Shortening CG250 push rods

[superjocko]

I’ve been looking over these forums for some time before deciding to buy a new CSC TT250. I appreciate all the info here.

I’m adding the motocult stage 3 kit and would prefer to shorten the pushrods rather than shim up the rocker carrier assembly to keep the tip of the adjuster in the proper relationship to the valve stem. I’ve shortened automotive engine pushrods before and am familiar with the process. That said, those pushrods are typically hollow, as are the ball ends. The ball ends on the CG250 are solid. I don’t know if the pushrods themselves are hollow or not. I presume they are at least hollow (drilled) on the ends where the ball end studs press in. Does anyone know for sure?

Thank you.

[TominMO]

Alternatively, could you shave the rockers where they contact the pushrods?

[XLsior]

you can buy some alternative length push rods for different CG engine configurations.


https://www.aliexpress.com/item/4001262738423.html?spm


However they are thicker and heavier than standard factory CG250 push rods.


I had to experiment with them trying to use roller cam followers...


I ended up going back to stock push rods and factory flat cam followers.


But I discovered you could shim up (spacer) the valve rocker assembly as an option.


The push rods are solid not hollow for oil passage reasons.

[superjocko]

Originally Posted by TominMO

Alternatively, could you shave the rockers where they contact the pushrods?

That’s a machined, hardened, and polished ball socket. It would be beyond the capability of the machining equipment that I have access to. It would also leave that end of the rocker arm dangerously thin. Shortening the pushrods would be much simpler. I’ll give it a go in the morning and see how it works out. If all else fails, I can use the supplied rocker carrier shim and stock length pushrods. I’d prefer not to though as the valve train geometry is slightly less than ideal with the shim.

[superjocko]

Originally Posted by XLsior

you can buy some alternative length push rods for different CG engine configurations.


https://www.aliexpress.com/item/4001262738423.html?spm


However they are thicker and heavier than standard factory CG250 push rods.


I had to experiment with them trying to use roller cam followers...


I ended up going back to stock push rods and factory flat cam followers.


But I discovered you could shim up (spacer) the valve rocker assembly as an option.


The push rods are solid not hollow for oil passage reasons.

Thank you!

[superjocko]

I had bought an extra set of pushrods to at least experiment on. What I found is that the pushrods are indeed hollow, but the ball ends do not have a stub end that is pressed into the hollow end of the pushrod. Rather, they are either electrically or inertially welded to the end of the pushrod. That still leaves me with an option for a solution to making the pushrods the overall length that I’d prefer them to be for ideal rocker arm adjuster tip to valve stem tip geometry. Upon finding a suitable outside diameter roller bearing needle to provide an interference press fit within the pushrod, I’ll cut the pushrod such that half the roller bearing needle with be pressed halfway into the pushrod on a cut off end approximately 6-8 mm from the ball end and the remainder of the roller bearing needle will be pressed into the shortened pushrod. I’m confident that will work just fine. I just need to get another pushrod as I sacrificed one that I got to experimentation to find out how it was constructed.

[superjocko]

Another picture of the ball end with a small amount of the pushrod remaining after cutting it off with a parting tool on a lathe.

[Deckard_Cain]

I'm curious why shimming the rocker assembly is not desired.

[superjocko]

Originally Posted by Deckard_Cain

I'm curious why shimming the rocker assembly is not desired.

The tip of the valve lash adjuster is no longer centered on the valve stem when using the shim. The shim is a solution, just a less than ideal solution. Shorter pushrods would be the best solution.

[Bruces]

Not sure if you have seen it ,but megadan installed a custom cam and sized his own pushrods .Cg250 custom cam install ,is the thread if you want to read it through .

[Deckard_Cain]

Originally Posted by superjocko

The tip of the valve lash adjuster is no longer centered on the valve stem when using the shim. The shim is a solution, just a less than ideal solution. Shorter pushrods would be best solution.

Gotcha.

I hadn't looked at mine since the last time I had it apart to see if that was going to be an issue.

Something to consider I suppose.

[superjocko]

Here are my completed shortened pushrods. The final image shows the type of stainless steel locating dowels that I used. I chose them for their availability and also their expansion coefficient, which is just slightly greater than the pushrod material. This will ensure that the interference fit is maintained even as the engine temperature increases. The inner diameter of the pushrod tubing is relieved for a good interference fit with the dowels centered between the joint in the pushrod tubes. I constructed a test pushrod first, then tried to bend it. It was at least as tough as the stock pushrod. I am well satisfied that these will work out fine.

I also have a video file of the pushrods rolling true on a flat surface, but this forum doesn't seem to accept the particular file type. You can trust me that they roll flat and true.

More photos to come later showing the relationship between the rocker adjuster tip and valve stem with the shim installed, and then with the shorter pushrods installed.

[superjocko]

Here's a photo of the test pushrod. It's quite scarred from having attempted to bend and twist the portion that has the ball end attached. The other end was used to initially test the interference fit. That end gives a decent representation of the diameter of the dowel relative to the pushrod diameter. Do note that the dowel visible on that end was just to test the interference fit and is not pressed fully halfway into the pushrod tube as the dowels are in the finished pushrods.

[superjocko]

Here are photos that provide a comparison of the lash adjuster to valve stem tip relationship with the shim installed under the rocker arm carrier with stock pushrods and then with the shim removed and shorter pushrods.