Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: cnrcpla on March 01, 2012, 01:30:49 AM
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When I gave my top end to the dealer, they told me to check the crank bearings to make sure they were still good. So, I took the connector rod and checked for out of place movement. It has no up or down movement, no back or forth movement, and it moves effortlessly. Is there any other way to check them? I want to make sure before I put the top end back on because the dealer told me that if the bearings were shot, the bottom end would be a grenade. I want to avoid splitting the cases, so anyone got any ideas?
Thanks in advance 
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You can check your big end side play with feeler gauges, and check your main bearings by pulling of your left hand engine case and grabbing the flywheel and giving it a good wiggle to check for movement, there should be none at all.
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Oh, ok. I haven't tried that yet. I will do that, thanks
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A quick and dirty way to check your conrod bigend bearing for play (wear) is to grasp the conrod with one hand and pull up and then strike down on this hand with your other hand.If you hear a "clank" it's time to split the cases.As for the crankshaft mainbearings,pull your stator and examine the crankseal area for leakage - a sure sign of wear.
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Ok. I'm going to pull it off now and check.
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you may not feel any play if you dont remove
flywheel and some times you have to remove on the right side too
move spindle up and down to check for play
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Sorry for the delay. Everything checked out ok, there were no leaks in the stator area and no play that I could detect, and since I had the clutch side open anyways, I checked those bearings to and there were no play. I also tested my radiator for leaks, and that checked out to. Can't wait to break all my new stuff in
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i have a friends wr 200 that we are working and it has some vibration issues so i took off the flywheel cover and let it run and when you give it a little gas (in neutral) the flywheel seems to rise toward the head slightly would this be an obvious sign of crank barrings shot
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I use a large screw driver as leverage to see if there is movement on both sides of the crank shaft.
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I am probably going to do a bottom end job next winter (not this winter I want to ice race). My crank only the stator side had an ever so slight amount of movement to the point where I wasn't even sure if it was moving. The right side was absolutely solid.
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The best way is to do just all, I mean you have to split cases to do one why not doing both?
And the flywheel side is the most dangerous leak you could have. Once the seal refuses to seal at WOT you melt your piston.
I do bottom end at 150 to 160 hours, if not a bearing forces me to do it earlier.
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I had to pressure test the engine after I had an air leak somewhere. I found the leak (in the boot that goes from the carb to the reed) and there wasn't anywhere else leaking air. There is also no leaking oil, so I'm thinking the seals are fine. But, when I do the bottom end, I do plan on doing everything, bearings, con rod, crank, and everything. That's going to be an expensive bill
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I think compared to the damage a failed bearing could cause the preventive repair or exchange of parts is economical feasible.
2 Bearings if OEM come to about US$ 60 both, the needle bearing OEM about 95 incl washers. Better a con rod kit for 105 or so.
That is the minimum I use.
If you are sure there is no leak great, but a play in the bearing will make the seal fail. That is the problem.
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So I don't have to get a new crank? If I don't that's a BIG chunk of change I can save. I will double check the stator side bearings for play as soon as I get home. If I can just go with all the bearings and seals and con rod kit, I can do that next top end job assuming the bearings aren't shot already.
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That's right one or two times I do just a bearing change (incl. the oil seals) and the con rod kit. I like Hot Rod.
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This thread got me all worked so I went and pulled my ign cover and sure enought there is the smallest amount of play as far as up and down movement goes . I'm not riding it until its fixed .
How much do you guys think the labor costs would be to have a shop change them for me if I brought them the motor minus the top end ?
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I've never had a shop do a bottom end but i put a 2002 CR 250 engine together last Friday wich took me about 3 hours, maybe thats slow, i dunno but i was doing lots of checking and double checking so i didnt stuff it up and have to do it all again. I would say for someone who does it all the time they could have a bottom end stripped, cleaned and reassembled in 4 to 5 hours??? that is my guesstimation..
no doubt someone will shoot me down 
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If you are just doing the bearings like I will be soon, then let me know how they do. Do you even have to split cases to do the crank bearings?
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Yep ya do, and whole ya there ya might aswell do all the bearings n seals including ya big end
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Oh yeah. If I am splitting cases, I will do the whole 9 yards. Con rod kit, bearings, seals, everything that needs to be done. But, I am thinking that with the help of you guys here on TSM, I should be able to split the cases my self and do this. I can pick up a few special tools I will need at the shop and bring them home when I decide to do this.
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Youll have plenty of help from all here thats for sure
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Oh yeah, I have come to rely on TSM more than the service people at the MX dealership where I live. You guys have helped me through an entire bike rebuild and re paint, all kinds of engine work, and have put up with some of my stupider posts
But, some good news. I checked the stator side crank bearings. No movement However, I will be keeping my eye on it every now and then, it didn't seem snug to me, but that just could be my lack of experience with crank bearings kicking in hahaha.
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Talked to my local shop that my friend Charlie owns and they said $150 for labour to replace it .
I'm getting an entire wiseco crank kit for $188 so $150 + $188 is $338 and she'll be back to new . Did I say how much I love 2 strokes? 
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Do it yourself, it is not as difficult, you need a flywheel puller and case splitter.
Other than that a press would be nice. If not find someone who has or get dry ice.
With dry ice you cool down the roller ball bearings and with an oven you heat the case up to 150 degrees.
Bearing should just drop in.
The reason to do it yourself is that along the years you have to do it about once a year if you ride each weekend.
More often if you ride 4 to 6 hours a week.
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Do it yourself, it is not as difficult, you need a flywheel puller and case splitter.
Other than that a press would be nice. If not find someone who has or get dry ice.
With dry ice you cool down the roller ball bearings and with an oven you heat the case up to 150 degrees.
Bearing should just drop in.
The reason to do it yourself is that along the years you have to do it about once a year if you ride each weekend.
More often if you ride 4 to 6 hours a week.
I plan on getting the required tools very soon to be able to do it myself but I'm gonna let the shop do it this time and shadow the tech thats doing it so I know what to do next time . The transmissin is what has me a little iffy . i dont know that If I were to take it apart and things fall out of place that I would be able to put it all back together the right way . The bike probably gets 25 hrs or less a year put on it .
I've been brainstorming a little now that I'm getting the bottom end freshened up about the Athena 144 kit but its just thoughts right now .
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It is quite easy, the tranny, stay in place when you take off the flywheel site first. I do it with my press and don't lose the srew with holds the gear cam shift. I did make my press small so I can do it with the gear still into the case. But to do it with the tranny out is not so back neither.
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The best,most accurate way I've found to check them is before you take anything apart.Put a dial gauge in the spark plug hole and rotate the engine around slowly until you hit TDC.The reading doesn't matter but if the gauge hesitates before starting back down,you've got play.
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Yamaha 2Ts have very few shims and are very easy to work on.Pop off your stator and primary drive gears,leave the clutch/kickstart/shift mechanism in place,split the cases and leave entire tranny assembly in case halve,wrap tape around trans/shift drum assy so it does not move and service crank assy..