The International Cessna^® 170 Association

At one time I read somewhere in the forum about ROLLER ROCKER ARMS. I checked the search and come up with nothing. Are these thing expensive ?? Does the plus side outway the cost. There has to be something good to them, everybody highlights them when they sell there aircraft. If anybody has put these on there aircraft I would really like to get some info..170mb

Roller rockers cost more than they are worth (about $1400 plus installation). At least one model has an emergency AD note out against them for complete removal. (Talk about expensive, not only did the proud owners have to buy them -$1400 and install them -$400 or so, but they had to remove them -another -$400 plus find some originals and reinstall them....$ ????)
Like a lot of seemingly great ideas....this is another that just doesn't pan out.

Thanks Mr. Gahorn..... I would think in this case , replaceing something with a wheel verses a flat surface, your are looking at problems down the road. 170mb

I've always wondered if roller rockers might be the cure for the valve guide problems that our C-145/O-300's seem to suffer from. That seems to usually be the culprit when the compression goes below minimum & we need to pull a cylinder--the guide gets worn,allowing the valve to wobble around & eventually fail to seat properly. I've always thought that maybe that was a result of some funky valve-train geometry & resultant sideways pressure on the valve stem by the rocker. Maybe roller bearings there would eliminate the guide wear.

Eric

That is the idea behind roller-rockers, Eric, it's just that the dollars/sense don't pan out. The two-grand you spend on the gizmos can be the reason the roller-rocker bearing pin-rollers are found in the remains of the engine's lower end at the emergency landing site.
These engines are frequently "overhauled" in the "field" and the existing rockers are reinstalled, sometimes after having been "re-bushed" and sometimes not, and sometimes having been "re-arced" and re-hardened and sometimes not. (There's never a record of how many times they've been "re-arced" etc. There was just a bunch of them in a plastic bucket at the shop and 12 of them were selected and bead-blasted and installed.)
How good they are at operating against the valve stems for 2500 RPM times 60 minutes times 1800 hours that stretched over 20 years is a direct result of the care that went into the "overhaul" and how often the engine sat for two months between the flights those three owners made and how often they remembered to change the oil.
It's one of the factors figured by TCM when they made the 1800 hour/12 year TBO recommendation. (And were those new valves installed in new guides two decades ago?)
New spec. parts, properly assembled, operated, and serviced should give the expected reliability. "Trick" stuff in my experience, rarely gives the return-on-investment, but if they are to give the proper return, they'd have to be installed at the beginning of the TBO, not mid-term. For the mid-life engine, I believe it's better to make a repair with new parts and go on down the road.

To expand on that Eric,
Yes you are correct about roller rockers as a supposed fix for the funky angles of the pushrod/rocker arm/valve tip interface, which can possibly cause premature valve and guide wear. John Schwaner's Skyranch Engineering Manual devotes many pages to this area of discussion, mostly applicable to the large, angle-valve Continentals more than the C145/O300.

I can find no mention of it in the C145/O300 overhaul manual, but I think some shops actually face the rocker tip at a very slight angle to rotate the valve in the guide. This would supposedly minimize valve face wear at the expense of valve guide life. But again, Schwaner states that the rocker must contact the valve face evenly. He says even .001" to .002" out of tolerance is enough to wear out a valve guide in 40 to 100 hours engine time!
There are other angles to consider, of course, but you are on the right track.
Schwaner also states roller rockers will do nothing to solve the wear problem, since the wear is sideways to the motion of the rocker arm.

Are you as confused as I am on the topic? Good!

I think what roller rockers (supposedly) do for you is reduce overall valve train friction. Better to use them in your Chevy than your 170.

Max

Of interest is that my experience with the Jacobs radials that have roller rockers is that we still get the normal amount of guide wear. Many of the radial engines have roller or ball bearings all over the place which is one reason why during combat they could take a round, loose all the oil, and still bring the flight crew home in a lot of cases.