Ideal Conditions Don't Exist in the Field
Motorsil D · Acetic Cure RTV Silicone
In rotating equipment maintenance — whether you're working on a gas turbine auxiliary, a lube oil system, or a compressor bearing housing — the textbook assumption of perfectly flat, clean, dimensionally stable joint faces rarely holds in practice.
Surfaces wear. Tolerances stack. Flanges warp under thermal cycling. After the third or fourth maintenance cycle, even a precision-machined cover starts showing micro-irregularities that let fluid find a path out. A conventional pre-formed gasket can only do so much when the substrate itself is no longer nominal.
Four conditions define the maintenance environment where conventional sealing systems reach their limits:
Thermal cycling causes dimensional changes between hot and cold states that open micro-gaps rigid gaskets cannot track. In turbine auxiliary systems, these cycles repeat with every start-stop sequence. Surface wear from repeated disassembly degrades seating faces over time, creating leak paths that a fresh gasket cannot fully address once the surface geometry has changed. Vibration in continuously running rotating equipment introduces micro-movement that progressively compromises static seal integrity. And tolerance accumulation means practical joint geometries in heavy equipment rarely match the clean assumptions of the original design drawing.
This is the gap that Arexons Motorsil D is specifically engineered to fill — not as a workaround, but as a deliberate maintenance tool for conditions where rigid sealing systems fall short.
Chemistry, Behaviour, and What the Cure System Means for Maintenance
Arexons Motorsil D is an acetic cure RTV (Room Temperature Vulcanizing) silicone sealant — a compound that cures in the presence of atmospheric moisture to form a flexible, elastic polymer structure in place. Not a rigid adhesive. Not a chemical anchor. An in-situ elastic gasket that conforms to the joint geometry it's asked to seal.
The acetic cure system crosslinks the silicone polymer network by reacting with atmospheric moisture, releasing small amounts of acetic acid vapour in the process — the characteristic vinegar odour that confirms curing is active. This is a normal characteristic of acetoxy-cure silicones, not a defect. It does, however, mean that enclosed or confined work areas require adequate ventilation during application and the early cure period.
"The value is not in the chemistry alone. It is in how the cured compound behaves under real operating loads — thermal movement, vibration, oil exposure, and the accumulated imperfection of years in service."
— TechMRO Inc Technical BulletinSkin formation occurs in approximately 10 minutes at ambient temperature and humidity. Cure proceeds through depth at approximately 4.5 mm per 24 hours. For planned maintenance, this is highly practical: the 10-minute window allows assembly alignment before the surface tacks, and the predictable depth cure rate means engineers can calculate when the joint is sufficiently cured before returning the equipment to service.
A critical characteristic is that the cured material exhibits no volume loss. The seal fills what it fills and maintains that fill under load — unlike anaerobic or solvent-based sealants that can shrink post-cure and create conditions for re-leakage over time.
The Numbers That Matter to Maintenance Engineers
The mechanical and thermal performance of a sealant needs to be understood in the context of its application environment, not read as isolated figures. Here is what Motorsil D delivers post-cure, and what each value means in practice:
| Property | Value | Engineering Significance |
|---|---|---|
| Tensile Strength | ~4.5 MPa | Adequate for auxiliary flange and housing applications |
| Elongation at Break | ~200% | Absorbs thermal and vibrational displacement without cracking |
| Shore A Hardness | ~50 | Firm enough to resist extrusion; flexible enough to conform |
| Compression Set | ~35% | Maintains sealing contact under sustained bolt load |
| Operating Temperature | −70°C to +250°C | Covers the full range of turbine auxiliary environments |
| Peak Resistance | Up to +300°C | Short-duration thermal spikes handled without degradation |
| Skin Formation | ~10 minutes | Assembly can proceed within tight maintenance windows |
| Cure Rate (depth) | ~4.5 mm per 24 hr | Predictable through-cure for joint gap planning |
| Volume Change Post-Cure | None | No shrinkage-induced re-leak conditions |
| Shelf Life | ~2 years | Suitable for MRO stockholding |
The pairing of 200% elongation at break with a Shore A hardness of 50 is the key performance combination for rotating equipment maintenance. A seal at Shore 50A is firm enough to resist extrusion under bolt load and resist wash-out from oil flow, yet flexible enough — at 200% elongation — to accommodate the thermal expansion differentials and vibration displacements typical of turbine and compressor auxiliary systems. This is the behaviour that keeps the seal in contact with both joint faces during operation, rather than cracking under stress as a rigid material would.
Chemical Compatibility
The cured silicone structure is resistant to mineral oils, synthetic lubricants, fuels and hydrocarbons, and cooling water. This combination of resistances is particularly relevant for lubrication system applications — bearing housings, oil cooler covers, filter housings — where the sealant is in direct or near-direct contact with lubricating oil at operating temperature.
Where in the Plant Does Motorsil D Belong?
In a combined cycle or gas turbine power plant, Motorsil D is applicable across multiple systems wherever metal-to-metal joints are subject to the operating conditions described above. The following represents the primary application areas based on field usage:
- Bearing housing covers
- Exciter housings and covers
- Slip ring enclosure covers
- Terminal box covers
- Turbine bearing housings
- Turning gear housings
- Auxiliary gearbox housings
- Bearing pedestal joints
- Lube oil pump housings
- Oil cooler covers
- Oil filter housings
- Seal oil auxiliary covers
- Cooling water pump casings
- Heat exchanger covers
- PHE inspection ports
- Coolant manifold joints
- Auxiliary skid junction covers
- Intercooler housing joints
- Pulsation dampener flanges
- Inlet filter housing seals
- Replacement of pre-formed gaskets
- Metal-to-metal flange sealing
- Vibration-prone auxiliary joints
- Emergency in-situ gasket forming
In compressor installations, the same properties that make Motorsil D suitable for turbine auxiliaries apply to skid-mounted auxiliaries, intercooler housings, and pulsation dampener flanges — environments characterised by sustained vibration, thermal cycling, and oil or coolant exposure.
Know When Not to Reach for the Tube
Competent use of any maintenance product requires understanding its limitations as clearly as its capabilities. Motorsil D is not a universal sealing solution, and applying it outside its appropriate scope creates problems rather than solving them.
Not for precision-machined joints requiring rigid gasket control. Where OEM specifications call for dimensionally controlled gaskets with defined compression load and thickness, an RTV sealant cannot replicate that controlled behaviour. The in-situ formed seal has no defined thickness or compression profile — dimensional control is lost once you move to a formed seal.
Not for structural pressure boundary sealing without mechanical support. Motorsil D is a supplementary sealing material, not a pressure boundary component. It requires mechanical retention — bolt clamping load and joint geometry — to perform correctly. It should not be considered a standalone pressure barrier in pressure-containing joints.
Not a substitute for OEM-specified sealing systems in warranty or compliance situations. Where an OEM maintenance procedure specifies a particular gasket material, thickness, or sealing system, confirm whether RTV sealant use is permitted before application. Deviation from OEM sealing specifications may have warranty and contractual implications.
The product's honest positioning — as a maintenance aid for real-world conditions rather than a replacement for precision engineering — is precisely what makes it a durable and defensible tool in a professional maintenance programme. Its scope is well defined; working within that scope delivers reliable results.
Handling, Safety, and MRO Storage Considerations
Motorsil D follows standard RTV acetoxy silicone handling protocols. The acetic cure mechanism releases low concentrations of acetic acid vapour during curing — ensure adequate ventilation in enclosed spaces such as bearing pedestals or confined auxiliary rooms.
| Requirement | Specification |
|---|---|
| Eye Protection | Safety glasses or face shield during application |
| Hand Protection | Chemical-resistant gloves |
| Ventilation | Adequate airflow during application and initial cure period |
| Storage Condition | Sealed original packaging; cool, dry location away from direct sunlight |
| Shelf Life | Approximately 2 years from manufacture date |
| Shelf Life Indicator | Degraded product: altered consistency, extended skin formation time |
The approximately 2-year shelf life makes Motorsil D a practical MRO stock item for plant warehouses and maintenance stores. Batch date verification before use is recommended, particularly for stock held at temperature extremes or in high-humidity environments.
"RTV sealants like Motorsil D exist because real maintenance environments aren't design environments. Used where it belongs, it is one of the more reliable tools in a maintenance engineer's consumables kit."
— TechMRO Inc Technical Bulletin