Slight drag when spinning crankshaft

queen of spodes
Edited Date/Time 3/5/2015 4:02am
I'm in process of building my first motor from having it completely disassembled and am running into a newb mistake and snafu. When installing the crankshaft, I inserted in the flywheel side first (I learned later that I should have gone in the clutch side first).

The cases came together relatively easily. The input shaft spins freely. When I tighted down the drive gear nut (right side of crank), the crankshaft had a little resistance. I grabbed my feeler gauges and got a quick measurement between the crank weights and cases (as looking down from above).

.034"


.046"


The measurements hold true at 12, 3, 6, and 9 o'clock, so the crank is still true. I'm thinking I didn't get the clutch side main bearing seated well enough, and that's causing the crank to lightly bind when I tighten it down on that side.

I tried lightly tapping on each crank end with a rubber dead blow to see if the resistance would lesson, but no luck. I re-checked for trueness and I'm still good there.

Will I have to split cases to finish seating the right side crank bearing? If so will I need to go ahead and get 2 new crank seals in case I bugger the new ones installed in the motor now? Is there a way of pulling that bearing back in its seat without splitting cases (or damaging them)?
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mxrose3
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mxrose3 3/3/2015 9:25pm
3/3/2015 9:25pm
So if you just loosen the drive gear nut and not remove it, does the crank spin freely?
MaxPower
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MaxPower 3/3/2015 10:04pm
3/3/2015 10:04pm
Wouldnt the tightened primary gear pull the crank against the bearing and correct the problem of the crank not being seated into the Or am I not understanding the problem right? Since the seal on the KX is on the inside is it possible to take a brass punch and smack the inner race into the crank?
queen of spodes 3/4/2015 3:25am
3/4/2015 3:25am
mxrose3 wrote:
So if you just loosen the drive gear nut and not remove it, does the crank spin freely?
If I loosen the nut there is much less resistance (easy to turn around).
queen of spodes 3/4/2015 3:26am
3/4/2015 3:26am Edited Date/Time 3/4/2015 3:28am
MaxPower wrote:
Wouldnt the tightened primary gear pull the crank against the bearing and correct the problem of the crank not being seated into the Or am I...
Wouldnt the tightened primary gear pull the crank against the bearing and correct the problem of the crank not being seated into the Or am I not understanding the problem right? Since the seal on the KX is on the inside is it possible to take a brass punch and smack the inner race into the crank?
The crank seals are on the outside of the case. I'm wondering if there is a way to fully seat the right side crank bearing without splitting the cases again. I tried lightly tapping with a rubber coated dead blow (with a spacer between the crank halves) but this didn't help. I double checked trueness and it is still OK. Maybe I'm not tapping hard enough.

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reded
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reded 3/4/2015 3:59am
3/4/2015 3:59am
Pull it apart. I know it sucks now but the peace of mind later will be well worth it.
ridinbeast932 3/4/2015 4:31am
3/4/2015 4:31am
MaxPower wrote:
Wouldnt the tightened primary gear pull the crank against the bearing and correct the problem of the crank not being seated into the Or am I...
Wouldnt the tightened primary gear pull the crank against the bearing and correct the problem of the crank not being seated into the Or am I not understanding the problem right? Since the seal on the KX is on the inside is it possible to take a brass punch and smack the inner race into the crank?
queen of spodes wrote:
The crank seals are on the outside of the case. I'm wondering if there is a way to fully seat the right side crank bearing without...
The crank seals are on the outside of the case. I'm wondering if there is a way to fully seat the right side crank bearing without splitting the cases again. I tried lightly tapping with a rubber coated dead blow (with a spacer between the crank halves) but this didn't help. I double checked trueness and it is still OK. Maybe I'm not tapping hard enough.
I ran into the same problem doing my bottom end a while back. I loosened the case bolts half a turn and gave both the cases and the crank a few stern wacks with the dead blow. Some people swear this is fine and others will frown upon it but I've seen no ill effects so far.
Dick Trickle 3/4/2015 4:37am
3/4/2015 4:37am
Theres a couple of things you can try. Looks like you had the crank rebuilt. Check to see if it has been rebuilt in spec. Recently, my rebuilt crank was assembled using larger shims from a kit and it ended up 1mm wider. YZ125 - 56mm.... mine was 57mm which caused the crank to tighten up when i nipped the cased up. Bike shop rectified the problem. If that is OK, tighten everything up and use a rubber mallet to tap the ends of the crank. Sometimes that can loosed a crank thats a bit tight and help center it up and you might get lucky and seat the bearing properly if its not quite in position. Good luck
slipdog
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slipdog 3/4/2015 5:21am
3/4/2015 5:21am
ridinbeast932 wrote:
I ran into the same problem doing my bottom end a while back. I loosened the case bolts half a turn and gave both the cases...
I ran into the same problem doing my bottom end a while back. I loosened the case bolts half a turn and gave both the cases and the crank a few stern wacks with the dead blow. Some people swear this is fine and others will frown upon it but I've seen no ill effects so far.
This is the correct answer^^^
tzmike
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tzmike 3/4/2015 5:41am
3/4/2015 5:41am
what Slip dog said...
queen of spodes 3/4/2015 6:15am
3/4/2015 6:15am Edited Date/Time 3/4/2015 6:17am
I couldn't find a spec in my factory manual that showed the gap between crank weight & case like I am measuring above. Right side gap is .046. Left side (flywheel side) gap is .034. Not sure which is more correct or if it's supposed be .040 on both sides.. Seems like something is binding when I tighten down everything question is which side? I put the crank half in the flywheel side first (it has the tighter gap).

If I have a bigger gap on the clutch side of the crank, would I need to bump the flywheel or clutch side? Or does it matter and am I just bumping it to try and get it to settle without moving it one way or another?

Seems like the right/clutch side is the problem.. if I get the light binding when I tighten down the main drive gear, seems like the crank is bumping up against the bearing a little. Pulling that right side crank bearing in the case .010 seems like it should get the job done (?) Please correct if I am off base.
ridinbeast932 3/4/2015 6:42am
3/4/2015 6:42am
You're thinking about it too much. Put the feeler guages down, loosen case bolts a bit, and wack the thing. It you think it needs to go a certain way try that first but I'd do both sides.
slipdog
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slipdog 3/4/2015 6:50am
3/4/2015 6:50am
Give the flywheel side 1 or 2 medium smacks with a plastic dead blow or brass hammer. It's always the side you put in first, it's binding because when you tighten the drive gear its trying to pull the crank over to that side. Instead of pulling the crank over, it's trying to pull the crank apart from the big end.
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slipdog
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slipdog 3/4/2015 7:01am
3/4/2015 7:01am
queen of spodes wrote:
Do I need to buy a jig to keep the crank true when whacking on it?
No, just dont wind up first like you're trying ring the bell on that deal at the State Fair.





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queen of spodes 3/4/2015 7:24am
3/4/2015 7:24am
Appreciate the replies, I'll follow up tonight if I can get my hands on a brass hammer this afternoon.
mxtech1
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mxtech1 3/4/2015 7:28am
3/4/2015 7:28am
Do not hit the ends of the crank with a hammer. Even a newb should understand.....think about....does it really sound like a good idea to hit the end of your crank with a hammer???

You first need to take the cases back apart. lay a machinists level (or something you know is 99% flat) and make sure the bearings are completely seated with the surface of the case. I think you will find that one of the bearings is sticking up slightly.

Re-assemble. If you want to do the job right, you need to invest in a crank wedge so you can properly space the crank gaps.
FGR01
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FGR01 3/4/2015 9:57am
3/4/2015 9:57am
queen of spodes wrote:
I couldn't find a spec in my factory manual that showed the gap between crank weight & case like I am measuring above. Right side gap...
I couldn't find a spec in my factory manual that showed the gap between crank weight & case like I am measuring above. Right side gap is .046. Left side (flywheel side) gap is .034. Not sure which is more correct or if it's supposed be .040 on both sides.. Seems like something is binding when I tighten down everything question is which side? I put the crank half in the flywheel side first (it has the tighter gap).

If I have a bigger gap on the clutch side of the crank, would I need to bump the flywheel or clutch side? Or does it matter and am I just bumping it to try and get it to settle without moving it one way or another?

Seems like the right/clutch side is the problem.. if I get the light binding when I tighten down the main drive gear, seems like the crank is bumping up against the bearing a little. Pulling that right side crank bearing in the case .010 seems like it should get the job done (?) Please correct if I am off base.
First of all, you need to tell us what bike we're talking about here. Because each tends to have it's own little peculiarities so it's not really best to speak in generalities.

That being said, I tend to agree with your assessment above. Either the right side main bearing is not fully seated in the cases, or the crank just needs to be pulled to the right a little.

Almost every time I've put cases back together I first pulled the crank into the right case and then pulled it into the left case. If I "over-pulled" it just a bit when bottoming the cases together it would shift the crank slightly to the left. I would then have to put the puller back on the right side and re-seat it to the right.

So, I think the right answer is to put a crank puller on the right and pull it back that way. I think that's a better idea than whacking on the left end with a hammer.
mxrose3
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mxrose3 3/4/2015 11:52am
3/4/2015 11:52am
I think this may have to do with you pulling the crank into the ignition side first. It may be too tight into the ignition side, and when the main gear bolt pulls the crank to the clutch side, it is pulling the crank halves in different directions. I would split the cases again, and put the crank in the clutch side all the way first , then pull it into the ignition side until its true.
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RM250racer 3/4/2015 2:52pm
3/4/2015 2:52pm
could it just be that the new mains arent worn like the old ones so it feels tighter? i just replaced mains along with a new crank in a cr250 and to me it felt tighter then when i took it apart, but it didnt feel like it was dragging, just more firm. is that normal with a new bottom end? the old bearings were pretty roached.
charley586 3/4/2015 4:06pm
3/4/2015 4:06pm
You're crank bearing isn't seated correctly. You can heat the case with a plumber torch and give crank some love with a brass hammer (fill all the motor hole with something to avoid brass falling inside...). Also you can add some premix oil in the hole that you can see on each side of the connecting rod right over the bearing crank.

Been there done that.
queen of spodes 3/4/2015 4:28pm
3/4/2015 4:28pm
charley586 wrote:
You're crank bearing isn't seated correctly. You can heat the case with a plumber torch and give crank some love with a brass hammer (fill all...
You're crank bearing isn't seated correctly. You can heat the case with a plumber torch and give crank some love with a brass hammer (fill all the motor hole with something to avoid brass falling inside...). Also you can add some premix oil in the hole that you can see on each side of the connecting rod right over the bearing crank.

Been there done that.
Which side do you think isn't seated right? Which side do you strike with the brass hammer?
queen of spodes 3/4/2015 4:45pm
3/4/2015 4:45pm Edited Date/Time 3/4/2015 4:45pm
Got it. Torqued down the main gear to spec. Worked up a makeshift jig, then gave a couple of love taps to the left end of the crank. Felt a little pop on the second tap. Crank now spins freely like I'd expect with new bearings & seals. Don't see a ton of difference in measuring the side clearance but it feels right now.

Mucho, mucho gracias.
Aceofspades 3/4/2015 5:16pm
3/4/2015 5:16pm
Ill be assembling my 2000 kx 250 in a few days and I dread shit like this lol.
queen of spodes 3/4/2015 6:51pm
3/4/2015 6:51pm
Aceofspades wrote:
Ill be assembling my 2000 kx 250 in a few days and I dread shit like this lol.
Just don't make my mistake. Put your crank on the clutch side first like the guys said above.
Dick Trickle 3/4/2015 8:38pm
3/4/2015 8:38pm
queen of spodes wrote:
Got it. Torqued down the main gear to spec. Worked up a makeshift jig, then gave a couple of love taps to the left end of...
Got it. Torqued down the main gear to spec. Worked up a makeshift jig, then gave a couple of love taps to the left end of the crank. Felt a little pop on the second tap. Crank now spins freely like I'd expect with new bearings & seals. Don't see a ton of difference in measuring the side clearance but it feels right now.

Mucho, mucho gracias.
There you go... when in doubt, use the fine tuner - a hammer!! Good to hear that you got it all working well.
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Aceofspades 3/4/2015 9:00pm
3/4/2015 9:00pm
Do kx cranks have threads on the clutch side or is it a circlip holding on the driven gear?
queen of spodes 3/5/2015 4:02am
3/5/2015 4:02am
Aceofspades wrote:
Do kx cranks have threads on the clutch side or is it a circlip holding on the driven gear?
Threads on this 125. I can't see why a circlip would be used there to be honest.

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