Lunati 60402 Cam Question

[cwestra]

I installed a Lunati 60402 cam in my '70 Cuda when I rebuilt it a couple of years ago and since day one the engine seemed to run rougher than I had expected.  Although I have no problem with a rough idle, I would have expected it to run smoother when the RPM's got higher.  It just seems to stay rough for some reason.  Has anyone else had a similar experience (cam related or not) with a rough running engine and any possible areas to look.  I have attached the specs on my cam below.  Not sure if the lower LSA is giving me this characteristic or not.

I'm not sure if it's related or not but I also have a vibration coming from somewhere in the drivetrain when I get above 3600 RPM's.  The probem is always there at the beginning of a road trip but seems to go away after some time during the trip, allowing me to spin it to over 4000 RPM without the vibration.  Anyone else ever experience this?

[Chryco Psycho]

well that is a relatively mild cam so I would say you have another problem , why a vibe would disappear after a while while it warms up seems odd to me , try unplugging the spark wire one at a time while it is running , Do Not lean on the fender while doing this !!
every cylinder should drop the Rpm equally if one or more do not start looking for a problem , bad wire or plug , vacuum leak sometimes into the runner feeding the brake booster  , loose intake bolts  , carb not feeding fuel equally .

[cwestra]

well that is a relatively mild cam so I would say you have another problem , why a vibe would disappear after a while while it warms up seems odd to me , try unplugging the spark wire one at a time while it is running , Do Not lean on the fender while doing this !!
every cylinder should drop the Rpm equally if one or more do not start looking for a problem , bad wire or plug , vacuum leak sometimes into the runner feeding the brake booster  , loose intake bolts  , carb not feeding fuel equally .

Thanks for the advice, CP.  I'll try checking on those things.  Right now I have the trans out, as I wanted to check to be sure the pilot bearing wasn't loose or worn, causing an inconsistent vibration.  Everything seems to look okay.  Sticking a spare input shaft into the bushing gives a good fit with virtually no slop.

Let me ask this, could the flywhel be out of balance causing this?  Or could I have gotten a clutch and/or pressure plate that was somehow out of balance?  While I have them out should I take them in to check balance on them?  If so, should each piece be checked separately or as an assembly?

[linetrash75]

  First I like the color of your car. I would definately have  flywheel and  clutch assembley looked at, also check harmonic balancer, is possible you got a 360 one? I know the 318 is internal balance I assume the 340 is also, but 360 is external. pretty sure fly wheels are different too. Good luck.

Jed

[Chryco Psycho]

if there are any holes drilled intothe ear of the flywheel it would be an offset balance , it could be checked for balance while it is out of the car ,can't hurt but it doesn't make sense , why would it change as it heats up ?
the cam has less duration than stock cam so it shouldidle very well .
 the 360 damper has 360 cast crank marked on it & has an offset part visable from the front , there could be an internal balance issue though

[cwestra]

  First I like the color of your car. I would definately have  flywheel and  clutch assembley looked at, also check harmonic balancer, is possible you got a 360 one? I know the 318 is internal balance I assume the 340 is also, but 360 is external. pretty sure fly wheels are different too. Good luck.

Jed

Thanks.  I believe it is the original damper for the car.  My engine should be balanced internally as well.  Here is a quick picture of the balancer on it.  Not sure if anyone can positively ID it from that.

[dodj]

I'm not sure if it's related or not but I also have a vibration coming from somewhere in the drivetrain when I get above 3600 RPM's.  The probem is always there at the beginning of a road trip but seems to go away after some time during the trip, allowing me to spin it to over 4000 RPM without the vibration.  Anyone else ever experience this?

I'm thinking this might have something to do with the ignition. Mechanically your balance can't change during a trip, then change again before the next trip. It's like it is dropping a cylinder until after a bit of a warm-up the spark plug/plug wire/ecu decides to co-operate and start working. Which as CP is thinking, may be the cause of your rough idle as well.....

Maybe it's a thermal electronic problem with the ecu?  or do you have an ecu?

[cwestra]

if there are any holes drilled intothe ear of the flywheel it would be an offset balance , it could be checked for balance while it is out of the car ,can't hurt but it doesn't make sense , why would it change as it heats up ?
the cam has less duration than stock cam so it shouldidle very well .
 the 360 damper has 360 cast crank marked on it & has an offset part visable from the front , there could be an internal balance issue though

There is a hole about 5/8" dia. and about 1/2" deep drilled into the front face of it so it looks like it has been balanced. 

By internal, I assume you would suspect things like pistons and rods, right?  I'm not opposed to pulling the engine apart to check them but are there other components that could also come into play inside?  Is it just a matter of weighing the reciprocating pieces like the piston/rod assemlbies and adjusting them to match weight?  Should they be weighed separately or as an assembly?  How close do they need to be in weight?  The pistons are KB and rods are originals.

[Chryco Psycho]

you need to weight each pioston , then weigh the small ends of the rods & the bigs ends , as the weight further away from the crank will have more effect on balance , once you have a consistant piston rod & brg weight then you can balance the crank  for the piston weight , if the pistons were changed & the engine was not balanced after then it will be off balance as new pistons will generally be lighter than the factory ones .
As is said before though if it goes away as it heats up I doubt it is a balancing issue check everything else first before you pull the engine down .

[Aussie Challenger]

I would suspect a vac leak myself but have you checked the distributor for a loose breaker plate or broken wire.   

[cwestra]

I would suspect a vac leak myself but have you checked the distributor for a loose breaker plate or broken wire.   

I have not checked that yet.  It is a fairly new electronic ignition unit but easy enough to check.  I do know that when I have a timing light hooked up, the faster I run the engine the more "bounce" or fluctuation I seem to get in my timing (according to what the light is indicating).  Not sure if there is a correlation there or not but thought I'd mention it.  I will check the plate and wires though, thanks.

[Aussie Challenger]

If the timing is bouncing around the drive gear could be worn or floating up or down,  the timing chain could be stretched and worn.
Still check out the vac leak though.

[PlumCraZRT]

Make sure you disconnect the vacuum advance on the distributor when you're checking the timing.  That can cause the timing to move around on you.

Have you tried driving with the vacuum advance plugged?  I would see if that makes any difference.

[cwestra]

well that is a relatively mild cam so I would say you have another problem , why a vibe would disappear after a while while it warms up seems odd to me , try unplugging the spark wire one at a time while it is running , Do Not lean on the fender while doing this !!
every cylinder should drop the Rpm equally if one or more do not start looking for a problem , bad wire or plug , vacuum leak sometimes into the runner feeding the brake booster  , loose intake bolts  , carb not feeding fuel equally .

I just tried pulling plug wires and checking for difference in idling.  All cylinders show noticeable reduction in idle smoothness except #5 and #8.  In fact, the engine sounds the same (roughness) if both of these wires are left off.  I checked cylinder pressure in #8 and it holds strong at 140.  Plugs look good (tan).  Could my problem be intake manifold leaking or something else?

[Chryco Psycho]

are 5 & 8 tied into the runner that feeds the brake booster sometimes it is 6&7
anyway my guess is a leak into the brake booster , try plugging the hose & see if the cylinders respond better , could be a vacuum leak under the intake also .
On a dual plane intake 5&8 also 6&7 are fed by the same runner so you have a leak into those runners somewhere