3.9L internally balanced??

[Redder]

I can't seem to find a straight answer on this subject, I seem to remember older generations's of the 60 degree V6's being externally balanced with a variety of different flywheels, flex plates.

I bought a 07' 3.9L LZ9 for an off road project, and want to make it a RWD application. I managed to find an 86' camero T-5 bell housing with the twin starter pockets and I ordered a Novak adapter to mate this to my AR-5 from an 04' 4wd colorado. behind that is an atlas T-case. anyways I just can't figure out what flywheel to order, the 3.4L variants of this style motor require a different flywheel for FWD and RWD applications or a spacer ring to compensate. the 3.8L style flywheel is its own unique 8 bolt Crank pattern so it won't bolt up. and older style 2.8's and 3.1's seem to have half balanced flywheel or ones with drilled holes to loose weight or weights added. The motor I purchased had no flex plate attached so I have no reference point and there appears to be no harmonic balancer on the front so am I wrong to assume it's internal??

this is the only post I've found on the web currently that claims my thoughts. so yes I searched hence why I'm here but when you look up late model flywheel the pics show what I can best described as drilled balancing holes. Flame away

They are called Harmonic Dampners. NOT Balancer's. The Dampner does NOT balance an engine. It removes inherent natural vibrations from the rotating assembly.

The engine is internally balanced. Old first gen 60v6's (Iron headed 2.8L's up to about 86) were Externally balanced on the flywheel/flexplate.

Harmonic Dampners use a rubber slip ring and dual steel sleaves to remove the normal internal combustion engine harmonics.

Think of it this way, when you strike a tuning fork on an object such as a table you produce vibrations and sound frequency from the tuning fork. You can visibly see this and hear the sound it produces. When the engine is running the force of Combustion acts like a sledge hammer on the top of the piston forcing it down. Harmonic Vibrations much like a tuning fork happen here, The force is transmitted through the rods to the crank which under load does flex and twist thousanths of an inch during opperating conditions. The harmonic dampner's job is to isolate and remove the natural frequency/vibrations from the crank.

Thus why its a stupid idea to run underdrive pullies that do not include or have a harmonic dampner built into them. People love to dissagree on this one but ask any engineer and you will recieve the same answer.

[dre256]

Re: 3.9L internally balanced??

Unfortianlly most of the good tech guys don't post much here anymore do to them moving on from G6s to other cars. Before you get to involved with the 3900, you are aware the 3900 has head gasket issues. It may not be the best engine to pick for a project especially if you plan on adding more HP as aftermarket on the engine is extremely limited and most other 60 degree V6 parts do not fit. And the 3800 is a 90 degree V6.

I will suggest best place to go for tech support is 60degreev6.com there use to be a lot of very involved tech racing guys on there.

[Redder]

Re: 3.9L internally balanced??

oops. forgot there a 90* the bell housing pattern threw me off I suppose. I'm well aware of the motor's "issues" but the pro's for it and the price I paid far outweight the possible head gasket replacement I may or may not need on a toy I might use twice a month. really don't plan to add more power, just delete all the anti theft, emissions, and Tranny from the PCM. I'll give that site a try, thanks for the lead.
Red

[Raydar]

Re: 3.9L internally balanced??

Pretty sure the engine is internally (or "zero") balanced.
Please keep us posted on your project. I'd like to use an LX9 or an LZ9 for a Fiero swap. Getting it to run "stand alone" is pretty much a requirement. Also don't want to lose the VVT.

[black07g6gtp]

Re: 3.9L internally balanced??

Go with the 3.6 instead. Much better motor.

[Alexander_Rychok87]

3 9L internally balanced

If you arent sure whether or not your motor is internally or externally balanced would there be any harm in going with a balanced flexplate? Seems to be if you werent sure, going with the balanced plate would be the "safe option".

The summit rep I just spoke with indicated that you would have to know which you had and that putting the wrong one on, in either case, would be very bad read: potentially catastrophic.

Can anyone comment with certainty either way on this?

Thanks