---------------------------------------------------------- JabiruEngine-List Digest Archive --- Total Messages Posted Mon 05/14/07: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:38 PM - Re: New rocker arm bushings in (Noel Loveys) 2. 07:11 PM - Re: New rocker arm bushings in (Lynn Matteson) ________________________________ Message 1 _____________________________________ Time: 06:38:06 PM PST US From: "Noel Loveys" Subject: Re: JabiruEngine-List: New rocker arm bushings in Lynn regarding the Teflon coating: Years ago GM tried Teflon coated camshafts in the 304 V8 engines. They were plagued with camshaft problems until the Teflon coating was ditched. One thing about Teflon, as strong as it is chemically its also physically weak and brittle. Noel Loveys, RPP, AME intern Campbellton, Newfoundland, Canada Kitfox Mod III-A, 582, B box, Ivo IFA Aerocet 1100s noelloveys@yahoo.ca > Behalf Of Lynn > Matteson > Sent: Friday, May 11, 2007 6:25 PM > Well, the old bushings were a Teflon-coated bronze over a > steel shell > (TPFE, I believe they are known as) and for whatever reason, they > failed at...or at least I discovered them failed at...273 hours. I > decided not to replace them with the original style bushings, > because > I don't know the history of how these bushings hold up under the > splash-lubricated, high-pressure (the valve spring), > environment they > operate in. Now to be perfectly honest, maybe nobody else has had a > problem with these bushings, but I did, so I elected to try my own > "shade-tree engineering" and put in oilite bronze bushings. In doing > so, I decided to supplement the oil that ordinarily makes its way > into the side of the standard bushings. The standard bushings are > allowed (according to my owners manual) .004"-.010" side > clearance. I > did not change this, but I did drill a .093" hole vertically > into the > rocker arm, at exactly the 12 o'clock position of the rocker arm. > This will allow the oil a chance to run into the hole and help lube > the bushing. > > If anybody cares, I'll continue to report how I installed the > bushings. They came 16mm wide and the rocker arm is 15mm, so I > shortened them on my lathe. I had pressed the old bushings out, and > after drilling the rocker arms for the oiling holes, I drilled the > bushing oil holes a little larger, then pressed them into place, > keeping the alignment of the holes in mind. They all came out > aligned > as hoped, and then I had to ream the bushings to the size suggested > in the owners manual... .474"-.475". This provides for 2-3 > thousandths oil clearance for the .472" shaft. I then swapped the > rocker shafts side-for-side, to enable the new bushings to ride on > the un-used part of the shaft. I also chamfered the sides of the new > bushings to further allow oil to make its way into the oil space > provided between the shaft and arm. > > I've got to further say that I don't know squat about teflon in > engine bearings...my only use of teflon (that I know of) is frying > eggs in a pan....low (relative) heat, no pressure, and the > eggs taste > fine. I wouldn't have eaten eggs cooked on the teflon that was > visible inside the removed bushings...they looked like the > frypan had > been attacked with a steel spatula, if you'll permit me the kitchen > analogy. : ) > > Again, I'm not saying that Jabiru made a mistake, maybe I just got a > lemon, and if my "fix" doesn't work out, I will have no apologies to > make. My engine is in a Kitfox Model IV *experimental* airplane, and > that's JUST what I'm doing...experimenting. > > Lynn Matteson > Grass Lake, Michigan > Kitfox IV Speedster w/Jabiru 2200 > flying w/275+ hrs > do not archive ________________________________ Message 2 _____________________________________ Time: 07:11:23 PM PST US From: Lynn Matteson Subject: Re: JabiruEngine-List: New rocker arm bushings in Thanks for recalling that info, Noel. A V8 camshaft (if it's a 90 V or thereabouts) is another case where the load is all centered in one small area...the bottom of the bearing takes all the pressure from the valve springs, as the rocker arm tries to lift the valve. At least this is my memory of all the V8's that I've worked on. Now an opposed engine would have equal load on both "sides" of the cam, so wouldn't have this problem. I haven't really been around any of the later engineering on engines so I don't know what the guys and gals have come up with lately. I now have about 6 hours on the new bushings, so in a few more days, I'll have a look and see how things are holding up. It won't be a very long-hour test, but unless it's a complete failure, I should rest a bit easier for the "big trip." One question, though...was it the lobes that were Teflon-coated, or just the bearing surfaces, or both? Lynn Matteson Grass Lake, Michigan Kitfox IV Speedster w/Jabiru 2200 flying w/275+ hrs On May 14, 2007, at 9:37 PM, Noel Loveys wrote: > Lynn regarding the Teflon coating: > > Years ago GM tried Teflon coated camshafts in the 304 V8 engines. > They were plagued with camshaft problems until the Teflon coating > was ditched. One thing about Teflon, as strong as it is chemically > its also physically weak and brittle. > > Noel Loveys, RPP, AME intern > Campbellton, Newfoundland, > Canada > Kitfox Mod III-A, 582, B box, Ivo IFA > Aerocet 1100s > noelloveys@yahoo.ca > > > > Behalf Of Lynn > > Matteson > > Sent: Friday, May 11, 2007 6:25 PM > > Well, the old bushings were a Teflon-coated bronze over a > > steel shell > > (TPFE, I believe they are known as) and for whatever reason, they > > failed at...or at least I discovered them failed at...273 hours. I > > decided not to replace them with the original style bushings, > > because > > I don't know the history of how these bushings hold up under the > > splash-lubricated, high-pressure (the valve spring), > > environment they > > operate in. Now to be perfectly honest, maybe nobody else has had a > > problem with these bushings, but I did, so I elected to try my own > > "shade-tree engineering" and put in oilite bronze bushings. In doing > > so, I decided to supplement the oil that ordinarily makes its way > > into the side of the standard bushings. The standard bushings are > > allowed (according to my owners manual) .004"-.010" side > > clearance. I > > did not change this, but I did drill a .093" hole vertically > > into the > > rocker arm, at exactly the 12 o'clock position of the rocker arm. > > This will allow the oil a chance to run into the hole and help lube > > the bushing. > > > > If anybody cares, I'll continue to report how I installed the > > bushings. They came 16mm wide and the rocker arm is 15mm, so I > > shortened them on my lathe. I had pressed the old bushings out, and > > after drilling the rocker arms for the oiling holes, I drilled the > > bushing oil holes a little larger, then pressed them into place, > > keeping the alignment of the holes in mind. They all came out > > aligned > > as hoped, and then I had to ream the bushings to the size suggested > > in the owners manual... .474"-.475". This provides for 2-3 > > thousandths oil clearance for the .472" shaft. I then swapped the > > rocker shafts side-for-side, to enable the new bushings to ride on > > the un-used part of the shaft. I also chamfered the sides of the new > > bushings to further allow oil to make its way into the oil space > > provided between the shaft and arm. > > > > I've got to further say that I don't know squat about teflon in > > engine bearings...my only use of teflon (that I know of) is frying > > eggs in a pan....low (relative) heat, no pressure, and the > > eggs taste > > fine. I wouldn't have eaten eggs cooked on the teflon that was > > visible inside the removed bushings...they looked like the > > frypan had > > been attacked with a steel spatula, if you'll permit me the kitchen > > analogy. : ) > > > > Again, I'm not saying that Jabiru made a mistake, maybe I just got a > > lemon, and if my "fix" doesn't work out, I will have no apologies to > > make. My engine is in a Kitfox Model IV *experimental* airplane, and > > that's JUST what I'm doing...experimenting. > > > > Lynn Matteson > > Grass Lake, Michigan > > Kitfox IV Speedster w/Jabiru 2200 > > flying w/275+ hrs > ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message jabiruengine-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/JabiruEngine-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/jabiruengine-list Browse Digests http://www.matronics.com/digest/jabiruengine-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.