7.4mpi head torque

[mwehrmei]

Hi all,

I have a 1998 7.4 mpi sn 0L042350. I had to replace the head gaskets, and I ran into a problem on reinstallation. I was following the mercruiser factory service manual 90-861326-1 torque specs, and one of the bolts sheared. Questions:

Is the torque spec in this manual correct for my boat? 30-59-89/92ft-lb, in correct bolt order and sequence. I’m wondering because a. These are supposed to be reusable, not torque to yield, and b. Most other sections have different specs for the mpi vs later variants

If the torque specs are correct, what could have caused this? I used aviation gasket on the threads, and the underside of the bolt heads were lubricated with oil. The bolt snapped at the threads. Luckily it was high enough that I could grab the remnant and get it out. It spun out easily.

Do I need to get new head gaskets? I noticed some of the cylinder crush ring left remnants on the head. I’d hate to rebuy gaskets, but I’d hate to do this again a lot more

Thanks for reading and helping. This forum has been a great resource in working on my boats throughout the years

Mark

 

[Scott Danforth]

those torque specs are for torque to yield bolts

I highly recommend new head bolts

Big Block Chevy Torque Specs​

The following specs apply to:

• Gen IV, Big Block Chevy
• Mark V, Big Block Chevy

​

Fastener Type​	Torque Specs​
Main Cap Bolt (396-427, 2-Bolt)	95 ft.-lbs.​
Main Cap Bolt (396-454, 4-Bolt, Inner and Outer)	110 ft.-lbs.​
3/8 in. Connecting Rod Bolt	50 ft.-lbs.​
7/16 in. Connecting Rod Bolt	67-73 ft.-lbs.​
Cylinder Head Bolts, Long	75 ft.-lbs.​
Cylinder Head Bolts, Short	65-68 ft.-lbs.​
Screw-In Rocker Arm Studs	50 ft.-lbs.​
Intake Manifold Bolts (Cast Iron Head)	25 ft.-lbs.​
Oil Pump Bolt	65 ft.-lbs.​
Cam Sprocket Bolts	20 ft.-lbs.​
Harmonic Damper Bolt	85 ft.-lbs.​
Flywheel/Flexplate Bolts	60 ft.-lbs.​
Pressure Plate Bolts	35 ft.-lbs.​
Bellhousing Bolts	25 ft.-lbs.​
Exhaust Manifold Bolts	20 ft.-lbs.​

 

[Bt Doctur]

the 95 is for the main bearing cap bolts not head bolts

 

[mwehrmei]

Thanks for the replies. Can you tell me, where do your numbers come from?
Again, the numbers I was using come from the Mercruiser shop manual, number 23, so I’m trying to figure out what I should be following if not that.

 

[Bt Doctur]

454 CID (7.4L) / 502 CID (8.2L)SERVICE MANUAL NUMBER 23
Page 3A-390-861326--1 MARCH 199
short bolts 85, long bolts 92

 

[Scott Danforth]

I would be more inclined to read the GM manual

 

[apw30534]

Any small or big block ive ever built has been 65-75ft lbs. I've probably built 50+ engines in the last 35+ years.

 

[mwehrmei]

454 CID (7.4L) / 502 CID (8.2L)SERVICE MANUAL NUMBER 23
Page 3A-390-861326--1 MARCH 199
short bolts 85, long bolts 92

Hi Doctur,

this is what I was going off of. The bolts definitely turned more than I would have expected for the final torque sequence, and the one sheared. Ordered a new set of head bolts, Felpro ES72264. These are identical to what I pulled from the engine. Engine was a reman longblock from Mercruiser installed by Mercruiser dealer, so not sure why things don't seem to be lining up with what is expected from the manual. Thanks for the reply.

Mark

 

[mwehrmei]

I would be more inclined to read the GM manual

View attachment 356228

Thanks for the table, Scott