Gm 3400 dohc timing belt question on a 1995 monte carlo

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1980RS
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Re: Gm 3400 dohc timing belt question on a 1995 monte carlo

Post by 1980RS »

If the engine whines from the timing belt it's too tight, won't really hurt anything as we had them right off the GM line sound like that, just gives them the super charger effect. We also had special tools from Kent Moore for those engines to setup the belts.
Nut124
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Re: Gm 3400 dohc timing belt question on a 1995 monte carlo

Post by Nut124 »

I have read about tight belts getting so hot that the Mfg printing comes off the outside of the belt. I would think it would hurt longevity as well.

My 4-banger belt gets tighter as the engine warms up, expands, so I set it pretty loose, cold, so it does not whine hot. Whining sounds even worse if one of the cam pulleys is not running true. Then the whine will have another frequency to it.
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Re: Gm 3400 dohc timing belt question on a 1995 monte carlo

Post by dfarr67 »

All I know about these is- let it idle for an hour, belt will stretch a bit and all will be good.
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Re: Gm 3400 dohc timing belt question on a 1995 monte carlo

Post by Schurkey »

drifter wrote: Sun Feb 10, 2008 8:58 pm No i didn't take off of the valve covers to use the special tools to hold the cams.I just took off the front cover and aligned the hard to see paint marks.But my question mostly is can and engine run good and have 20" of vacum but the cams not be aligned 100%??
Yes. The question is how far off of "100%" did you end up at? The cam pulleys are not keyed to the cams, they have "infinite" adjustment. They can be "way off" or "microscopically off".

I have done a few belt replacements on my two Lumina 3.4L--a 92, and a '93. The '94-newer engines have a cam sensor and more-sophisticated fuel injection. (Sequential instead of batch-fire) Yes, the cam-gear-to-camshaft system is different on the later engines than the '93 (?) and older. I'm sure that the cam gears are still not "keyed" to the camshafts, they just have a different method of infinite adjustment. Older engines use a "corrugated" spacer; newer are--I think--male tapers on the cam that fit into female tapers on the gear.

First one, I didn't use the special tools. Just marked the old belt and all the notched pulleys with a paint-pen, counted the notches in the belt between markings, marked the new belt by counting the notches, put it all together with the markings on the new belt aligned with the markings on the pulleys. Worked great.

Second and subsequent times, I used the Kent-Moore special tools. Something of a time-saver; but the engines didn't run any better afterwards. "Official" belt replacement schedule was 60K miles. Given that this is a waste-spark engine, it is completely possible to screw-up the cam timing of one bank, so that the companion cylinders fire at the same time. Runs rough, but all cylinders run. I suppose at high load, the ignition system may not be able to fire two plugs both on the compression stroke.

There shouldn't be any way to over-tension the belt unless you've brutalized the tensioner. For the record, some folks call it a "hydraulic" tensioner, but it's not. It's merely spring-loaded with an oil-fill for lube.


Intake gaskets are a known problem on this engine family. Air leaks into the ports that screw-up the idle, mainly.

I suspect--but have little evidence--that head gasket problems on #1 and #6 are also an issue. Specifically, I think the head casting has a localized "soft spot" that collapses; unloads the fire-ring of the gasket, and leads to erosion of the fire ring, head, and block with eventual coolant leaking into those two cylinders.
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