[tcw]

Why don't cars that come with SMFW's have chatter issues?

[The Ghost]

Originally Posted by Gugs

Will never happen. Good luck waiting. While your waiting learn about how a DMFW works and youll understand why a single will never be as quiet/chatter free as a dual. Never

I understand how they work. I am more interested in knowing if the idle adjustment is a decent work around.

I also wonder what is unique about engines with DMFWs that require it versus all of the other engines which don't need it.

[Dave W.]

Originally Posted by The Ghost

I understand how they work. I am more interested in knowing if the idle adjustment is a decent work around.

I also wonder what is unique about engines with DMFWs that require it versus all of the other engines which don't need it.

AFAIK it's just a matter of having some sort of damping medium between the crank and trans. The OEM clutch has a rigid friction disc (#2 in the pic below) paired with the DMFW. Other cars that have solid flywheels will pair it with a sprung center friction disc, see second pic.

[OpenFlash]

Originally Posted by Dave W.

AFAIK it's just a matter of having some sort of damping medium between the crank and trans. The OEM clutch has a rigid friction disc (#2 in the pic below) paired with the DMFW. Other cars that have solid flywheels will pair it with a sprung center friction disc, see second pic.

+1
That's exactly right.

[ign335i]

If that's the case, how do you explain the rattle from an SMF paired with a sprung clutch disc?

[Dave W.]

Originally Posted by ign335i

If that's the case, how do you explain the rattle from an SMF paired with a sprung clutch disc?

The rattle comes from the trans, and I've never had the chance to open up a 335 trans to see what makes it tick.

[MDORPHN]

Originally Posted by Dave W.

The rattle comes from the trans, and I've never had the chance to open up a 335 trans to see what makes it tick.

And the rattle emanating from the tranny is aggravated by light flywheels.

Just another trade-off to be considered.

Neil

[ign335i]

Originally Posted by Dave W.

The rattle comes from the trans, and I've never had the chance to open up a 335 trans to see what makes it tick.

Right, and you stated that you need damping medium between the crank and trans to avoid rattle. At least thats what I thought you were saying. If that's all you need, then why do SMFs with sprung (damped) clutch disks rattle?

[BEAR-AvHistory]

Originally Posted by ign335i

Right, and you stated that you need damping medium between the crank and trans to avoid rattle. At least thats what I thought you were saying. If that's all you need, then why do SMFs with sprung (damped) clutch disks rattle?

Could be a spring tension thing. Sprung disks have short springs with a constant spring rate while the dual mass usually has two sets of springs of longer springs one set softer then the others. The soft set should soak up vibrations that the harder set would pass on.

[OpenFlash]

UPDATE (12/26/12): Confirmed the solution. Just got word from Georgiatech335i. Hi just replaced his stock dual-mass flywheel with a single-mass flywheel and the high RPM misfire is gone

Theory turns in to reality. Props to tmo335tt to figuring this out!

[Dmacc]

Originally Posted by shiv@vishnu

UPDATE (12/26/12): Confirmed the solution. Georgiatech335i just replaced his stock dual-mass flywheel with a single-mass flywheel and the high RPM misfire is gone

Good news!

[CaptainInsano]

Originally Posted by shiv@vishnu

UPDATE (12/26/12): Confirmed the solution. Just got word from Georgiatech335i. Hi just replaced his stock dual-mass flywheel with a single-mass flywheel and the high RPM misfire is gone

Theory turns in to reality. Props to tmo335tt to figuring this out!

Hell yeah.

[OpenFlash]

This is a perfect example of someone working through things properly rather than simply turning off diagnostic systems that would merely mask a pretty serious underlying problem. This is seriously good news.

[Rotorocious]

Originally Posted by shiv@vishnu

UPDATE (12/26/12): Confirmed the solution. Just got word from Georgiatech335i. Hi just replaced his stock dual-mass flywheel with a single-mass flywheel and the high RPM misfire is gone

Theory turns in to reality. Props to tmo335tt to figuring this out!

Great news.
Anyone know how many miles were on that DMF ?

[GeorgiaTech335coupe]

Originally Posted by Rotorocious

Great news.
Anyone know how many miles were on that DMF ?

I had 60k on the DMFW. It didn't look pretty when I took it out. Lots of hot spots. Probably from the 400+ drag strip passes lol.

Condition may or may not be an issue though. JMARS DMFW has only 20k on it, and his car was misfiring (although not with the frequency mine was).

[Fully_Bolted]

Originally Posted by shiv@vishnu

This is a perfect example of someone working through things properly rather than simply turning off diagnostic systems that would merely mask a pretty serious underlying problem. This is seriously good news.

Could you provide a breakdown of what serious issues would result from turning misfire detection off vice replacing the DM flywheel with a SM one?

[Dmacc]

Originally Posted by Fully_Bolted

Could you provide a breakdown of what serious issues would result from turning misfire detection off vice replacing the DM flywheel with a SM one?

Turning it off could potentially mask other problems, it is nice now that we actually know the dmfw caused the high rpm misfire, so there is no need for the guys who are dmfw running high hp to disable misfire detection.

[OpenFlash]

Originally Posted by Fully_Bolted

Could you provide a breakdown of what serious issues would result from turning misfire detection off vice replacing the DM flywheel with a SM one?

If movement in the dmfw is causing falling edges of the CPS signal to not be where they are supposed to be (triggering misfire diagnostics) then ignition timing is also going to be erratic. Each tooth width is equal to 3deg of advance and that is a potential for a lot of timing jitter. Especially for a high HP engine that needs tight timing control.

[JMARS]

But I don't want to buy another clutch/flywheel and pay for labor again... :-/ I guess I'll be short shifting it for a while :-(
I need a post Chrsitmas Miracle!

[DallasBoosted]

Originally Posted by shiv@vishnu

If movement in the dmfw is causing falling edges of the CPS signal to not be where they are supposed to be (triggering misfire diagnostics) then ignition timing is also going to be erratic. Each tooth width is equal to 3deg of advance and that is a potential for a lot of timing jitter. Especially for a high HP engine that needs tight timing control.

Could this same issue to a lesser extent cause intermittent misfires in lower-power applications as well?

[Rotorocious]

Originally Posted by DallasBoosted

Could this same issue to a lesser extent cause intermittent misfires in lower-power applications as well?

That's what I'm worried about. I don't plan on anything higher than RB's power range but it still concerns me.

[jpsimon]

Roto - dzenno has had misfire issues with his RB's, sounds like he'll be going smfw eventually even though he's content with just turning off misfire detection.

I'm glad I got a SMFW to begin with!