Turbo Axys top end shot, bad scoring, debris damage? 1k miles

[dnk]

I recently picked up a 2018 pro rmk 800 with 1k miles that had a Silber turbo installed on it. Got what felt like a crazy deal on it at $6k. Now I'm not so sure.

Idle was super low, bouncing between 1500 and almost stalling at 1100. It was leaking coolant, from what looked like the MTNTK tunnel chop kit with the plastic fittings.

Compression was low; 95 Mag/105 PTO. I inspected the top end with a borescope and found bad cylinder scoring and head/piston damage on the mag side. Looks like some debris got sucked in and bounced around. There was still bad scoring on the PTO side, but no debris damage. Haven't looked at the reeds yet.

I'm going to replace the top end, cylinder included. Was able to polish down the head and I think it is salvageable. I want to make sure I'm getting to the root of the issue though.

Does anyone have any ideas on what could have caused this? Debris coming through turbo for mag side? Water ingestion? There was no sign of anything missing in the top end; piston clips were there, needle bearings all intact, no sign of damage on the bottom end.

What about the scoring on the PTO side? The tunnel was chopped with the MTNTK plastic kit, which was leaking, and I have a feeling this guy was running the sled way too hot.

Think I am going to weld in the CR Racing cooler kit rather than try to fix the leak in the MTNTK kit. Thing is, there was some coolant pooling near the hoses under the fuel tank, and some drips coming down from the middle of the bottom of the tunnel after a couple minutes of running. My thought was the coolant was just dripping down under the tunnel from the chopped end, working its way through the riveted seams, but is it possible that there is a leak in the tunnel body itself?

New to sleds, but not to general mechanic work. Any and all help or thoughts is appreciated.

 

[spoon]

Looks like a combination of overheating and detonation. If it was run on boost low on coolant I am not surprised by the damage. Inspect everything to be safe. Look at turbo impeller and turbine as well for damage.

 

[dnk]

I haven't looked at the turbo yet, but definitely will. Going to test tolerances on the bottom end. Shipping my cylinder out to MCB for a hone which will give me some time to work up the courage to tig in that cooler.

 

[Mac-Daddy-Racing]

Are there two different pistons? Did the PO replace rings to get the compression up? Agreed, looks like the motor has seen some heat. Pull charge tubes and look for any debris..


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[Sheetmetalfab]

I recently picked up a 2018 pro rmk 800 with 1k miles that had a Silber turbo installed on it. Got what felt like a crazy deal on it at $6k. Now I'm not so sure.

Idle was super low, bouncing between 1500 and almost stalling at 1100. It was leaking coolant, from what looked like the MTNTK tunnel chop kit with the plastic fittings.

Compression was low; 95 Mag/105 PTO. I inspected the top end with a borescope and found bad cylinder scoring and head/piston damage on the mag side. Looks like some debris got sucked in and bounced around. There was still bad scoring on the PTO side, but no debris damage. Haven't looked at the reeds yet.

I'm going to replace the top end, cylinder included. Was able to polish down the head and I think it is salvageable. I want to make sure I'm getting to the root of the issue though.

Does anyone have any ideas on what could have caused this? Debris coming through turbo for mag side? Water ingestion? There was no sign of anything missing in the top end; piston clips were there, needle bearings all intact, no sign of damage on the bottom end.

What about the scoring on the PTO side? The tunnel was chopped with the MTNTK plastic kit, which was leaking, and I have a feeling this guy was running the sled way too hot.

Think I am going to weld in the CR Racing cooler kit rather than try to fix the leak in the MTNTK kit. Thing is, there was some coolant pooling near the hoses under the fuel tank, and some drips coming down from the middle of the bottom of the tunnel after a couple minutes of running. My thought was the coolant was just dripping down under the tunnel from the chopped end, working its way through the riveted seams, but is it possible that there is a leak in the tunnel body itself?

New to sleds, but not to general mechanic work. Any and all help or thoughts is appreciated.

Look for the ring locator pin on the bad side.

They loosen with detonation.

The 18-19 800 axys with silber turbo have a tune prone to detonating.

Run a higher octane mix of avgas with non ethanol and they are fine. (Compared to a 16-17 axys silber 800)

Vary your octane mix based on elevation you plan to ride that day. (Treat it like jetting for each specific mx track with a 2 stroke 125 bike)

This will affect response time and sled enjoyment.

Run GOOD clutching that holds 82-8450 rpm. (Overrev AND underrev are detonation prone)

Boost leaks are the first culprit with most any anomaly in runability after assembling.

Highly recommend pistons every 800 miles on boost.

Also NEW exhaust valve slide pieces. (The loose pieces) like every 6-700 miles.

These break often and take out the turbo hot side.

The light scoring on the other side is likely snow ingestion.

^^^^ things i wish i knew before buying my silber.

 

[Sheetmetalfab]

I haven't looked at the turbo yet, but definitely will. Going to test tolerances on the bottom end. Shipping my cylinder out to MCB for a hone which will give me some time to work up the courage to tig in that cooler.

Get the cylinder re-nicasil plated.
It needs more than a hone.

Clean out the bottom end carefully.

 

[gtwitch]

If your going to get the Cylinders done and replace the pistons, please take the crankcase apart and check the PTO main bearing, because if that is coming apart like mine did , have that done by INDY Spec , see my input on the other AXYS thread!!
gtwitch in wyoming

 

[dnk]

Good info thanks y'all. Just got the cylinder back from MCB and will be inspecting everything else and getting it back together in the next couple weeks. Finally starting to snow here in Oregon.

 

[dnk]

Update:

Gave everything a once over, got the top end back together, and replaced the reeds. Been running great. Only issue is a bit of a low idle when the engine is cold but it goes away as soon as I give a good pull. Not sure what would be causing that.

Secondary got stuck open today when I had it pinned getting it unstuck, but went away as soon as I got it out. Maybe bad rollers? Will probably redo clutching and take a look at the secondary.

Appreciate everyone’s help!