replace valve guides, or new heads?

p.exeter_bleu · Nov 2, 2007

well heres the deal, my 351w, has been having smoking problems for a while, i purchased the engine off of a friend. when he first got it the heads needed a valve job and that stopped the smoking, fast forward a couple years and its smoking again, and some of my spark plugs have heavy oil caked on them. my other friend who worked at the shop where the motor was built says its the valve guides and always has been. the heads are pro topline 200 cc aluminum heads. my question is do i get the heads fixed? or just try and sell them and buy new heads? if it were my engine i would have purchased AFR heads. if i go with AFR do they make a 200cc head? i know the oil on the plug can also be piston rings, how can i make sure that the valve guides are the problem? the car seems to cut out during acceleration and doesnt seem to have the power it should have. could this be causing the car to run rich? any help is greatly appreciated.

Fast63 · Nov 2, 2007

as a general guide, the engine will smoke all the time if it's piston rings. If it's valve guides, it will smoke a lot on start up, and when you take off the line. I think the biggest difference to tell is when it idles. I don't think it smokes much from the valve guides at an idle, but I could be wrong.

As for heads, the AFR 185cc heads probably outflow the pro topline 200cc heads, so you could just get those, or they make a 205cc version that will definitely outflow them, but they are about 1800 bucks. How much is it to get the heads fixed in your area? One way you can check is to pull the heads off and take the valve springs off, then wiggle the valve in the guide to see how much it moves. I don't see why the guides would go bad after 2 years use, unless someone did shoddy work before.

p.exeter_bleu · Nov 2, 2007

what can cause the piston rings to go bad, the motor was originally built in 04 with forged pistons and moly rings. could it be whoever put the motor together did a bad job, or improper break in? the motor was built by texas hot rods. also how long would you consider the car to be out of start up and at constant idle? is there a certain temperature i should look at the idle to see if it smokes?

Fast63 · Nov 2, 2007

Rings can go bad from improper break-in, hard abuse, nitrous, but more commonly: running too rich for too long. Running really rich will coat the cylinder walls with fuel and the oil will not do its job, destroying the rings. This happened to me twice.

I would consider out of start up to be about 10-15 minutes minimum. For constant idle, I would say about 2 minutes, about the time you would sit at a stoplight. Have a friend drive behind you and watch you take off to see if there is a significant puff of smoke produced. If it then goes away, it's probably guides. Also, under wide open throttle, if there is constant blue smoke coming out, I think it's the rings, but if it only happens right when you punch it, it's guides.

Another thing I have noticed about rings in particular is that they smoke a LOT more when the car is at operating temp.

Rick 91GT · Nov 4, 2007

Do a leakdown and a compression test this will help narrow down the problem. Replacing all the guides and new seals will run you atleast $250 by a machine shop if they dissassemble and reassemble the heads. AFR makes a 205cc and a 225cc head.

p.exeter_bleu · Nov 5, 2007

how would i go about performing these tests? i was hoping i could figure out whats wrong without having to remove the valve covers or more. any help on how to do these tests would be greatly appreciated.

p.exeter_bleu · Nov 6, 2007

bullitstang1313 · Nov 6, 2007

A compression test is where I would start. This can be easily done with out removing anything from the engine except spark plugs. This will at least give you a baseline to see if all cylinders are running the same. If some cylinders show lower numbers you can add a little oil in the spark plug hole and try again. If the numbers jump up then you have piston ring / cylinder issues.

p.exeter_bleu · Nov 6, 2007

what tool do i have to have in order to run this test and do you have any links on how to do the test itself?

mike93lx · Nov 6, 2007

you'll need a compression tester, something you can pickup at autozone, walmart, sears, etc. try google for instructions. i'm sure it'll come up with something

p.exeter_bleu · Nov 6, 2007

basically i run the car get it nice and warm first, then i have to disconnect the tfi module or what do i disconnect? i found links that werent mustang or ford specific. after this i hold the throttle open, and crank the engine?

on a side note i removed all the spark plugs and saw 2 that are really badly covered with carbon/oil, ill have pics up in a bit.

what would be normal compression per cylinder? i saw that if all cylinders are within a 10 percent change of each other each crank that the problem is somewhere else? and if after adding oil the compression increase greatly then im most likely looking at a bad ring? sorry i have so many questions i've always had an engine with stock internals and i really dont want to take the car somewhere so they can screw me. i want to be able to find out the most likely suspects then if i have to ill take it to be fixed. i appreciate all the help.

Rick 91GT · Nov 8, 2007

p.exeter_bleu said:
basically i run the car get it nice and warm first, then i have to disconnect the tfi module or what do i disconnect? i found links that werent mustang or ford specific. after this i hold the throttle open, and crank the engine?

on a side note i removed all the spark plugs and saw 2 that are really badly covered with carbon/oil, ill have pics up in a bit.

what would be normal compression per cylinder? i saw that if all cylinders are within a 10 percent change of each other each crank that the problem is somewhere else? and if after adding oil the compression increase greatly then im most likely looking at a bad ring? sorry i have so many questions i've always had an engine with stock internals and i really dont want to take the car somewhere so they can screw me. i want to be able to find out the most likely suspects then if i have to ill take it to be fixed. i appreciate all the help.

I would look for 150psi, however I have seen some motor only pump 135psi there are many variables. if they are within 10% that is the key, however they should not be 80psi. if you add a tsp of oil to the cylinder and it increases the rings are where your losing comp, if it doesnt change it is most likely in the heads. Then do a leakdown and that test will fill in the gaps. you can rent both testers from your local parts store if you do not want to buy them, both are very handy pieces.

p.exeter_bleu · Nov 10, 2007

compression test numbers

1-130
2-145
3-140
4-125

5-150
6-155
7-150
8-147

as you can see one side of the engine seems pretty healthy the other not so much.
i didnt get to try the tsp of oil as i ran out of sunlight.

funning thing about cylinder 2, when i pulled plugs, number 2 had the ugliest looking plug with baked on carbon/oil sludge, and number1 was the cleanest most normal plug, number 4 wasnt too bad either. where do i go from here?

p.exeter_bleu · Nov 11, 2007

351 smoking, valve guides or piston rings

video of rev after idling for about 3 mins, engine still not at operating temp. ill have other vids up soon, after this rev once the smoke cleared it wasnt really smoking at all, 5 mins later i rev'd slightly holding it for a bit and i could see smoke ill post that vid in a bit. then about 15 mins into it after the reving the car was sitting there and was smoking a bit at idle.

p.exeter_bleu · Nov 11, 2007

351w smoking, after 7 mins

after about 7mins slight reving.

operating temp 15mins

round 15min mark this is what i would consider operating temp.

p.exeter_bleu · Nov 11, 2007

Fast63 · Nov 12, 2007

after seeing your videos, your car has the same exact smoking problem mine had and my problem was rings. I am a little worried about your first video though, it looks like black smoke, and I think that would mean you are running reaaaally rich.

p.exeter_bleu · Nov 12, 2007

yeah im not sure if it was black smoke because of running rich or the turndowns picking up dirt off the driveway??

p.exeter_bleu · Nov 12, 2007

replace valve guides, or new heads?

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