Gentlemen (and Ladies), Please excuse the cross-posting across vintage and technical forums. I just received the following compression and leakdown data for a type 209 engine (e.g., 1960s 330 GT). Any opinions and rationale for their interpretation would be greatly appreciated. I know that there have been a few other posts like this, but as every set of numbers is a bit different, I'd like to hear people's reactions to these particular results. Thank you in advance. cylinder 1: compression = 155; leakdown = 8% [apparent source, crankcase] cylinder 2: compression = 165; leakdown = 10% [apparent source, crankcase & minor exhaust valve leak] cylinder 3: compression = 155; leakdown = 13% [apparent source, crankcase & exhaust valve] cylinder 4: compression = 140; leakdown = 24% [apparent source, crankcase & minor exhaust valve leak] cylinder 5: compression = 160; leakdown = 18% [apparent source, crankcase & exhaust valve] cylinder 6: compression = 155; leakdown = 20% [apparent source, crankcase] cylinder 7: compression = 158; leakdown = 20% [apparent source, crankcase] cylinder 8: compression = 155; leakdown = 12% [apparent source, crankcase & minor exhaust valve leak] cylinder 9: compression = 145; leakdown = 18% [apparent source, crankcase] cylinder 10: compression = 140; leakdown = 4% [apparent source, crankcase] cylinder 11: compression = 155; leakdown = 24% [apparent source, crankcase] cylinder 12: compression = 150; leakdown = 20% [apparent source, crankcase]
Was the compression test done hot or cold? As it stands you seem to have slightly more than 10% variance between "best & worst" on the cylinders. 10% seems to be the accepted norm but not sure whether its relevant for an engine like yours. The best guy to ask would probably be Tom Yang who occasionally visits these parts - otherwise check out his website at www.tomyang.net . If he doesn't know then he can ask his mate the French engine guru. rgds Iain
Compared to a GTC that I just saw, your results look great! The best we got was 110. Dr "Buy it fool" Who
Ditto the question on temperature. Leak downs in the 20s are high, but what was the norm for the models? Philip
I think the simple answer is "Lots" !! You will get completely different results between hot & cold. Warm engine compressions are generally much higher than cold. I.
I'm looking at these readings, and I have to say right off this just dont look right : cylinder 1: compression = 155; leakdown = 8% [apparent source, crankcase] cylinder 2: compression = 165; leakdown = 10% [apparent source, crankcase & minor exhaust valve leak] cylinder 3: compression = 155; leakdown = 13% [apparent source, crankcase & exhaust valve] cylinder 4: compression = 140; leakdown = 24% [apparent source, crankcase & minor exhaust valve leak] cylinder 5: compression = 160; leakdown = 18% [apparent source, crankcase & exhaust valve] cylinder 6: compression = 155; leakdown = 20% [apparent source, crankcase] cylinder 7: compression = 158; leakdown = 20% [apparent source, crankcase] cylinder 8: compression = 155; leakdown = 12% [apparent source, crankcase & minor exhaust valve leak] cylinder 9: compression = 145; leakdown = 18% [apparent source, crankcase] cylinder 10: compression = 140; leakdown = 4% [apparent source, crankcase] cylinder 11: compression = 155; leakdown = 24% [apparent source, crankcase] cylinder 12: compression = 150; leakdown = 20% [apparent source, crankcase] First off, #9 only gives 140 psi, yet only shows a 4% leakage, yet #2 pumps up 165 psi and shows a 10% leakage? You have a 24% loss on #11, which pumps out 155 psi, yet #'s 1, 3, and 8 pump the exact same compression pressure and vary around a 10% loss. I also dont understand the description of the word "apparent" when regarding the location of loss on a leakdown test. You can easily hear where the air is escaping and its not apparent, its a fact. If you hear air in the oil filler cap hole, its leaking past or through the piston, if you hear in it the tailpipe, its exhaust valve leakage, and if its at the air cleaner, its an intake valve leaking. I could see large carbon deposits on a leakey cylinder having higher psi on a compression test, but you are all over the map on this, and without seeing your car I would have it redone a few more times around and triple check it. As far as doing a test on a warm engine, the pistons expand when hot and fill the cylinder whereas when cold that are shrunk and tend to wobble more and give less than correct readings as air slips around the wobbly rings. Run it hard, test it hot. YMMV.
I agree with your confusion; indeed, it is part of the source of my question, to see if others can help me make sense of these readings. Readings for cylinder 10, for example, certainly caught my eye too... I remain interested in others' interpretations, both of the "oddness" of some of the pairs of compression/leakdown findings, as well as what they mean, if accurate. Specifically, it makes logical sense to me that compression and leakdown numbers should be significantly, and positively, correlated -- is that necessarily the case, though? If not (as is the case here), why not? I'm hoping to learn from others, and I appreciate everyone's input. I'd love to hear more... I don't know if the test was done cold or hot, but will find out. Finally, by "apparent" I meant only that according to the mechanic, this was the source of the leak (no doubt deduced by him as you indicate).
I read this earlier and did not have time to respond and in the interim Paul brought up some of my concerns. #4 and #10 are ringing an alarm bell. While having the same compression and different leak down is quite common it should not be different to the tune of 20%. If we consider the possibilities that either the equipment was faulty or the test procedure was faulty we are all wasting our time and this set of numbers is worthless. If we accept them as accurate there is a problem. There are several possibilities including but not limited to, Tight valves to the point of almost no clearance on #10, bad cylinder scoring on the lower part of #10 as you would experience with a failed wrist pin retainer and #4 just having more advanced wear than 10. I could probably dream up more scenarios if I wanted to devote more time but the simple fact is, for whatever reason we do not have the whole story. The problem with trying to analyze this data is we did not collect it and there are many nuances in collecting it that will tell a much greater story. It is as though I have an Xray and am talking on the phone to you, a Doctor, and I am trying to tell you what I see so you can tell me what is wrong. Probably won't work unless we are looking for a compound fracture or something of a similar nonambiguous nature. In taking a compression test for example if the compression comes up slow but steady with each stroke of the motor it means one thing, if it comes up strong but unsteady it can mean another. During a leak down test I start with no pressure on the input gauge and slowly crank it up watching the cylinder side. If the input rises much faster and suddenly the cylinder side catches up it is probably a sticky compression ring. No problem, an Italian tune up will probably fix it. How do you record that in this chart? That is why the person doing the testing has to be dialed in, there can in some cases be a lot of interpreting to do. Taken at face value I would have to say pass. If I had done the test and knew how these numbers came to be, my answer may be different. What did the mechanic that did the test have to say?
oops, i meant negative correlation earlier... And, the input has been very useful so far. As for the nuances of these tests, you bring up some worthwhile points, Rifledriver. Of course, not having done the test myself, I can't address them specifically. So far I have only the data you're also seeing. I was read the results over the phone only -- I will see the written report to confirm the numbers soon (it's possible, but unlikely, that the numbers were read to me incorrectly), and chat with the mechanic further to see if I can get some much needed clarification.
Additional information after speaking with the mechanic who performed the tests: - all tests were done with a cold engine - all tests were dry, with some followups done wet to confirm source of leakage (crankcase versus valves; if numbers improved from dry to wet, for example, that indicates leakage source as crankcase, i.e., rings most likely) - attempted to catch readings "as soon as I blasted the air" and to be consistent across cylinders - valve lash checked to confirm that none were sticking and to see that they were adjusted correctly - numbers I reported before were correct That's what I know now...hope the additional information is of value in interpreting the results.
I have no idea as to the background or the ability level of the mechanic and I do not want to sound as though I am showing disrespect but in a case like this the guy on the ground should either have some answers or be able to come up with some. You simply do not get a situation where you have a single low cylinder with almost perfect leak down (10) and the cylinder next to it (11) have good compression with six times as much leakage without explanation. 140 is ok and 4% is great. 155 is pretty good compression and 24% is lousy leakage. Does not make sense on it's own. Verifying that test on the internet is impossible but I do not trust the results. As I said we are not getting the whole story and your mechanic may not be either. If you are rolling dice on a $25-30k engine you should be paying for the best advice you can get.
Brian Does any result have validity when done on a cold engine? As a minimum shouldn't he repeat the test with a warm engine? Philip
Can someone explain to me how how a leakdown test is conducted? What's this about air pressures & input side & cylinder side? I'm only familiar with the old "screw-in compression tester" down the plug hole and cranking the starter for each cyl in turn. What these tests & Brian's comments appear to refer to is some external pressurising unit, so I'm lost!
For a 330 type 209 engine these compression numbers look really good......almost too good. Couple that with the mismatched leak downs and me thinks you need to have another test run. Maybe by a known Ferrari or expert mechanic. You might want to take a look at the plugs while you are at it. Light brown or powder gray shows all is well. When there is oil there is trouble. When there is gas/wet means fouling of some sort. And note that these old carb engines will carbon the valves in short order if not run hard enough. That by itself will mess up your leakdown tests. Seems like some more PPI work is in order. Steve Cantera Dudeasaurous
A really good motor will do well hot or cold but to be fair on an older motor with some time on it, it should be done hot.
A leak down test pressurizes a cylinder with a known pressure and measures the amount that escapes the cylinder.
If this is not being represented as a fresh or recent motor I would agree that the compression numbers on their own are fine. If however the high compression numbers with corrosponding bad leakage is a result of excessive oil getting into the cylinder due to bad rings he needs to know that and the guy with the spark plug wrench in his hand should be telling him that.
Brian, your post also refers to both the "input side" and the "cylinder side". Are there 2 gauges involved, and how are they rigged-up? I assume one measures the pressure in the cyl above the piston, but what else is monitored?
Input pressure and it has a regulator to adjust it to the desired pressure. Many of them use a 60 lb scale and the race engine guys like them because they hold the motor to a higher standard. I use one that has a 100 lb scale that will often do a better job of unsticking recalcitrant rings etc. On older motors like this they should not be held to that high a standard, they will never see a starting grid at Imola.
Question 1. Why did you have the tests run in the first place? I have never heard of doing a compression test on a cold engine? Have you searched the web "engine compression test" "leakdown testing engine" Compression: http://www.motorage.com/motorage/article/articleDetail.jsp?id=16170 leakdown: http://www.findarticles.com/p/articles/mi_qa4078/is_200502/ai_n12412339 I have always been told that the engine should be brought up to operating temperature, disarm the ignition, and test the cylinders in firing order. The only contridictions that I can remember hearing from mechanics is that some remove all the sparkplugs to conduct the test and a few others remove one sparkplug at a time. A good mechanic may be able to do a leakdown test on a cold or non-running engine and tell something about the general condition of the engine ... Best wishes
I guess I am older than I feel sometimes, but this used to be basic mechanics and I thought all mechaincs knew it. Compression test: Engine hot, all plugs out, ignition disabled, throttle wide open so it can breathe air. Leakdown should be tested the same. Rifledriver, its been a long time since I heard someone mention a wrist pin dragging a cylinder wall, funny how a dumb engine can be so complex sometimes. On aircraft we use 80 psi on the first guage, and using the prop as our turning arm, we allow the motor to turn a bit either side of TDC to both "pop" the rings, as well as see if there is a difference in leakage between TDC and slightly below. I would say at least 70% of all the cylinders we tested would pop the rings, and you could both hear it as well as feel it. I guess if this V-12 were mine, I would test it myself. If I was relying on an independent shop to do it, and I was from out of town, I would use this website, Flist, or something comparable, and ask for some local help. If these numbers are accurate, and your doing a PPI, I would either run from the car, or ask for a considerable reduction in its price to account for you to tear into it. I just dont think it would be logical to assume anyone would get by with a top end overhaul on something like that, and besides, its showing loss past some rings. I would seriously get a retest at another garage with a hot engine and a good competent mechanic. I would not be afraid of using an aircraft mechanic for that test either. They have the tools.
