Bottom end rebuild... again...

[Hondacrrider]

So, this is my second bottom end rebuild since I have bought this bike. I am really getting frustrated with it. Anyways, I have learned two things in the process, one is: Be sure you find a guy to do the rebuild who knows what he is doing, and Hot rods cranks SUCK! Well, I think they do anyways. The connecting rod went after a few months of riding. Sure, I ride my bike hard, I tend to scream my bike as opposed to lug it(it's a 125, that's what you do), but still, the connecting rod should have more life in it. So, I talked to a mechanic and he said that it would be cheaper for me to buy a new crank(funny, he suggested Hot rods) than to rebuild my old stock one from long ago. My problem is, I really do not want to buy another Hot Rods crank. I looked at a wiseco crank, and it is fairly reasonably priced. What do you guys think of Wiseco cranks? Also, I found this used ebay motor, do you think it would be smart to just go that route? http://cgi.ebay.com/ebaymotors/2001-HONDA-CR125-ENGINE-CART-MOTOR-_W0QQcmdZViewItemQQhashZitem3cb3c4d54aQQitemZ260714059082QQptZMotorcyclesQ5fPartsQ5fAccessories

[Charles Owens]

It's always nice to have a back-up.
And yes it is VERY important to have it done by someone with experience.

Go with an OEM crank if you can.

[SachsGS]

I recently overhauled an old Honda CR80 and the OEM crank was the cheapest way to go - same for an 03 CR125 as well. What mixer oil at what ratio are you using?

[eprovenzano]

check with MR cycles.  I helped a friend rebuild his KX125 with a new crank from MR Cycle.  It was less expensive to get a new OEM crank than to have one rebuilt.

[Coop]

Ron Ayer lists the OEM crank for $168, I have no idea if that is cheap for EOM, just throwing a number out there. I did a quick search on ebay and see the Wiseco is a lot cheaper. I used a Wiseco crank on my nephews KX60, but keep reading more and more about them coming from the factory out of true. So maybe keep that in mind if you decide to go Wiseco. The one I put in Nick's 60 has performed like a crank should .

[MyckMcClung]

I'd say crappy bearings, poorly balanced crank, failure to replace the crank bearings at the last rebuild, or too lean an oil fuel mixture are the culprits here.
Some mechanics will get less expensive bearings to put a few dollars in thier pockets. some will skip replacing the crank bearings altogether if they don't "seem" to be shot.
I have put hotrod crank rods on both of my bikes and have not had any problems, the first has over 80 hours on it and the weisco piston with 20 on the new rings.
the build all has to do with the quality of the balancing.

[Hondacrrider]

Well, I did some research, and the OEM crank is 40 dollars more than the wiseco, not including gaskets(the wiseco includes gaskets). I would love to buy an extra motor, but at the same time, I think it is too much a risk. I had no idea that there was so much involved in rebuilding the bottom end. I am very glad that I am spending the extra money this time to hire a proper mechanic. So, my second problem is that the cylinder needs to be redone. How should I go about this? Would it be cheaper to bore out the cylinder, or buy a new cylinder all together, what are my options here? Also, what are some brands that make oversized pistons?

[MyckMcClung]

depends on the cylinder, it is an iron bore or lined?
if it's an iron bore take it to a machinist and find out how much material he's gonna need to clear before you get a piston. Then get a piston just a little larger than what he needs to clear.
If it's lined. get a L.A.Sleeve take the jug,sleeve w/ the instructions and head to your machinist. He'll bore the jug, press the sleeve and clean up what needs to be done according to the instructions.
Wiesco is the way to go

[mj4trax]

Assuming it's a stock cylinder with a nikasil (or equivalent) plating, I would recommend to just have it replated.  (Millenium Technologies is a good source for this work). ..  the plating will cost a bit over $200. . .  but IMO is well worth it.

I've spent YEARS dealing with trx steel sleeved cylinders and am so much happier with the newer tech plated cylinders that transfer heat better and don't require oversized pistons, etc. 

[TMKIWI]

Assuming it's a stock cylinder with a nikasil (or equivalent) plating, I would recommend to just have it replated. 

X2

[SachsGS]

Two cycle engines are actually incredibly simple and easy to work on and this is one reason why they are superior to 4Ts as an offroad race engine.Take your time,get the correct tools and don't be intimidated by your CR125 engine and you will feel comfortable working on it in no time.

I once watched a mechanic of mine roll a YZ80 into my shop,disassemble,split the crank,replace the rod and balance,reassemble and ride the bike out.Total time involved - 4 hours.

[eprovenzano]

I had no idea that there was so much involved in rebuilding the bottom end. I am very glad that I am spending the extra money this time to hire a proper mechanic.

Splitting the cases to replace the crank is not overly difficult.  I'm not saying its easy but its really not too difficult.  Other than a flywheel puller, basic hand tools is all thats needed. Besides a good repair manual...

[SachsGS]

RPM manufacturing sells how to videos for overhauling 2T's cheap ($15).

[metal_miracle]

whats important is centering your crank in the crank cases, 

and grease the crank case seals and oil the bearings good

[evo550]

I've said it to you before and I'll say it again, ditch those old Hondas, and get a new YZ/KTM.