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Discussion Starter #1
I get an engine knocking sound from my 98 mod 2.0lt TS. I am 99% sure it's from the engine and sounds like it comes from the area of number 1 cylinder (from that side anyway). It only appears when the engine is fully warmed and in fact the warmer it gets the louder the knocking. At it's worst I can feel it through the gear stick though not a lot.

It is not pesent when there is no load on the engine or under heavy load (like when I gun it). It comes under light load, just pressing the gas pedal lightly when going up hill, for example.

The engine starts and runs fine. Uses virtually no oil between changes. No over heating. It doesn't feel as smooth as my other 156 with the 1.8lt engine but I think it has more power than that car. The 2.0lt feels like a VW or old Subaru with the "boxer" type engine at times

I have had the big end shells changed although the old shells showed little sign of wear. New head gasket about 3 months ago due to a blown gasket. It was only a slight CO leak into the cooling system.

I did a compression test before the gasket went and all was fine. I have been over all the engine mounts, brackets and anything else that might be loose. Nothing helps.

I don't get it!? Something is wrong and I am just waiting for the engine to blow one of these days. I would really like to get on top of this and find out what it is before that happens.

Any ideas?... Anyone?

Bill
 

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Do you mean conrod bearing.. piston slap? I thought that would be more present when the engine is cold. There is no knocking before the engine reaches about 85 degrees.

Bill
Hi Bill,
Yes, that's the sort of stuff from my gut reaction to what you described.
It's difficult to diagnose this type of problem without actually hearing the noise and frequency so I'm probably wrong.
Is it momentarily worse when going from power on to power off? Is it a heavy or light knocking/tapping?
If you can possibly get a stethoscope to the side of the engine block you should be able to locate the source by varying the RPM with the engine warm. I presume that you had no trouble before the head was removed to replace the gasket or has it become worse over time?

Peter
 

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Discussion Starter #5
Thanks Peter. The knock has been there since I bought the car 9 months ago. Both before and after the bearings and head gasket change. It's real quiet and smooth for the first 10-15 minutes of driving so I never noticed it when I took the car for a test run before buying. Of course the seller knew nothing about it and the car was bought "as is".

It's worse when going from power off to power on actually but there is no knock if I really hit the gas pedal or drive the car hard.

I will listen with the stethoscope but so far there i sno knock on idle or just reving the engine.

I start to wonder if one of the valves might be just "kissing" the top of one piston. The head was skimmed when the head gasket was done.. but then again the knock was there before the HG blew.

There is a sound track here. Alfaknock - YouTube

The knocking is a low pitched thudding sound best heard toward the end.

Bill
 

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A metallic rattle under light load is normally piston slap but a metallic rapping at light load indicates big end bearings. If it's the big ends, removing the spark plug on the effected cylinder should significantly reduce the noise.

Sounds like big ends to me.
 

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Could either be a big end or a small end.

If either of them wear ther extra play can cause the piston to tap the cylinder head.

Also when the had was done was the timing set with the correct locking tools?

Incorrect cam timing can cause all sorts of weird problems.
 

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Thanks Peter. The knock has been there since I bought the car 9 months ago. Both before and after the bearings and head gasket change. It's real quiet and smooth for the first 10-15 minutes of driving so I never noticed it when I took the car for a test run before buying. Of course the seller knew nothing about it and the car was bought "as is".

It's worse when going from power off to power on actually but there is no knock if I really hit the gas pedal or drive the car hard.

I will listen with the stethoscope but so far there i sno knock on idle or just reving the engine.

I start to wonder if one of the valves might be just "kissing" the top of one piston. The head was skimmed when the head gasket was done.. but then again the knock was there before the HG blew.

There is a sound track here. Alfaknock - YouTube

The knocking is a low pitched thudding sound best heard toward the end.

Bill
Bill,
1/ Did you do an oil change on it (when you changed the big ends)??
The previous owner may have 'accidentally' put in thicker oil.
2/ I presume that you checked visually the piston tops and valve recesses and cylinder bores when you did the head gasket job. Did you see anything unusual?
3/ Does it knock in every gear?
4/ Are you absolutely certain the cams and followers are OK?

From your sound tracks it is a more solid knock than I had expected and sounds to be a reciprocating part rather than a rotational one.
I still feel that using a stethoscope to pin point the location is your best bet for a diagnosis.
Peter
 

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Ok, I am prepared for the derision on my two penny worth but, these sounds are always difficult to trace and nail down. The first thing I would do is take the drive belt off and listen, there is an awful lot going on there, discount the easy and obvious first, it drives so many things that can fool you. To be honest, I have not experienced little end bearing failure for many years. Good luck.
 

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Discussion Starter #11
Bill,
1/ Did you do an oil change on it (when you changed the big ends)??
The previous owner may have 'accidentally' put in thicker oil.
2/ I presume that you checked visually the piston tops and valve recesses and cylinder bores when you did the head gasket job. Did you see anything unusual?
3/ Does it knock in every gear?
4/ Are you absolutely certain the cams and followers are OK?
Yes they did an oil change when they did the big ends and I have done another since then. The old shells showed only slight cavitation but were actually ok. The head was skimmed, valves checked and piston tops cleaned. It knocks in every gear (and also in neutral with a hot engine, as the sound clip shows) but today I was trying to hear if the knock followed engine revs or driving speed. Difficult to tell but I think it follows engine speed. I plan to check the cams and followers as well as check that the cam timing is to spec.

The mechanic who did the top and changed the cambelt at the same time said something like "I adjusted the timing a touch as I thought it idled smoother that way" Not sure if he advanced or retarded it via the cams or by some other way. However the knock was there before the head gasket and cambelt was changed.

If anything the engine is a bit sluggish at low revs, like under 2000 rpm. The power really kicks in at 3000 but that's typical of the TS.

I will use the stethoscope on the weekend and update when I check the cam timing.


Bill
 

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The mechanic who did the top and changed the cambelt at the same time said something like "I adjusted the timing a touch as I thought it idled smoother that way" Not sure if he advanced or retarded it via the cams or by some other way. However the knock was there before the head gasket and cambelt was changed.

If anything the engine is a bit sluggish at low revs, like under 2000 rpm. The power really kicks in at 3000 but that's typical of the TS.

I will use the stethoscope on the weekend and update when I check the cam timing.


Bill
Hi Bill,
I think that it is significant that your mechanic may have altered the 'timing' to improve the tickover!
There must be a problem for him to have chosen to do this. Did he check the cylinder compressions?
By the way, did you use an Alfa dealer or a local garage to do the work?
If a local did he have the equipment to set up the cam timing correctly?
I recollect that my twin spark was smooth on idle so check your exhaust (at the manufacturers idle speed there should be even and distinct pulses at the tailpipe)

This is quite relevant because, although you confirm that the engine has knocked since you bought it, it seems now that the above may be another symptom of the fault.

By the way, 2 oil changes in 9 months? Was the oil dirty when you changed it yourself??

Best wishes with your investigations this week end. You will need cam clamps to check the timing properly.

Peter
 

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Discussion Starter #13
Getting back to this again. I did a compression test today. Engine at operating temperature. Injectors relay out. Throttle fully open. I got 220psi on 1,2 and 3 cylinders and 213psi on number 4. Reading through other posts this looks very high if anything.

My theory for the knocking is that the head has been skimmed too far and when the engine is warm and everything has expanded with heat then one of the pistons is touching something. Maybe the head or a valve.

On another note.. I put way too much oil into cylinder 4 to do a second test. Now I am afraid to start the engine in case something blows with having too much oil in there. Any thoughts on that?

William
 

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I may have misunderstood but you got those readings having put oil in each cylinder or not ?
On the last point if there is residual oil either leave it til it empties or you could try a trigger mech and tube from an old kitchen cleaner bottle to pump it out
 

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Discussion Starter #15
I may have misunderstood but you got those readings having put oil in each cylinder or not ?
No oil in the cylinders for those readings. I didn't get a second reading on number 4 with oil as I had put way too much oil in. Got it all cleared out now though.

William
 
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