GM 3100 – 3400 Engine – Issues With Head, Manifold Leaks, Rocker Bolts

GM 3100 - 3400 Engine With Intake Manifold Removed
GM 3100 - 3400 Engine With Intake Manifold Removed

Surprize ! GM 3100 – 3400 engine issues are still happening and are being repeated.

We still have leaks, installation problems as well as cylinder head and rocker bolt issues.

That’s because most people are still confused about the GM 3100 – 3400 engine issues.

Lets try and solve the most common issues with some basic information. And, Yes I know this is old but, there are just so many repeat failures.

Always do your research before you start this job or any job for known issues.

Do you own a vehicle equipped with a GM 3100 – 3400 engine ? If so, chances are that you have already experienced this intake gaskets leaking coolant condition (and have repaired it). Or you’re experiencing it right now or will be soon enough.

So, what do you do to avoid a repeat of this particular problem:

  • It involves using an updated type of intake manifold gasket made by Felpro.
  • Tightening the intake manifold bolts with a torque wrench to the proper specification.

Common Issues On GM 3100 – 3400 Engine

  • Too many casting numbers, some are interchangeable and some are not.
  • They come with or without air tube holes.
  • They can have 8mm or 10mm rocker bolts and still have the same casting number.

First thing is there are 2 different bolt sizes, 8MM (usually on passenger cars) and 10MM (usually on trucks and SUV’s). The 8MM torque is specification: 89 in/lbs plus 30 degrees. The 10MM specification is 24 ft/lbs. Since the 8MM and the 10MM are interchangeable same year, you could get either one.

  • There are many suppliers offering cylinder heads that fit from 1996 to 2005 but, are not explaining the differences.
Rocker Arm And Bolt Assembly
Rocker Arm And Bolt Assembly

The most common issue is, I have the cylinder head installed but my rocker bolts don’t fit ! ( Customers are telling me they went to a wrecking yard to find rockers that would fit ). Other issues are Rocker Bolts pulling the threads out during installation.

Do not torque a rocker with the valve in the open position. Consequently, this can pull out the rocker bolt threads. Because, of the valve spring pressure pulling out the threads before the bolt is fully seated.

Exhaust and Intake pushrods are different lengths. If mixed up you could end up with bent pushrods or valves.

Exhaust Pushrod Is Longer Than Intake Pushrod
Exhaust Pushrod Is Longer Than Intake Pushrod
Bent Pushrods
Bent Pushrods

Exhaust pushrods on G.M. 3100 – 3400 engines are longer than their intake counterparts. It’s critical to reinstall the correct length pushrod in the correct place.

So, how do you commit to memory which pushrod goes where?

It’s easy if you remember this short phrase… “It’s been a long, exhausting day.” This should help you remember that the long pushrods belong to the exhaust valves.

Conclusion

So, how did all these problems start ! Both the 3.1 and 3.4 engines used plastic intake manifold gaskets with soft sealing beads around some of the ports. Over time, the plastic would soften and the seals would leak. That would allow coolant to seep into the crankcase, or allow oil to seep out of the intake.

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