Can the experts here chime on the following: (1) when cold the engine compression is ~125 PSI across all cylinders (not great, but acceptable >100 PSI?) (2) when hot, one cylinder is dropping to ~65 PSI (3) leakdown is poor hot or cold Engine runs but poorly. Any thoughts on what the issue may be...thanks!
Tell us more Which vehicle ? Just one cylinder is bad in leak down ? Did this just happen or was the car sitting for a long time ? Tell us what made you do the tests in the first place and when was the last time the car ran well ..anything transpire between good to bad running car Hope that helps us help u Sent from my moto g(7) using Tapatalk
This should tell you a lot just by listening for where the air is escaping to from each (bad) cylinder: out the intake system = bad intake valve; out the exhaust system = bad exhaust valve; out the crankcase = bad rings.
Valve clearances might be to tight. Just barely OK when cold, but not allowing the valves to fully seat when hot due to thermal expansion.
Car is a 365 GT4 2+2 which has sat around for a while...assume history unknown. Makes this more difficult. Only one cylinder is bad on compression when hot, I'm going to have the mechanic re-do the leakdown on all cylinders when hot - I assume leakdown @ hot is more important than cold?
I was poking around online and found a simpler procedure to just add compressed air into the cylinders one by one through the spark plugs and with each cylinder at TDC to watch for air out through the intake (intake valves issue), exhaust (exhaust valves issue), oil tank/cap (rings issue), and coolant reservoir/cap (gasket issue)? Is this reasonable? Should the engine be run to temperature and then this test done? Maybe start with it cold and run the test and then do with it hot? Thanks again.
This is how it’s done on small airplanes with reciprocating engines. It’s a great way to tell what the problem is in the low cylinder. I would do it again with the engine warm. If the same cylinder reads low again, go drive it hard for a while, and re-test, before you tear it apart. It could be a piece of carbon stuck under a valve or in the rings. Sent from my iPhone using FerrariChat.com mobile app
Sure (but, for me, using the leakdown tester is just the easiest way to connect an air pressure source to a spark plug hole ). +1 to Extreme1 comments.
Well you have evidence something not right. But you have to make sure the conditions are right to have potential good running. At this point I would make sure the assembly marks are on or nearly on. That ensures timing is acceptable. Every ferrari will run ok set there. Then I would make sure all tappets are in spec.. then do your compression and leak. Honestly doing this with hot motors is problematic. The motor is not as hot by the time you get to cylinder 12. Battery condition after cylinder 12 can be suspect too. I do not think comp or leak is much different hot or cold. Once I got data if bad I'd be looking at condition of valves with manifolds off to see condition. A bunch of coke fouling means you really need to clean that off and check comp leak again and give one last chance that you have a motor that might be salvaged. If the chambers look good you are in for a rebuild. If you fail comp leak again you rebuild.
See a picture of my 400i cylinder head. You can see a Crack in the cylinder dome that starts between the two valve seats and expands toward the exhaust port. The big crack on the exhaust port is "always leaking" while it takes some heat so as to make the cracked cylinder dome leaky. https://www.ferrarichat.com/forum/threads/engine-rebuild-suggestions-tips-needed.633958/page-2#post-147630733 Here the diagram of a 400 head. That's basically the same as yours, except for the injector, so you can get an idea of how thin the head is: This is a major drawback of the 365/400 compared to the daytona (apart from the long timing chain): the side mounted carbs do require a tight turn on the exhaust port. So all the exhaust heat puts a great deal of stress here. To crown it all the "wall" is extreemly thin: this is good for enhanced cooling, but not so nic for long term reliability. This being said I must say, this is the first time I would see this in a 365. The 365 is usually running rich (even richer than 400 carb), unlike the injected cars that are lean (i.e more heat in the dome).
So a crack in the head (or block?) could be a worst-case scenario which we should look at as well. I assume the heads can be tested if taken outside the car by a specialized shop? Would there be a way to test at hot and cold? Are these issues repairable (in the worst case scenario)? Thanks!
If the engine is runable, there is also a simple tester that looks for CO gas in the cooling system at the radiator filling cap that would detect a crack, or a head gasket, leaking into the coolant system.
First of all, please do perform the suggested cheap tests that were provided to you (CO² test, valve clearance test). Once these diagnostics are performed you may consider to remove the head and perform more expensive repair. When pressure tested on the bench, this is usually the cylinder dome that is put under pressure, not the exhaust port. This beaing said a crack on the exhaust port is highly visible and in an area so thin that as long as it is visible it has to be fixed. A crack in the dome may or may not leak. You did not ask, but "Block Seal" and other magic repair liquid do not work on our heads... Cost : from memory 1200€ to weld the head + 30hrs of work. Biggest challenge is to find a machinist that can properly weld the head. These cracks are hard to fix as the exhaust port is "thin" so you will have to crush the dome significantly in order to reach a strong area that can sustain the fix. If you can add 10~20hrs to the bill, this is a good opportunity to change the timing chain, replace the valve guides, adjust timing and adjust valve clearance. So all in all this is a good opportunity to tune the engine and restore its performance. Please note that: 1) if coolant is leaking in the cylinders, you may damage the cylinder rings and liners and bearings, which is much more expensive. 2) in order to avoid overheating issue you should follow the owner manual guidances and use the right amount of coolant (i.e not too much): unlike the 400 and 412, the 365 does only have two cooling fans and it was not meant to be used with -35°C coolants (these do not evacuate as much heat as -10°C coolant). Image Unavailable, Please Login
Too much clearance and the engine gets noisy (plus you do not open the cam enough, i.e you loose power). Too little clearance and when the engine expands due to heat, there is not enough clearance so as to properly close the valve (i.e leaky valve which is a big no-no). Should be checked quite often in our cars. In order to perform the adjustment, you just open the 4 valve covers which will let you access the camshafts. While the piston is in the proper position you check with a gauge the clearance between the camshaft lobe and the valve shims. If the clearance is not within spec you just have to use another (smaller or bigger) shim. In order to replace the shims you can buy a special tools from Hill Engineering (superformance.co.uk is their major distributor).
You should grab the workshop manuals (a.k.a WSM) and Owner Manual (a.k.a OM) from Erwin's blog https://www.ferrarichat.com/forum/threads/wire-diagram.564951/#post-145737999 https://drive.google.com/drive/folders/0B8teqGKDb3gkdmxtWFBrX0xXYTg Abstract from Workshop Manual Section B36 Image Unavailable, Please Login Many knowledgeable enthusiasts on the dedicated 365/400/412 FerrariChat Forum: https://www.ferrarichat.com/forum/forums/365-gt4-2-2-400-412.89/
I’m no pro, and I have no experience with this particular engine. With that said, I’d do a wet compression test on that cylinder. Should help differentiate between rings and top end issue. Sent from my iPhone using FerrariChat
