Need help finding size of bolt threads

[Brandon H.]

Ok, as some of you may know already, I scored a 1994 YZ 125 for $80. It needed a stator (which is one its way via UPS thanks to Ebay), and other small TLC. So far the bike itself has been overhauled and is ready to go, so now im doing motor work.

The threads where the nut goes to hold the flywheel on the crank is all boogered up (not my fault). I will need to get a die and try to recut the threads. I need to know what size it is.

I downloaded a sheet and printed it to scale off boltdepot.com . According to the sheet, its either

3/8 - 24
or
10mm x 1.25

Which one is it?? I am leaving in a few hours to get a die. Also, if I need to go one size small, what size should I get???

I also need to get a new nut and washer for it (because the owner didn't have it. I know bikebandit.com has em, but can I just buy a nut and washer from lowes?? Any specific kind??

 

[IndyMX]

Well, it's a Jap bike, and since every other fastener on the bike is metric, it would stand to reason that this one is metric also.

Sometimes a little bit of common sense goes a long way. :nener:

 

[Brandon H.]

Well, it's a Jap bike, and since every other fastener on the bike is metric, it would stand to reason that this one is metric also.

Sometimes a little bit of common sense goes a long way. :nener:

Hey... I know every bolt has been metric, but you know.... you gotta be sure :)

 

[IndyMX]

Factory Service Manual is your friend.. ;)

 

[Brandon H.]

Factory Service Manual is your friend.. ;)

Yeah yeah yeah.... I looked it up after you said this, except the manual was for a 2001. According to it, its 10mm x 1.25 just like I thought. So hopefully I can use a die to restore the threads, cause it looks like some jacka$$ took plyers the the threads. Might have to go a size smaller if it don't work.

Thanks Indy :cool:

 

[GoldDrum]

If you have a hardware store near they would be the cheapest place for a bold. Lowes may have it, but I have found that a HW store has much more in stock. Bike Bandit is good, but a long way from the cheapest.

 

[Brandon H.]

If you have a hardware store near they would be the cheapest place for a bold. Lowes may have it, but I have found that a HW store has much more in stock. Bike Bandit is good, but a long way from the cheapest.

The problem is though, is that the threads are on the crankshaft, so I need it repaired. The only replacement I need is a nut and washer.

I talking about the end of the shaft where the flywheel goes.

 

[IndyMX]

If the threads are just bugged a little, chasing them with a die will do the job just fine.

The flywheel is held in place by the key, not the nut.. The nut does hold tension on it, but as long as it's tight, everything will be fine.

I'm never shocked by some of the crap people do to their bikes.

 

[Brandon H.]

If the threads are just bugged a little, chasing them with a die will do the job just fine.

The flywheel is held in place by the key, not the nut.. The nut does hold tension on it, but as long as it's tight, everything will be fine.

I'm never shocked by some of the crap people do to their bikes.

They are a little worse then that, but I figured I might try chasing them first. I might have to go with plan "B"...what that is, I have no idea :whoa:

If this doesn't work Indy, what should my next option be?? I mean I don't want to do it the wrong way, but maybe if this fails, I can file down the threads and use whatever size will be slightly smaller then the original, an use a different nut.

Either way, im not buying a new crank :fft:

 

[IndyMX]

Good question what the next option would be.. Bob?? Rich??

 

[Brandon H.]

Good question what the next option would be.. Bob?? Rich??

Where's them old guys when u need em :laugh:

 

[Brandon H.]

 

[Brandon H.]

The bike so far, pictures are about a week old. Little more done since then.

 

[Brandon H.]

Homemade adapter for steering wheel puller case splitter.... total custom mad :laugh:

 

[IndyMX]

I'd go ahead and try the die.. If that fails, you can always get a helicoil for it..

 

[whenfoxforks-ruled]

The end of the crank used to have a bevel on it, before some bozo beat on it with a hammer. The bevel can be put back with a little careful filing, at about a 45 degree angle. The outside diameter needs to be a specific size, the od of the thread. This means no high spots or the die will strip. Knock it down by stroking the file around the flat of the thread, how ever much as needed to get the dents flat/the height of the thread. The hammer mushrooms the end. You need the bevel to catch the beginning of the thread, it tapers down to nothing, with the bevel. They also make a thread file that is handy, it matches the threads per mm. Keep steady pressure on the die, after its started, back off a quarter turn for every half turn to clear the threads. Tapping fluid is preferred, wd40 would work. Vintage Bob

 

[jsantapau]

If the threads are just bugged a little, chasing them with a die will do the job just fine.

The flywheel is held in place by the key, not the nut.. The nut does hold tension on it, but as long as it's tight, everything will be fine.

I'm never shocked by some of the crap people do to their bikes.

splitting hairs here but the key way is more of a locating point than a fixture.....the nut holding the tension against the tapered fit is what keeps it there..but as you say if you can clean the threads and the nut will tighten properly you should be fine

by looking at those pictures it is possible some body tried to force that 3/8 nut on their besides the hammering and beating
I think I would start with a thread file.. starting at the good threads and working my out compared to running a die down that mess and hoping to match up to the original threads

 

[Uchytil]

First I'll say good luck. I'm curious, how many hours on that engine, specifically the bottom end? At the point you are at I'd have a new bearing put in the crank. It'll cost you more to use a shop unless you can press the crank and true it. While its apart you could have a machine shop repair the thread by either weld and recut or sleeve and recut. Maybe my eyes are bad but those threads look pretty wasted. I'm sure there are a few used cranks out there you could get cheap and rebuild too. I've got a 97 crank but the plastic stuffers are melted and it need a bearing. The stuffers alone cost a pretty penny.

 

[whenfoxforks-ruled]

If the crank has the plastic fillers in it, they go as a first sign of the big end bearing going out. I would have concern why the 1 main bearing stuck to the crank, the case bore should have held it. Unless,, you did not drive against any inner bearing races to disassemble did you? Check the bore that bearing came out of, and use some loctite bearing seal, if its still good. Replace the main bearings and seal for sure at this point. Check the thrust washer clearance on the big end bearing, inspect the cage and pins with a magnifier. Or for peace of mind, and a known sound engine, get the crank fixed/replaced. Vintage Bob

 

[Brandon H.]

If the crank has the plastic fillers in it, they go as a first sign of the big end bearing going out. I would have concern why the 1 main bearing stuck to the crank, the case bore should have held it. Unless,, you did not drive against any inner bearing races to disassemble did you? Check the bore that bearing came out of, and use some loctite bearing seal, if its still good. Replace the main bearings and seal for sure at this point. Check the thrust washer clearance on the big end bearing, inspect the cage and pins with a magnifier. Or for peace of mind, and a known sound engine, get the crank fixed/replaced. Vintage Bob

I don't know why the bearing stuck, but it came out that way. The outer bearing race looks cllean and perfectly round, as well as the case bore for the bearing. Probably just my luck :nod: ??

I will be replacing the main bearings, and seals. I looked at the crank bearing (big end) with a magnifying glass, it looks good. It has no vertical play. It sucks I have the case split already because I could have used my dial indicator to check the trust bearing clearance.

I removed the bearing today, and the machined area on the crank where the bearing sits looks good to...so idk. Im going to try and fix the threads hopefully tomorrow.

 

[Uchytil]

If the crank has the plastic fillers in it, they go as a first sign of the big end bearing going out.

So true, I've had that crank on the shelf for 10 years. When it went I was lucky enough to have a new OEM crank to throw in. The stuffers make a rebuild more costly since you have to change them as well as the bearing.

I would have concern why the 1 main bearing stuck to the crank, the case bore should have held it.

I've seen a few YZ125's have that side main bearing stick to the crank upon removal. Never seemed to be a big deal but that's just me. Checking the bore size is mandatory and using locktite bearing seal is ok.

 

[Brandon H.]

Hmm, which loctite should be used?? I know in the gun world we use Loctite bearing something (I think 609), anyways that stuff is strong enough to hold a barrel on a rifle. I dont the bearings staying on forever, I want to take them off in a couple years.

What should be used? Im picking up a 10mm x 1.25 die in a bit, as well as some cutting oil. And some Permatex Ultra Grey, and hopefully some of this loctite stuff :-)

 

[whenfoxforks-ruled]

The blue is basic. The red loctite is proper, the green is meaner. Vintage Bob

 

[Brandon H.]

The blue is basic. The red loctite is proper, the green is meaner. Vintage Bob

I have the blue and red, but I thought I had to use a "bearing" loctite like yall are saying. Can I get away with red?

 

[whenfoxforks-ruled]

Thats what the red is, stud and bearing lock. Vintage Bob