why is my engine blown

Today I pulled the top end, and to my surprise: cylinder and piston are fine. I now discovered, that at least one main bearing is damaged. Crank has no side to side or up and down Play, but when you turn the motor over, you can feel the individual balls grinding in the bearing rings.

So that leads me to two questions:
1. How can new genuine brand main bearings of that size, be trash after 2 operating hours. Of yourse I was very gentle when instaling them. No hammering on the inner ring whatsoever

2. Why did the motor have no compression? Maybe the main seals were damaged also, and somehow that leads to no air that could be compressed getting in the cylinder?

I'm no engine expert by any means, so please help me out guys. Before rebuilding the damn thing again, I at least want to know, why it failed.
 
I would say you probably have a case leak. Either a main crank seal was damaged or the cases halves were not sealed.
 
Did you use open or closed main bearings? If open, the cause could be missing lubrication due to a blocked hole. There are vertical holes on the crankcases leading the oil/petrol mix to the bearings.

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Did you centre the crank in the cases after installation? If not then the bearings would have been loaded up and possibly the cause of failure.
 
Thanks guys,
today I disassembled the engine, but got stuck at the left main bearing. It does not want to come out of the case, or the crank out of it either. It is also the faulty bearing, it feels very rough and has lots of play. Tomorrow I'll build a more beafy puller, as the 3 M5 threads in the case won't cut it.

@SS109: The crankcase looked clean, no debris or anything, so I guess the seals were fine. Also it ran perfectly.

@Anders: I used open type bearings. The two lubrication holes were not clogged.

@Gasser Nate: I centered the crank after installation, but now when disassembling the engine, I saw that it was shifted to the left side.
 
If you warm the case up to about 350*F, it should be possible to slide the bearing out without much trouble. Let the crank get cold then use a heat gun on the bearing so it can be pulled off the crank.
 
grachal said:
Thanks guys,
today I disassembled the engine, but got stuck at the left main bearing. It does not want to come out of the case, or the crank out of it either. It is also the faulty bearing, it feels very rough and has lots of play. Tomorrow I'll build a more beafy puller, as the 3 M5 threads in the case won't cut it.

@SS109: The crankcase looked clean, no debris or anything, so I guess the seals were fine. Also it ran perfectly.

@Anders: I used open type bearings. The two lubrication holes were not clogged.

@Gasser Nate: I centered the crank after installation, but now when disassembling the engine, I saw that it was shifted to the left side.
Click to expand...

The crank cannot shift to the side without either a case shattering crash or other major forces. There are no lateral forces on the crank when running. I would say it was not quite right on the installation mate. I install seals after the crank is centred where possible to make sure it spins easily with no drag.
 
With a gastorch and a puller I got the bearing out of the case. Removing it from the crank took raw violence tbh.
The bearings cage is broken in 3 spots, parts of it were completely broken of. I think it got very hot and shrunk on the crank very good.
So I guess i will just replace both crank bearings and seals, and try again :confused:
 
I'm sure you guys are right on the temperature. I'm just used to having the oven at 350*F for everything. How else do you know it's done unless it's smoking when you open the door? (I'm single)
 
So today I slapt it back together, and took the bike for a quick spin. Runs like it used to, but I have a bad feeling about the motor.
When driving I hear a slight whine. Comparable to what a lengthened timing chain would sound like.
At a standstill I can't hear it, and I can't tell where it comes from exactly.
Main bearings must be fine now. They are not loaded up or anything, crank spins super easy and freely.
 
(F5) said:
After making sure the crank is still true. Polish the bearing journals too.
Click to expand...

+1 on checking the crank.

I would start looking for the root cause of the main bearing failures, rather than repeating the same steps and expecting a different result.

Here are some possible causes for main bearing failures:

Dirt 45.4%
Misassembly 12.8%
Misalignment 12.6%
Insufficient lubrication 11.4%
Overloading 8.1%
Corrosion 3.7%
Improper Journal Finish 3.2%
Other 2.8%
 
I did not have the possibility to properly check if the crank is still true with a gauge, but if it was not, you would expect it to slightly bind when turning it by hand in the assembled case, right? The journals were polished, as suggested.
Thank you for the possible main bearing failures. I guess I'll start looking at some exploded drawings, to confirm proper assembly
 
I did not find anything wrong and I do not feel like pulling the motor back apart. I'll just send it till she blows, lets see :rolleyes:
DSC_002345.jpg
 
One more question. Bike ran fine the last 400 kilometers, but I noticed, that my coolant turned black. It looks like dissolved aluminium particles in there if i would need to guess. Any idea what this comes from? I have no water in the crankcase or in the oil. But the water level got slightly less, about 150ml since the rebuild. Maybe it burns the coolant due to a leaky head gasket and this again leads to carbon in the water :confused:
 
Thanks for your suggestion. I checked the impeller and it is good. Flushed the radiators and it showed that it was not as bad as it looked before. Clear water with some dark sediment in it.
Maybe some Oxidation residue from the radiators (cheap chinese ones) or the engine itself?
I refilled the system and i'll check again later.
But the next thing that concerns me is clutch rattle getting worse. The sound does not change when actuating the clutch and also no difference if its in gear or not.

All in all not a very pleasing experiece so far. Never had that amount of uncomfortable events with my KTM SX
 
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