Cummins ISX Head Bolt Kit, 3678506 / 3678804 | ISX15 X15, New

Cummins ISX / ISX15 / X15 Head Bolt Kit — 3678506 / 3678804, New

One kit covers every ISX ever built. Cummins never changed the head bolt spec: from the first 1999 dual overhead cam ISX through the 2026 X15 — CM570, CM870, CM871, CM2250, CM2350, and the latest CM2450 — these are the same bolts. Whatever year your truck is, this is the kit.

Required on every head job. ISX head bolts are torque-to-yield — they stretch permanently when torqued and are single-use by design. Reusing stretched bolts cannot hold spec clamping force, and the usual result is a blown head gasket within months.

Kit Includes

(22) Hex flange head cap screws — OEM# 3678506
(4) Cylinder head bolts — OEM# 3678804

Standard or Cryo Treated

Standard — precision-machined to OEM specifications, heat-treated for strength
Cryo Treated — cryogenically processed to relieve residual stresses in the fastener for added fatigue resistance. For high-cylinder-pressure, fire-ringed, and high-horsepower builds.

Fitment — Every Generation, 1999–2026

Engine	Years	Generations
ISX (dual overhead cam)	1999–2010	CM570, CM870, CM871
ISX15	2011–2017	CM2250, CM2350
X15	2018–2026	CM2350, CM2450

Send us your engine serial number if you want fitment confirmed — but on this kit, the answer is yes.

Pairs With

Cummins ISX15 / X15 SOHC Cylinder Head (4374091)
ISX15 Head Gasket Set (4376104) or X15 Upper Gasket Set (5406187) — for head-only jobs; in-frame overhaul kits already include it

Frequently Asked Questions

Can I reuse my old ISX head bolts?
No. These are torque-to-yield bolts — they stretch permanently the first time they are torqued and cannot hold spec clamping force a second time.

Will this fit my year?
Yes. Cummins used the same head bolts on every ISX, ISX15, and X15 from 1999 through 2026, across every generation from CM570 to CM2450.

When is the cryo kit worth it?
Fire-ringed heads, high-horsepower builds, and engines that run sustained high cylinder pressure. For a stock rebuild, the standard kit is the right choice.

Weight	10.886 kg
Dimensions

We offer free standard ground shipping within the USA! If you need your parts in a hurry and would like to get them overnighted or expedited, please give us a call !

NOTE - CUT OFF TIME FOR SAME DAY SHIPPING IS 3PM CENTRAL TIME. ORDERS PLACED AFTER 3PM WILL SHIP OUT NEXT BUSINESS DAY. NEXTDAY SHIPMENTS THAT DO NOT ARRIVE ON TIME ARE NON-REFUNDABLE.
-FOR ORDERS INCLUDING HEAVY ITEMS(INFRAME KITS, HEADS,ETC.) WILL BE PLACED ON A SHORT HOLD WHILE WE VERIFY ADDRESS AND SHIPPING IS CORRECT.

We have a 30-day return policy, which means you have 30 days after receiving your item to request a return.

NOTE - All open orders will have a 20% restocking fee. All returns will have a shipping fee.

1 YEAR WARRANTY

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