Mopar 440 Valve Cover Gaskets: Which Brands Are Worth It
TL;DR: On a Mopar 440 the valve cover gasket is one of the cheapest parts on the engine attached to one of the most annoying repeat repairs, so the brand question is really a construction question. Plain cork seals well once and hates heat cycles; cork-rubber composite is the sensible stock-replacement default; a rubber gasket on a steel carrier is the better choice for a cover that comes off often or a flange that is not perfectly flat; and a premium reusable silicone-on-steel gasket earns its keep on an engine you expect to open again. Brand matters less than picking the right construction for your covers and then not over-torquing it. This guide covers all four, the RB-specific fitment traps, and how to install one so it stays sealed.
Why 440 valve covers leak in the first place
The 440 is a raised-deck RB big block: a pushrod, overhead-valve V8 with cast-iron wedge heads and a rocker shaft assembly under each cover. There is no overhead camshaft and there are no lash adjusters up there. What the cover has to contain is oil thrown off the rocker shafts, plus whatever the crankcase is pushing up from the valley. That last point is the one people miss.
Four things cause a fresh gasket to weep on one of these engines, and only one of them is the gasket:
- A distorted cover flange. Original stamped-steel covers are thin. Decades of people cranking down the fasteners leave the flange dimpled around each hole and bowed between them. A new gasket laid onto a wavy flange will leak at the low spots no matter what it is made of.
- Crankcase pressure. A plugged or wrong PCV setup, or a breather arrangement that cannot vent, pressurises the crankcase and pushes oil past every seal on the engine. If oil is also appearing at the dipstick tube or the front seal, fix the ventilation before you blame a gasket.
- The wrong construction for the cover. Aftermarket cast-aluminium and fabricated covers have thicker, stiffer flanges than factory stampings, and they generally want a different gasket than a thin stamped cover does.
- Over-torque. Cork extrudes. Once it has been squeezed out past the flange edge, the material left in the joint is too thin to seal, and the joint keeps relaxing as it heat cycles.
Gaskets and seals for these engines are grouped under gaskets and seals, and the engine family itself sits under Mopar 440 RB parts.
The four constructions, and what each is actually good at
Almost every valve cover gasket sold for a B or RB big block falls into one of these four groups. Pick the row that matches your covers and your habits, then buy a reputable manufacturer's version of that row.
| Construction | What it is | Strengths | Weaknesses | Best for |
|---|---|---|---|---|
| Plain cork | Compressed cork sheet, sometimes with a light binder | Cheap, conforms to an imperfect flange, widely stocked | Shrinks and hardens through heat cycles, extrudes if over-tightened, single-use in practice | Budget repairs on an engine that will not be opened again soon |
| Cork-rubber composite | Cork particles bound in a rubber matrix | Much better heat-cycle life than plain cork, still conformable, forgiving of a slightly wavy flange | Still takes a permanent set, still single-use in practice | The sensible stock-replacement default on original stamped-steel covers |
| Rubber on a steel carrier | Moulded rubber sealing beads bonded to a rigid steel core | The core resists crush and helps pull a tired flange flat, survives repeated removal, consistent sealing pressure | Costs more, less forgiving of a badly warped flange because it will not conform to it | Covers that come off regularly, and stamped covers that have been straightened |
| Reusable moulded silicone on steel | Thick silicone sealing rails on a steel frame, designed to be removed and refitted | Genuinely reusable, excellent heat resistance, seals well against a thick aluminium flange | The most expensive option, and cover or hardware clearance needs checking | Race and show engines, aluminium covers, anything you expect to open repeatedly |
Which brands are worth it
There is no single brand answer, because the same manufacturer often sells two of the rows above under one catalogue heading. What separates a gasket worth buying from one that will annoy you is visible before it goes on the engine.
Established OE-replacement gasket makers are the safe default for a stock rebuild. These are the long-standing full-line suppliers whose head gasket and full-set catalogues you already know, plus the brands that supply original-equipment-style parts into the aftermarket. Their big-block Mopar valve cover gaskets are typically cork-rubber composite or rubber-on-steel, the material is consistent from one box to the next, and the catalogue data is reliable. On a fifty-year-old engine family that last point matters more than it sounds.
Specialty and race gasket makers are where the steel-core and reusable silicone options live. If the covers are coming off for valve lash checks, rocker shaft work or a leak-down test, a reusable gasket stops being a luxury quite quickly.
Budget sets bundled with dress-up covers are the ones to be careful with. A chrome or finned cover sold with a thin cork gasket in the box is not necessarily a matched pair - the cover flange is often thick cast aluminium while the gasket is the cheapest cork available. If you buy a cover kit, plan on buying the gasket separately to suit the flange you actually received.
Three checks that beat brand loyalty every time:
- Confirm the current part number against the manufacturer's catalogue using your engine family and year, rather than assuming a B and RB part interchange. The 383 and 400 B engines and the 413, 426 wedge and 440 RB engines share a great deal, but the catalogue is where that gets settled, not a forum post.
- Check whether the set includes the spreader bars, load spreaders or grommets your covers use. Plenty of listings are gasket only. Fasteners and small hardware are grouped under accessories and hardware.
- Look at the gasket in good light before it goes on. A composite gasket should be uniform, with clean square edges and no crumbling at the bolt holes. A steel-core gasket should sit flat on a bench without rocking.
Fitment traps specific to the RB big block
A few things catch people out on a 440 in particular.
- Stamped-steel covers are almost always distorted. Before fitting anything, lay the cover flange-down on a flat surface and look for daylight. Work the dimples around the fastener holes back down with a small hammer and a flat backing block until the flange sits level. Ten minutes here saves a second teardown.
- Clearance is real on both sides. Tall aftermarket covers, thick gaskets and long-tube headers do not always coexist, and on a car with a large brake booster the driver's side is the tight one. Check clearance before you commit to a cover and gasket combination.
- Rocker shaft hardware sits close to the cover. If a stud, shaft girdle or aftermarket rocker assembly has raised anything, verify the cover is sealing on the gasket rather than resting on hardware. Rocker and shaft components are listed under valves and valvetrain.
- If the engine is apart anyway, valve cover gaskets normally arrive in the same box as everything else - see full gasket sets instead of buying pieces individually. Parts common across the wider family are under Mopar B and RB big block parts.
Installing it so it stays sealed
The gasket is not the hard part. The preparation is.
- Scrape both surfaces genuinely clean. Old cork bonds itself to cast iron. Get the head rail and the cover flange back to bare, dry metal, then wipe both with a solvent that leaves no residue.
- Flatten the cover flange as described above. A rubber-on-steel gasket will not hide a wavy stamping - it is stiff by design, which is exactly why it needs a flat mating surface.
- Decide about sealant deliberately, not by habit. Composite gaskets are commonly fitted with a thin film of gasket adhesive on the cover side only, so the gasket stays with the cover and the head side separates cleanly next time. Moulded rubber and silicone gaskets are generally designed to be fitted dry, with a small dab of RTV only at a step or corner the manufacturer identifies. The instruction sheet in the box is specific to that gasket and it wins over habit.
- Torque in the factory sequence to the value given in the service manual, working from the centre outward in stages. This is a low-torque joint, and treating the fasteners like head bolts is the single most common cause of a leaking new gasket.
- Heat cycle, then re-check. Run the engine to full operating temperature, let it cool completely, and re-check the fasteners to the same specification - but only if the gasket manufacturer permits it. Some rubber and silicone designs specifically say not to re-torque.
- Fix the ventilation while you are there. Confirm the PCV valve is correct for the engine and actually flowing, and that the breather side can draw. Fresh oil and additives are grouped under oil, coolant and additives.
Done properly this is a modest job on a big block with reasonable engine bay access - commonly quoted in the one to two shop labour hour range per side, longer where headers, a booster or accessory brackets have to move first.
Frequently Asked Questions
Will a 383 or 400 valve cover gasket fit a 440? The B-series and RB-series big blocks share valve cover architecture and many catalogues list one gasket across the family. Even so, confirm the current part number against the manufacturer's catalogue for your specific engine and year rather than assuming. Head casting and cover changes across a long production run are exactly what catalogues exist to track.
Are cork valve cover gaskets reusable? Treat them as single-use. Cork and cork-rubber composite take a permanent set when compressed and lose thickness after heat cycling, so a reused gasket seals on a thinner, harder surface than it did when new. If you need something that survives repeated removal, buy rubber on a steel carrier or a moulded reusable silicone gasket instead.
Do I need RTV silicone with a valve cover gasket? Usually not as a substitute for the gasket. Composite gaskets are commonly fitted with a thin adhesive film on the cover side; moulded rubber and silicone gaskets are typically fitted dry. Where sealant is called for it is normally a small amount at a specific step or joint named in the instruction sheet. Running a bead of RTV around the whole rail on top of a gasket tends to create leaks rather than prevent them.
How tight should 440 valve cover fasteners be? This is a low-torque joint, and the correct figure comes from the factory service manual for your engine together with the instruction sheet for the gasket you bought. Tighten in the factory sequence, from the centre outward, in stages. Over-tightening is the leading cause of a brand-new gasket weeping within a few hundred miles.
My covers still leak with a new gasket. What now? Work the three non-gasket causes in order. Check crankcase ventilation first, because pressure in the crankcase pushes oil past any seal on the engine. Then check the cover flange for distortion and straighten it if the fastener holes are dimpled. Then confirm the gasket construction suits the cover, since a thin cork gasket on a thick aftermarket aluminium flange is a common mismatch. If oil is also showing at the front seal or dipstick tube, the problem is almost certainly ventilation rather than gaskets.
Is a reusable silicone gasket worth it on a street 440? If the covers come off once a decade, no - a good cork-rubber composite or rubber-on-steel gasket is better value. If you check valve lash, run adjustable rockers, or are still sorting the engine out and expect several more trips inside, a reusable gasket pays for itself in the gaskets you do not buy and the scraping you do not have to do.
Sources
Written from the general design characteristics of Chrysler B and RB big block valve train and valve cover architecture, published gasket-material construction descriptions from major aftermarket gasket manufacturers, and standard shop practice for stamped-steel flange preparation and low-torque fastener sequencing. Specific part numbers, torque values and fitment ranges should be confirmed against the manufacturer's current catalogue and the factory service manual for your engine and model year.
Questions about a specific 440 build? Reach the Core Powertrain Parts tech team at sales@coretransmissionparts.com.