The lowdown on leakdown testing a 330

Discussion in 'Technical Q&A' started by Smiles, Jan 12, 2004.

  1. Smiles

    Smiles F1 World Champ
    Lifetime Rossa Owner

    Nov 20, 2003
    Pittsburgh, PA
    Full Name:
    Matt F
    Hello. I'm in the market for a 330 GT 2+2. I'm coming up with some great leads, thanks mostly to Kerry Chesbro's 330 GT registry. I'm going to take the next few months and narrow down the field. And also see what crops up in the spring. Hopefully, I will have a new V-12 by May.

    I plan on doing (or, more probably, paying for) a compression test and a leakdown on any car I seriously consider. What should I look for in the results? What's the standard compression for each cylinder in a 330? What pressure would tell me to keep looking? What kind of deviation between cylinders is OK and isn't OK? Anything else to watch out for?

    Also, is there somewhere on the engine that I could easily attach a vacuum gauge? Wouldn't monitoring one on a running engine be pretty good information, too?

    Thank in advance, guys. I'd rather know what I'm looking for ahead of time.

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  3. Smiles

    Smiles F1 World Champ
    Lifetime Rossa Owner

    Nov 20, 2003
    Pittsburgh, PA
    Full Name:
    Matt F
    OK. Here are some specific numbers from one test.

    1 2 3 4 5 6
    155 153 157 156 148 158
    7% 7% 6% 6% 12% 6%

    7 8 9 10 11 12
    145 144 141 140 148 150
    12% 10% 12% 10% 10% 7%

    Around 60,000 miles.

    Do you guys have any comments on the compression numbers? What should I make of half of the cylinders having 10% or higher leakdown?

    I know that there's information in the archives, which I've been searching and researching, but I was hoping you could give some feedback on this specific test.

    Thanks again,

  4. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    Full Name:
    I have no direct experience with a 330. I have experience with my 308 which (only) might be instructive.

    Leakdown: 7 cylinders ranged from 4 - 7%; one cylinder (#3) 12% - likely rings was the LFSC assessment. LFSC also opined "better than a lot of newer cars" and "we generally start to advise something more major at 14%".

    Compression: 2 years later. Continental master tech. Warm car (sorry, don't recall if this is 165 degrees or 185 degrees). Crank until no further compression. All 185 to 195 (stock cams). I am told the absolute number is less relevant, variation is more relevant and +/- 10 psi from the midpoint is "good" or acceptable.

    My assessment of your numbers, based on feedback to me: some wear. Not enough to pull the motor apart at this stage. Go and drive it.
  5. Ferrari_tech

    Ferrari_tech Formula 3

    Jul 28, 2003
    Full Name:
    Malcolm W

    We have just finished overhauling a 330GTC engine that had 70,000 miles on the clock, we replaced the following main engine components that would result in low compression and or high leakdown data :-

    Cylinder liners
    Pistons complete
    Valves and valve guides

    Although the figures you have posted are "unbalanced" and not what they should be, you must bear in mind that the engine is over 35 years old and one should expect some variations.

    The bottom line is it's not that bad for an old car.

  6. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    Bank 1-6 is completely servicible. Bank 7-12 is in need of at least a top end rebuild. You are down 10% in compression (compared to the better bank) and you are above 10% leakdown across the bad bank.

    An engine in this situation is serviceble (barely)
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  8. Tony Fuisz

    Tony Fuisz Karting

    Nov 5, 2003
    Bethesda, MD
    Full Name:
    Tony Fuisz
    So now its settled. I'll look at home for the results from my 330 when it was PPIed at Continental Ferrari. The tech there (highly recomended from the guys at FOW) said they were reasonable numbers.
    My guess is that there are not going to be many 330 s out there that just had total overhauls. So what you're probably looking for is the least worn-out one you can find. Mine drives fine, doesn't smoke, and is fast enough to get tickets. I personally don't care if it currently dynos out at the 1964 listed power levels. I'd feel totally different about a 355 or something like that. OR, find one with serious engine issues thats cheap and make that the first order of business.
    I still think that the best you can do is find one someone is using regularly-and that has most of the cosmetic stuff at least on the car. I bet a top end valve job is easier to do that replacing a headlight bezel.
    They are really nice cars to drive.
  9. rudy

    rudy Formula Junior

    Jan 13, 2004
    Los Angeles California
    Full Name:
    Rudy Hassen
    My '64 330 GT 2+2 can still spin/chirp the tires in the first three gears. That ain't bad. Michelin "Green" environmental tires, not bald. What a great old crate! Bruno of Modena Sportcars rebuilt my engine. Anyone know what he's up to?
  10. wax

    wax Four Time F1 World Champ
    Lifetime Rossa

    Jul 20, 2003
    Full Name:
    Dirty Harry
    Smiles, are you going for Series I (dual headlight) or II (single headlight)?
  11. Smiles

    Smiles F1 World Champ
    Lifetime Rossa Owner

    Nov 20, 2003
    Pittsburgh, PA
    Full Name:
    Matt F
    Thanks, guys, for your responses. Thanks especially to Mitch for a good analysis of the numbers.

    This is a car I'm thinking about buying, so I think I'm going to pass on it. Although I'm sure that MW's cure of new cylinder liners, pistons, and valves and valve guides would work. Unfortunately, it would also blow past my budget.

    Tony, I'd really appreciate to hear the numbers you got that were "reasonable". Thanks also on your advice on what to look for.

    I've already found a fairly decent Series I (a different car), but I really prefer a Series II for the pedals, the 5-speed, and definitely the single headlights.

    By the way, can anyone give me some idea of what the power steering feels like on these cars? I'm familiar with the way a 308 feels, and my only other point of reference in a 1960's car with power steering is a 1968 Buick LeSabre convertible. I sure hope that a 330 GT feels more like a 308 than a Buick!
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  13. ferrarifixer

    ferrarifixer F1 Veteran

    Jul 22, 2003
    Full Name:
    Phil Hughes
    I wouldn't pass on that car so readily.

    Firstly, how is the rest of the car????

    Secondly, those results are really not too bad. 10% is fine, 12% is really not much worse, and I'd even venture to suggest that if the same test was done the next day the results would be slightly different. Better or worse........!

    Thirdly........once a percentage leak is recorded, it is then the duty of the tester to comment on where the leak is to......most leakdowns of around 10% are past the rings into the crankcase, audible through the oil filler or ventilation system. In which case a top end overhaul will serve no purpose.

    Most leaks of valves or head gaskets are considerably more than 15% in my experience. These are audible through the carbs/exhaust or cooling system.

    Drive the car briskly for a while, get someone to follow to observe smoke signals and general handling, then do the leak test again.

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