4.6 severe "gallop" when cranking

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GRWeldon

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Just a fore-note... I'm assuming that most of you know what I mean when I say "gallop" and not the gait of a horse. I mean that when you crank the engine, the pitch of the starter changes at different stages of crank rotation instead of being steady and uniform.

My most recent acquisition, a 95 4.6 Thunderbird, it has the worst uneven cranking sound I've ever heard. It won't start because it need a fuel pump. I mean, there hasn't been one that I've bought yet that didn't. With as many as I have I should probably keep several in stock, but I digress.

When I went to look at this thing before I bought it, the guy was trying to use starting fluid to make it fire. Maybe he did, I don't know, but he said it would start but not stay running...duh! When he cranked it for me it backfired through the throttle body as he had the intake tube off. I told him to stop, immediately thinking that the cam timing had jumped. I don't know why but that was my initial thought.

When I got it home, first thing I checked was the firing order and coil pack wiring. It was correct. I then replaced the starter and installed crimp-on battery terminals to straighten out the half-assed attempt at shitty aftermarket terminals. And then I cranked it. I may have to record a sound clip and uploaded it. It was horrible! So then I removed all the plugs. They were all carbon fouled due to an extremely rich mixture. Seeing the shape of the exhaust system, I can believe it.

I then cranked the car with plugs removed and it sounded as you would expect. Everything uniform with no gallop.

So I should know this, and I think the answer is yes, BUT....is the 4.6 an interference engine? If this was indeed the case than I think my initial impression may be correct. There certainly are other things that could cause the uneven crank like maybe a rubbed-off cam lobe, but I've never heard of this happening with a roller cam. I suppose there could be broken valve train components, but I don't think this would cause a backfire.

I'm leaning towards broken timing chain tensioners and if this is an interference engine, that means I could have bent valves and/or holes in pistons which would certainly cause a gallop. A stuck valve could certainly cause a backfire. Some advice on my troubleshooting theory and how to proceed would be helpful. I think the next thing I'm going to do is pull the valve covers and take a look. Such a fun thing on these cars...NOT.

Drop me a line and let me know what you think...Thanks!
 
Yes, it is an interference engine. Most/all late model (1995 is "late model" to me) engines are. Might as well do a compression test to see if you have one or more low cylinders. That's where I would start at least. How long has the engine been inop for? Usually when I have valve train timing issues causing valve interference it affects every hole and you get no compression across the board. Could be a burnt valve, but a compression test should help you narrow it down.
 
This is what I found after removing the passenger side valve cover. I suppose two missing valve followers would cause a gallop, eh? :)

I have never removed a cam with the cam still in the engine with the timing chain on. Is it even possible? I could probably slip and pry the followers back in without removing the cam but that wouldn't allow me to investigate why they fell off. I suppose if the valves were bent and didn't come back up would explain how they came loose. Also, if these valves were bent and not seated, that would explain a backfire.

As far as compression is concerned, when the plugs were removed there was no gallop. With them in, there was an extreme gallop so at least SOME of the cylinders have compression.

The cam needs to come out so I can inspect the valves and springs so the question is: can I do it by just leaving the cam gear in place and not removing the timing cover? Of course I would need to mark the cam and the gear before separating, but would chain tension allow me to get the cam gear back on?

I really don't want to remove the other valve cover but I suppose I should just for inspection. If valves are bent there are sure to be more I believe...
 

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GRWeldon said:
I have never removed a cam with the cam still in the engine with the timing chain on. Is it even possible? I could probably slip and pry the followers back in without removing the cam but that wouldn't allow me to investigate why they fell off.
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Yes, it is possible... there are risks, but it sounds like you know what those are. In your case you could remove the caps and elevate the cam slightly to give you more room to work, without really moving the sprockets or chains. This would be the least risky.

When I did my first PI cam swap I left the front cover on, "propped up" the cam gears with tools then unbolted them from the cams. Then I removed the caps, R&R'd the cams, and reinstalled everything. It worked out... but in hindsight I was lucky. All too easy for the tension on the chains to slack off when moving the sprockets, and the tensioners could have clamped down on me.

OTOH, it's probably worth considering just taking the front cover and re-timing it. That'll also give you an opportunity to inspect the condition of he guides and tensioners.
 
So is this condition something that is a known issue with the 4.6? I mean...isn't it a bit irregular for a cam follower to "slip off" for no reason? I'm wondering what could cause this and the only thing I'm coming up with is a bent valve where it can't seat. In this case we are talking quite a bit of internal damage, right?

I'd love to be wrong. Anybody know of anything else that might cause a follower to "fall out" of place?
 
I hate to be the bearer of bad news as well but that’s been my experience. I’ve had a few optimistic thoughts where I’m going “yay I just need to put the followers back and I’m good” only to realize the valves are bent and/or kissed a piston. It can happen through overrevving but not before the stock limiter kicks in. It’s either something happened on the valve end to let them loose or the lash adjuster end (collapsing from lack of oil pressure which is also not good)
 
Grog6 said:
I spit one out doing a burnout with a tune with no redline and a pi intake. It's not easy.
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My old PI heads I ran had a spit out lash adjuster(or I should say missing) when I bought them. This was why

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I had a spare couple valves from a set of junk heads I parted earlier and lapped it and sent it in the end but that was quite the unpleasant surprise
 
Mine cracked the guide.lol. I bought a pi engine. The npi heads brought 25 bux as recycled waste. :) I break stuff good.
 
Thanks guys. That's what I figured. I'm not going to be keeping this car (I don't rhink). I have a set of 96 heads I can put on it assuming no pistons have been dinged, but I have a spare used set of them as well. Guess I better pull the heads.
 
My comment on the compression test was to do that first so you could get an idea of where the trouble cylinder was before you started taking things apart.

This is pretty common on Chrysler 3.7 and 4.7 engines. One known fix on those is to shim up the valve lash adjuster. I've never seen it on a 4.6. Even if the valves smacked the pistons I'm sure they (the pistons) are fine. '96 heads should have the longer valve guides so that will be an improvement.
 
The regrind cams Nick sold needed a shim to work, but that was due to the reduced base circle after regrinding.
Stockers don't need them.
 
KevinVarnes said:
My comment on the compression test was to do that first so you could get an idea of where the trouble cylinder was before you started taking things apart.

This is pretty common on Chrysler 3.7 and 4.7 engines. One known fix on those is to shim up the valve lash adjuster. I've never seen it on a 4.6. Even if the valves smacked the pistons I'm sure they (the pistons) are fine. '96 heads should have the longer valve guides so that will be an improvement.
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Well, I don't have a compression tester and I'm not patient enough to wait until payday to think about buying one. I should probably have one in the shop since I do a fair amount of engine work but it's hard to spend the $$ when you need so many other things...

I would think that after seeing two cam followers sitting in the bottom of the head that I know of at least two bad cylinders. I highly doubt that the lash adjusters failed or that the engine was severely over-reved, so that really only leave skipped timing chains, right?

I'm in the process of removing the timing cover to verify timing. I worked about 3 hours today before I could no longer stand but I'm almost there. If the timing marks don't line up that pretty much settles the issue, right?

If the timing marks DO line up then I might believe that I don't have piston damage and I'll try to decide where to go from there.
 
If the motor sits for a long time, the lash adjusters can bleed down, that might cause a thrown lash adjuster.
 
I took the driver's side valve cover off this morning and found two more cam followers sitting in the bottom of the heads. Then the timing chain cover comes off. No apparent failures. I attempt to put the chains in the correct orientation and I got through about 45° rotation and hit a hard stop. Then I went in reverse until I hit another hard stop. Then I went forward again counting the degrees I could turn.

I could only complete about 250° of rotation. Since the motor has been cranked with the starter by both the previous owner and me, I know that there is piston and/or valve damage. I figured I'd be removing the heads from the first time I personally cranked it and heard the gallop.

Continuing on with head removal! I've removed heads while the engine is in the car once before. They CAN come out with the exhaust manifold still attached, right?
 

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GRWeldon said:
Yep. It would be nice if it were just down the street. I live in very rural Alabama. Nearest parts store is 25mi. away. It's all academic anyway... see following post.
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This is the problem with living in the sticks, still I have to admit I'm a little jealous. Good luck with all the work.
 
The biggest challenge with removing the heads IME are the lower head bolts close to the shock towers. They can't be removed from the head because they hit the shock tower, and gravity pulls them back down into the block. The solution is to use a rubber band or old piece of tubing (whatever) to hold them up out of the head enough so you can R&R it.
 
The worst part really is on the reinstall with the dipstick tube in the mix. That’s quite the balancing act
 
theterminator93 said:
The biggest challenge with removing the heads IME are the lower head bolts close to the shock towers. They can't be removed from the head because they hit the shock tower, and gravity pulls them back down into the block. The solution is to use a rubber band or old piece of tubing (whatever) to hold them up out of the head enough so you can R&R it.
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I remember doing this the last time I did it, probably almost 10 years ago (edit: just looked at my photos. It was 2020. Just seems like 10 years!).

I'm actually having much trouble with the EGR tube and associated DPFE switch and mounting. Can't get the intake out because of the tube trailing near the exhaust manifold. Can't get the head off because of tube and brackets attached to the back of the head. I was able to get the bottom nut off without much trouble but can't even get to the top nut.

I've got two fasteners at the rear of the passenger head that need to come out but I can't access. I worked until I couldn't stand once again so I'll wait for a fresh look in the morning. This isn't going as well as remember the last time, by that was a 96 instead of a 95. There are a few differences...
 
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It’s honestly less effort pulling the whole engine, if you have a hoist obviously. 94-95s have the added frustration with the EGR tube that is inexplicably fragile
 
Yeah. It was a bitch getting the heads and intake off. It would probably be easier to pull the engine, my hoist cylinder is rusted. I guess harbor freight doesn't chrome plate their rods. I'll still end up pulling the short block. Might have to use the loader on my tractor.
 
I have not found any piston or valve damage when inspecting them after removal. I did find some cam journals in the head that looks pretty bad, also one or two cam journals are very bad looking. Since the cams are hard, I'm surprised to see ANY damage to the journals when running in aluminum. I would think that the aluminum would melt before damaging the cam.

I may have put the engine back together with new gaskets and such before I pulled the heads but I'm not going to put it back together now without making it right. I'd like to do a PI head swap but I really don't feel like pulling a set of heads from a donor, IF I can find one.

Also, I'm really not crystal clear about what years and what vehicles fits a 95 Tbird block without modifications so there's that...plus the $$ they would cost...
 
I use a slide ammer. You did remove the bolt? The o-ring swells in the fluid, but that's it.
 
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