Alfa Romeo Forums banner

1 - 11 of 11 Posts

·
Registered
'91 164L 3.0 V6 12V 5-speed
Joined
·
81 Posts
Discussion Starter #1
The S piston has higher compression ratio compared to L version but are the piston weights different? Rods seem to be the same between these models.
 

·
Richard Jemison
Joined
·
7,517 Posts
Yes but it won`t affect balance. Reciprocating weight IE: crank, big end of the rods and the flywheel and front pulley on the V612 motors are the things that are critical. All pistons in as set are balanced. In any event true balance is only at a particular small range of RPM.
 

·
Registered
'91 164L 3.0 V6 12V 5-speed
Joined
·
81 Posts
Discussion Starter #3
Swapped the crankshaft from a S engine (bought new without flywheel or pulley). I’ve been asking local machine shops if I should balance this, and they said that only if pistons are weighed differently.
 

·
Premium Member
Joined
·
27,090 Posts
Rotating mass - front pulley, crankshaft and flywheel usually are balanced as an assembly if you are building a highly spec engine. However, easier said than done. I have mixed cranks, pulleys and flywheels for a daily driver without serious vibrations.
 

·
Richard Jemison
Joined
·
7,517 Posts
If you have a 3.0 liter flywheel and front pulley they are the same regardless of S or whatever.
If you have a thick flanged 2.5 liter I can lighten it and balance it with a fixture designed to return the 2.5 after lightening to the correct "offset" balance.

A early thin flange 2.5 will not be usable with a 3.0 liter.
 

·
Registered
'91 164L 3.0 V6 12V 5-speed
Joined
·
81 Posts
Discussion Starter #6 (Edited)
I don’t think there would be any problems with it but if there’s any excessive vibrations I really wouldn’t like the take the engine apart third time.

Of course, I understand the necessity of balance when building race engine or so but this car is going to be only a summer car.

The crank is more specifically from/for a SZ/RZ/164S engine which is 3 liter indeed (OEM 96412842)
 

·
Registered
Joined
·
316 Posts
I believe all 3.0 cranks are the same. If it's new don't mess with it. Did it come with the correct color coded bearing shells?
 

·
Registered
'91 164L 3.0 V6 12V 5-speed
Joined
·
81 Posts
Discussion Starter #8
Pretty much. Flywheel bolts were different, though.

New crank with red bearings. Machined to fit perfectly, the main line was off and caps were all over the place. Hopefully this crank saga is now finished.
 

·
Premium Member
Joined
·
27,090 Posts
Now do you have correct coarse or fine thread flywheel bolts to match the new crankshaft. Early ones had M10 coarse thread later ones have M10 fine thread and different lengths for 5-speed or automatic transmissions.
 

·
Registered
'91 164L 3.0 V6 12V 5-speed
Joined
·
81 Posts
Discussion Starter #10
M12 you mean? That's what I got and what fits. Old crank had coarse thread, now it's fine. Got new ones quite easily. Is there different tightening torque for the fine threaded ones?
 

·
Premium Member
Joined
·
27,090 Posts
OK M12 my bad memory. I think the torque is the same in the shop manual.
 
1 - 11 of 11 Posts
Top