Lycoming SI 1454A - rocker arm replacement

I'm overhauling my IO-540-C4B5 currently under the guidance of my IA. Everything (bottom end, rocker arms, various accessory drives, etc) is at the machine shop being inspected and overhauled. It is a well known engine shop in the Portland area.

However, I've taken on the compliance stuff myself, and I was studying up on SBs and SIs this evening and ran across Service Instruction 1454A. I'm of the opinion that while I'm not necessary beholden to the manufacturer bulletins and instructions, they exist for a reason so I might as well try.

My engine was built new in 1976 and is a first run with ~2400 hours, so I'm pretty sure it has the rocker arms superseded in this instruction.

What i am trying to figure out is if this is a mandatory part replacement at overhaul, or just a "if you are replacing rocker arms, using this new part number" kind of S.I.

Mine appeared fine and the shop stated they would rebush them. They would tell me if they were a suggested replacement item at overhaul, right?

Thanks

Engine

That would depend on Exp. engine or certified.
Bob

6 Gun said:

That would depend on Exp. engine or certified.
Bob

Click to expand...

Definitely experimental. Like I said though, I'd like to comply with SBs and SIs that are safety oriented and make sense.

I get the feeling this rocker arm thing is maybe a CYA or liability thing? Or they don't want to manufacture that part number anymore?

As I understand it, on parallel valve Lycoming engines, a different rocker arm was used on intake and exhaust valves. Different part number for intake and exhaust. To save on parts inventory, a change was made to a rocker arm that would work on either intake or exhaust.

June 5, 1991 SI 1454 was issued about rocker arms.

Insert Text from SI 1454: (Note: copied from PDF and there may be errors)
Textron Lycoming currently specifies one (1) Rocker Arm Assy. P/N 17F19353 for both intake and exhaust on all cylinders that incorporate parallel valves.

The new rocker arm assembly supersedes Rocker Arm Assy. P/N LW-18790 which also was used on both intake and exhaust.

Prior to the aforementioned rocker arm assemblies, one (1) each of Rocker Arm Assy. PIN 69444 (intake) and PIN 74636 (exhaust) were installed. Rocker Arm Assy. PIN 69444 (intake) is identified by the oil drain hole located under the push rod end of the body. Rocker Arm Assy. PIN 74636 (exhaust) is identified by the oil drain hole located under the valve end.

CAUTION
ROCKER ARM ASSEMBLIES PIN 69444 AND P/N 74636 ARE NOT INTERCHANGEABLE WlTH ONE ANOTHER. ASCERTAIN THAT THE PROPER
ROCKHR ARM ASSEMBLY IS INSTALLED AT THE CORRECT LOCATION.
ROCKER ARM ASSY. PIN 69444 MUST BE INSTALLED ON THE INTAKE SIDE.
ROCKER ARM ASSY. PIN 74636 MUST BE INSTALLED ON THE EXHAUST SIDE.
EITHER ROCKER ARM ASSEMBLY, PIN 17F19353 OR LW-18790?, IS A DIRECT
REPLACEMENT FOR ROCKER ARM ASSEMBLY PIN 69444 (INTAKE) OR PIN
74636 (EXHAUST).
? These rocker arms must be in compliance with latest edition of Service Bulletin No. 477 (A.D. #87-10-06).
END Insert.

February 25, 2011 revised to SI1454A.

Insert text from SI1454A.
The supersedure history for the Rocker Arm Assembly is as follows:
LW18790 -> 17F19353 -> 17F19357

NOTE
Before reusing Rocker Arm Assembly P/N LW18970, refer to the latest revision of Lycoming Service Bulletin No. 477 (AD 87-10-06).

NOTE
The new Rocker Arm Assembly P/N 17F19357 can be installed in either the intake or exhaust valve position without changing the other rocker on that cylinder.
END insert

Supplement 1 Insert:
This supplement corrects the Part Number in the following NOTE of Service Instruction No. 1454A dated February 25, 2011.
NOTE
Before reusing Rocker Arm Assembly P/N LW18790, refer to the latest revision of Lycoming Service Bulletin No. 477 (AD 871006).
END insert

SB477A list model number and S/N of engines that LW18790 rocker arms may be too thin and crack.

In other words, DO NOT use rocker are LW18790 in your engine even if it is Experimental.

Hope this helps.

Thank you Gary. I need to find out what the part numbers are on my rocker arms, which are at the shop 20+ miles away.

Rocker arms

Regardless of the part numbers. Make sure the exhaust rockers have the correct bushing with the annulus to allow oil flow to the exhaust valve. Check this by putting the rocker shaft in the rocker and blow shop air into the hole in the pushrod socket, insure that air comes out of the hole below the rocker tip. I have seen several cases where incorrect bushings were installed by o/h shops, and more cases where the engine builder installed exhaust rockers on intake valves and vice versa (parallel valve engs)
The bottom line to this story is extra oil flow to the exhaust valve & guide. The latest configuration where the rockers are interchangeable all have the bushing with the oil passage.
Don B

RV - 9. Rebuild in Progress

I was told by the machine shop that the rocker arm part number is old enough to not be addressed by any AD/SB/SI.