grey motor knock

[fcee]

    My fc has a stock grey motor which has an annoying knock /rattle at idling speed,the motor uses no oil,starts  and runs perfect ,good acceleration 27 miles per gallon. the common theory from people who have heard it is ,gudgeon or piston slap, my question is  ,would it be a possibility to fix the noise without a complete engine rebuild considering the overall condition of the motor .the knock stops when the revs are increased to a little over idle speed .opinions please .cheers Steve .

[Errol62]

You really need to take the head and sump off so you can pop the slugs out either way. If the comp is good which by the sounds it probably is then just replace gudgeons and bearings. Resize rods I don't know maybe. Seals and gaskets you're done. If the rear seal is good I would probably leave the main bearings alone and maybe just do big ends I dunno.


Sent from my iPhone using Tapatalk

[Billy Blackarrow]

Steve
I would turn up the radio and idle speed  I know i am an idiot
Billy

[KFH]

It is possible that it is the "standard" grey engine gudgeon pin rattle which is noticeable at idle.  If the motor has done quite a few miles since it has been worked on this could well be the case.  My motor with 55000 miles on it is original and exhibits a little gudgeon knock at idle.  I am not worrying about it.

Keith

[ardiesse]

Steve,

It's neither piston slap nor gudgeon pin noise.  I reckon your harmonic balancer has had it.
Take your fan belt off, start the motor and let it idle.  It should be quiet.

Are there any rusty marks around the rivets on the harmonic balancer hub?  As another check, with the fan belt off, grab the steel disc of the balancer in both hands and rotate it back and forth, while feeling for looseness.  Then do the same with the pulley.

My FX used to make an annoying, hard-to-pinpoint "nack-nack" sound at idle, much like a 186 with collapsed lifters.  The harmonic balancer pulley had come loose, but only slightly.

A loose camshaft timing gear also produces a similar noise.  I've had that happen too.  The easiest check for that is: take the distributor cap off, and turn the engine back and forth with the fan.  The distributor rotor should move back and forth in time with the movement of the crankshaft.  If there's any lost motion, where the crankshaft turns but the distributor rotor doesn't, you might have a loose camshaft timing gear.  To make a positive confirmation of this, you need to remove the fuel pump.  Take a screwdriver and pry on the side of the eccentric cam, first forwards, then backwards.  If the camshaft moves back and forward at all, you have timing gear or thrust washer problems.

But I'd go for the harmonic balancer first.

Rob

[ardiesse]

Steve,

And I forgot - excessive backlash in the timing gears can also produce these symptoms.

Rob

[Gary C]

Have you checked oil pressure at idle?
Have you experimented with different grade oil and type, also any difference hot or cold engine.

[fcee]

Thanks for your comments ,seems like will have to dismantle the motor to find what the cause is ,at the same time will fit steel timing gears that have been in the boot for a couple of years ,will post when I find the cause of the noise .cheers Steve