ALFAGTV6.COM

I've just realised that there's a knock sound coming from the engine. It looks like it comes from the piston No.4. It sounds when cold or hot and on almost all the rev-range. The more you rev the engine up, the more often it knocks. Sometimes the sound disappears over 3.000rpm but not always and not at the same revs. It is more noticeable between 1.000-2.000rpm but you can't hear it from inside the car (still )

What can it be?

hmmm, whats the mileage on the motor? sounds like a con rod end.


mjr

Hey my 164S has the same knock. I think Rod bearings, most pronounce in the 1-2K rpm range. Sounds like cluk cluk cluk, especially when there is no load. Engine has about 280k KM.

if it is a small end or big end bearing, depending on how loud the knock is, you may get away ith it for a long time. I had a 3l supra with a worn small end bearing. I just ran it on a slightly thicker oil, and it lasted another 40,000 miles before it gave in, and I didnt nurse it either,I just drove it normally. if its loud, then the chaces are it wont last.


mjr

If you look on the old site at this thread:

http://www.alfagtv6.com/discus/messages ... 20000117pm

(or just search for "push rod" (in quotes)) you find a discussion that the noise may be from the valve train and not the bottom end.

A quote from that thread from someone named Tim:

"This is a very interesting thread regarding the mysterious warm engine knock that seems to be common for the Alfa V-6.

I don't believe this knock is always lower-end related as some suggest. The lower end of the Alfa V-6 is built especially rock solid as independent test have proven; for example as the Callaway turbo dyno bench test showed.

Wrist pin knock typically will occur when an engine is cold and then it will decrease with the rise to operating temp. My BMW 2002 has this type of knock.

I believe this myterious V-6 knock is coming from the upper end, perhaps worn cam bearings, push rods, rockers or something up there? Obviously temp related.

BTW: A decent test for worn main bearings is to run the engine to full temp and put the gas on hard, if the oil pressure drops while doing this then more than likely the main bearings are badly worn. For accuracy sake it is probably a good idea hook up diagnostic digital oil pressure meter while doing this type of test.

A good test for rod bearings is to run the engine to full temp and then increase the gas, then let off the gas suddenly. During this transition, when letting off the gas, worn rod bearnings will knock slightly. Also at cold start the rods will knock until oil pressure comes up, sure fire sign that the rod bearings are worn."

"Knock knock"
"Who's there?"
"Rod"
"Rod who?"
"Rod bearing"

I had a knock in the exact same rpm range...it turned out to be cracked rings and scored liner...big end and little end in spec...

I suspect this top end engine knock when the engine is hot maybe due to excessive ingnition timing. (detonation) Retarding the ignition slightly should reduce it.

Ha ha Ben, thats good !

This site is well managed. Who is ben?

x-rad wrote:I had a knock in the exact same rpm range...it turned out to be cracked rings and scored liner...big end and little end in spec...

Long day, huh Ben ?

Wow... my Knock knock joke is 2 years old now!

Did you get a cake for it?

I have a reverberating knock at tick over it gets louder and then dies off again to repeat the same pattern, you cant hear it from inside the car only when the bonnet is up? i have no idea of the real mileage of the engine as it is a 3.0l out of a crashed 75 and I bought it without any verification. PS it does sound very sewing machine like over 2-3000 rpm.

I think this is a common noise from this style engine when hot. most likely due to worn intake valve fowlers (tappets) . replace the intake valve fowlers .adjust intake and exhaust valves. I would check engine comppression first before doing the valve adjustment. No sense adjusting valves on a severly worn engine, it may need a overhaul. I wish Alfa had the fiat spider intake valve setup. You do not have to remove the cams to adjust the valves on the Fiat. A much better design I think.