why is my engine blown

[grachal]

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.

[SS109]

I would say you probably have a case leak. Either a main crank seal was damaged or the cases halves were not sealed.

[Anders]

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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[Gasser Nate]

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.

[grachal]

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.

[Neil E.]

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.

[Zman]

IMO 350F is too hot. I find the bearing drop in between 150 and 200F.

[SS109]

Originally Posted by Zman

IMO 350F is too hot. I find the bearing drop in between 150 and 200F.

Yeah, I normally do 200F. Works perfectly and I take no chance of damaging seals.

[Gasser Nate]

Originally Posted by grachal

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.

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.

[grachal]

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