Purchased restored 1965 Mustang with 1971 302 rebuilt 19000 miles on odometer, Started and ran good except ruff idle which being cammed though was ok just needed tuning. Did vacuum test had bouncing needle between 2&10. So did a compression test which you can see in picture. Number 2 cylinder has zero, put some oil in it ,still zero. The number 3 cylinder would come right up to 130 then drop back right away to 125 and seem to hold. Being that bank is over all lower then left bank and what's going on with compression do you think its head gasket. Knowing I will have to, don't want to tear down anymore if I should check something else first
Since you have the valve cover off, hand roll the engine over and observe the rocker arms on #2. Are they moving the same amount as the other arms? If not, could be a cam lobe wiped out, rocker arm issue, or bent pushrods. If so, either a blown head gasket or busted piston.
Visual as mentioned. A leak down test will tell you more (than just a compression test) about where to air/compression is escaping from without tearing it apart.
I just run the distributor around to #2 so both valves are closed, can wiggle rockers back and forth slightly. Hooked up compressor direct with 20#. Pressure has stayed the same for 15 minutes so far.
20 lbs. isn't very much. I would try 100 psi. If you can't hear air escaping, then you have something very unusual. A dead ignition will allow a cylinder to pump oil but it should have compression.
The first couple times I tried it yesterday I thought I could hear air slightly but couldn't pin point then nothing. Also when I first did compression test I just tried the push in plug on tester before hooking up threaded connection. I'm 99% sure I had 75# once in that cylinder once after getting the zero first. I'll try some of the things mentioned above and see. I guess either way its got to come apart.
I'm wondering about a possible sticky valve guide or something holding one of the #2 cylinder valves open when you ran your compression test. When you pumped the cylinder full of air it closed the valve and held pressure. Just throwing ideas at you. Good luck and let us know what you find. Oh, and I'm sure this engine isn't in a Mustang...pretty sure it's in a hotrod.
The idea you mention of air closing valve crossed my mine, because when I first put air to the cylinder the first 2 times I swear I heard air hiss but couldn't detect where from.
I think the implication is that Mustangs don't really fit what the HAMB's primary focus is. The site primarily caters to 1964 and earlier customs and traditional hot rods. You'll likely get better responses by deleting photos of the car and just referring to it as an "off topic" vehicle, or not mention it at all.
Rule #4 in the HAMB guidelines... "We cover traditional '65 and older American cars only. All other threads will be deleted. We don't cover rat rods, muscle cars, mustangs, or VWs." Otherwise, the thread will likely be moved to the off topic section...but not as many tend to follow along...so I offer genuinely, this engine is probably in a hotrod.
there's an off topic forum for stuff like this https://www.jalopyjournal.com/forum/forums/off-topic-hot-rods-customs.98
With zero compression your hot rod shouldn’t hold any air pressure. That would be a large leak. Are you sure the compression gauge is accurate and not leaking?
You can see by my reading it worker on the other 7. I still think when I did put pressure to the cylinder the first couple times I could hear a faint hiss but couldn't locate I was putting air to it with push in rubber tip , but after hooking direct now it has very slow leak by compressor gauge but can hear. I'm removing the intake manifold needs new gaskets anyway, so will put pressure to it again maybe will hear something.
Although probably not the problem, verify the firing order. Ford changed the order when the 302 HO came out. Early 302 engines had the order 15426378. 302 HO and 351s used 13726548. Especially with an aftermarket cam, the latter firing order may be there.
pulled the intake will check with pressure tomorrow. I thought the anti freeze looked cloudy when I drained but now with intake off can see brownness color in water jacket of bad side, also when dumping anti freeze, residue brown and oily gas smell. Head gasket??
beings you are that far pull the heads... probley could have saved all that slowley pouring a quart or 2 of marvel down the carb... that and running lucas in the gas tank...probley just sticky carboned valves....just went through this on my 302 and 289... the 289 was junk so new motor. and 302 blew the head gasket between 3 and 4 put the heads on the ground with plugs in and fill the chambers if its a bent valve it won't hold the gas..
It’s pretty rare to happen but a cracked head between the seats could be the problem if the engine was ever severely overheated. Usually the head gasket is the weak link though. Good luck.
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