3.1 engine rattle

[calgarylumina]

I've been having a problem with my heater so I pulled out the blower motor. To do this I removed all the panels from under the dash and pulled back the carpet on the passenger side. This is my only vehicle so I had to drive it "as is" to go take care of some other business. One thing I noticed was how engine rattle I can hear with all the sound absorption under the dash on the passenger side gone. The rattle definitely got louder the more I accelerated. I'm thinking this must be the valve train. Although later I opened the hood and there is also some rattly sounds coming from the drive belt area(alternator, water pump etc..). I have a 91 3.1L. My questions are: what are possible sources of the rattle, and are the possible causes serious?

[jeffcoslacker]

The 3.1 has a noisy valve train, especially when cold. It goes away on mine as it warms up. It is possible you may be hearing the belt tensioner if it is getting old. The tend to get weak, and the bearing gets rough, causing it to jerk and jump, instead of riding the belt smoothly, and produces some rattle as it does. Watch it with the motor running. A little movement is normal, but if it is hopping with noise associated with the movement, it's shot.

[richtazz]

I agree with Jeff. If the tensioner seems ok, you may have some piston slap starting, which is not uncommon in 3.1's as they get older. Since it seems to be coming from the passenger side, I would put my money on the tensioner.

[KenInKenmore]

richtazz, I don't know a whole lot about iner engine problems or how to dignose them, what causes piston slap? and how do you fix it when it happens?

[jeffcoslacker]

Piston slap usually occurs when the cylinder bore or piston rings are wallowed out enough to permit the piston to "rock" in the bore, instead of remaining mostly straight up and down in the bore. As it does the lower area of the piston skirt will slap the cylinder wall each time the piston rocks in its' bore (usually on direction change), producing a kind of hollow, deep rattle in the motor, especially at startup. Not much you can do about it, short of disassembly and machining of internal parts. Is normal and common on some engines (3.1, apparantly) with high miles. Some engines have this noise inherent even when new, and teflon coated pistons are available to protect against excessive wear and noise.

[tblake]

Piston slap is exactally what Jeffco stated, although I'd like to add that It occurs in all vehicles, new and old. It only happens in most when the engine is first started, and not had time to warm up, Metal expands as it warms up, and therefore the rings provide a better seal between the bore and piston, which prevents the piston slap. This is why the first few minutes after you start your car are the most crucial.

[calgarylumina]

That sounds like what may be happening to me. I took a look at the belt tensioner and it seems ok (it moves but only rocking back and forth with the belt 1/2 ince end to end). thanks for the info.

[Kooterskkar]

My 2.8 makes the same noise, I was almost thinking it may be a loose timing chain. (which I should check anyway, now how to check it without taking off the cover... )

[jeffcoslacker]

You can check it by taking a valve cover off, rotating the crank in one direction manually, then back the other way and see how many degrees of crank movement it takes before the slop picks up and the valves start to move.

[Kooterskkar]

About how many degrees of play would be acceptable?

[richtazz]

anything more than a couple of degrees is unacceptable. If it's loose enough to rattle, you should have plenty of slop.

[maine6-pack]

I had the same problem in a 95 cutlass 3.1. Found a very worn and lose timing chain. Have the enginweapart and am in the process of changing it .