Engine Diagnosis Q's - 400cid

[Furyus1]

OK, first a quick history lesson: The PO of my truck, Bob, who is quite a competent mechanic and has a reputation to back it up, bought this truck with the intention of fixing it up to use to tow his trailers around; go camping in; etc... After finding that the original engine was pretty much shot to hell, he bought a remanufactured complete engine from a company out of Phoenix, AZ, called Motor Replacement Company, Inc. "The Roadrunner Engine (R)". From the paperwork I've got on this engine, it appears he did this in 2004. After un-crating the engine; putting it in the truck; getting everything hooked-up/set-up; and whatnot (plus all the other work he'd done on the truck in the meantime), he got it running and found that it would not idle smoothly - I call it a "lope". It smoothes out when you give it a bit of gas but at low-idle, you can definitely tell something is not right... At the time, he proceeded to diagnose the problem to try and find out what was going on and tracked it down to the #1 cylinder which he said was only showing about 7lbs pressure on his guage when he ran a compression test on it. He ran a wet test on it and the compression went back up. This would indicate that the rings in that cylinder are not quite right, yes? It was right about that time that Bob decided he'd had enough of the whole ordeal and let the truck pretty much sit for the next few years until I came along and bought it off of him for $500.00... He'd drive it around and run it every so often just to keep the fluids flowing and whatnot but he was so disgusted by the engine that was sent to him he didn't really have any ambition to do anything with it. There was a warranty on the engine, but when he tried to contact the company, he'd found that they had gone out of business. Gee, I wonder why... And now, it's up to me to try and find a way to remedy this situation... A couple of weekends ago, I replaced the spark plugs and checked the way plugs were fouled. Cylinder #1 was the worst - which was to be expected - the deposit buildup on the plug was enough to keep it from firing. However, the plugs from cylinders #2 and #3 were also heavily fouled - not as bad as #1 - I'd say, in succession, #1 was most heavily fouled; #2 was medium-heavy fouled; and #3 was medium fouled. The plug from cylinder #4 looked normal. I don't know if any of that made sense - I was going to take pictures of the plugs but never got around to it... Cylinders #5 - #8 all looked normal... I found my compression guage but I've not been able to run any tests yet as I've been fighting some migraine-related health issues and sunlight/heat are not my friends right now... So, based on what I've told you guys so far, does it sound like I'm on the right track so far? I realize I won't know much more until after compression tests have been run... If it turns out that it is the rings in the #1 cylinder, given that I would have to pull the intake; unbolt the exhaust; pull the head; etc, about how much time and effort am I looking at for slapping a new set of rings on this piston? I've done motorcycle pistons so I have a basic understanding of how it's done but this is no motorcycle... I have a Chilton manual for this truck, but I like to hear from people who's done this sort of thing so I can get a feel for what I'm getting myself into... Thanks.

[Jermafenser]

Fouled as in what? Too rich?

You're getting there. Spark plugs tell a lot about the engine.

[johnboy427]

If the rings are bad I would suggest pulling the entire engine it will be easier in the long run. I would check it out pretty good, might just be a gasket since it is only affecting one bank, or mabey that head is bad the lower end might be fine. This really could be a lot of things, intake gasket, head gasket, valve guides, or rings. If it showed a true 7psi on #1 there is some thing seriously wrong with that cylinder. Could be head gasket but more likely piston sealing problem or a bad valve issue. These aren't motor cycles I have reringed many a dirt bike but it really won't work on your truck. You will most likely have to have it bored to the next over size to get it right and you will have to do them all. Like I said if you really are getting 7psi out of #1 it will most likely need machine work in one form or another, normal is in the 150psi range.
-Johnboy

[Furyus1]

Originally Posted by Jermafenser

Fouled as in what? Too rich?

You're getting there. Spark plugs tell a lot about the engine.

Fouled as in... Well... Deposits of some kind... Who knows what kind of additives they put in the gas and I believe the "oxygenated fuel" they run around here has a higher alcohol content in the winter time... We're figuring that the side of the plug that was facing the intake valve is where the deposits formed...

First: The "good" plugs. From left to right are the plugs from cylinders 5, 6, 7, and 8 (in that order.) The plug from #8 is rusty but it was put in at the same time as the others...




Now come the "bad" plugs. From left to right are the plugs from cylinders 1, 2, 3, and 4 (in that order.)




Here's another view of the plug from cylinder #1:



And the one from cylinder #2:



And, finally, the one from cylinder #3:



As you can see, plugs 1, 2, and 3 have deposits built-up on them in a way the other plugs don't (well, not as bad, anyway). Plug 1 is showing other issues which may be related to the compression issue (which I still need to check out.)

For the record, these are Champion Copper Plus #RV17YC plugs. The ones I put in are Autolite 25's...

[Furyus1]

Update:

I'm working on my truck while fighting a migraine so if the following doesn't make sense, please bear with me...

It seems my compression gauge may have bit the dust. I can feel air blowing out of the spark plug hole on the #1 cylinder but it barely even moves the needle on my gauge... I tried putting some dielectric grease on the rubber seal on the fitting to see if maybe it wasn't sealing or something but I can't get any compression reading off of the #1 cylinder no matter what I do... I haven't tried it on another cylinder yet - I'm typing this in the middle of working on the truck - I'll try it on another cylinder and see if it is, indeed, the gauge...

I did, however, pull the rocker cover and found something interesting... I watched the rockers while cranking the engine over and found that while the engine was making its "rerereRAWRerereRAWRerereRAWR" noise (the "RAWR" being the point of no compression), that it was making the "RAWR" noise on cylinder #2, not #1. I took a quick video with my digital camera which can be downloaded here (no audio):
http://myweb.cableone.net/tvjw/Rockers.AVI

In the video, you'll notice I have a gasket scraper resting on one of the rockers - when that rocker opens that valve, that's when the engine makes the "RAWR" noise... Is that the intake valve?

Time to go out and start putting things back together - It was a bugger peeling that rocker cover off... Who was the genius who decided it was okay to use RTV to seal those covers on, anyway?...

[johnboy427]

Yes that is the intake valve for #2. Valves should not make noise like that, but it may not be the valve it could be something else that just happens to make that noise when #2 is opening. From what I saw in the video valve train looked pretty normal. Get that compression gauge checked out let us know what the rest of them read.
-Johnboy

[Furyus1]

Cylinder #1 - Nothing, Nada, Zilch - barely moves the needle...

Cylinder #2 - ~110psi

Cylinder #3 - ~130psi

I don't think I need to check the rest... The problem seems painfully obvious... I just don't know how to go about fixing it

[johnboy427]

First off I would rotate the engine till both valves on #1 are closed and remove the rocker arms. Watch the valve as you are doing this to make sure they are not moving, if they continue to move as you are taking the rockers off you might have some kind of valve lash problem that is not letting them close all the way. If the rockers come off with no valve movement I would go a head and pull the head, leave the other one alone it seems to be fine. As little compression as you have I think what ever is going on will be fairly obvious, like hole in piston, god awful bore or broken valve. That noise you hear could be problems in #1cyl that just happen to line up with the opening of #2 intake. I really almost wandering if mabey they didn't leave the compression rings off the piston or something when they reassembled the engine.
-Johnboy

[Furyus1]

Originally Posted by johnboy427

I really almost wandering if mabey they didn't leave the compression rings off the piston or something when they reassembled the engine.
-Johnboy

That's almost exactly what Bob said when I spoke to him about it last week...

Thanks for the help Johnboy, it is greatly appreciated...

[Furyus1]

Update:

I'm in the process of tearing the engine down and trying to find the problem now...

I think I may have found the problem...

I need to know what you guys think, though...

Here's a couple of shots of the head:




Cylinder 1:



Cylinder 2:



Cylinder 3:



And cylinder 4:



Here's a shot of the pistons:



OK, now, referring to the closeup shot of the valves for cylinder 1, notice how one of them is sunken in? I'm guessing that's the intake valve...

Could that be causing my lack of compression in that cylinder?

Also, there are "060" markings on the pistons which I'm told indicate the bores are bored .060 over...

Can't find my valve spring compressor so I'll have to go rent one so I can pop that valve out and see what the seat looks like...

[Furyus1]

Update:

I've got the head down at a machine shop right now...

The exhaust valve seat for the #1 cylinder is all but completely gone - the valve stem was bottoming out but the valve wasn't seating at all...

And, come to find out, the rebuilder reamed-out the valve guides then put in valves with oversized valve stems to compensate...

I'm having the old seat cut out and a new seat put in and ground down. A new standard sized valve guide will be pressed in and a new standard sized valve will be installed. The spring is fine.

If I'm right about this, this should cure my compression issue with the #1 cylinder...

Just wish I had the time and money to have this done with all the valves on both heads ...

[johnboy427]

That is your exhaust valve, and yeah it is most likely what is causing your lack of compression. .060 is kind of iffy on these motors, some times you get away with it some times you don't. And the exhaust valve in number 4 looks like it has some chunks out of it, if it actually does its gotta go. I would investigate further because I still feel like you should get some compression out of a burned exhaust valve unless the seat was so torn up the valve couldn't close.
-Johnboy

[Furyus1]

Originally Posted by johnboy427

That is your exhaust valve, and yeah it is most likely what is causing your lack of compression. .060 is kind of iffy on these motors, some times you get away with it some times you don't. And the exhaust valve in number 4 looks like it has some chunks out of it, if it actually does its gotta go. I would investigate further because I still feel like you should get some compression out of a burned exhaust valve unless the seat was so torn up the valve couldn't close.
-Johnboy

What you're seeing on the #4 valve is a shadow from some gunk on the head
- the valve itself is fine.

Whoever re-ground the seat for the #1 valve ground so far down the valve couldn't make contact. The valve didn't fit tight in the guide, either...

I had the guy at the machine shop give me both the old valve and old guide...

Here's a shot of the old valve:



And here's the new valve in place with the new seat:



I'm going to get a feeler gauge and slide it down between the piston and cylinder wall to check the top ring - I've had 2 different people suggest that so I'm thinking "hmm"...

There is 1 question though... When I was buying the valve, I found out that there was more than 1 kind of valve available for the 400. I told the guy at the parts counter that the engine was a rebuild but he wanted to know what it was in so, I told him... I had to take that valve back because it was the wrong one - the one he gave would have been correct had the engine actually came out of a 1977 but, apparently, it didn't and I told him from the beginning that markings on the air cleaner said '78 T-bird... The valve I had to get is for a 400 built after 1977... The only real difference I could see was one had multiple grooves for the spring retainer and the other had a single groove... Anyone know why the difference in valves?

[johnboy427]

Single groove was earlier and is used in most high performance applications, the multi groove promotes better valve rotation and thus longer seat life. A lot of people go with the single groove as they are not as known for dropping valves at high rpms and with big cams.
-Johnboy

[mark a.]

I'd find out what caused this in the first place or you probably will end up right back where you started from. Check valve train geometry. Something is really messed up to tear those guides out so quickly, assuming they were in there & sized right in the first place.