rebuild time?
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rebuild time?
I have a 78 460 that has 140,000 miles on it, but runs decent. I did a compression test on it and it only put out 90 psi on all cylinders. I squirted oil in the cylinders but it didn,t make much difference.
I was wondering if this is a low number. If it is are the rings shot or the heads?
I was wondering if this is a low number. If it is are the rings shot or the heads?
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If one hole was way off I'd be concerned but a consistent 90psi all the way around is pretty darn good, especially considering your mileage. If it's not burning much oil (no more than a quart every 1500-2000) and runs well in other respects, then I'd probably leave it alone other than regular preventive maintenance.
About the only thing I'd do is swap in a new timing chain set (pre-71 spec). The factory pieces rarely last past 100K and yours are probably on their last leg. It'll pick you up a decent amount of power and all it takes is about $40 in parts and a couple hours of your time. If you fee advanturous you might also replace the valve stem seals. They have a nasty habit of leaking. A lot of oil usage problems in 460s are misdiagnosed as ring/bearing issues needing a rebuild when the real problem was only a couple of weepy valve seals.
Brad
About the only thing I'd do is swap in a new timing chain set (pre-71 spec). The factory pieces rarely last past 100K and yours are probably on their last leg. It'll pick you up a decent amount of power and all it takes is about $40 in parts and a couple hours of your time. If you fee advanturous you might also replace the valve stem seals. They have a nasty habit of leaking. A lot of oil usage problems in 460s are misdiagnosed as ring/bearing issues needing a rebuild when the real problem was only a couple of weepy valve seals.
Brad
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In looking through all of my old Ford performance books, I came across one spec for a 429 CJ. It said the compression psi should be between 180 and 200! All of the other books just said the lowest testing cylinder should be at least 75% of the highest tested one. In either case, I remember doing an actual test on my '71 429, and came up with about 150 psi, although the engine had over 100K on it. It was also rated at 10.5:1. 90 sounds a little low to me. If you have already done the "oil in the cylinder thing" and used a fairly heavy oil like a straight 40 weight, then this would tend to point to the valves. I mean, what else could it be? If the rings are sealed, then the pressure has to be leaking from the valves (or head gaskets). Is there water in the oil, or oil in the coolant? If not, I would suspect you need a valve job and that the compression is leaking by the valve seats. Of course, while your at it you would want to get the valve guides at least knurled and replace the stock valve seals with some good Teflon ones. Just my $0.02.
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Originally Posted by Brad Johnson
If you fee advanturous you might also replace the valve stem seals. They have a nasty habit of leaking. A lot of oil usage problems in 460s are misdiagnosed as ring/bearing issues needing a rebuild when the real problem was only a couple of weepy valve seals.
Brad
Brad
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I remember doing an actual test on my '71 429, and came up with about 150 psi, although the engine had over 100K on it. It was also rated at 10.5:1. 90 sounds a little low to me.
Brad
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Brad is right, For a smog **** special with some age that's not ungodly bad, not great but not bad. As long as every thing is even it is a indication of good even wear.
One thing you may try is a engine decarbonizing agent. Mercury power tune Sea foam etc. Will help clean things up and could possibly up your comp. and perf.
Just a thought. It dosent always help, but is worth a shot. I have seen it do wonders with the marine motors were I work. Just remember to change your oil and filter when you finish.
One thing you may try is a engine decarbonizing agent. Mercury power tune Sea foam etc. Will help clean things up and could possibly up your comp. and perf.
Just a thought. It dosent always help, but is worth a shot. I have seen it do wonders with the marine motors were I work. Just remember to change your oil and filter when you finish.
Last edited by doccamel; Oct 23, 2004 at 11:12 PM.
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Thanks for all the replies. The motor does run well. The motor just doesn't seem veery strong for a 460. It uses a little oil, about a quart every 1,000 miles, though I not sure if it burns it or if it just leaks out of the valve covers. The little filter in the air cleaner has oil on it. Does that mean blow-by?
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That little filter will always have some oil in it. There will always be some blow-by, that's why you have a PCV valve to keep crankcase pressure from blowing out the seals.
Do a simple leak down test to make sure you have even valve and ring seal on all eight (judging by your cyl pressure numbers, you are probably okay). It's a good bet that your oil usage is valve stem seals. Very, very common. Luckily, they are relatively inexpensive to replace.
Do a good tune up, swap the timing chain set, and get your ignition system in order. That should have you motoring happily down the road for some time to come. The timing chain swap alone will up your power to a noticeable degree. It might not be a bad idea to have the carb rebuilt. That many miles and years is tough on carb seals. Not a priority, but always a good idea on an older carb just to make sure you have everything in order.
Brad
Do a simple leak down test to make sure you have even valve and ring seal on all eight (judging by your cyl pressure numbers, you are probably okay). It's a good bet that your oil usage is valve stem seals. Very, very common. Luckily, they are relatively inexpensive to replace.
Do a good tune up, swap the timing chain set, and get your ignition system in order. That should have you motoring happily down the road for some time to come. The timing chain swap alone will up your power to a noticeable degree. It might not be a bad idea to have the carb rebuilt. That many miles and years is tough on carb seals. Not a priority, but always a good idea on an older carb just to make sure you have everything in order.
Brad
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