1990 Ferrari Testarossa piston clearances

Are you a machinist looking for boring specs?

Where's @Rifledriver when you need him??

Ray

 

Both are shown in Tab. 4 on page B17 in the TR WSM.

 

Myself, I usually like to run my ring gaps a bit larger than the standard .004 to .0045" x piston diameter numbers you see floating around. I would much rather run an additional .010" or even .015" on the gaps than butt the ends of my rings should the motor be pushed extra hard on a long hill or track day or something. A tiny amount of extra blow-by isn't gonna kill anyone, but binding the ring ends could cause nasty internal damage if you aren't careful. Not everyone might agree with me, but I feel like it's cheap/easy insurance when building any high performance motor.

Just my 2 cents.

I also usually like to run about 10% more gap on the 2nd rings in order to allow blow by gases from the top ring to escape more rapidly and prevent unsettling of the compression ring(s).

For cylinder wall clearances, a lot has to do with the alloy used in the pistons and also if you are employing any sort of modern coatings (especially with regard to side skirts). Coating on the skirts can add up to .0008" in a lot of cases - but again it depends if you are using stock pistons or something custom.

Are you the person boring and/or replacing the liners?

Ray

 

Also, please don't take offense to this Hoh, but usually these aren't the type of questions experienced engine builders need to ask on public forums. Are you just curious what Ferrari specifies or is this your first motor you've ever tackled?

Ray

 

My mistake -- see the text on page B19 stating to "check the end clearance is within the values indicated in fig. 16." (which is on page B16). Although it's not clear what the diameter of tool ALZF 08202 is.

 

You just never know what you might find inside a motor huh?

I rebuilt a motor on my pickup a while back and someone had accidentally installed STD size rings on short block that had been bored over .020" - fun times.

Ray

 

That was the rule of thumb back in the dark ages. Mahle rewrote that book a long time ago. Ring gaps are dictated by the ring manufacturer, not the engine manufacturer. Same with piston clearance. Mahle was OE and no one else has been able to run as tight as they do and none of those parts are available anymore.
The specs in the book are as clear as can be. My book is 100 miles away or I'd look it up.

 

Its muddy and I canotread a thing. In any event those numbers do not matter. They apply only to the OE parts that are NLA.
The replacements supplied by Ferrari I would never use even if I was willing to pay the price.

I can tell you this because I have done them much more recently. The Mahle rings used in the 355 have an end gap od .imm. .004 inches. The skirt clearance is similar.

What happened to the engine? TR motors typically go multiple hundreds of thousands of miles.

 

I'd assume that the ID of Tool ALZF 08202 is the same as nominal ID of the cylinder liner, but don't know that for sure. This is how to "read" page B16:
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The specification is a range -- meaning anything from 0.20 mm to 0.35mm is OK for a new build (and Ferrari is looking to have as wide a range as possible to keep costs down; whereas, a custom engine builder might choose to aim for smaller range, or one end of the range, and use more time to do so). Remember, this is an Iron ring in a (mostly) Aluminum liner, not an Iron ring in an Iron block (i.e, the Aluminum liner grows more in diameter with temperature than an Iron block).

 

What rings are you going to use? As Brian mentioned above, typically the end gap specs are provided by the ring manufacturer. Different alloys have different coefficients of expansion, etc. Often times the material used on the top ring is different than the 2nd ring (at least w/ modern rings - not sure what Mahle was doing in the 80's).

I'm attaching spec sheets for the rings I use here (Total Seal) and the pistons I used recently (Keith Black). As you can see, there can be a lot of variation based on the specific ring, ring location on the pistons, piston alloy, etc. At least based on these two charts, a gap factor of .0040" would be under the min specs slightly.

You mentioned you have OEM pistons and liners. What rings do you have over there?

Ray

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You might enjoy this video also. They provide a pretty good discussion of ring gaps as I recall.

Ray

 

So now you guys know better than Mahle. Thats hilarious.

Mahle made the liners, pistons and rings. The ring material is designed to match the expansion rate of the liner. Their new rings are fit even tighter.
The gap spec is .008 to .012 inches. And it should be .008 on the compression ring and .012 on the scraper ring. As I said 355 is .004 inches on compression ring. Those are correct numbers.

If you have current production Ferrari replacement rings they are not Mahle. You need to know what you have and you need to do a far better job of educating yourself on modern auto technology.

 

Are these item NOS [new old stock] parts or something you just bought recently online or via a Ferrari dealer or something?

Rings made today are radically different than rings made back in the 80's or 90's.

Listen to what Brian is saying here.. he's the expert in this area.

Ray

 

Whoever sold you these parts, should provide you with the proper guidelines.

That's the reason why you pay the Ferrari premium.