390 low compression

[coop]

Hi all

Well about a month ago I posted a engine miss well I think I found the problem. Here are the symptoms, 1970 390 F250

Added new performer carb, performer intake, timing chain "lined up the marks right" and fuel pump

Had the heads redone for unleaded gas.

The miss has gotten worse, I just did a compression check it looks bad as follows. Also the vacuum gauge reading is fluttering between 15 to 20 and slows when excellerated.

#1=30 #2=140 #3=140 #4=80 #5=60 #6=140 #7=140 #8=140

I added oil to the low cylinders no change. What the heck went wrong? Did the heads not get rebuilt correctly? Regardless it is going back on the operating table.

[convincor]

got a air compressor?
If you compression gage has a quick connect hook that to compressed air on the cylinders that are low.
Start with that cylinder on the compression stroke so the valves are closed. You should be able to hear were the air is leaking.
If it's loadest out the valve cover breath, it's ring. Thru the intake, intake valve. Thru the exhaust, exhaust valve.
Around the head, head gasket..

[cep62]

The FE motor has 3 ? different push rod lengths.
If you have some that are too long they will keep the valve from sealing.
Did they mill the heads when they did the valve grind ?
That would change the length needed.
Did you do a compression test before the head work ?If so were those cylinders low?
See if you can collapse the lifter at T D C on the affected cylinders if not that might be the problem.

[coop]

Thanks guys, my gauge does have a quick coupler that's a great idea I will give it a shot. The machinist did resurface the heads how much I don't know. I did keep track of the rods they, went back from where they came.

[coop]

Well I just tried the compressor suggestion, the air runs out just as quick as it can get in. I heard air coming from the exhaust pipe and also the valve cover. I pulled the valve cover and tried it again and it sounds like it is coming right around the valve at least that is where it is the loudest. I could spin the push rods there is no slop, and the rocker is not tight but not loose. Is it the valve seat or guide?

[furnitureguy-123]

For the compression rading to be that far out of wack you have to have a valve problem. I agree with the push rods being too long. You should adjust to the proper size based on the amount that was milled from the heads. Replace them all with the proper length and recheck you compression.

[70_F100]

If you did a wet compression check (oil in the cylinders) and it didn't change the readings, it's either a hole in a piston or a valve-related problem (not ground correctly, wrong push rods, etc.).

Based on what you said earlier, it's doubtful that there is a problem with the pistons unless you dropped something into the cylinder while working on the engine.

To see if the push rods are at fault, loosen each of your rocker shaft bolts a couple of turns (not too much, just enough to be sure they're letting the valves close completely) and recheck the compression. Make sure you loosen them all the same amount, or you risk bending the shafts.

Most likely, the machine shop goofed for it to be as bad as you say.

[coop]

Thanks, I just removed the rocker assembly and rechecked the cylinder with compressed air and it is the same deal. The reason i had the heads redone was to replace the ex valves for unleaded gas. I think the machine shop goofed. I did speak to the machinist and he thought there might be a problem duh. What should my recourse be besides him fixing the valves? Should I back charge him for gaskets and labor? Thanks for your input.

[70_F100]

If nothing else, he should be willing to pay for the gaskets if, in fact, it was a mistake on his part. Any reputable shop would probably do that much for you.

Good luck getting him to pay labor. You can try, but don't hold your breath.

I hope you had the seats replaced, not just the valves. The original valves are fine to run with unleaded, but installation of hardened seats is definitely recommended.

[coop]

Well I talked to the Machinist about the heads. He told me that the exhaust valve guides were worn real bad and that they wallowed out the valve seats and that's why they were leaking so bad. He said he had replaced the guides with new ones when he rebuild the heads. What the heck could of caused that, the heads had less than 4000 miles on them. The engine has 45,000 miles on it and everything seemed fine I never did a compression test on it before. I did have a problem with the exhaust manifold staying tight. He machined them for me before I reassembled the engine I used new gaskets and some gold spray sealant on everything. It did look like there might of been a little leak but not like before. could the rocker assembly be warped. He had said thet because the oil travels through the assembly that it may be clogged and staving the valve of oil. The odd thing is that it is the outer valves cylinders 1-3 and 5 What do you think?

[70_F100]

Did you get an itemized bill for the original machine work?

If so, it should have the replacement guides listed, along with additional labor for the installation.

Nowadays, machine shops, just like dealerships, charge for every little thing.

If there's nothing about it on the repair order, it's doubtful that he replaced them.

On the other hand, if he did actually replace them, it sounds like you've got oiling problems. If you didn't have problems before, it's possible that you put the head gaskets on wrong or there is some trash in the oil passage that blocked it.

If you can get a piece of hex stock the same size as the oil pump shaft, get a piece that's long enough to run the oil pump using a drill and see if you have good oil flow with the heads removed. Then, once you have the heads back on and before you install the rockers, check for oil flow again. Finally, do it again once you have the valve train completely installed. You should easily be able to tell whether or not oil flow is an issue and also if the rocker arms are worn enough to starve the end cylinders.

One other thing that may be a possibility, but I don't know for sure. On some engines, when the rockers run on a shaft, the bolt hole through which the oil is pumped is drilled bigger on one side of the shaft than the other, with the larger diameter hole turned toward the cylinder head. Is it possible that you installed the shaft upside down, effectively blocking the oil passage? You would have had to remove the bolts from the rocker shaft during disassembly for this to happen. Not sure if an FE is designed this way or not, so somebody else chime in here!!!

[coop]

Did you get an itemized bill for the original machine work?

If so, it should have the replacement guides listed, along with additional labor for the installation.

Nowadays, machine shops, just like dealerships, charge for every little thing.

If there's nothing about it on the repair order, it's doubtful that he replaced them.

On the other hand, if he did actually replace them, it sounds like you've got oiling problems. If you didn't have problems before, it's possible that you put the head gaskets on wrong or there is some trash in the oil passage that blocked it.

If you can get a piece of hex stock the same size as the oil pump shaft, get a piece that's long enough to run the oil pump using a drill and see if you have good oil flow with the heads removed. Then, once you have the heads back on and before you install the rockers, check for oil flow again. Finally, do it again once you have the valve train completely installed. You should easily be able to tell whether or not oil flow is an issue and also if the rocker arms are worn enough to starve the end cylinders.

One other thing that may be a possibility, but I don't know for sure. On some engines, when the rockers run on a shaft, the bolt hole through which the oil is pumped is drilled bigger on one side of the shaft than the other, with the larger diameter hole turned toward the cylinder head. Is it possible that you installed the shaft upside down, effectively blocking the oil passage? You would have had to remove the bolts from the rocker shaft during disassembly for this to happen. Not sure if an FE is designed this way or not, so somebody else chime in here!!!

The bill wasn't itemized, he said they always replace the guides.

I thought the head gaskets went on pretty straight forward at least that's what I thought, I will double check this time. The trucks oil pressure runs close to 50psi at cruising and a little over 25psi at idle when hot 50+cold.

I will do as you suggest with priming the engine I did that when I installed the new cam, that's a good idea. I did remove the rockers from the shaft to see if it is straight, I rolled it on a flat surface it looked ok. It did look like there could be some crud inside the shaft I will clean it and do the same to the other. The rockers themselves do have a slight rock to them side to side. The shaft has a little ware on the underside of it.

I did have the rocker assembly installed correctly there is a bigger port with a longer bolt that goes into it. I believe the oil baffle is installed correctly it does have a bigger hole that lines up with the head oil port.

How does the oil actually get to the valve guide? As far as I can see it looks like oil shots through the rocker to the push rod ball and the other hole shoots oil onto the top of the head. Does it just run down the valve guide? Then wouldn't it be burning oil and then there is the valve boot.

I am picking the heads up tomorrow and will start reassembly and use any input I can get.

Thanks

[70_F100]

I don't know what I was thinking before.

Theoretically, a valve guide should need and/or get minimal, if any oil. If oil comes down through the guides enough to lubricate the valve stems, it will either be sucked into the combustion chamber or burned through the exhaust, dependent upon which valve you're talking about. We don't live in a perfect world, so a certain amount will get to the stems, but the amount is miniscule.

Either way, this would mean oil loss through the tailpipe. You really don't want oil loss anywhere. An engine in good shape will go 3,000-5,000 miles without using any oil. If oil were getting to the valve guides, this wouldn't be possible.

Each of the valves is sealed ABOVE the guide to prevent oil from getting to the guides. Ever seen an engine with bad valve stem seals? Let it sit for a while, get in and crank the engine, and PUFFFFFFFFFFFF!!!!!!!!! You get a huge blue/white ball of smoke out the tailpipe.

I'll go back to my original response. The heads weren't repaired right in the first place.

[coop]

It was the exhaust valves. I drove the truck on a 3000 mile vacation and at the end is when it started acting up. about that time it was half a quart low and there was never any noticable smoke even before I tore it apart. It sure did stink when idling running rich. Any input is always appreciated.

[papabug71]

Im with 70_F100. Sounds to me like a hack job on the machine shops' part.

I would be leery to believe them if they said "we always do this, or always do that" yet they have no proof of having actually done it. (I.E. reciept) In my opinion that is short for, "we didnt think they were bad so we left them alone".

I hate to hear that. I had the same deal with a sb chebby motor I had rebuilt years ago. Me & the machine shop went round & round. I hope you get it fixed soon. Good luck!