Mercury MerCruiser Quicksilver Cylinder-Block Bolt M8 x 90 803509
In stock items ship same or next day.
Free returns on all eligible orders
You have 30 days to request a return. All sale items are final sale.
Product Description
Mercury MerCruiser Quicksilver 10-803509 is the M8 x 90 mm bolt specified in the cylinder-block / cylinder-head assembly on selected Mercury and Mariner 4, 5 and 6HP FourStroke outboards.
Key Features
- OEM bolt, full reference 10-803509.
- Nominal thread diameter: M8.
- Catalog length: 90 mm.
- Cylinder-block / cylinder-head assembly location.
Engine Compatibility
Verified diagram application includes Mercury 4HP FourStroke, serial numbers 0R000001–0R067089. The part also appears in later 4 / 5 / 6HP FourStroke cylinder-block diagrams. Confirm the exact engine serial range and bolt position.
Installation Notes
The same assembly contains shorter M8 bolts with different part numbers. Keep each bolt in its specified position and inspect the threads before installation. Follow the engine service manual for tightening sequence, torque, thread preparation and any replacement requirement.
Parts Desk Insight
803509 is the 90 mm bolt. The similar 8035091 reference is listed as M8 x 60 mm in the same engine family; the suffix changes the fastener.
Manufacturer Parts Lookup
Use Mercury’s official parts finder to check the part against your engine or drive serial number.
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.