Should I do a complete rebuild?

kawi_guy07
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kawi_guy07
I have a 2012 KX250F that just rolled over 115hrs. A little bit of the engine maintenance history:

60 hrs: Wiseco high compression piston and rings kit
85 hrs: Replaced the valves

Everything else on the engine is stock. So i guess my question is, should i look to do another piston and rings kit or a full rebuild?

I'm far from a mechanic and I'm not sure what would give me the biggest bang for my buck.

I keep getting told that if i push it too much I might sling a rod through the case.

What do you guys think?
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seth505
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seth505 4/15/2020 9:42am
4/15/2020 9:42am
I'd do full rebuild but better answer is to check the play in the rod and see if it out of spec/if there is any up-down play.
kawi_guy07
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kawi_guy07 4/15/2020 9:56am
4/15/2020 9:56am
seth505 wrote:
I'd do full rebuild but better answer is to check the play in the rod and see if it out of spec/if there is any up-down...
I'd do full rebuild but better answer is to check the play in the rod and see if it out of spec/if there is any up-down play.
So is the piston and rings kit considered a top-end rebuild?
seth505
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seth505 4/15/2020 9:59am
4/15/2020 9:59am
seth505 wrote:
I'd do full rebuild but better answer is to check the play in the rod and see if it out of spec/if there is any up-down...
I'd do full rebuild but better answer is to check the play in the rod and see if it out of spec/if there is any up-down play.
kawi_guy07 wrote:
So is the piston and rings kit considered a top-end rebuild?
Correct, all top end and head work it sounds like you've done in the past. Doing the bottom end would include splitting the cases and rebuilding the crank (with a new bearing and rod and new crank bearings?seals in the cases) or installing a new crank.
kawi_guy07
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kawi_guy07 4/15/2020 3:49pm
4/15/2020 3:49pm
What do you think is the most common hour range to do a full rebuild?

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pcm_918
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pcm_918 4/15/2020 4:40pm
4/15/2020 4:40pm
Needs a crank soon.
Matt_B_#57
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Matt_B_#57 4/16/2020 11:48am
4/16/2020 11:48am
I think it’s important to consider your skill level and how you’re riding the bike. Are you putting around in your backyard or are you a lap time hero at your local track? If you just cruise around then your bottom end is probably fine but if you’re constantly bouncing off the rev limiter at the tracks then you have a valid concern.

To give yourself piece of mind, tear into the top end and check the crank for up and down play – you shouldn’t have any. Side to side play is OK. If you feel up / down play then it’s time for main bearings but if you don’t feel anything then I personally wouldn’t pull it apart.

Just my 2 cents.
kawi_guy07
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kawi_guy07 4/16/2020 4:57pm
4/16/2020 4:57pm
Matt_B_#57 wrote:
I think it’s important to consider your skill level and how you’re riding the bike. Are you putting around in your backyard or are you a...
I think it’s important to consider your skill level and how you’re riding the bike. Are you putting around in your backyard or are you a lap time hero at your local track? If you just cruise around then your bottom end is probably fine but if you’re constantly bouncing off the rev limiter at the tracks then you have a valid concern.

To give yourself piece of mind, tear into the top end and check the crank for up and down play – you shouldn’t have any. Side to side play is OK. If you feel up / down play then it’s time for main bearings but if you don’t feel anything then I personally wouldn’t pull it apart.

Just my 2 cents.
Thanks man that's helpful advice.

I'm like a low level C rider so not crazy fast, but also not just putting around either. I spend all my time at the track so i am a little hard on my bike.

I'll do what you said tho and just check the crank for any play and see how it is.

I got quoted $800 parts and labor for a full rebuild using Wiseco parts. Does that sound about right?
yvaillancourt371 4/16/2020 7:28pm
4/16/2020 7:28pm
The oem crank over 100 hours i think it's playing with fire. I will do a complete rebuilt if it's my bike
Matt_B_#57
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Matt_B_#57 4/17/2020 5:23am
4/17/2020 5:23am
yvaillancourt371 wrote:
The oem crank over 100 hours i think it's playing with fire. I will do a complete rebuilt if it's my bike
Hey man, I see your concern and yes, the easy answer would be to just rebuild the bottom end but his question was what's the biggest bang for his buck. Engineers specify tolerances for a reason so the biggest bang for your buck would be to check those tolerances. If they are in spec then 90% chance you'll be fine but at least you'll know, especially when you ride on a budget. I've had 4 bikes so far that topped 120 hours without touching the bottom end because my mains were still in spec so I felt safe leaving it alone for now.
The chance of metal fatigue is always present and increases with time, hence why factory teams frame their race bikes after every race but I think the budgetary answer would be to check the tolerances.
Matt_B_#57
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Matt_B_#57 4/17/2020 5:41am
4/17/2020 5:41am
Matt_B_#57 wrote:
I think it’s important to consider your skill level and how you’re riding the bike. Are you putting around in your backyard or are you a...
I think it’s important to consider your skill level and how you’re riding the bike. Are you putting around in your backyard or are you a lap time hero at your local track? If you just cruise around then your bottom end is probably fine but if you’re constantly bouncing off the rev limiter at the tracks then you have a valid concern.

To give yourself piece of mind, tear into the top end and check the crank for up and down play – you shouldn’t have any. Side to side play is OK. If you feel up / down play then it’s time for main bearings but if you don’t feel anything then I personally wouldn’t pull it apart.

Just my 2 cents.
kawi_guy07 wrote:
Thanks man that's helpful advice. I'm like a low level C rider so not crazy fast, but also not just putting around either. I spend all...
Thanks man that's helpful advice.

I'm like a low level C rider so not crazy fast, but also not just putting around either. I spend all my time at the track so i am a little hard on my bike.

I'll do what you said tho and just check the crank for any play and see how it is.

I got quoted $800 parts and labor for a full rebuild using Wiseco parts. Does that sound about right?
Sure thing. Post what you find, I'm curious to see how the well the ’12 era bikes hold up.

$800 all-in sounds reasonable I guess, the bottom end kits from Wiseco aren’t very expensive though. $200 will get you the main bearings, new crank, rod, seals, and gaskets for the bottom end (click here for link). Bottom ends take a little more time and a couple specialty tools so if you’re going to have a shop do the work, you might save on some labor if you pull the engine out of the bike and take the top end apart. Labor is usually always more expensive than parts so if you can help cut the labor portion then you’ll save yourself a few bucks.
kawi_guy07
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kawi_guy07 4/17/2020 1:16pm
4/17/2020 1:16pm
So according to that link the Wiseco bottom end isn't even compatible with my bike. It was a guy that quoted me $800 not a shop so he must not be aware that it won't fit my bike.

If I do end up going the complete rebuild route, do you have any suggestions on which kit i should get?

All i'm really seeing as far as kits go on Motosport and RMATV is the wrench rabbit kit. Are those any good? Any other kits you'd recommend over it?

Thanks!
SLOWTIME
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SLOWTIME 4/19/2020 5:48am
4/19/2020 5:48am
Unless you want to rebuild it twice, avoid the wiseco crank.
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kb228
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kb228 4/19/2020 9:15am
4/19/2020 9:15am
Ken oconnor rebuilds OEM cranks within .001” for $220 with a prox rod. Thats 100% the best bang for your buck.
yvaillancourt371 4/19/2020 10:00pm
4/19/2020 10:00pm
yvaillancourt371 wrote:
The oem crank over 100 hours i think it's playing with fire. I will do a complete rebuilt if it's my bike
Matt_B_#57 wrote:
Hey man, I see your concern and yes, the easy answer would be to just rebuild the bottom end but his question was what's the biggest...
Hey man, I see your concern and yes, the easy answer would be to just rebuild the bottom end but his question was what's the biggest bang for his buck. Engineers specify tolerances for a reason so the biggest bang for your buck would be to check those tolerances. If they are in spec then 90% chance you'll be fine but at least you'll know, especially when you ride on a budget. I've had 4 bikes so far that topped 120 hours without touching the bottom end because my mains were still in spec so I felt safe leaving it alone for now.
The chance of metal fatigue is always present and increases with time, hence why factory teams frame their race bikes after every race but I think the budgetary answer would be to check the tolerances.
Sorry my english is not Perfect, i miss a part of the question. Yes it Will be better To check the clearance before all. Check the big end and small end gap of the connecting rod . For the small end , check if he have always the "babbitt bearing" coating all around the inside and for the rest if he is in the specs of good To go.
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