SOmeone saif that doing a valve job on an old engine is a gamble,becasue the increased compression will put increased stress on lower end parts.
I am replacing the head gasket on a 3.9 dodge with 151,000 on it. I am debating with having a valve job done or not. I will have it crack checked and milled if necessary.
Or I thought about just laping the valves at home. I put fluid in one of the heads and it seeped out slowly of every valve but one.
stryped fired this volley in news:4fa97790- snipped-for-privacy@k2g2000yql.googlegroups.com:
You're _supposed_ to get about 50% blow-by on that motor. It was never intended to burn the gas in the cylinders, but rather, in the exhaust where it creates that cool exhaust tone that motor is famed for, along with the hyper-cool tailpipe flames it makes.
You shouldn't mess with leaky valves. You'll screw up the "street coolness" of the vehicle.
LLoyd
It happened to me on an old Ford 360. The blowby was intolerable after installing rebuilt heads.
151,000 miles is still in the new end of most engines these days.
My Ranger (3.0)..a 2001 model passed smog yesterday with flying colors,, better by far than the minimum requirements.
Now yours IS a Dodge...but 151k is only the half way point for most engines.
Gunner
"Somewhere a True Believer is training to kill you. He is training with minimum food or water,in austere conditions, day and night. The only thing clean on him is his weapon. He doesn't worry about what workout to do--- his rucksack weighs what it weighs, and he runs until the enemy stops chasing him. The True Believer doesn't care 'how hard it is'; he knows he either wins or he dies. He doesn't go home at 1700; he is home. He knows only the 'Cause.' Now, who wants to quit?"
NCOIC of the Special Forces Assessment and Selection Course in a welcome speech to new SF candidates
This is the point where you get out the bore gauges and start checking against the factory specs in the manual. If you've got no scoring, the bore size is in spec and there's no out-of-round or taper wear, you should be OK. But without dropping the crank and looking at the bearings and journals and measuring same, you've got NO idea how much more wear, if any, you can get out of the thing. And if you go that far, you might as well commit to a rebuild.
I would have started looking for a donor engine at the local U-Pull- its, myself. They usually go for $300-400 around here. Heads are usually $25 or so. Certainly cheaper than messing around with machine shop rates.
Stan
It works even better if you can plumb an old air pump out of a '68 Mustang into the exhaust header.
Shouldn't be a probem if you have kept up with your oil changes. A lot of people do this every day. But do you really need a valve job? Perhaps just disassemble, decarb, lap and reseal.
Slight fluid seepage in not unusual in even a heath head. Lapping at home may be a good idea. You can at least see how bad it might need a valve job. But if you just lap them, keep each valve in it's original seat. It often makes a difference.
I had low compression on two cylinders, 90 on one and 95 on the other. Would lapping raise the compression much? My manual says 100 is the minimum PSI per cylinder
Not modern engines. Crank and bearing materials, and even more so the lubricants, make modern lower ends very beefy. I use to do rod and main jobs frequently in the cars I had as a kid. Haven't done a bearing job, nor had it done, in many decades. Don't worry about it. Do the valves.
Besides, that high compression only comes with full throttle. When you are at less than full throttle, the BMEP is considerably reduced. So unless you are driving full throttle all the time you are unlikely to hurt lower end.
I had low compression on two cylinders, 90 on one and 95 on the other. Would lapping raise the compression much? My manual says 100 is the minimum PSI per cylinder
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Examine your cylinders carefully. Look for any vertical scoring, and measure the wear just below the ring wear ridge, about 3/8" down in the cylinder. If these look good you can probably assume the compression problem was in the valves. Most likely it is.
If your valves are not to pitted to lap smooth, you will be fine. If not, best to have them ground. Be sure to use a wire brush on a drill or die grinder to decarb your seats, and a wire wheel on a bench grinder to buff your valves.
???????
stryped wrote in news:4fa97790-25a5-4b12-b06f- snipped-for-privacy@k2g2000yql.googlegroups.com:
It's not going to make any difference, or much anyway as to the lower end. All engines since 1995 or so are designed with a minimum "as new" life of
150,000 miles on internal components. This is due to the emissions laws. Having the head job done shouldn't be an issue. Your motor is just now to that stage, so only now will it begin to actually wear to any significant amount.
Consider the restriction of the throttle plate . You're *NOT* going to get full cylinder fill , and therefore maximum cylinder pressures at part-throttle operation .
stryped fired this volley in news:59f024dc- snipped-for-privacy@g20g2000vba.googlegroups.com:
That's just because you were testing the motor at cranking speeds. A ten or fifteen thousandths gap in the valves won't matter at all at
15,000 to 20,000 rpm.Lapping is just to make the valves look pretty while you have them out of the motor.
LLoyd
That's outside of spec all right... I hope they weren't next to each other; if so, did you inspect the head gasket while you were taking the head off?
The spec is for testing at cranking speeds. It is of course completely true that the condition of the valves will matter very little after a few seconds at three times the engine's red line...
And to correct sealing problems in the valves, of course.
I expect he meant high force or high pressure.
Joe Pfeiffer fired this volley in news: snipped-for-privacy@snowball.wb.pfeifferfamily.net:
Joe, you're _really_ going to regret feeding this troll.
He'll sap the patience of Job, and make every 'right' answer given to him sound like blather by the time he's done.
Just read some of his prior threads.
"Which way do you turn a right-handed screw to tighten it" might be in the genre of his questions. When you tell him "clockwise", he'll ask if you mean viewing it from the top or the bottom.
Just wait...
LLoyd
Joe Pfeiffer fired this volley in news: snipped-for-privacy@snowball.wb.pfeifferfamily.net:
One can hope.
LLoyd
There is an extremely small chance that a valve job MAY increse the vacuum in the cyl enough to draw oil past weak rings, causing oil consumption. USED to be a real consideration back when rings were generally worn out, and cyls bell-mouthed, tapered, and out of round by 60,000 miles or less.
Those days, thankdully, are behind us. Not at all uncommon to have virtually no measureable cyl wear at 300,000km today. I've had engines with more than that on them where you could still see the crosshatch from the final cyl honing.
Don't waste your time and money doing a half-assed job. Lapped valves will NOT maintain a seal long. Today ALL engines have at least a 3 angle valve job, with at least a 1 degree mismatch between the valve and the seat to make a line contact, self cleaning seal. Lapping cannot do this.
If you just lap the valves and put in a new set of head gaskets, the gaskets are wasted when the valves fail, again.
To have the heads properly checked the valves come out anyway - and they come apart to install the new valve seals.
Have them ground properly - both valves and seats, or just tow the truck to the scrapyard and safe everyone a lot of headaches.
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