slip fit vs. interference fit

ok guys and girls I'm just posting up because I'm not to knowledgeable on this and don't have quite a good understanding on this. what is the benafits of a slip fit crank over a interference fit (press fit crank) or vise versa. I know carting guys use a slip fit crank but never heard of it being used on a bike, wouldn't it be much easy to use a slip fit design because of the ease to strip the engine or does it wear down reliably?

Some bikes use slip fit cranks like Honda CRF's but those are the only bikes that I have seen that uses that design all though I am sure there are many others.  For bikes that don't use a slip fit crank you just need to purchase the proper tool for installing and removing the crank.  I bought a "tusk" branded tool from RMATV that does exactly this.  It was cheap and it works perfectly.


Also with the interference fit cranks sometimes the main bearing comes out with the crank and needs to be removed.  Tusk also makes a tool for that job as well...

I have a cr125 know if there slip fit? That's weird I never knew the crfs were slip fit

I have a cr125 know if there slip fit? That's weird I never knew the crfs were slip fit


I am not sure about the cr125 but If I had to guess I would imagine it is an interference type fit.  When you get one of the case halves off if you can't just pull the crank out of the other side with your hands then it is an interference fit and you will need to purchase the correct tools to remove it.  You might be able to infer what type it is by looking at the service manual for your bike.  If it shows the use of tools to install the crank then it has to be an interference fit.  The service manual for my CRF just shows dropping the crank into the case half and makes no mention of special tools.

The crank in my GasGas 300 is a slip fit. Has a roller bearing on the ignition side(this side slips right off when you unbolt the cases) and has a ball bearing on the clutch side, the crank is secured to that side of the case by a nut on the counterbalancer. It makes dis-assembly very easy with no special tools or pullers. Also its a pretty much bulletproof bottom end. It's possible the CR125 would be the same, as the GasGas engines loosely resemble an older honda CR250. I believe the CR crank can even be used in the GasGas with minor modification.

The idea of modding a press fit crank to slip fit is due to bearing loading, when the engine comes up to temperature tolerances change, with ball race bearings both sides you can side load the bearings, they will not last as long and will be worse with high rpm running (carts).

The crank will locate on the clutch side because it's pulled up with the main crank gear Bolt, but will slip in the ignition side slightly if needed to keep things true.

The ktm 2 strokes use one ball race as a locator, and one roller that can 'true' things up.

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