Mercury Marine — Flame Arrestor Sealing Washer — 86400
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Mercury MerCruiser Flame Arrestor Sealing Washer 86400
The Mercury MerCruiser 86400 is a genuine OEM sealing washer used with the flame-arrestor mounting hardware on select carbureted and EFI/TBI MerCruiser gasoline engines. Mercury diagrams position this washer beneath the retaining nut on the flame-arrestor stud to keep the correct factory hardware arrangement.
Compatible Applications
- 3.0L / 181 CID L4
- 4.3L / 262 CID V6 EFI/TBI
- 5.0L V8
- 5.7L / 350 V8
- Additional carbureted and EFI MerCruiser gasoline engines using the specified flame-arrestor stud arrangement
MerCruiser used several flame-arrestor, stud, nut, and washer combinations across different engine generations. Confirm 86400 against your engine serial number and the applicable intake or carburetor diagram before ordering.
Part Details
- Part number: 86400
- Full service number: 12-86400
- Brand: Mercury Marine
- Official product type: Sealing / flame arrestor washer
- System: Air intake / flame arrestor
- Quantity typically required: 1
- GTIN: 745061200739
Related Parts
- 826709109 — Flame arrestor stud nut
- 863200 — Flame arrestor on applicable 3.0L engines
- 805298A1 — Flame arrestor on applicable V8 engines
- 805161 / 91842 — Flame arrestor studs on selected applications
When This Part Needs Replacement
Replace the washer if it is missing, flattened, distorted, corroded, or damaged during flame-arrestor removal. A worn sealing washer should not be substituted with unrelated hardware simply because the diameter appears similar.
Installation Notes
Install the washer in the original flame-arrestor mounting position. Applicable diagrams commonly pair 86400 with flame-arrestor stud hardware and retaining nut 826709109. Verify the flame arrestor is seated correctly before tightening the retaining hardware.
Alternate/Superseded Part Numbers
- 86400 — Mercury OEM part number
- 12-86400 — full Mercury service number
- No verified superseding replacement
Technical FAQ
How many washers do I need? Applicable diagrams typically call for one washer per flame-arrestor mounting stud.
Can I reuse the old washer? If you are unsure whether the original washer is still flat and undamaged, replace it. A crushed or corroded washer won't seal correctly against the retaining nut.
Parts Desk Insights
Best use case: This washer keeps the factory flame-arrestor mounting stack intact whenever the arrestor is removed for cleaning, service, or replacement.
Common mistake: This washer is easy to overlook during flame-arrestor removal. If you are missing the original, substituting a similarly sized washer from unrelated hardware can leave a poor seal at the retaining nut.
Sizing and fitment: If you are unsure whether 86400 matches your engine's flame-arrestor stud arrangement, confirm against your intake or carburetor parts diagram and serial number before ordering.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.