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Cummins 3999672 is the heavy duty alternator with a multi groove pulley, cast frame and mounting ears. It is used on Cummins 6BT engines. This aftermarket version has the same mounting and electrical connector as the original, so it plugs in and bolts on where the old one came off.
Sold as one unit. Check the number on your old part, or in the parts manual for your machine, before ordering.
| Part Type | Alternator |
| Replaces | Cummins 3999672 |
| Fits | Cummins 6BT engines |
| Condition | New, aftermarket |
| Stat. HS-Code | 851150 |
| Country of Manufacture | China |
Cummins machines
Check the part number on your old unit before ordering.
| Cummins Part No.(SPM Part No.) | Fits |
|---|---|
| 3999672(SPM-HEP-4491) | Cummins 6BT engines |
Battery not charging
A charge warning light or flat batteries every morning point to the alternator once the belt and wiring check out.
Noise
A worn bearing whines or grinds.
Low voltage at idle
Weak output shows as dim lights and slow electrics at idle.
Fit with a new belt
Change the belt and check the tensioner when fitting the alternator.
We check what other aftermarket sellers charge for this same part. Their prices on the date we checked:
| Seller | Price | Checked |
|---|---|---|
| SINOCMP | USD 649.00 | 30 Oct 2026 |
| eBay (3 aftermarket sellers) | USD 843.00 to 919.99 | 30 Oct 2026 |
| Spare Part Mart | USD 529.58 | Today |
Our price of USD 529.58 is 18% to 42% less than these sellers.
Found this part cheaper somewhere else? Send us the listing and we will beat it by 5% under our Price Beat Guarantee. Every order is also covered by our 30 day money back guarantee.
Yes, it is a direct replacement for the Cummins 3999672 with the same fitting.
Typically 5,000 to 10,000 hours, depending on how often the machine is started and how well the batteries are kept.
A charge warning, low battery voltage with the engine running, flickering lights or bearing noise.
Check the old unit before you send it away. Pulleys and fans are often fitted to suit the machine and have to be moved across.
Battery voltage under load, the earth strap and the main cable. A weak supply makes a good alternator look faulty and will burn out the new one.
No. It is an aftermarket alternator made to replace the Cummins 3999672. It is not made by the original manufacturer; the number only shows what it replaces.
Live rates for the quantity selected, delivered to your door. Confirmed at checkout.
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Join Marty Mates and we put 200 points on your account, worth $10 off an order over $75 USD. Then a point for every dollar you spend after that.
No password: you enter your email, we send a code, and that is you in.
