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Valve guides

jabber800

Extreme
Joined
Nov 22, 2007
Messages
68
Location
Coniston Ont.
Im in the process of repairing a Nytro engine that burnt one of the exhaust valves. The engine has what I would consider low mileage at 10,000 km's so the burnt exhaust valve was a bit of a surprise! Even more of a surprise where my results when I decided to check the valve guides on the exhaust side. Wear limiters where exceeded by over 8 thou near the valve pocket side. Has anyone seen this before on these engines? I will be installing new guides and cutting the valve seats on all the exhaust side. Just curious as to why this has happened with this little mileage. I don't even think the Yamaha mileage spec to have valve clearances checked was reached. Any input would be appreciated!
 

Srxspec

Ulmer Racing
TY Advertiser
Tech Advisor
Joined
Apr 17, 2003
Messages
5,096
Location
Menno, SD
Website
www.ulmerracing.com
Country
USA
Snowmobile
2014 Yamaha SR Viper LTX, 2014 Yamaha SR Viper RTX SE, 2015 Yamaha SR Viper MTX SE 162 (turbo), 2015 Yamaha SR Viper MTX SE 153
LOCATION
Menno, SD
WEBSITE
www.ulmerracing.com
Stock, boosted, any modifications to the sled previously?
 

jabber800

Extreme
Joined
Nov 22, 2007
Messages
68
Location
Coniston Ont.
Totally stock sled. Major carbon deposits in and around valve seats and valves.
I'm going to replace all the exhaust side guides and seals. Just seems a bit odd to me.
 

grizztracks

Tech Advisor
Joined
Feb 24, 2005
Messages
3,047
Age
57
Location
Scio, NY
Country
USA
Snowmobile
FX Nytro RTX, RS Vector, SR Viper RTX SE
I believe a burnt valve was the reason for the tear down.

Was it ran for an extended period with bad exhaust donuts? Was it ever overheated? What type of oil? I haven't heard of any Nytro motors having valve problems.
 

jabber800

Extreme
Joined
Nov 22, 2007
Messages
68
Location
Coniston Ont.
Engine had lost compression in 2 cylinders. I did a leak down test and verified I had valve leakage on the exhaust side. A burnt valve was what I was expecting to find. The bad valve guide on all the exhaust valves was a very big surprise.
 

mike3577

Expert
Joined
Oct 18, 2009
Messages
309
Location
auburn hills,mi
Country
USA
Snowmobile
09 nytro xtx, 8 inch slydog powederhounds, mbrp silencer, ulmer racing clutching, fast track studs,cr10ek sparkplugs,
Could of burnt a valve from poor fuel or broken flex pipe carbon might be from efi system trying too make up from the burnt valve causing a real rich fuel air mixture
 


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