Thorp Air Command - T18.net

If you are bored and want something to do on your Thorp, take a trip through Lycoming Mandatory Service Bulletin 388C. Until recently, I had never heard of this document and have been blissfully operating Lycoming engines for thousands of hours. It says, to paraphrase, "ALL engines must have their exhaust valve guide clearance checked every 400 hours." My IO-360 "chuggled" in flight a couple of times recently, so I went to the experts who acquainted me with the aforementioned document.

Sooo...last week was spent prepping and accomplishing the inspection and subsequent valve guide reaming.



My man Herman doing the deed.



Valve guide boss on number four cylinder.

Note the cooked on oil on the outside of the guide boss. This indicates a lot of heat caused by excessive fiction. This valve was also tight and dragging when we moved it manually.

We removed all of the valves, reamed and honed the guides and now everything is smooth as silk. Haven't run it yet, so time will tell.

Based on what I found in my 485 hr. cylinders, I would urge you to consider SB 388C, if you are experiencing any roughness.

_________________
Bob Highley
N711SH
SN 835
KLAL

As the little man on Laugh In use to say..."Very Interesting!" There is a follow up Lycoming Service Instruction 1485A which might prove interesting (or Very Interesting) having to do with "new and improved" valve guide material shipped from Lycoming . If you have the new guides it is no longer necessary to complete the mandatory 400 hour inspection in the latest revision of SB No. 388 . It is "recommended" that the inspection from SB 388 be completed at 1000 hours or 1/2 way to TBO . New valve guide material was introduced in 1996 and since March 1998 all engines , cylinder kits and spare valve guides contain the new material .

RB

This is very true, My good Rich. ...However, my engine man, Herman, says the issue was/is not completely fixed by the introduction of the new and improved guides. I have also been advised that MMO (Marvel Mystery Oil) goes a long way to keep things running smooth. When queried a few years back, a noted Lycoming rep said, "It can't hurt."

_________________
Bob Highley
N711SH
SN 835
KLAL

We used synthetic based oil . had no problems . The 98 oct mogas has cleaning agent it keeps your valve and engine components clean i use periodically J.P..

Where do you get 98 octane? I think 92 is the highest rating I have seen in mogas.

_________________
Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

MMO ? I'll try some on my Cobb salad !

RB

Every country but United States.

You know that MMO is now owned by the Turtle Wax company, right??
I recall "hearing" that an NTSB report/analysis of MMO found constituents included mineral oil, Stoddard solvent, and lard!!

I'd buy some if "Hidden Valley" owned them. (See Cobb salad reference above)

Hummmmmm...lard ! Homer like lard !

RB