C90 rocker arms

[Guest]

I learned something in the last couple of weeks.

Probably old news to many of you.

C90's have an intake rocker arm and an exhaust rocker arm that are different.

Apparently the intake one is not drilled with an oil hole to the valve.

Seems to me that I have never seen such a rocker though.

Do the get commonly replaced by the drilled version?

Dave R

[PA1195]

Re: C90 rocker arms

3-23. ROCKER ARMS AND SHAFT
Two rocker arm assemblies are pivoted on a tubular
steel shaft, which is ground on its outer surface to a
push fit in the cylinder head support bores. The rocker
is a steel forging with a bronze bushing. A pushrod
socket is machined in the lower end. The valve
contact surface, at the upper end, is hardened and
ground to an arc. A small oil hole, drilled from the
center of the pushrod socket, intersects a hole drilled
upward and through the bushing wall. A groove
around the bushing's inner surface carries the oil
channel to a second vertical hole, which ends in a
squirt nozzle facing the valve stem. An orifice in the
valve stem end of the exhaust valve rocker arm
provides lubrication to the exhaust valve stem during
engine operation.

P/N 639614 Intake; 639615 Exhaust

[Guest]

Re: C90 rocker arms

Thanks Gary,

I have never seen them, each engine I have seen has drilled rockers on each valve.

Makes me curious.

Dave R

[PA1195]

Re: C90 rocker arms

As an owner and non-A&P I asked the same question Dave. On one C-90 overhaul of mine we sent them out to be yellow tagged and what came back were all drilled 630615. I guess the interesting question would be what's the problem with that? Maybe oil on the intake would contribute to oil consumption? These parts are around $500 new from Continental. Reconditioned likely less. Maybe Dr. Tim knows or other rebuilders here?

Gary

[Guest]

Re: C90 rocker arms

I suspect the bigger problem is NOT having them all drilled because then there is a good possibility that an exhaust valve gets a non drilled by accident.

Where as if they are all drilled all valves get cooled and lubed.

Dave R

[PA1195]

Re: C90 rocker arms

Yes. Good point Dave. Unless there's a disadvantage to having a drilled oil rocker on the intake, then why not offer that option? Maybe those that deal with this overhaul process can comment.

In the meantime......http://www.tcmlink.com/pdf2/M77-19.pdf which offers some fog clearing info and this link implies AES can drill the arms to meet 630615 oiler specs http://www.aircraft-specialties.com/...s-rocker-arms/ which may be why they returned all of mine drilled?

Gary

[N96337]

Re: C90 rocker arms

Yep, I remember an O-200 that the mechanic got distracted while reassembling and swapped the drilled and non drilled rockers. It made it about 35 hours before it ate the exhaust valve over Stevens Pass in WA. Lesson learned! I'll take them both drilled anyday!
John

[LostnSpace]

Re: C90 rocker arms

Yep, I remember an O-200 that the mechanic got distracted while reassembling and swapped the drilled and non drilled rockers. It made it about 35 hours before it ate the exhaust valve over Stevens Pass in WA. Lesson learned! I'll take them both drilled anyday!
John

On the pilotsofamerica website, there is a mechanic in Washington state that put an 0-200 together, put in a C150 and the engine quite 35 or 40 hours later, the FAA found the bolts in the camgear broke and fell out with the saftey wire in two of the bolts, and the cylinders had "a black substance" around the skirt and cylinder base O-ring on 3 of the cylinders, the 4th cylinder didn't have anything on the cylinder skirt, the case halves had the same "black substance" on the mating surfaces, later the mechanic said the bolt were "owner supplied", but he is still an IA, so I guess the FAA gave him a pass, sure doesn't sound like the engine was assembled according to the MM