84 ford 460 engine

I've never seen valve guides affect compression readings. Burnt valve faces and damaged seats yes. worn valve guides/seals usually result in oil consumption. Most notable blue smoke on start up after sitting for awhile, and puff of blue on acceleration. And I've never seen just exhaust or just intake guides go. And if the valve guides and seals are letting enough oil pass, then fouled plugs. A better test is a leak down test, or bringing each piston to TDC, install a "chuffer" and apply compressed air to a wet cylinder listening for escaping air at the tail pipe and carb. Doesn't have to be really high pressure,

It has also been my experience that doing valve work on an engine with time and mileage on it is usually a waste of money in the long run. The compression is raised from better valve sealing putting stress on old and worn rings which soon fail..

If you have a good engine shop in your area I would have what you have rebuilt. This would be a good time to upgrade the cam to one more suited for you RV , and even a manifold and carb update to something more geared to your RV as well. Its hit and miss trying to buy a "good" rebuilt engine. The low end parts houses are stay away places, such as Autozone, Advance Auto Parts, Pep Boys etc. Ford does sell reman engines with a good warranty, but your going to be stock form, and engine mods void the warranty. Things to beware of: Resized rods, re-machined cam shafts, polishing cranks is fine, but turned if they wont guarantee in writing less than .010 under on the mains and rod surfaces, stay away. Same with "machined" valve guides, that means they knurled them, not replaced them. Knurling never lasts. If rockers are worn they should be replaced, not "re-machined" Doing it right costs a bit, but doing it right means it will last. That all said, because its an RV which means lots of sit time and no run time, it might just be the valve seals have dried out, cracked etc. Replacing valve seals if all else is ok is fine, and often can be done with out removing the engine or the heads.

Whitelightning

"exhaust valve guides were worn out" diagnosed with a compression test?? "$1200-$1500" to fix???

Run, Don't walk away from this guy! He is either totally incompetent, or a thief, or worse both.

If it is running fine, don't worry about it. If you haven't done a full tune up (new: plugs, plug wires, rotor, distributor cap, air filter, PVC valve oil and oil filter) since you don't know when, do that now. I'm betting any slight miss you have at idle will be eliminated by that.

Back up here a bit guys, a 460 in motor home duty can be very hard on exhaust valves over a extended period of time and the sustained high temps of the valve would accelerate valve guide wear because it would tend to burn lube of them. Then when the valve guides wear a good bit, the vavle will tend to wooble in seat a bit and not always align correctly which will accelerate valve seat wear. Before you hammer this guys mech completely, you do not know what or how he tested it and like I said in that duty cycle, they are hard on exhaust valves and this guy may know this as well. Intake valves tend to do a lot better.

----------------- The SnoMan

If the seals or guides are worn, would there be any harm in me keep driving it that way?

Thanks,

Mark

SnoMan wrote:

That's why I recommended the leak down and using compressed air. I would find it hard to say it has valve guide issues from just a dry and wet compression test. unless we get the oil burn on start up and acceleration. Nor do we know mileage figures. I've seen 15 year old RVs with less than

If it does have valve damage then driving it long distance or on heavy grades will only accelerate that damage, to the point that the valve seat could come out, jam a valve open, or break a valve at the base of the stem dropping it through a piston. Some how that's not something I would want to happen coming down a steep grade

Whitelightning

A bigger concern is if there is leakage now in some of the exhaust seats, when it get to a certian point, it can rapidily accerate the burning and burnout the valve and seat on one trip and at the very least loose power and in a worst case senerio, damage the head or heads and in extreme case when the valve super heats because seat is badly burned (the only cooling a exhaust valve sees is when it is firmly in the seat and well seated so it can transfer heat to head) it can crystalize the metal in valve and case head to snap of and really raise "H" with the engines interanls as it trys to compress the valve head on compression stroke. If compression is low and does not come up much when oil is squirted into cylinder, you have leaking valves and you need to do a valve job because unlike a car where the engine is not working hard, in a motor home it is working all the time and not much room for to nurse it long.

----------------- The SnoMan

Reading all of the posts on this, they are all good and are all valid points.

As a Mechanic, I want ALL the details. Please tell me/us ALL of the symptoms you have. I also have some questions.. What did this mechanic find on a compression test? How many miles on this engine and was it ever rebuilt in its 22 years?

When were the distro cap, rotor, plugwires, and spark plugs replaced? if they were replaced, what did the plugs look like? Black, White, or Grey? If you havent had the plugs replaced, do this... you state it seems to miss at idle, so when the engine is cold, start it, make sure it is missing, shut it off, pull the plugs 1 by one and inspect them. See what one is different in color. Thats the one that is misfireing, or not fireing. Replace that plug, might want to inspect that plug wire too. If it is found to be OK, then replacing the plug should have gotten rid of the miss, for now.

Here is the deal... As a mechanic, I would have done this with the few facts we have here....

Spark check (inline spark checker) Rules out/confirms wires, rotor, and cap. Spark plug inspection combined with compression check Its just smart to do both at once. .............

As for ok driving it? sure, in most cases it is ok to do so, but spark plug life is about 1/10 of what it should be. You will need to replace some things prematurely like the Cataletic converter, and need to check your oil level often.

I think you really need to tell me/us ALL of the symptoms you have.

djdave

Thank you for all who has taken the time out to help me!

Ok, this is what I know, and what I have done thus far.

I bought the motor home in Nov 2005. The person who I bought it from told me that the engine and transmission were rebuilt. He also told me that there is approx 20K miles on the rebuilt. When I got it home, I had a mechanic go through the whole thing. He found I needed a new intake manifold and carburetor. Both were leaking and rusted. I did replace both. The intake I replaced with an Edlebrock, and the carburetor a Holly 4160.It definitely started and ran better. It did seem to not have the power it used to have after the change. Also, I started hearing a clanging noise coming from the engine. It doesn't happen when I rev up the engine at idle, but it does happen when I get over 50 mph and gets progressingly louder the faster I go.

I also replaced the spark plugs/wires, distributor, fuel filters, oil change/filter and motor mounts. I took it to another mechanic (because the first one couldn't look at it) and he is the one who did a compression test, and told me about the exhaust valves. He tested 2 cylinders @ 60psi and one @ 90psi. All the others were @ 120-150psi. I don't notice any blue smoke when I start it up. As for the condition of the spark plugs, they seemed to be grey colored. I replaced them because I was trying to eliminate any problems.

Thats all I can think of now, I welcome any more comments.

Thank you very much!

Mark

djdave wrote:

On 9 Jun 2006 09:45:48 -0700, "marknts" snipped-for-privacy@gmail.com wrote:

"snipped"

This is just my $0.02 but, if those compression readings are accurate, the 60 and 90 psi cylinders definitely have problems. The spread on the others is borderline at best. If this engine only has 20 k miles since overhaul, and already having valve or cylinder problems, then, it is likely that this was a shoddy overhaul and the heads may not have been propery overhauled at the time or, the engine was not properly broken in after overhaul. I note that you changed out the intake and carb on this engine for whatever reason. It may be that the carb is not correctly jetted for this application resulting in a lean mixture which will burn exhaust valves and, even pistons if allowed to continue. If you continue to operate it in it's current condition, it is almost certain that you will cause more damage which may include damage beyond reasonable repair of the engine. IMHO, your very least repair at this point is removal of the heads and a good valve job which will probably include replacement of some or all of the valve and, possibly, seats. Make sure the machinist checks the valves before he starts work to make sure the bad valve lcations coincide with the bad cylinder readings. If they do not, you may have piston and ring problems to deal with. Many well equipped machinie shops can vacuum check the valve to be sure where the problems are. You must also make sure the carb is properly calibrated and the ignition timing and curve are proper for the application just to make sure you don't have excess timing advance because of a weak or missing advance spring. As Warman told you, this ain't gonna be cheap but, the only way to repair an engine that lives at heavy work is to do it right the first time.

Good luck

Lugnut

With all this new info, there is definitely a problem. The "rebuilt" drive train throws a lot of left handed monkey wrenches into the mix becuase you have no idea how good a rebuild it was. I concur it sounds like the carb is running way lean. I love Holly carbs, on hot rods, but for daily drivers and RVs, its Eldebrock with vacumm secondaries.. At 60 PSI the valve is seriously burnt, or you've started a hole in a piston. The clang thats a weird one, ping I could see with lean. Only thing I can think of for clang is loose flywheel to convertor bolts, or binding u-joints causing a resonance in the drive shaft perhaps.

At this point one has to ask what kind of shape is the rest of the rig in? If its a good clean rig, then placing a good engine in it is worth while. If the body and interior is getting long in the tooth it might be time to cut your losses.

Whitelightning

I am thinking that the clang is detination at higher rpm's and this same detination is really hard on valve too and can lead to their buring because when it "pings' hard it can vibrate valve in seats and start the errosion that leads to burn valves over time. While this can go on for a ling time in a lightly loaded engine, one that is being worked hard in motor home duty will suffer from its effects a lot sooner.

----------------- The SnoMan

One more question,

Could worn valve springs give low compression readings too?

Thanks,

Mark

SnoMan wrote:

Weak valve springs would normally show up as misfire at higher rpm. They typically seal just fine at low rpm until the sealing surfaces are damaged by operation at higher rpm and load. IE, if you rebuild the heads with weak springs and run a compression test you would not know an iffy weak spring existed yet, the situation would deteriorate very quickly with the engine at higher rpm as a weak spring would not be able to control the valve and valve train in sync with the cam profile. As the valve fails to seat properly, you should notice a misfire and the sealing surfaces will be quickly eroded. Yes, the springs could result in this type failure which eventually shows up as low compression. Unfortunately, the only repair is a head rebuild. A good head rebuild will include checking for proper spring installed height, on and off seat tension. There are ways to adjust this within limits which a good head man will be fully aware of. Your choices in correcting the problem you have described with the readings can only be corrected with at least head work and, maybe, piston and ring work. If the head man checks the heads and finds no leaking valves that coincide with the low pressures, you should consider a rebuilt long block assembly from a reputable builder with a good warranty. Any way you approach the problem, it ain't gonna be cheap to "fix it". You can, of course, patch it with unknown results.

Lugnut

SOme good points by LugNut. Bite the bullet and pull the heads now as it will likely only cost more to fix the longer you wait to do it.

----------------- The SnoMan

I'm taking all the information everyone has told me, and coming up with the conclusion to get a new motor.

I'm thinking of a Jasper engine. Please let me know your thoughts Jasper engines. Are they reliable, built well ect..?

Thanks,

Mark

lugnut wrote: