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You are better off doing a leak down test (plus it will be easier on your own), you can probably rent or borrow a tester from your local auto parts store, although they aren't overly expensive to purchase. You'll need a compressed air source as well.


Thanks for the leak down suggestion. I was hoping to not go there due to my lack of experience and short on patience; however it's the right next step. I looked at some youtube and getting to top dead center may be a bit tricky for me, plus it seems I would need to get behind the bulkhead to rotate to get top dead center. I thought my center piece may have been connected separately so I'll see if just that part can be removed. But I did check the next cylinder compression and it was 125. I was kind of hoping to use this compression test guide below as a crude reference, but I can't watch the gauge and crank from the drivers seat at the same time. Or maybe I can rig the gauge to watch from the rear window/firewall while I crank.



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Hi Jan -

You are getting good advice. 

Minor comment...  really have to spin the motor rapidly to get a good compression reading (Which really isn’t that hard, with all the plugs removed and the starter motor cranking the engine).

Regarding a leak down test, you have to figure out a good way to lock the engine at top dead center. When you apply the 125 psi to the cylinder, unless you are at exactly TDC, The engine will want to rotate. In our cars you can probably lock it by putting a transmission in gear, and making sure the rear wheels can’t turn.

You will also want to mechanics stethoscope to listen at the intake runners, the crank case, or the exhaust - if you find that your engine leakage is above specification.

you may be taking yourself down a rabbit hole, by trying to fix/test too many things at the same time. Why don’t you wait till your hardware comes back from the shop before you decide that you need to do a leak down test?

They are not as easy to do as it would appear by a quick skim of the Internet, or watching a couple YouTube videos....


But that’s just my $.02

I do applaud you for getting in there and getting your hands dirty.




Last edited by rocky

Thanks everyone. Yes when I get to the point of a leakdown test I may have someone else over to help with that.  First just trying to test all the cylinders compression. I did hold down the gas pedal to open the valves to do the compression check, but I found it didn't make any difference in the reading when I kept them shut either.  I can rig the compression gauge to see it from the drivers seat, so will just continue to use the key to turn the car over for the remaining cylinders. Battery and strokes are very strong when doing it one by one and after I do a couple cylinders then I charge it over night. So far everything is about 120 except for the first cylinder tested (90). Yeah Rocky I shouldn't have gotten into the stacks/butterflies without doing the compression check first, but I found they were so dirty so I just cleaned them and yes went down that rabbit hole as noted. Didn't send in the valves & linkage yet either. I figure if the engine needs to get pulled I will let a shop arrange all that.

True it would have been best to remove all the plugs and then test, but I'm half way through now so I figure I should follow the same procedure since I am really looking for any strong variance. In my car anyway its a true pain in the crotch because the plug holes are so deep and I'm trying to be extra careful not to cross thread the aluminum or get the compression socket stuck so I can't reach it. Took me almost two hours to fish the tool out of one cylinder and I'm not tightening either. My compression tool comes with a stiff braded hose making things even more difficult to turn it in tight spaces, but its what I have on hand at the moment. So I put the compression socket in first then thread in the hose. In hindsight for anyone doing this, I would think the more flexible rubber hose would be easier to angle & turn. For the spark plugs I found that using a small piece of rubber hose on the end of the sparkplug at least helps me reach further too.

Well here's the overall results of compression test in green and header temps in orange that I recorded a few weeks ago. Looks like cylinder 1 is most likely the culprit and as mentioned leak down would be best to do next on that. Probably need to now tow it in somewhere anyway since I don't have the capabilities of fixing whatever is wrong regardless of the issue. Problem with non stock engines is no one wants to touch them, but at least I can go in the garage and look at it.IMG_E6176


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@rocky posted:

Regarding a leak down test, you have to figure out a good way to lock the engine at top dead center. When you apply the 125 psi to the cylinder, unless you are at exactly TDC, The engine will want to rotate. In our cars you can probably lock it by putting a transmission in gear, and making sure the rear wheels can’t turn.

You will also want to mechanics stethoscope to listen at the intake runners, the crank case, or the exhaust - if you find that your engine leakage is above specification.

Starting to fart around with this again. I found this link on the web below which seems may be pretty accurate in finding TDC other than screwdriver method or other. Would just need a + - gauge. To turn the engine couldn't I just put it in gear and jack up the rear and turn the rear wheels by hand to rotate the engine? I don't prefer jacking just one side of the car because I have the fitted/flush windshield glued in and I have heard jacking one point of the car may have the potential of damaging the windshield or popping out. If I found TDC I suppose I could lower the car and take it out of gear and apply maybe 40 PSI or so from my compressor to cylinder 1 noted above and listen at the various potential leak points by ear or my stethoscope? Thinking 40 PSI to begin with may not rotate the engine but still allow me to listen.


I am sure you could, but a true leak down test requires a minimum input PSI, and uses a calibrated gauge to give you an answer (some systems read in % leakdown, some just “good”, “marginal”, “bad”).

I guess it’s not clear what you might do with the information you collect....  how do you know if your cylinders are truly bad without measuring the leak down properly?  How do you know the status if you don’t check all cylinders and compare them....  although you have some indication based on your compression test. 

If you are able to hear leakage, and (best case) it’s only coming from either intake, or exhaust, or both - I guess there is a chance that the problem could be corrected by removing the heads, and performing a valve job.

I am sorry - I didn’t go back and re-read your thread, but on your compression test, have you put oil in the offending cylinder, and repeated the compression test on the low compression cylinder? If compression goes up, that may tell you if you have a ring sealing problem.

Again - I applaud you for getting your hands dirty. I found a home leak down test on one of my cars was very unsatisfying.... I had too many questions about my technique, and it raised more questions than it answered.  It was probably because it was the first one I did, and I have no experience to compare my results with.

And in the final analysis - there are only really two (maybe three) answers....  leave it alone, rebuild the engine (or maybe redo the heads alone).

Anyway - good luck.  I am trying to be helpful, not discouraging.  Give it a shot.  Let us know what you find.

Keep all those parts organized!



Jan, just a comment but on your notes it looks like 'front' written at the top of the page, if that is indeed the front of the engine then the uppermost RH cylinder (your current #8) is the #1 cylinder and vice-versa in normal terms.  Not critical or personal notes, but if you take it somewhere and talk to #1 cylinder an engine builder will likely assume #1 in the standard orientation.

Thanks for the input. Yes I am still trending toward having someone experienced come over and do the leak down, at least on that one cylinder since it seems that one is showing the most issues. I didn't put any oil in the cylinder and recheck compression because I didn't want to possibly have that alter the leak down test. Yes, that numbering on the sheet was my own numbering to track what I was doing, but when I get it to someone for a fix I will need to make it clearer about the correct cylinders. Its kind of funny because I originally bought these cars partly because they are easier to work on or to find someone competent to work on them, but I am now finding my Lambo is actually easier at least in this instance. With all the hot rods in Southern CA no one in this area wants to touch that engine. Could be I'm just getting old & grouchy. I could just let it sit & rot in my garage and look at it like artwork, but it is really fun to drive when it runs. Plus longtime sitting just creates even more issues. I've been chatting with Tommy about it, so maybe he would be willing to take it on. He has been real good with my cars and is somewhat local.

Tommy was able to take a look at it and we both worked on the engine all day. 64 years old in the engine bay all day sure ain't good for the hips & legs. Leakdown wasn't too bad on that one cylinder, but he decided to pull off the valve covers and found that all the valves were way too tight (no lash). So all were adjusted and then got 175-180 on all cylinders on compression check. I was surprised to see such a dramatic increase, so of course that was real good news. Started the car and sounded real good. Just need to get it out on the street when I recover & see how it goes.

@joules posted:

That is great news Jan, glad to hear it was a relatively easy fix and no tear down of motor required. Did you get all the issues with the throttle bodies worked out?

Yeah throttle bodies still need to get sorted out. But they have been like that for the life of the car and it always ran fine, odd but true. I just found that imbalance by accident where the left side opens faster and fuller than the right. Tommy may just fix the fulcrum, who knows. He just wanted to get the car running good for now because he did see a valve stem marred somewhat so he wants to redo both sides in his shop a few months down the road. Im thinking around that time maybe we will address the throttle bodies. Im just glad it fired up so good, sounds like the devil. I would assume the increase in compression may give more power too. This was me on start up:



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