NorthBayPete

Just incase the cam was not ground properly ?

Runner4Luke

Basically yea, I asked earlier if anyone thought an improperly ground lobe could case these symptoms.. no takers.
Also I don't have another cam to try out.

bswarm

You could pull the plugs out, turn the engine by hand with your finger over #1 plug hole, and check for pressure as the timing mark lines up, then there would be vacuum after it goes past tdc to btc, then the exhaust valve opens on the next stroke to tdc, then the intake valve opens on the way back down. Have the valve cover off to watch the valves in action.

Shady Cadence

I have run into an improperly ground cam before, but that engine had hydraulic tappets. #1 cylinder was a dead hole running, AND during a compression test. Next logical step was a cylinder leakage test, which we did....


less than 3% leakage on #1 cylinder.


What was happening was the hydraulic tappet was bleeding down after shutdown and allowing the valve to close, but with oil pressure present the valve would not fully close because the base circle of the cam lobe was ground too large.

Since these tappets are mechanically adjusted, any base circle issue would show up as a slight power imbalance between cylinders, not cause a dead hole.

bswarm

I had a hydraulic lifter pump up, just the opposite, it hung the valve open. They were TRW anti-pumpup lifters too. Luckily it didn't bend the valve, I had to wait a few hours for it to bleed back down.

NorthBayPete

Basically yea, I asked earlier if anyone thought an improperly ground lobe could case these symptoms.. no takers.
Also I don't have another cam to try out.

If there is a prob with the cam it would be with the base circle of the lobe. Just rotate it and see if the clearance is the same over the whole base circle. Ok just another thought ... are there and vacuum lines connected near the #1 runner? Try squeezing them off. I wish we were closer ..I like working on stuff like this. Please be sure to post when you get it figured out.

Runner4Luke

Yea interesting. And an improper base circle would only prevent a valve from closing if it had a hydraulic lifter, because of the no lash condition. As you said, the mechanical tappets have lash, at least exactly at TDC, good compression numbers seem to contradict any base circle problems as well.

Haven't done a running compression test on all cylinders yet, to compare them.

Propane increased idle RPM, but number 1 remained dead.

Interestingly number isn't completely dead when I first start the engine and it's cold. I get a slight RPM drop and pick up as I disconnect and reconnect the ignition lead. Also idling higher of course of because of cold idle up.

Shady Cadence

Just for kicks, try the same test warmed up, but hold the idle at the cold rpm.

bswarm

If the cam is bumping a valve open twice, it should be noticeable on my finger test described above. If it is a problem in the top end, I would look closer at that, or possibly a loose valve seat, valve guide, or rocker shaft. This is indeed a unique misfire, and I would love to get my hands on it. I'm the one that always got the problem childs everyone else gave up on, loved it.

NorthBayPete

Interestingly number isn't completely dead when I first start the engine and it's cold. I get a slight RPM drop and pick up as I disconnect and reconnect the ignition lead. Also idling higher of course of because of cold idle up.

The engine gets a richer mixture when its cold so thats probably why it produces a bit of power when cold. I just went and looked at mine. Did you try blocking off the vacuum line from the power steering or the large crankcase breather hose from the valve cover? Check around the plenum to intake and intake to head gaskets with acetalene or propane. Sure seems to me like a small vacuum leak.

Shady Cadence

This is what I'm leaning towards, as it makes the most sense so far.

Runner4Luke

Hey guys, sorry it's been awhile. I've had exams and school projects and such.

To answer some of those questions/suggestions.

@Shady,
No engine change when pulling the ignition lead at cold idle RPM

@BSwarm,
If it was bumping open twice because of a bump on the base circle grind, wouldn't that should up in a compression test? i.e. Loss of compression?

@NorthPete,
I ran the engine for awhile with all vacuum lines disconnected and plugged off while looking for intake leaks, none. Also sprayed propane and starter fluid everywhere, no change. Also sprayed propane & starter fluid directly into intake to richen mixture, still missed on number 1.

Also, just blocked of the EGR completely to be sure (it actually dumps into the forward part of the plenum, even though its bolted on the rear). No change.

Doing running compression on ALL cylinders later today to compare. If #1 varies significantly then I'll know it's mechanical.

Shady Cadence

So it's there a little when cold, but quits completely once warmed up. Interesting.

I still say either the guide is walking in the head somehow, or there's a flaw within the head casting itself.


Do you by chance have your old head laying around?

Runner4Luke

Alright so significantly lower compression on #1.
Had my buddy do it this time, (still busy with school stuff)

Running Compression
#1 -> 60-70psi
#2 -> 115psi
#3 -> 110-115psi
#4 -> Didn't do it.

So it definitely still appears mechanical with the number 1 valve.
Also, Horrible screeching when doing the compression tests, that decreased in volume as the compression tester moved from #1 to #3.
I heard this before when I did a normal compression test, completely goes away(??) when running with spark plugs.

I'm not sure if the noise is going away, or is only audible when the compression tester is connected (creating a pathway for sound?)

bswarm

Cam timing is off, or chain tensioner (or chain) is worn, or all rings/pistons have blowby.
EDIT: Wait, running compression? Disable the ignition, those numbers won't be accurate. You need at least 100psi and it should be around 150psi. The screeching noise is probably from the compression gauge when you force pressure in them too fast, the pressure is going through what is basically a tire schrader valve. You won't get accurate numbers that way.

Runner4Luke

I've done a normal compression test before, I wasn't tying to do one now.
Those results where:
170-180 on all cylinders.

I'm not trying to do a normal compression test here. I'm doing a running compression test. Something else is going on when the engine is running..

http://www.misterfixit.com/dyncompr.htm

I was specifically looking for a different running compression on #1, which there is, it's significantly less.

-Cam timing definitely is not off.
-There is some blow by on cylinders #2-#4 as indicated by Tod when I showed him the head, #1 had minimal blowby.
-Timing chain has been replaced in the last 40k on that engine, plus a stretched chain retards valve timing on all cylinders, not just number one.

bswarm

That's not going to be accurate with a regular compression tester, the one-way valve in them is basically a tire schrader valve and won't push pressure through them fast enough, hence the screeching noise. It would only work if you turn the idle speed way down.

grumpin

You guys are deep into this, but thought I would add this. Years ago we had and aircraft piston engine that would run rough. We checked everything again and again. We had checked all the valves for movement. Later we had all the rocker box covers off and were looking at something and an old timer came up and found an exhaust valve moving a lot side to side. He said you checked these right? And we had. The valve guide was broken in about half. When we checked it the guide was moved out and the valve seemed OK. Can't remember where the rest of the guide was. Compression and timing and all were good, but ran rough.

bswarm

The correct way to do a compression test:
Engine warm.
Fully charged battery.
All spark plugs out.
Ignition & EFI disabled. (disconnect distributor pickup)
Throttle wide open. (it doesn't say this in the FSM, but that's the general rule)
Crank it over for 5 or 6 "puffs"
FSM says normal is 171 psi, Minimum is 142 psi
Difference between each cylinder 14 psi or less

Shady Cadence

You seem hung on this, why? He did a normal compression test, it revealed nothing, and he still had a dead hole. Spark and fuel checked out. So he did a test under malfunction conditions, ie running. While there is no test "spec" for this procedure, the value is in the comparison between cylinders. 1 is noticeably lower than 2&3, I suspect 4 will be in line with those two as well.

We've proved that cylinder has a compression issue when running. Hence the running compression test.