My Alfa Romeo 33 rebuild - FIRST TIMER

[Guy Croft]

I DON'T THINK IT'S THE TAPPETS

GC

[Brit01]

Guy,

You don't think it's the tappets or bore clearance? Tappet could be good but clearance between bore and tappet maybe just too great when it gets hot?

Sorry just to be clear on your opinion.

Thanks

Chris

[Guy Croft]

nah - you've been over and over the tappets. I reckon it's a small end.

G

[Brit01]

I did think about the small end - piston 3 did have the most wear and is prone to damage more than the other pistons. This would create a clicking sound when very hot to the increased clearance?
But I can't hear anything above idle when accelerating BUT do hear rattling under compression braking.

Can I post a youtube video with a clear sound of it once I record it again this weekend?

See what you think?

Well the heads and cam supports need to come off anyway to get to the small end bearing. Bit of work, oil sump off, piston out etc. workshop would need to press a new one in to fit the current pin.


Best regards,

Chris

[Guy Croft]

Are the wrist pins press-fit in rods or full-floating (bush in rod)?

G

[Brit01]

Not sure but here's a photo (press fit I assume) :

[Nobby]

I was just curious - and looked on the Alfa Romeo eper online (its not hard to find a copy via google) and ALL of the Alfa 33 look like they have bush in rods??

[Brit01]

Thanks Nobby. I wasn't sure of the difference. But the small end bearing is pressed in of course so I need to take it to a workshop.

Yes just found this good explanation:

Full Floating
- The full floating type of wrist pin retention is probably the best of all. The pin is kept in place with either a plastic button in the end of the pin, or more commonly, a snap ring. This makes bearing surfaces in the connecting rod, and the piston; and gives three times the bearing surface of the piston locked type. The full floating type is also easy to disassemble and assemble. All you have to do is remove the snap ring. No press is required. Always
replace the circlips, or buttons, on re-assembly. Never try to re-use previously used clips, or buttons.


Chris

[Urbancamo]

They are full-floating pins as picture shows circlips that fold gudgeon pin in place.

[Brit01]

Wondering now if it's possible to remove the rod/pin from inside the crankcase underneath.

Slide the piston in just enough to show the clips, pop them off and slide the pin out, leaving the piston in with rings still compressed.

mmmmm... depends on the room between the crank.

[Guy Croft]

No way. Pull the pistons and rods as an entity and give them a good going over. Don't split them. It could be loose pin-piston or pin-rod. I don't go for re-using pin clips but if you must be sure to bend them into a circle before refitting.

While you're about it check piston skirt-bore clearance with a feeler gauge.

You can get a good look at all the bearings while you do this but do Not remove them from their housings.

G

[Brit01]

Thanks Guy.

Ok if I'm going to go ahead and inspect the small end bearings I understand I need to do this:

Right head off.

Oil sump off - rod bolts off.
Feeler gauge down the side of the piston to see the clearance. (Compression we know is very good already)
slide piston 1 and 3 out carefully.
Inspect it as a whole, feel for any excessive movement.


Remove clips and slide out pins/rod.
The piston/rod/pin will need to be taken to a workshop to be measured and new small end bearing pressed in I believe (or new rod also if the rod/piston wear is evident but this is less likely I believe).


Regards

Chris

[Brit01]

Before I attempt this I want to do another final check by removing the spark on the suspected piston when the sound appears.

But I need to short the spark to ground first.

What is the best and most convenient method to do this?


This is a good description of a small end/pin wear noise:

A wrist pin knock has a very unique sound. And this sound will be different depending on how many of the wrist pins are making the noise. If all the wrist pins are loose, this will sound like an overwhelming rattling inside the engine.

This sound is described as a double knock, because it will cause a noise at the top of the piston travel and when the piston changes direction it will make another noise. This noise is most notable when the engine is idling and the engine is also hot.


Thanks

Chris

[Guy Croft]

Do not take the pistons off the rods. Do not take the rings off the pistons. Keep them all assembled. The best way to check a wrist pin is with it fitted - rock the piston and make an assessment of how loose it really is.

I don't know if I mentioned it before but it is possible the noise may just be 'piston slap' - excessive bore-skirt clearance. In that case however the noise is usually worse when cold before piston warms up. I would however want to know what the clearances are while it's apart. To measure it effectively follow my photo above. You put the gauge in the bore and slide the piston onto it - the true measurement will be about 1/2" down the bore at the middle of the piston skirt (they are oval).

G

[Brit01]

Hi Guy,

99.9% sure it's not piston slap. The engine runs really quietly and smoothly until the temperature gets really high. (but if I have the piston out of course I'll measure the clearance)

I am actually going to change the radiator sender unit. I believe mine was changed at some time and a 80/90 unit was put in. I was just recently made aware of this when I changed the radiator a week ago and cleaned off black paint from the sender unit and saw the stamping on it.

90 is too high for a boxer running in a hot climate and with our traffic conditions.
also 80 is a bit low. Thermostat begins to open the water flow at about 83-86 and so the fan should be kicking in about 86 or so. Some in hot countries have even out 83 degree senders in and keeps the engine more stable.
Ticking starts when then fan has been on for some moments so the temp is pretty high then(above specs of the thermostat opening).


I'll be doing a 60km round trip to work today to see how it performs and tomorrow hopefully pick up a new water sender and try it out again.

thank you

Chris