when me and dad replaced the head gasket on my car last summer we took a look at the piston walls and they were shinny like brand new. i plan to make some mods to my car but nothin over the top (300cfm autolite, valve job, head shave, durasparkII ignition system). the engine runs fine, i just bought some molly piston rings for it but i have yet to install them.
Do I need to rebuild my engine
- Thread starter 250coupe
- Start date
As long as you have consistent cylinder pressure across all 6 (within 20% of each other), decent oil pressure, no major leaks, I wouldn't do anything except your desired upgrades. Otherwise you are repairing good parts which makes poor financial sense.
But on the flip side if you are already replacing rings, it's very minimal additional work to replace rod bearings. And then the slippery slope to Main bearings, oh and a high volume (not high pressure) oil pump sure wouldn't hurt...
-ron
But on the flip side if you are already replacing rings, it's very minimal additional work to replace rod bearings. And then the slippery slope to Main bearings, oh and a high volume (not high pressure) oil pump sure wouldn't hurt...
-ron
If you were going to take it far enough apart to do rings I would everything else at the same time. I would not just put rings in and not work on the bores. Chances are good there is wear and new rings are not going to be able to seat properly. The old rings have worn with the bore and pistons so things are happy. If you do machine work you need it all apart for cleaning anyway. If it was running poorly and you were willing to chance that the new rings were going to help it would be different but if its running good now why mess with it. The little 6's I have worked on the bottoms tend to be in pretty good shape. The issues that caused the problems mostly seem to be in the head. Things like worn valve seats, valve guides, and totally shot seals.
shmoozo
Famous Member
I agree with the others here. If you have the engine torn down far enough to replace the rings, then go ahead and replace the bearings in the rods and perhaps the mains at the same time. You'll have them apart anyway.
Replace the front and rear seals while you are at it, and all the gaskets, of course.
If you have the block out of the car (and I suspect you likely do if you're replacing the rings) then you may want to consider doing any other work that might be warranted. Some things to look at:
How are the bores? Are they so worn that an overbore is needed or justified? If so, then now would be the time to do that. If not, then from what I can recall about building engines it would probably be a good idea to at least rehone them before installing the new rings. I seem to recall that it helps with breaking them in.
How are the cam and lifters? If they are showing their age, then it could be time to think about replacing them. (Or, perhaps, upgrading them for a bit more performance if your inclinations run in that direction.)
Is the top deck of the block nice and true? Have you thought about milling it slightly to compensate for the thicker head gaskets that are sold these days?
Just some things to consider.
Replace the front and rear seals while you are at it, and all the gaskets, of course.
If you have the block out of the car (and I suspect you likely do if you're replacing the rings) then you may want to consider doing any other work that might be warranted. Some things to look at:
How are the bores? Are they so worn that an overbore is needed or justified? If so, then now would be the time to do that. If not, then from what I can recall about building engines it would probably be a good idea to at least rehone them before installing the new rings. I seem to recall that it helps with breaking them in.
How are the cam and lifters? If they are showing their age, then it could be time to think about replacing them. (Or, perhaps, upgrading them for a bit more performance if your inclinations run in that direction.)
Is the top deck of the block nice and true? Have you thought about milling it slightly to compensate for the thicker head gaskets that are sold these days?
Just some things to consider.
8) take a good look at the cylinder bores, if they are out of round by a substantial amount then it is time for an overbore. if the crankpins are out of round substantially then it is time to regrind the crank. if on the other hand things are with in tolerance, i would install new rings and bearings and call the short block good. i would also add a new oil pump, but NOT and high volume OR a high pressure pump as you wont need them, and they only cause problems. at the same time i had the engine down for freshening up i would install a new cam and lifters. dont go too big on the cam though to avoid losing low end torque. and as long as the head is off, i would likely have the valves done as well. one more thing, if you are just reringing the engine, DONT hone the cylinders since you are using moly rings. moly rings seat quickly on a smooth cylinder wall, and you dont get any microscopic crude in your engine.
Based on your comments, I wouldn't touch the block. All the mods you listed can be done by pulling the head.250coupe":3kyvtysh said:
Why'd you get moly rings? They won't gain you anything unless your bores/pistons/rings are worn - and after you fix all that, moly rings won't gain anything other than restoring the engine to good running condition. Note: you can't tell anything by looking at the bores, you need to measure w/ a micrometer.
I hope you don't mind me putting your PM out here..
You can indeed replace rings with the engine still in the car. You are going to have to figure out how to get the steering linkage and the 'belly bar' out of the way so you can slide the pan out. You might be able to raise the front of the motor for clearance (while still attached to the transmission) to aid with one or both of these impedements. Then remove all the pan bolts and take the pan off and lay it aside. Your next challenge will be removing the rod cap nuts and pushing the pistons up through the top of the motor. This really shouldn't be a problem. But at this point you have access to the rod bearings and you should inspect them, replace as necessary. Also once you have all the pistons pushed out the top of the motor you only need to losen ALL main bearing caps, then take them off one at a time to inspect and replace as necessary the main bearings. Do not tighten them back up until you have them all inspected/replaced, just snug the bolts up (not too tight). The real problem that I've noticed with in-car rebuilds is that when you push the pistons back into the motor you have to be extremely careful to make sure you don't knick the crank with one of the rod bolts or the rods themselves. Most people will slip a length of rubber hose over the bolts when they are tapping them back into place. The other problem that I've personally experienced is that when you are not 'good' at pushing pistons back into place it is possible to put the ring compressor on too lose, and when you tap the piston back into place there is a chance that you can break off the ring land, the strip of piston between the sets of rings. I did this on a 283 that was my first rebuild eons ago (circa 1990) then you are looking for a single new piston (which sucks).
I personally don't have any experience with messing with rings enough to say one style is better then another, the only thing my Dad ever said was that with 'normal' rings the rings will wear to match the cylinder. And with 'moly' rings the cylinder will wear to match the rings (because the rings are harder). So in my eyes I've always gone with stock replacements figureing I can always replace another set of rings for less $$ then finding a new block. Again I've never used moly rings so my statement should be taken with atleast a grain of salt (maybe a whole shaker)
Another way to look at it is this. If you do the headwork now and put it back together and the oily condition persists, you are really only out the head gasket price to get back to the same level of tear down. So the question is do you expend the of time/energy now when the problem could be just the head or do you expend a little more time and money later (just the head gasket price) if you find out that it is the rings that need replacing.
As I said before if it were me I would do the headwork and re-asses later, I've made myself the victim of the slippery slope far too many times.
Lots of Luck,
-ron
I understand that you have identified a problem, but have you verified that the resolution is a tear down of the bottom end? It could be that your valve guides are worn and or your valve stem seals are allowing oil down the valve stems and that is what is causing your oily plugs.250coupe":gl1dpg6v said:
You can indeed replace rings with the engine still in the car. You are going to have to figure out how to get the steering linkage and the 'belly bar' out of the way so you can slide the pan out. You might be able to raise the front of the motor for clearance (while still attached to the transmission) to aid with one or both of these impedements. Then remove all the pan bolts and take the pan off and lay it aside. Your next challenge will be removing the rod cap nuts and pushing the pistons up through the top of the motor. This really shouldn't be a problem. But at this point you have access to the rod bearings and you should inspect them, replace as necessary. Also once you have all the pistons pushed out the top of the motor you only need to losen ALL main bearing caps, then take them off one at a time to inspect and replace as necessary the main bearings. Do not tighten them back up until you have them all inspected/replaced, just snug the bolts up (not too tight). The real problem that I've noticed with in-car rebuilds is that when you push the pistons back into the motor you have to be extremely careful to make sure you don't knick the crank with one of the rod bolts or the rods themselves. Most people will slip a length of rubber hose over the bolts when they are tapping them back into place. The other problem that I've personally experienced is that when you are not 'good' at pushing pistons back into place it is possible to put the ring compressor on too lose, and when you tap the piston back into place there is a chance that you can break off the ring land, the strip of piston between the sets of rings. I did this on a 283 that was my first rebuild eons ago (circa 1990) then you are looking for a single new piston (which sucks).
I personally don't have any experience with messing with rings enough to say one style is better then another, the only thing my Dad ever said was that with 'normal' rings the rings will wear to match the cylinder. And with 'moly' rings the cylinder will wear to match the rings (because the rings are harder). So in my eyes I've always gone with stock replacements figureing I can always replace another set of rings for less $$ then finding a new block. Again I've never used moly rings so my statement should be taken with atleast a grain of salt (maybe a whole shaker)
Another way to look at it is this. If you do the headwork now and put it back together and the oily condition persists, you are really only out the head gasket price to get back to the same level of tear down. So the question is do you expend the of time/energy now when the problem could be just the head or do you expend a little more time and money later (just the head gasket price) if you find out that it is the rings that need replacing.
As I said before if it were me I would do the headwork and re-asses later, I've made myself the victim of the slippery slope far too many times.
Lots of Luck,
-ron
I would not expect just new rings to buy you that much time for the trouble. I would say do the work on the head and see if that takes care of it. Did you look at the valves when you had the head off? They could look like this
Have you done a compression test? Are those 2 worse than the rest? Many compression testers will let you hook on an air hose to put air in the cylinder. If you just put a little air in with the valves closed (not too much or it will just push the piston down) you can listen for where the leak is coming from. Exhaust means exhaust valve, carb means intake valve, oil breather means rings. Its normal to get some leakage by the rings. Compare all 6. Main thing you are looking for is differences between them.
Im not sure if the Mav is any worse than the earlier mustangs but I think my first time pulling the 6 out with the C4 took less than 2 hours. Working on an engine in the car is always a pain in the neck, and back, and usually does not do the car much good. I have also found that its is much harder to get things sealed up again. In a stand its so much easier to work and you can flip the motor upside down so you dont have oil running down to wreck your new gasket job.
Have you done a compression test? Are those 2 worse than the rest? Many compression testers will let you hook on an air hose to put air in the cylinder. If you just put a little air in with the valves closed (not too much or it will just push the piston down) you can listen for where the leak is coming from. Exhaust means exhaust valve, carb means intake valve, oil breather means rings. Its normal to get some leakage by the rings. Compare all 6. Main thing you are looking for is differences between them.
Im not sure if the Mav is any worse than the earlier mustangs but I think my first time pulling the 6 out with the C4 took less than 2 hours. Working on an engine in the car is always a pain in the neck, and back, and usually does not do the car much good. I have also found that its is much harder to get things sealed up again. In a stand its so much easier to work and you can flip the motor upside down so you dont have oil running down to wreck your new gasket job.
Patrick66
Famous Member
CoupeBoy":2sxs9vfk said:
you make this sound easier than it really is
first things first; what are your compression numbers?
did you buy standard rings? theres 2 problems. the engine may have been bored before, the only way to know is to measure with a micrometer (echo echo). also, your bores may be out of round or worn, and you'll have to bore it over.
you should probably check your clearances here too with some plastiguage.
if your going to do this, be prepared for a full rebuild. but if its not giving you any trouble sometimes its better left alone. so make sure that your rings are the problem, do a comp. test and squirt some oil in there. if your numbers go up with the oil then its all in your head.
Odds are really good that the oil is coming in through worn valve guides and seals, rather than worn rings. The valve guides and seals usually wear a lot faster than the cylinder bores. Worn rings will usually show up as low power, lots of blow-by and oily vapor coming out of the crankcase breather or oil fill cap, and blue smoke out the tailpipe. Worn valve guides will let in enough oil to foul plugs, more if the engine idles for awhile.
Regarding standard Cast Iron vs. Moly rings, Moly rings are same/same as Cast Iron rings, except they have a layer of Molybdemun on them as a high-pressure lube (similar to Moly high-pressure grease). They don't wear the bores any more than Cast iron (they can actually reduce bore wear), but their main benefit is nearly instantaneous break-in. Cast Iron rings often don't seat until they've been put under a couple of heavy loads. Moly rings, especially the Plasma Moly ones, seat in the first couple of passes up and down the bores.
After all that, I'd second the above comments about working on the head first. Yank the head off and start on it, and while it's off you can beg/borrow some micrometers and measure the bores to see if they're worn, out of round, or what. My nickel bet is that they're fine.
Another consideration ( for the lower end) is your oil pressure. I'd put a gauge on it. If it has at least 20 psi at warm idle and 10 psi for every 1000rpm, then you're pretty safe in assuming your bearing clearances are fine.
Regarding standard Cast Iron vs. Moly rings, Moly rings are same/same as Cast Iron rings, except they have a layer of Molybdemun on them as a high-pressure lube (similar to Moly high-pressure grease). They don't wear the bores any more than Cast iron (they can actually reduce bore wear), but their main benefit is nearly instantaneous break-in. Cast Iron rings often don't seat until they've been put under a couple of heavy loads. Moly rings, especially the Plasma Moly ones, seat in the first couple of passes up and down the bores.
After all that, I'd second the above comments about working on the head first. Yank the head off and start on it, and while it's off you can beg/borrow some micrometers and measure the bores to see if they're worn, out of round, or what. My nickel bet is that they're fine.
Another consideration ( for the lower end) is your oil pressure. I'd put a gauge on it. If it has at least 20 psi at warm idle and 10 psi for every 1000rpm, then you're pretty safe in assuming your bearing clearances are fine.
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