cloakedvillain
Well-Known Member
Are you actually getting more power from rpm that high? These engines usually max out a little bit below 7k and just lose power after that.
High rpm crank?
- Thread starter jasone
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GW's Motorized
Well-Known Member
Perhaps you could try to lighten up a stock crank. I know there are shops that can do it for you
GW's Motorized
Well-Known Member
What bottom end are you using? Most don't have a 12mm wrist pin. You'll need to get some bushings.
One of my first engines I bought was a bt100. Iv now realised how these are the best china cases. 6203 mains, much better transfers, thicker case with extra bolts. Deck is 5mm higher, 12mm pin and even the casting is way better quality
Nickt919
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In my limited experience with the Minarelli hybrid engine a balanced and trued China crank lasts me a little better than 500 miles then the bearing cage comes apart.
Fretting wears a trench in the crank pin and rod. This lets the bearing cage drag on both of those surfaces, eventually wearing down, and coming apart.
Engine timing can speed up or slow down bearing failure.
The Chinese metal is soft.
Fretting or one of the other types of metal failure usually sets in a little past 500 miles for me.
www.linearmotiontips.com
I have been treating the cranks as consumables and switching them out around 500 before the cage comes apart and goes thru the engine.
A zl40mm crank is $30 shipped in the USA at CDHPower.
While the engine is apart I change the 4 bearings also. Buying 10 packs of PGN bearings makes it a little more affordable.
It does no good to try and install a better rod bearing because once the pin is pressed out then back in, the fit will no longer be tight enough to hold the crank lobes in place.
Even without removing the pin, I’ve found normal running to get the crank out of true after lots of work balancing and truing.
A few photos of what will typically happen running the Chinese cranks till they fail…
Fretting wears a trench in the crank pin and rod. This lets the bearing cage drag on both of those surfaces, eventually wearing down, and coming apart.
Engine timing can speed up or slow down bearing failure.
The Chinese metal is soft.
Fretting or one of the other types of metal failure usually sets in a little past 500 miles for me.
What's the difference between brinelling, spalling, and fretting?
When discussing bearing damage — especially in the context of linear bearings — three terms that come up quite often are brinelling, spalling, and fretting.
www.linearmotiontips.com
I have been treating the cranks as consumables and switching them out around 500 before the cage comes apart and goes thru the engine.
A zl40mm crank is $30 shipped in the USA at CDHPower.
While the engine is apart I change the 4 bearings also. Buying 10 packs of PGN bearings makes it a little more affordable.
It does no good to try and install a better rod bearing because once the pin is pressed out then back in, the fit will no longer be tight enough to hold the crank lobes in place.
Even without removing the pin, I’ve found normal running to get the crank out of true after lots of work balancing and truing.
A few photos of what will typically happen running the Chinese cranks till they fail…
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