GMNA 9986495 PDF

Note: The words must, shall or will as used in this document mean a mandatory requirement.

Material Description. This silicone adhesive/sealant requires no catalyst or heat to cure. When applied wet (uncured) it reacts with moisture in the air (condensation cure) releasing an alcohol (methanol) by-product and fully cures to an elastomeric product adhering to most clean surfaces without need of a primer. Adhesively bonded and fully cured adhesive/sealant acts as a barrier against oil migration across mating surfaces. The curing reaction releases methyl ethyl ketoxime (2-butanone) and is not acceptable for GM Europe use.

Symbols. Not applicable.

Applicability. Formed-in-Place Gasket (FIPG) for sealing engine covers, pans or mating of other components for oil seal integrity or to restrict dust or unwanted air and water intrusion.

Application Temperature and Assembly Sequence. Unless otherwise specified by the adhesive/sealant manufacturer, apply this adhesive/sealant on the intended surface whose temperature is from 18 °C to 40 °C (65 °F to 104 °F). Below 20 °C, adhesion and cure rate slows. It is the responsibility of the applicator and the adhesive/sealant manufacturer to establish the accepted conditions, e.g., process time from applied bead to assembly to air test, temperature and adhesive/sealant cure rate to provide acceptable adhesion and leak test performance. See Assembly, Sealing and Fastening Bill of Materials (BOM) Level II for minimum process time.

Other Surface Treatments. The adhesive/sealant approved to this standard must be applied after paint or coated part treatments (e.g., electrodeposition (ELPO)/Uniprime coatings of stamped steel covers). It is the responsibility of the applicator and the adhesive/sealant manufacturer to establish the accepted conditions, e.g., time, temperature and coating cure to provide acceptable adhesion and leak test performance. Use standard test panels if available.

Cleanliness of Mating Joint Surfaces. It is the responsibility of the applicator and the adhesive/sealant manufacturer to establish the accepted surface conditions, e.g., washer cleaner concentrations, drying time, and storage protection from airborne contaminants to provide acceptable adhesion and leak test performance.

Gap Limitations. Adhesive/sealant is capable of sealing a gap from 0.1 mm to 1.0 mm (the blowout test determines the maximum gap).

Unlike silicone sealant chemistry, silicone sealant poses no contamination risk to oxygen sensors or increased oil foaming due to oil absorption and extraction during curing.

Remarks.

Cost. Unless otherwise specified, pricing shall be based on 20 kg (5 gal) pails compared with existing products. Material cost comparison is sealant price per mass (grams) times specific gravity. The quantity of sealant per pail varies with manufacturer. Cost comparison for decision making must be from engine specific use (grams per component, engine) and annual volumes.

Sealant unit cost increases with decreasing container size. When conducting cost studies, remember that sealant cost will vary with the global region.

Methyl ethyl ketoxime (MEKO) sealants are a 0.40 USD (United States dollar) less per engine cost versus non-MEKO containing sealants. Unless your application region regulations (not product engineering) requires MEKO free sealant, a MEKO product is more cost effective.

Process Behavior.

Cure Rate. This adhesive/sealant has a lower viscosity, faster cure and higher elongation than 9986493 MEKO-free alcohol adhesive/sealant from 10% to 100% relative humidity (RH). Depth of cure inward from an exposed 1 mm edge for 7 days at 20 °C, 50% RH is 2.3 mm (see 3.2.2.4 and 7.1.1).

Open Time to Joint Assembly. All room temperature vulcanizing (RTV) sealant joints must be closed and clamped within 8 minutes of the sealant application to the mating flange. Clamped is defined as having a minimum of 80% of the fasteners tightened to the final torque with no two adjacent fasteners untightened.

Shelf Life Limitations. This sealant is packaged in service and repair cartridges with foil sealed ends. With proper storage, the un-opened sealed packaging has a 9 month shelf-life. Once opened, shelf life is limited by how well the opened container is protected against moisture before it is emptied.

Large Scale Operations. Due to the moisture sensitivity of this sealant, use small pails (20 L (5 gal) maximum) with strict limits on storage stock rotation. Product left in delivery lines over extended holiday periods may require a purge.

Materials Engineering recommends all RTV adhesive/sealant (regardless of cure system) be used in a ventilated area.

Joint Performance. Lap shear strength of alcohol cure silicone adhesive/sealants is lower than silicone ketoxime and acetoxy cure systems on all metal substrates.

This MEKO adhesive/sealant higher elongation is best in joints with significant differences in thermal expansion or motion. The MEKO-free alkoxy version (9986493) works best on oily (contaminated) metal surfaces producing cohesive rather than adhesive failures.

Proper Use of Test Methods. Testing for this standard is based on coupon surfaces and conditions different from those of assembly or service. Standard tests permit comparison between products while attempting to represent a worse case condition related to end use. Testing actual production processes and surfaces is necessary before actions are taken. Use the test matched with the desired property/definition.

For example: Lap shear strength may be used to measure the effect of sealant and/or process variation (e.g., ineffective surface cleanliness, build variations, etc.) on bond strength provided it mimics the actual production application with all its known variables. Lap shear is a cured property, not a wet uncured characteristic.

Worst Case Test Conditions. Since bondline adhesion is the most essential sealant property, the following conditions shall be considered for testing the robustness of a sealant.

Adhesion:Worst finish (e.g., smooth or as cast surface finish); worst contaminated surface (e.g., oily or washer residue), maximum recommended gap, slowest cure speed (e.g., lowest temperature and humidity for 7 day cure period). Seven days is the industry standard for all cured test conditions.

Regulatory Restrictions. This sealant is approved for use in every global region except the European Union due to restrictions on the release of methyl ethyl ketoxime (2-butanone) during curing.

Fuel Dilution in Engine Oil. This sealant lap shear testing to GMW16678 A-E fuel dilution (see Table 3, Note 1) produced adhesive with cohesive separation from the test panel substrates. Testing of production surfaces for adhesion evaluation is mandatory for engine joints where the fluid level is above the joint whether the engine is on or off. The results on engine joints exposed to measured fuel dilution conditions will dictate use.