all checks out.