RCMK Failure

I have not heard of this happening before on an RCMK EVO. The engine was stock, never dunked and about 4L of fuel run through it. It was running on 20:1 or 16:1 Castrol A747 and always taken care of. I was in the process of testing different props on my cat to find one to further test with when it came round a corner and went quiet.

The bearing spacer on the connecting pin failed and bounced around the engine before it siezed. The damage was extensive, whole top end & crank. Mr Park has very generously agreed to send replacement parts to get the engine up & running again when I sent these pics to him to show him.

Has anyone else seen this type of failure before?

Disassemble further down to wrist pin and rod to view better the damage :S

The only reason I could think of is that if the crank was bent it put excess stress on the spacer & it snapped, but the engine seized hard after the bearing failed so the crank is probably bent from that anyway. The bearing spacer was in pieces throughout the engine with the largest piece shown on the paper between the jug & the case.

This angine has never taken a dunk or hydro locked before. so I don't know how the engine would bend a crank.

Seen it ... Sadly yes. Found a cure, yes. Gotten RCMK to understand what I was trying to share ... No

Design issue of the wrist pin thrust washers being contacted by the needle bearing race and not having enough counter bore so side to side thrust guidance is rod/washer/piston boss with needle floating within. Way it is rods side thrust at wrist pin end allows to much rod cocking loading up the bearing causing excessive side loading against washers.

Saw the error of design early on addressing it here:
www.modelgasboats.com/Magazine...e_Modification/
** Supplement area bottom of article.

This just my personal opinion

Scott

Thanks for the info Scott. I've got some spare Zen washers lying around. I'll send them to my engine modder & instruct him to follow that thinning process on them when he mods the engine when I get the parts. Figure I've run a stock EVO, I may as well compare it to a modified one now.