Marc_B Posted January 28 Report Posted January 28 Was reading an article about valve lapping and replacing the rotocoils, and it made me wonder if there was a typical replacement interval recommendation for this or if this is just "on condition"? Certainly understand if you have early signs of valve asymmetry or a drop in compression that's repeatable, then it may make sense to lap the valve in place and replace the rotocoil. But if your valves look good and your compressions look good...would there be an hour interval that you'd think a routine replacement of rotocoils would decrease chance of future cylinder/valve issues? If you replace one rotocoil (due to issues) do you typically replace them all? If you have one cylinder that needs replacement, do you also replace the rotocoils on the other cylinders?
pkellercfii Posted February 4 Report Posted February 4 My simple answer to this is "On condition". To elaborate, I do all of my own preventative maintenance and observe an oil change interval of earliest convenience after topping 25 yours, or four months, whichever comes first. I own my own borescope and pull all of the top spark plugs and take a quick look at all of the exhaust valve faces with the borescope at every engine oil change. Doing this, I found a valve problem about two years ago. Picture of problem valve is below. This was my first problem found in about seven years of borescoping at every oil change. What you're looking for on the exhaust valves is an uneven heating or cooling pattern. The valve below shows this. You're looking for an azimuthally asymmetric pattern on the valve face. My A&P & I changed the rotocoil immediately for this one. A case could be made to leave something like the below valve alone and fly it one more time to see if the valve is rotating. If not, then change it. Yes, replacing rotocoils is cheap--Airpower has rotocoils for the TSIO-360-MB &-SB engines in stock for slightly over $50. Realize that there are also tab washers involved which retain the rocker arm shaft nuts. Those tab washers are one time use parts and need to be changed every time a rocker arm is removed. The borescope I'm using is a Vividia VA-400, which I purchased new from Amazon in 2017. Replacing it with a more modern instrument is on my wish list. The 640x480 image below is full resolution. The Vividia VA-406 is something I have an eye on. Got to play with one at OSH last year. It has a smaller six mm head and a 1280x720 pixel camera. Using one of those at David Pasquale's borescope use seminar at OSH last year I was able to get a picture of a cylinder valve guide from inside a cylinder through a spark plug hole. --Paul Keller 3
kortopates Posted February 4 Report Posted February 4 Good job Paul. At Savvy we concur with replacing on condition and any time the valve is lapped. I would add though rotators can be tested as soon as you pull off the rocker shaft by staking the valves. Mike B demonstrates this in his video on youtube showing how to lap valves.Sent from my iPhone using Tapatalk 1
dkkim73 Posted February 5 Report Posted February 5 I am going to have a low threshold for prophylactic rotocoil replacement. One burnt valve snuck up on me over about 50 hrs.. passed up on empirically replacing it earlier for time. Different plane but Continental. BTW one Savvy guy recommended a Teslong scope that is great. Next time I will get a model from them with a replaceable stalk/camera since they can get caught and damaged. One of the local mechanics has an inexpensive borescope that connects to his phone. Takes fairly good pictures. 1
Ragsf15e Posted February 7 Report Posted February 7 On 2/4/2026 at 8:21 PM, dkkim73 said: I am going to have a low threshold for prophylactic rotocoil replacement. One burnt valve snuck up on me over about 50 hrs.. passed up on empirically replacing it earlier for time. Different plane but Continental. BTW one Savvy guy recommended a Teslong scope that is great. Next time I will get a model from them with a replaceable stalk/camera since they can get caught and damaged. One of the local mechanics has an inexpensive borescope that connects to his phone. Takes fairly good pictures. I also recently bought a Teslong scope on Amazon and it’s surprisingly good! 1
Marc_B Posted February 7 Author Report Posted February 7 so... 1) replace individual rotocoil on condition of valve asymmetry (+/- compression drop) --> I think this is established. BUT... 2) if you need to replace one, replace them all? 3) rotocoil replacement interval (i.e. 600, 800 or "x" hrs) prophylactically?
kortopates Posted February 7 Report Posted February 7 #1 only, when lapping a valve is what we recommend 1
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