717 rotary valve gear stripped, why?

[77Eltigre]

machine ran great, had a previous issue with the start stop button. Machine suddenly died, figured out the rotary valve was not spinning, pulled the shaft and see that the gear is stripped all the way around. Most likely not a issue with the valve seizing.

The gear looks to be almost left alone on the outside edge that faces out of the engine, the piece that faces into the engine is flattened completely.

Ideas? Please don’t tell me it’s a crank issue

Thanks

 

[Spider4real]

Was the rotary valve submerged in oil? How are the bearings. There is one on the rotary valve you removed and one in the case.

 

[etemplet]

I always suspect lubrication failure. Some people put gas in the oil tank by accident and don't drain the oil tank. Could be a bearing problem but that's unlikely if the lubrication didn't fail first. If you replace that shaft and use good oil it shouldn't be a recurring issue.

 

[77Eltigre]

[QUOTE="Spider4real, post: 729343, member: 24467"] Was the rotary valve submerged in oil? How are the bearings. There is one on the rotary valve you removed and one in the case. [/QUOTE] lots of oil in the chamber when i pulled it. Bearing on the front looks great, the shaft spun freely except when it was catching the odd ridge when it was in the case.

 

[77Eltigre]

I always suspect lubrication failure. Some people put gas in the oil tank by accident and don't drain the oil tank. Could be a bearing problem but that's unlikely if the lubrication didn't fail first. If you replace that shaft and use good oil it shouldn't be a recurring issue.

it’s a new to me machine so that is a possibility. I’ve been wondering if it was pushed in not far enough when someone else was in there (someone was kind enough to scratch the timing position into the case.

Although there’s no brass to be found (although I haven’t split the case) and I’m wondering if a worn out gear was stuck in there from the get go

 

[mikidymac]

Just a FYI, if you try to force the gear and shaft in from the side without splitting the cases it will ruin and shred it again.

 

[77Eltigre]

Just a FYI, if you try to force the gear and shaft in from the side without splitting the cases it will ruin and shred it again.

It seems like this is a high probability, however considering the gear on the crank appears to be centered, I had lots of oil sitting in the passage, and its late in the season I'm going to risk it. If she hangs in there great, if not I'll pull the whole dam engine and do a proper rebuild over the winter

 

[etemplet]

You'll have a TON of brass in the chamber. If anyone did get a gear back in there without splitting the cases there is so much brass in there it will destroy the new gear and bearings. Took me a while to clean all the brass out with the cases split.

 

[Mattman4494]

I just had a very similar failure with my rotary valve gear. Engine has about 20 hours with a new WSM crank. The chamber was definitely full of oil so I’m not sure what could have happened. I still need to pull the shaft to inspect further. @etemplet did you ever find the root cause of your failure?