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Question Cold rattle?

Is it normal for these older generation engines to generate a subtle rattle when cold, which dissipates away as the engine warms up?
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Old 01-08-2007, 01:05 PM
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Is the noise new, or has it always been there?
Old 01-08-2007, 04:38 PM
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hmmm, kind of new I guess. Been there for the last 2-3 months I'd say.
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Old 01-08-2007, 05:24 PM
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Presuming you have lots of cycles on the engine in the last couple months and the noise has not changed (worsened) it's likely not an issue. A few things that come to mind however is valve train, piston/cylinder clearance, and tensioners. These items do have differences when cold versus warm which could make various sounds.

Sometimes exhaust systems can have loose or rubbing components which rattle a little when cold or warm due to expansion. Think - heat exchanger boxes on the headers.

Tough to be of much help without being there to listen with a stethoscope, but if the noise is minor, consistent, and dissipates, then it's probably a non issue.

Jim
Old 01-08-2007, 06:05 PM
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Thanks. I'll take closer notice if it dissipates fully or not once fully warmed. I'm a little worried cause it's more prevalent now, than before. Hope it's not a spun bearing or something. Doubt it though. Full engine rebuild wasn't done THAT long ago, but who knows if it was done properly or not

Unlikey it's a heat exchanger rattle. I'm running heaterless headers.
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Old 01-08-2007, 06:48 PM
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Maybe a screw was dropped somewhere? Licence Plate could rattle! A barrel nut that has come undone can shake up inside a valve cover! The boxed tin located just above each oil return line under the engine sometimes get flimsy! I'd get a long screwdriver and poke at them while the engine runs! I'm not really sure what they are for though. I guess they help in guiding air between the cylinders. Get a long rubber hose and try scoping that noise out.

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Old 01-08-2007, 08:19 PM
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Buy a stethoscope and see what you can find.
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Old 01-09-2007, 11:29 AM
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Merv, I call it, the Turbo rattle.
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Old 01-09-2007, 12:42 PM
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Maybe the tensioners are not extending properly till the oil is warmed up? Were the tensioners bled before they were installed from the last build?
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Old 01-09-2007, 12:53 PM
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Quote:
Originally posted by YermanCars
Merv, I call it, the Turbo rattle.
Tony, does yours do the same too?

As for the tensioners, I don't know the specifics of what was done during the full rebuild.

I'm going to keep a close ear on this one and see how it goes over the next couple weeks.
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Old 01-09-2007, 05:05 PM
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Quote:
Originally posted by WERK-I
Maybe the tensioners are not extending properly till the oil is warmed up? Were the tensioners bled before they were installed from the last build?
Don't the tensioners auto vent from the holes in the top when the engine runs due to the oil pump pressurising them ?

I didn't do any special venting on my pressure fed ones...
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Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
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Old 01-10-2007, 02:03 PM
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Piston Expansion?
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Old 01-10-2007, 02:46 PM
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He did mention that it goes away when the engine warms up, Possibly the piston ring tolerances are a tad loose.
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Old 01-10-2007, 02:49 PM
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Quote:
Originally posted by Frank@AMS
He did mention that it goes away when the engine warms up, Possibly the piston ring tolerances are a tad loose.
Oh OH! That doesn't sound like a cheap fix
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Old 01-10-2007, 03:23 PM
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Nothing to fix, thats completely normal. When you first start the engine, the pistons and rings are cold. When the pistons and rings are cold, the metal is contracted. As you progressively warm up the motor, the pistons and rings will expand, and then the noise goes away. Most people refer to this as piston slap, im guessing that this is the rattle that your speaking of.
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Old 01-10-2007, 03:33 PM
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Quote:
Originally posted by Frank@AMS
Nothing to fix, thats completely normal. When you first start the engine, the pistons and rings are cold. When the pistons and rings are cold, the metal is contracted. As you progressively warm up the motor, the pistons and rings will expand, and then the noise goes away. Most people refer to this as piston slap, im guessing that this is the rattle that your speaking of.
Thanks Frank. Yup, that's the noise I speak of. I haven't heard it over the last few days as it's been quite warm down here, so it definitely sounds like a heat related issue.

Mind you, *IF* I ever have to replace the P&C's, I think I'd opt for some nice 3.4 P&C's next
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Old 01-11-2007, 03:17 PM
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Merv,

No problem. I know Yermancars motor started to do that after they built the motor to a 3.3

Its very common with high performance rebuilt motors.
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Old 01-11-2007, 03:26 PM
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Frank, have you heard of people "gapping the rings" for such high HP setups? I believe my engine builder just used OEM 930 rings, but I've heard that for such big HP applications, these rings need to be gapped appropriately to accommodate ring expansion in big power motors?

I guess this only relates to track cars tho, right?
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Old 01-11-2007, 03:37 PM
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Merv,

No mater if the rings are OEM or after market, the way the rings are gapped are all dependent on the engine builder. During the build process the builder will file gap the rings to what his personal preference is. Some builders will gap tighter, while others gap looser. However, if the motor is being built for a high boost application, an engine builder will usually gap the rings to a larger tolerance like you mentioned.
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Old 01-11-2007, 03:43 PM
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Thanks for clarifying... makes sense
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Old 01-11-2007, 03:56 PM
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