[REDRIDER]

There's another thread around titled,  bad. He had that same issue and i think he found replacement bearings from a Toyota or something?  I think they also went over the engine tear down. 

[REDRIDER]

http://cfmoto-forum.com/800ex800/bad/

[Ricky King]

Thank you REDRIDER! Now I know the difference between Mark A & B.  Very interesting thread, exactly the same issue. Same side on the crank as well.

But I´m still not clear of what´s causing this issue.. theories so far are:

1. Trimbox and slipon? (too lean mixture overheating the crank?)
2. Bad Oil pressure regulator valve? (reliefs the oil pressure on higher rpm too early?)
3. Oval cylinder (Uneven loads on the rod?)

Thankful for more input about the cause! I will measure the cylinder and inspect the regulator valve today.

[davidpaul]

Hi, same problem I had, pictures show part numbers for replacement bearings so you can re-grind your crank.

[davidpaul]

I had thought the oil had been draining back from the oil cooler, but this is not the case, when I flushed my cooler out it was full of oil, one thing I did notice was how much force it took to push the oil through the oil cooler system.
The next thing I noticed was how much the rubber hoses expand when starting and the system pressurises.
As the oil pump is fairly small I wonder if this is too much for the pump to cope with on start up causing a delay in getting full pressure.

I have been thinking about mounting an oil cooler in the rear bed somewhere with steel braided hoses.

Just my thoughts

[Cosmosdan]

I have never had to deal with oil pump issues thus far. I might be off track on this, but I recall talking about a prestart electric oil pump that would prime the system. For the life of me I can't remember the engine it was used on. I do remember the claim was eliminating start up engine wear.

[davidpaul]

Normally used in big engines like ships or trains, in the early days they would have been hand pumps, I would think the newer ones are powered by electric.

[davidpaul]

Saw this simple diagram that shows the difference between mineral and synthetic oil molecules.

[davidpaul]

Looks like the new z8's have better oil cooler pipes

[Ricky King]

Thanks David for the pics and info!

Yesterday I measured the cylinders, they where all fine and within limits. Still a big question mark about the cause though...

I will contact the agent for CF-Moto tomorrow and see if I can get some goodwill or better price on the parts needed.
The engine is only 1 year old.

[REDRIDER]

Did it overheat at all? I seem to remember people running into rod bearing failures after a multiple overheating events.

[Ricky King]

No, I haven´t found any trace of overheating so far. No warning lights before the engine started to rattle etc..

UPDATE! We might have found the cause now, we measured both rods today with a three point precision gauge (micrometer)
The rod on the failing bearing was 7/100 too tight in comparison to cylinder #1´s rod. This might have cause the bearing getting too little oil between crankshaft and the rod bearing (if any oil...). We will machine the rod to the right specs and hopefully I get the new crank and bearings before this weekend

I guess they don´t control measure every single rod in the production line in China...

[Cosmosdan]

How does the measurement compare to the manual specs

[Ricky King]

I need the new bearings and crank before I can do a correctly measurement. The manual only specifies service limit of the clearance between bearing and rod.

The normal tolerance is 14/100 for the crankpin, maximum clearance is 9/100 but that is way too of now with the failed crankshaft.

What I can confirm is that the failing rod had a smaller diameter of 7/100 than the other rod.

[davidpaul]

CF Moto have different size rods and cranks, depending on what mark is on the item in question they used 3 different size bearing shells.

So if you have rod number 1 and crank A you would use the bearing shell marked with a black stripe.

The 3 different sizes are only a few tho different in size, I understand they are only for making up the difference in tooling when the crank or rod was machined.

I think the sizes are blue red and black.