Hot Rods Compression Test on 331 Hemi

Hi again.
Trying to dive deeper into learning about doing some basic testing on this engine. When doing a compression check on a hemi, do the valve covers need to be off? If not, how do I tighten the fitting into to sprk plug hole with the hose in the way?
Also, will a compression check let me know if I have a bad in/ex valve or do I need a leak down tester for that?
What leads me to look into testing this engine is it seems like it has a miss/rough idle. I think I narrowed it down to #1 piston. I think.
When engine is running, I removed plug wires "one at a time". Every wire I removed made the engine noticeably fall off and stumble. However, when #1 piston wire was removed it was very hard to detect a difference in the idle.
I made sure I was getting spark to the plug, I am. then I tested the plug. It's firing. So, now I am thinking leaking valve? Any advice is appreciated. Thank you.

 

There are compression meters with a rubber tip you just push down against the head to seal, might not seal perfectly every time so some care is required, but something like that may be useful when it's hard to get in there to tighten a screwed in fitting.

A compression test alone will only tell you what the compression pressure is, not where it's leaking. A second compression test with a squirt of oil in the cylinder will tell you if it's leaking down past the piston, if the reading improved the oil helped sealing that leak. Little difference implies it's a valve (or head gasket), but it doesn't say which it is.
A leak down test should show you where the leak is. You can improvise a leak down test relatively easy.

It does sound like your #1 cylinder isn't contributing much at idle. Could be a leaking valve, could be something else, but if it improves at higher rpm and bigger throttle openings (where there's less time to leak and more that has to leak out before it's dead) a lack of compression would seem likely. Getting worse instead would imply it's something else, such as ignition lacking the strength to ignite anything.

 

Technically, the valve covers shouldn't need to be removed. Never done a compression test on an early Hemi but have done a few Mopar slant sixes over the years and they also use a deep tube around the spark plug hole. That's about the only similarity between a slant six and a Hemi.

I would think that you could slip the threaded end of compression tester hose down the tube while slowly wobbling and wallowing things around until the fitting finds the spark plug hole. It should hand tighten easily and doesn't need to be seriously torqued down.

I suppose if the hose was really a "wet noodle" sort of affair, you might try wrapping it with a coil of stiff wire (like you might see wrapped around a brake line) to make it hold its shape and be a bit easier to guide into the plug hole.

 

Have you checked for vacuum leaks in/around the inlet manifold?? (especially No1)

 

Hmmm. I have never had a problem snaking a compression test hose with a metal fitting on the end and being able to get it to screw in properly Once you get it snug by turning the hose it should be tight enough. I don't further tighten the tester in any engine, hemi or not.

 

A compression test will tell you the condition of each cylinder and valves as a unit, were a leak down test can help determine what is leaking if you do have an issue. Have you had the valve covers off to inspect anything? Badly adjusted rockers or adjustable push rods or even a broken valve spring could be the culprit on number 1 being dead.

 

If your tester has a long hose, getting in the plug hole is doable. Make sure the throttle is wide open and turn the engine at least 6 revolutions for an accurate reading on all cylinders. Usually, bad valves will result in a close to zero reading. A weak cylinder with a broken top ring might read 50% of a good cylinder. If I remember correctly, you will lose 5lbs. per thousand feet of elevation.

 

Yep, I have one older SW (I think) with the rubber end. It’s a two person job in a vehicle. A few years back I picked up one the have disconnects for different spark plugs hole sizes and a long hose. I just thread it snug via the hose as long as it’s a taper seat plug.
Thankfully the only engines with washers I have, are small one and two cylinders and the rubber “push in” one works for them.

 

I would first check a few easy things: pull #1 plug and inspect; try a different plug and/or wire on #1; pull valve cover and inspect valve adjustment and springs. Then if no improvement do dry and wet compression tests.

 

Leak down or actually air will help a lot. Put on TDC, open the throttle Full and hold with a spring, add regulated air, 50 psi will do, and listen at the carb, exhaust pipe or oil breather cap. Even check the radiator. I made an air to plug adapter by buying a spark plug oil problem extender and screwing in an air hose adapter with epoxy on it…Good luck.

 

Heck of a lump to learn basic diagnostics on, but good for ya!

 

Ok, I finally got to get to attacking this problem. I hope my video link works. But the #1 intake valve isn't moving. Collapsed lifter? Wiped cam? When I took the rocker assembly off, I could take #1 push rod and push down on the lifter, and it felt springy up and down. All the other lifters were stiff/not springy at all. Would new lifters be the answer? And if so, could I get away with replacing just one?
Edit: After looking closer at video, does the #1 exaust rocker seem to be not moving far enough?

Can't get video to post. Here's the youtube link. https://www.youtube.com/shorts/I_0xNKbDkeg?feature=share

 

I just did a compression test on my granddaughter's OT import car that has a dual OH camshaft setup and spark plugs down in wells between the cams. My tester has a hose that's about 10" long that you tighten fittings for various plug threads, and then a QD gauge on the other end. The spark plug fittings all have a rubber O-ring at the end so you just hand tighten them by twisting on the hose and they seal easily.
One thing I'm always conscious of is checking the fittings prior to threading them int the plug holes! I was a little too casual one time and after testing a cylinder I unscrewed the hose and the fitting styed down in the hole! Luckily I threaded the hose back in, and tightened it as much as possible and the fitting came out the next try!

 

Yeah, you have a problem there. I hate to suggest it but, you'll need to set aside some time to start pulling parts.
The rocker is not moving or, very little anyway, and that points to cam/lifter/pushrod.
Best of luck.

 

#1 doesn't seem to be moving at all! And from the angle of the video I can't even see the pushrod end on the rocker, so not sure what's causing it? Is the pushrod going up and down, or is it not moving at all? Could be a collapsed lifter, or a flat lobe on the cam. Only way to know for sure is to pull the intake and remove that lifter so you can check it, and the cam lobe for inspection.
I have a cheap Ebay endoscope that cost me $14 and plugs into my cell phone. Great for inspecting down into holes like a lifter bore to see cam lobes.

 

Ok , looks like I'm doing a new cam and lifters. There is a damn hole worn in #1 intake lifter. What am I in for? How far do I have to go into this? Complete disassembly and new bearings?

 

Yes, and a proper clean out of oil passages, etc.

Damn, bad luck there.

 

Yes, to do it right it's coming completely apart. What's the history of the engine?

 

Roller cam time.

 

I'm going to have to calm down and think on this awhile. My first thought is small block chevy time. I need to think of cost of course.
How does the rockers get oil in this hemi? I'm looking at the push rods and there are no holes in the ends. I don't know if that's how they are or are they screwed up. I know on sbc the push rods, the oil goes up through the rod and oils the rockers. Same on early 331 hemi?

Like I said, I need to get some time between discovery and solution before I just start going the wrong direction. Crap!

 

Rocker shafts are oiled from holes in the heads. Rocker arms are drilled and oil the pushrod tips.

 

All of the material from the bottom of that lifter has been ground off, washed down the center drain holes, splashed around by the cam, crank and rods, then sunk into the pan to be picked up by the pump and circulated. Everything must be pulled apart, cleaned and inspected.
Time to determine what that is going to cost and learn how hemis work, or just SBC it.

 

Fix what you have please. It will actually be cheaper in the long run and make the car more valuable.

 

A small block chevy will cost way more then a cam, lifters, bearings and a gasket set.

 

NO SBC's! I had the TV on for background noise this morning and there was an episode of :My Classic Car"on (you know, the guy with the goofy mustache?). Anyway, he was at some car show somewhere that had some ostensibly interesting cars. When the opened the hoods? ALL SBC's. I ended up watching it because hood after opening hood revealed another one. It was like watching a train wreck; horrible, but you can't look away. I think the hobby has gotten to the point where engines are no longer nearly as important as the cars. (For me, it's always been the other way around.)

 

Yes, I think I'm going to rebuild. A SBC would look like a little peanut in place of the hemi but, I need a machine shop to install cam bearings. And depending on how the block needs to be cleaned, a shop may need to do that work too.

 

Pull the bearing caps and look for metal if they look good the oil pump screen and filter may have done there job On the early hemi the mains get the oil first if they dont show damage the filter may have caught the metal and kept it out of the oil passages .

 

That's enough for today.

 

See that oil pressure sending unit on the back of the block? REPLACE!

 

That makes my head hurt. 331's you CAN get a cam for, I'd do that before I'd swap it for a Chevy, you should be able to get most of the parts you need for about the same as an engine would cost, not to mention the effort and hassle of swapping an engine in a finished car. Bear in mind I have no bias against a SBC, it'd be a big job in that car though.