defakto

I was out for a drive in my FB 12A (Loves the cold weather with the cold air intake) and noticed a deep rumble that starts about 6500 rm and gets louders above that. Quickly backed off the throttle at that point because it had never done this before.

The engine only has about 52k on it, original

My question is, is this apex seal chatter? Or is this from another cause?

If it is chatter, could it be caused by excess carbon buildup in the engine and would runnning something to clean the deposits from the engine help?

I'm planning on going pre-mix with it very soon would this also help in the long run?

RXnos1200

iTrader: (24)

fuel delivery; check the secondaries on the carb and make sure they are working, check your spark plugs and make sure you're not running lean, , check your timing too. sounds like its detonating. good luck

rOtAryIsbEttEr

i dont think you could hear chatter even if it was chattering
it could also be drivetrain realted. does it make 'rumble' in all gears, and neutral or just one gear?

RXnos1200

iTrader: (24)

^^^ throw out bearing? hard to say.

defakto

It does it in all gears that I can safely hit near redline on without too much excessive speeding and not sure if it does it in neutral I'll need to check that. If it's the throw out bearing that's no big deal, replacing the clutch soon anyway. Haven't tried it in 4th or 5th but it does it in 1st, 2nd, and 3rd.

Timing should be good it was tested only a few hundred miles ago, but I should probably do it again just in case at this point to be sure

Not sure on the secondaries I'll have to look into that tomorrow when it's light out. Also, planning on replacing the sparkplugs tomorrow as well anyway. How can you tell if it's running lean by the sparkplugs? Not too familiar with that.

RXnos1200

iTrader: (24)

try pushing in the clutch when you rev it out in neutral and see if it still make s that noise. Could be the throw out bearing.

rOtAryIsbEttEr

ive also heard of clutch disks shattering in such a way that the car is still driveable but it shakes and rumbles while the engine turns

K-Tune

iTrader: (26)

chatter you can see in the tach and feel in the car when it happens. if this is a case..it isn't carbon, its lack of lubrication.

RXnos1200

iTrader: (24)

The spark plug insulator should be like a tan color, indicating that the everything is running ok. Ashy white insulator on the plug means it is running abit lean.

YOu have a few possibility on what that noise actually is. I'd take some caution and try to check everything out that is suggested to you.

trochoid

iTrader: (6)

He should be chattering at 6500 rpm, unless there are other internal issues. Detonation doesn't sound like a deep rumbling. Take off your cold air intake and see if the noise stops.

RXnos1200

iTrader: (24)

He should be or shouldn't be chattering at 6500 rpm? hope you find out the problem. keep us posted. good luck.

trochoid

iTrader: (6)

Oops, should not be. Thanks for the catch.

RXnos1200

iTrader: (24)

Haven't been in the rotary scene for awhile. So just making sure. Just going by my previous experiences. Thanks for the answer.

Siraniko

iTrader: (13)

Is this James???

RXnos1200

iTrader: (24)

That would be me. Who are you?

Nicholas P.

iTrader: (1)

My brothers use to do that on his 1st gen. He would get going real high in the gear, and it would start to shake really bad. It shook worse when he was slowing down. His driveshaft had warped before we had it.

-nick-

defakto

It doesn't shake at all, it's a low frequency rumble that increases after 6500. Other than the sound there is not other evidence.

RXnos1200

iTrader: (24)

Do you feel the rumble on the shift ****? Try checking the trans mount. Just a suggestion.

defakto

Looks like I have alot to check tomorrow, I'll come back with an update on any finds.

RXnos1200

iTrader: (24)

you'll figure it out. good time to just check out the whole car.

1badFB

iTrader: (1)

Maybe try describing the noise a bit better. A deep rumble is prety vague.

How is the exhaust on the car? I wouldnt necessarily come to that conclusion from "a deep rumble" but if theres no vibration in the car / power loss, you perhaps could have lost an exhaust hanger or blown a little hole in the exhaust pipe?
There are no other symptoms but a deep rumble?

Kentetsu

Okay, I'll take a shot at this one too... 1. Make sure that the exhaust system is still isolated (not in contact with frame or body). 2. Verify timing (if this is the issue, you want to identify it right now!). 3. Could be carbon causing an apex seal to stick. Add 1 can of Seafoam to 1/8 tank of gas and you should see improvement within a few miles (I do this on a regular basis and always see improvement). Good luck...

defakto

Alright, Update time:

It's a low frequency rumble that you can barely feel in the car.
It does it in neutral
There are no signs of detonation on the spark plugs
I looked over the secondaries, how's the best way to tell if they are working correctly. You can feel the secondaries kicking in on the road but that's all I have to go by at this point.
The exhaust system has a broken pipe but this is unrelated as it's had it for about 3 weeks and never experienced this problem(yes I'm working on the money to replace that particular piece at the moment.
The exhaust system is isolated from the frame as well.

defakto

I'm planning on running some pre-mix into the system to see if that helps at this point, anyone have any other suggestions?

RXnos1200

iTrader: (24)

makes the noise in neutral? try pushing down the clutch pedal and see if you hear that rumble.