125-200cc Part 1: Tear down and install procedure for WB165 Kit

Part 1: Tear Down

Background:
I have a 2008 CR125. Here is the tear down procedure that I used to remove my original 125 top end. It should be applicable to other model years as well. I probably removed more things than needed, but it made the job easier for me. I will be installing a WB165 big bore kit. When upgrading to the WB165 kit, you will need to send Motosportz/Wallybean your old cylinder, head, and power valves (still assembled in the cylinder). Those parts will be modified for the new 165cc piston.

Since this was my first tear down of a top end, I got some helpful tips from Walt (Wallybean). These are included below along with pictures that I took to help document the process. Hopefully, this can help others that are also be new to this. The top end guru's are welcome to post their comments. Any tips/tricks that can help make it an easier process would be great to have.

NOTE: I have omitted some of the basic steps like removing gas tank, exhaust pipe, and pv cover. Everyone has done these at some point.

General Note:
Power wash your engine area of the bike before you do any disassembly to remove most of the dirt that could get into the crankcase. Use a little brake cleaner after you get the pipe off to get the rest. Always keep your open engine parts covered to eliminate the chance of dirt/dust/flying parts getting in where it doesn't belong.

VERY IMPORTANT: Always stuff rags, old towels, etc. in the lower end BEFORE removing the piston circlips.



A new thread has been created for Part 2: Installation of the WB165 Kit.

Remove the power valve linkage covers and all the linkage arms. This will give you access to front right cylinder bolt.

In the pic below, the plastic link has been already removed. The plastic link can be gently pryed it off the round post shown in left box. You will want to also remove the bolt in right box and remove the upper metal link arm and spring.



In the pic below, the lower metal link has been already removed. This is done by removing the bolt (in bottom left box) which attaches the lower metal link arm. This will allow you to slide off both the metal link and plastic link together.

I forgot to mention... there is an exhaust port shim that fits between the pipe and the cylinder. It is really easy to miss or lose. When you pull the exhaust pipe, make sure you remove that first so you don't lose it.

There is a drain plug (in left box) on the water pump housing for draining your coolant. After removing the exhaust pipe and PV linkage, this is probably the one of the next things to do.

After coolant is drained, loosen the hose clamp in right box and disconnect hose.



Then, remove the bottom radiator hose running side-to-side. The pic below shows the radiator connection points for this hose (ignore the fact that my head is already off... I took this picture out of sequence... sorry).

Also, remove the spark plug when you pull the hoses to make it easier to reach the head bolts later.

Unbolt the upper bracket mounted between head and frame. These are the 3 bolts in the boxes below.

Remove the cylinder head by unbolting the 5 head bolts and washers.
Recommend: replace 5 washers if needed.

Important: Remove your head orings and put them somewhere safe. Don't get any kind of chlorinated cleaner on them or they swell.
Recommend: replace both head orings if needed.

Here is a picture of the cylinder head and both orings removed.

Unbolt the PV cover backing plate which is attached to the cylinder. This is attached with 1 screw (shown in top right box) in the pic below.



Pull off the PV cover backing plate. Note: it fits very snug onto the cylinder boss (shown in right box below). There is also an oring seal.
Recommend: replace oring if needed.

The front right cylinder nut can now be accessed easily. This is the nut that I mentioned in the very beginning.

Unbolt the 5 cylinder nuts and remove cylinder.
Recommend: replace cylinder base gasket if needed.

VERY IMPORTANT: Always stuff rags, old towels, etc. in the lower end BEFORE removing the piston circlips.

To remove the piston from connecting rod, first remove the circlip from one side of piston. Grab the circlip with needle-nose pliers and pry/twist out of the groove (use access slot shown in box). Then, remove the circlip from the opposite side of piston.
Recommend: Always replace both circlips. DO NOT REUSE CIRCLIPS.

Next, you will need to push the wrist pin out of the connecting rod. I used a small socket that just fit inside the piston's wrist pin hole. Make sure that you support the piston and connecting rod as you press out the wrist pin.

Here is a pic of the piston, wrist pin, and wrist pin bearing after removal.



Here is a pic of the small end of the connecting rod after the piston is removed. As mentioned above, always stuff rags, old towels, etc. in the lower end BEFORE removing the piston circlips. And yes... those are old boxer shorts... hey, they make good rags LOL.

I was surprised on how clean my piston looked on top. It looked new and same with the inside of the cylinder head. Either my premix is very clean burning or it may have been slightly lean. Interesting thing is that my plug looked wet like it was rich with my current winter jetting. This is probably more related to how I was running my bike just before shutoff. Out of curiousity, I checked my compression and it was 165psi with about 45 hours on this piston. When I checked it new, it was about 160 psi. Piston had very little blow-by pass the ring from the color on the side.

FYI... I run my premix at 36:1 and 92 octane pump gas. The premix is Amsoil Interceptor.
http://www.amsoil.com/storefront/ait.aspx



Here is the condition of my CR125 top end at 45 hours.

(reserved for future post)

(reserved for future post)

Well, this concludes the tear down process that I used. I think it would be great if some of our 2-stroke gurus could share their tips/tricks below. I'm sure there are areas where time could be saved. Unfortunately, I do not have that top end experience yet.

Let's make this thread a collection of how-to instructions for tear down of the top end. I will start another thread for installation of the WB165 Kit.

Great report, THANKS!!!

I use Amsoil too and my pistons come out looking great. I love that stuff. Their motor oil makes my bikes shift nicer too. Great products from those guys.