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Garloch Seals

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Morning fellas

Getting mixed reviews about running 254 in engine and triple nickle in the gearbox. Some guys are saying to change it up wait for the overhaul other are saying changit up to MOjo2 all way round. But is there a chance of fudging up the garloch seals even with a flush. But also concerned about a free wheel transfer and 555 mixing with 254 and gelling up.


Suggestions and opinions welcome


P5 - PRM

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The whole idea of using 555 type oils (DOD-85734) in the gearbox and 254 (third generation HTS MIL-PRF-23699) in the engine is to use an oil with the most desirable characteristics for the application. The 555 type oils are desirable for low speed, high torque, gearboxes because they have an EP (extreme pressure) additive to maintain a specific oil film thickness under high loads by sticking to the metal surface. The 254 type oils have an anti-coking additive that ensures the oil slides off of the hot surfaces of a high speed gas turbine engine.


The 555 oils do tend to eat up silicon seals (by the way, Garlock was a manufacturer of oil seals and their name became synonymous with oil seals like Ski-Doo is for snowmobiles). In addition, because the oil tends to stick to the surface it lubricates, it makes it difficult to properly seal because it wants to keep the seal off of the sealing surface.


It is best to change to the 555 type oils following an overhaul when 555 oil has been used to lubricate parts during build up of the component. All things being equal, a gearbox serviced with 555 oil will have the gears and bearings last longer than one serviced with Mo Jet 2 or other similar oils. MO jet 2 works well in high speed low torque gearboxes like a turbine engine gearbox. But the third generation high thermal stability (HTS) oils like MO 254 work better and produce less carbon contamination.


Hope this helps in your decision.

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I forgot to mention that many of the seals used today are made from Viton which is a synthetic elastomer impervious to the DOD spec oils. As far as oil migration between the free wheel and the engine, as long as the recommended seals are used and installed with the proper tools, they tend to work fairly well.


The use of MO Jet 2 all around will be a compromise and over the years has worked reasonably well and precludes the possibility of someone who isn't paying attention from cross contaminating by using the wrong oil.

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We use 560 in our engine and 555 in the tx gearbox..in 407 and L4...had the freewheel seals go in the L4 and did not seem to have a problem when they mixed...replaced seals and kept on truckin..this has only happened once in thousands of hrs B)

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