CAT C15 Head Bolt Torque Specs and Sequence (3406E, ACERT)

The CAT C15 head bolt torque specs, as reproduced from Caterpillar's service text, are three passes over all 26 bolts in numerical order: 200 ± 11 lb-ft (270 ± 15 N·m), then 330 ± 11 lb-ft (450 ± 15 N·m), then 330 ± 11 lb-ft again. Coat the threads and both sides of each washer with 6V-4876 lubricant, and confirm the procedure in Cat SIS for your serial prefix.

What are the CAT C15 head bolt torque specs?

Three straight torque passes, with no angle step in the Cat text we found, all 26 bolts in numerical order on every pass. That's the Caterpillar service text as reproduced on a 3406E cylinder head procedure page, and the same wording appears in a C15 rebuild thread quoting the manual.

Know the limits of that table before you rely on it. The Cat text we could find is written for the 3406E and 3456 industrial engines, and it's hosted on third-party sites, not on cat.com. The truck C15 and C15 ACERT use the same 26-bolt head, and mechanics working from the manual report the same 200/330/330 on both. Cat publishes procedures by serial number prefix, so pull the cylinder head procedure for your prefix in Cat SIS or the OEM service manual and check it against this table before you start. If the two disagree, the SIS printout wins.

Which engines and serial prefixes share this head bolt procedure?

The 3406E, C15 and C15 ACERT all use the same 26-bolt head, and TTM's head bolt kit is listed for all of them plus the C16 and C18. What differs is how well each engine's torque number is documented in public sources, which is why the serial check matters.

One forum post gives a different final-pass number for the C15 SDP. We couldn't verify it, and it conflicts with the expert answer for the same engine, so we're not printing it. If your SIS printout for an ACERT prefix shows anything other than 200/330/330, follow the printout.

What is the C15 head bolt tightening sequence?

Numerical order, bolt 1 through bolt 26, on every one of the three passes. Run all 26 to 200 lb-ft before any bolt goes to 330, then make a full 330 pass, then a second full 330 pass.

The bolt numbers come from a Cat illustration in the cylinder head procedure (illustration g01025099). We haven't redrawn it here, because the layout wasn't available to us as text and a wrong diagram is worse than no diagram. Print the illustration from SIS or copy it out of the service manual and keep it on the fender while you work.

Don't substitute a generic center-out crisscross pattern from an automotive guide. The Cat procedure is numbered, and freelancing the order on a 26-bolt head is guesswork on the one step you can't easily redo. If you can't get the numbered diagram, stop until you have it. Your Cat dealer can print the procedure for your serial number.

Why does the internet disagree on C15 head bolt torque?

Most of the different numbers you'll find are the same Cat spec written a different way. A few are just wrong. Here's how to read them.

The math explains most of it. 450 N·m converts to about 332 lb-ft, so Cat prints 330 and some rebuilders round to 333. Cat's tolerance is ± 15 N·m, which is about ± 11 lb-ft. A kit seller printing 319 to 341 lb-ft is writing 330 ± 11 as a range. A sheet that says ± 15 lb-ft widens the window beyond what Cat's text allows.

The rest is noise. AI-generated answers on Q&A pages give 30/60/90 lb-ft or "up to 150," and at least one spec site lists 16 bolts. A C15 head has 26. If a page gets the bolt count wrong, nothing else on it is worth trusting. And don't add an angle step to a straight torque procedure on the strength of an online answer; if Cat has changed the procedure for your prefix, it will be in SIS.

Why does the C15 procedure repeat the 330 lb-ft pass?

The second 330 pass is a check. It catches a bolt that has stretched or a wrench that isn't reading right. On a healthy install, every bolt should already be at torque when you come around the second time.

Here's what that looks like on the bench. In a thread on a 3406E 5EK head job, a mechanic's first 333 pass went fine, but on the repeat pass one bolt "kept going and going." The replies were the ones you'd hear at our counter: that's exactly what the repeat pass is for, and if you've already made a full pass with a bad wrench, replace all the bolts, not just the one that moved.

If a bolt keeps turning on the repeat pass, stop pulling on it. Check the likely causes in this order:

• Torque wrench out of calibration or used past its range
• Missing or wrong lubricant on the threads or washer faces
• Grease, oil or debris in the bottom of the bolt hole
• Damaged threads in the block
• A bolt that has yielded

Find the cause before you finish the job, and confirm in the OEM service manual how Cat wants you to recover from a bolt that won't hold torque.

What lubricant goes on C15 head bolts?

Cat's text calls for 6V-4876 lubricant on the bolt threads and on both sides of each washer. Both sides, not just the threads.

The reason is friction. A torque wrench measures how hard the bolt resists turning, not how hard it's clamping the head. Change the friction at the threads or under the washer and the same 330 on the wrench gives you a different clamp load. A parts seller's head gasket page puts it bluntly: you won't reach proper torque without 6V-4876.

Keep the holes clean, too. In the same 5EK thread, a poster reported new bolts that wouldn't reach 330 and suggested washing grease out of the holes before trying again. That's one shop's experience, not a Cat bulletin, but it fits the basic rule: whatever is in the hole changes what the wrench reads. Don't substitute engine oil or anti-seize unless your OEM manual allows it.

Which C15 head bolts are long and which are short?

Ten bolts are long and 16 are short. The long bolts go in the positions marked X on Cat's diagram.

The bolts have 12-point heads, so you'll need a deep 12-point socket to pull them. Lay them out on the bench in position order as they come off. That makes it easy to match long and short holes on reassembly and to spot a bolt with damaged threads.

Don't mix the two lengths. A long bolt in a short hole, or the reverse, won't clamp the way Cat intended, whatever the wrench says. If your bolts arrive loose, measure them before they go in and sort them against the X positions on the diagram.

Can you reuse CAT C15 head bolts and washers?

No. Replace the bolts and the 5H1504 washers every time the head comes off.

An aftermarket head bolt maker, quoted in a trade-press article on C15 head bolts, says the hardened washers "must be replaced with the head bolts as instructed by the OE Service information," and describes the C15 bolts as torque-to-yield. That label is debated: the Cat text we found is a straight torque procedure with a repeat pass, not the torque-plus-angle procedure usually associated with torque-to-yield fasteners. The answer doesn't change either way. Treat them as one-time bolts; most rebuilders replace bolts and washers every time.

The economics are simple. The bolt kit is a small line on the invoice next to the labor of pulling and setting a C15 head, and a gasket that lets go because a reused bolt didn't hold clamp means paying for that labor twice. Our CAT C15 head bolt kit (1241854 / 1241855) fits the 3406E, C15, C15 ACERT, C16 and C18. Check the product page for exactly what's in the box.

What should you check before the C15 head goes on?

Torque is the last step, not the only one. Run this list before the gasket comes out of the box:

1. Chase every bolt hole. Run a tap through each one and blow it out, as one tech on an ACERT SDP head gasket job recommends. Fluid or old grease at the bottom of a blind hole throws off the torque reading.
2. Inspect the block threads. Repair damaged threads properly before installation; a bolt that won't hold torque in a damaged hole is a problem no new bolt fixes.
3. Check both decks for flatness and finish. Use a straightedge and feeler gauge across the full deck and over short spans, against the limits in the OEM manual for your prefix. A head can pass an overall check and still have a local low spot. Confirm the surface finish your gasket requires in the OEM manual or the gasket instructions.
4. Measure liner projection. Measure at several points around each liner and compare both the height and the variation between liners to the Cat spec. Projection that's out is a sealing problem no torque wrench can fix.
5. Check the spacer plate. The spacer plate is part of the stack the head clamps. Our CAT C15 spacer plate (6I4421) is listed from standard to 0.004 in under; the OEM procedure and your measurements decide which thickness you need, and a damaged plate gets replaced.
6. On an SDP, check the hollow dowel. The hollow dowel on the C15 ACERT SDP takes O-rings only.
7. Verify the torque wrench. Use a calibrated wrench rated comfortably above 330 lb-ft, not one you're running at the very top of its scale.

There's no retorque-after-warm-up step in the Cat procedure. The idea shows up in AI-generated answers and in one owner's report of exhaust-side bolts near cylinders 4 and 5 losing torque on high-boost builds at about 55 to 60 psi. If you're chasing repeat gasket failures on a hot-rodded engine, look at heat and cylinder pressure, not a different torque number.

What to order for a C15 head job

Order by engine serial number, not by engine name. The 3406E, C15 and C15 ACERT share the head bolt pattern, but parts such as injectors and valve cover gaskets differ between arrangements, SDP versus BXS, NXS and MXS for example.

• Head bolts and washers: the head bolt kit above, every time.
• Gaskets: the C15 / 3406E head gasket kit, the 3406E / C15 head gasket only, or the 3406E / C15 cylinder head reseal kit. Check each product page for what's included.
• Spacer plate: 6I4421, standard to 0.004 in under, if your measurements and the OEM procedure call for it.
• Cylinder head: if the old head is cracked, a new CAT C15 cylinder head, 2239250 (3406E / C15 ACERT universal).
• Bundled option: the Caterpillar 3406E / C15 / C15 ACERT cylinder head replacement kit. Check the product page for contents.

New heads carry a 12-month warranty against defects in material and workmanship unless the product page says otherwise, and there's no core charge on a new head. The warranty doesn't cover labor, removal and installation, freight or downtime, and damage from improper installation, overheating or low coolant voids it. A head torqued to a number off a forum is an installation problem. Full terms are on the warranty page.

Before you order, call (713) 675-2435 or email sales@ttmdiesel.com with your engine serial number. The wrong part showing up at a truck that's already apart is a bad week for everybody.

Frequently asked questions

What is the head bolt torque spec on a CAT C15?

Caterpillar's service text, as reproduced on service-procedure pages, calls for three passes over all 26 bolts, tightened in numerical order from 1 to 26 each pass: 200 ± 11 lb-ft (270 ± 15 N·m), then 330 ± 11 lb-ft (450 ± 15 N·m), then 330 ± 11 lb-ft again. Coat the threads and both sides of the washers with 6V-4876 lubricant. Confirm the procedure for your serial number prefix in Cat SIS or the OEM service manual before you start.

Is the C15 head bolt sequence a crisscross pattern from the center out?

No. Caterpillar numbers the 26 bolt positions on an illustration in the cylinder head procedure and calls for tightening them 1 through 26 in numerical order on each of the three passes. Don't substitute a generic center-out pattern from an automotive guide. Print the numbered diagram from Cat SIS or the OEM service manual before you start, and don't guess the order if you can't get it.

Can I reuse CAT C15 head bolts?

Replace them, along with the 5H1504 hardened washers, every time the head comes off. An aftermarket bolt maker cites OE service information saying the washers must be replaced with the bolts. Whether the bolts are truly torque-to-yield is debated, since Cat's text is a straight torque procedure, but the safe practice is the same: treat them as one-time bolts. A bolt kit is a small cost next to doing the head job twice.

How many head bolts does a CAT C15 have?

Twenty-six, in two lengths. Ten long bolts, part number 1241854, measure 216 mm (8.5 in) and go in the positions marked X on Cat's diagram. Sixteen short bolts, part number 1241855, measure 194 mm (7.6 in). Each bolt takes a 5H1504 hardened washer. The heads are 12-point, so plan on a deep 12-point socket, and keep the long and short bolts separated during teardown.

Is the C15 ACERT head bolt torque the same as the 3406E?

The 3406E, C15 and C15 ACERT (BXS, NXS, MXS, SDP) use the same 26-bolt head, and mechanics report the same 200, 330, 330 lb-ft procedure on C15 ACERT engines, including the SDP. One forum post lists a different final-pass number for the SDP that we could not verify. Cat publishes procedures by serial prefix, so check the SIS printout for your engine and follow it if it differs from anything you read online.

Why won't my C15 head bolt reach 330 lb-ft?

Stop pulling on it and find the cause. The repeat 330 pass exists to catch exactly this. Common causes are a torque wrench out of calibration, missing 6V-4876 lubricant, grease or debris in the bolt hole, damaged block threads, or a bolt that has yielded. If you've already made a full pass with a bad wrench, replace all the bolts, then confirm the recovery steps in the OEM service manual.

Do C15 head bolts need to be retorqued after warm-up?

Caterpillar's head bolt procedure for this engine has no retorque-after-warm-up step. The idea mostly comes from AI-generated answers and one owner's report of exhaust-side bolts losing torque on high-boost builds running about 55 to 60 psi. If head bolts are losing torque on a modified engine, look at heat and cylinder pressure, and confirm any additional steps in the OEM service manual for your serial prefix.

Sources

• 3406E and 3456 Industrial Engines: Cylinder Head (Cat service text reproduced)
• NewAgTalk: C15 rebuild thread quoting Cat head bolt procedure
• JustAnswer: C15 ACERT head gasket installation guide
• The Diesel Garage: Stretched head bolts or bad torque wrench
• The Diesel Garage: Cat C-15 overhaul torque specs
• Trucks, Parts, Service: Cylinder head bolts for Caterpillar C15 engines
• Caterpillar 3406E / C15 / C15 ACERT head bolt kit with washers (kit contents)
• Caterpillar 3406E 1539653 cylinder head gasket (lubricant note)
• TheTruckersReport: Need to pull head 3406E 1LW (12-point socket)
• TheTruckersReport: Performance 3406E head gasket solution (high-boost report)

Written by the TTM Diesel Tech Team, Houston, Texas. Published October 15, 2026. This article was researched and drafted with AI tools by TTM Diesel and checked against the sources listed before publishing. Confirm specifications in the OEM service manual for your engine serial number.