Hello- I have a 68 olds 425 that rattles after the motor gets warm. The oil pressure gague drops to about 10psi at an idle. Upon start up I am runing 50psi and as the motor warms up it gradually drops until 10. When you rev the engine it picks up pressure but still rattles. The motor is freshly rebuilt. I reused the cam from the motor (crower aftermarket) and new pushrods. The heads are "C" heads and the block is a "D" The heads are from a later 455. I know as the engine warms up the everything should be expanding and getting tighter so I dont think the rockerarm studs are loose... I just dont know.. Should I go with a new cam and lifters... or do I go to a heavyer weight oil? Any help..

 

I don't think heavier oil is going to be much help. You better start by taking the pan down and checking bearings and the oil pump. Did you have the cam out of the motor? Cam bearings could also be a problem. Lifters might make some noise but they won't cause you to loose oil pressure. Good luck

 

Id pull the oil filter an cut it open, also drain the oil and look for bearing material...

Were the lifters kept in order with the cam lobe they were mated to???

What kind of oil are you using???

 

I will pull the oil filter and drain it and look for anything there as well as an oil change. If that does nothing I will pull the pan and look at the bearings as well as oil pump. When I rebuilt the motor I replaced all the bearings and was also told not to put a high volume oil pump in the car due to olds being notorious for pumping all the oil up into the heads and starving the bottom end. I am running a napa brand 10w 30. When I first ran the motor I used valovline racing oil. As far as the cam and lifters being in sync they were until I had a local shop do some head work for me but the tolerances were to tight on the valve guides and the end result was bent rods. So I came across another set of heads off a 455 and did the transplant in which I used brand new rods. This is the first motor I have ever built so any help is appreciated. I just don't understand why the oil pressure starts out so good then drops off.

Thanks!

 

The oil loses viscosity when it gets hot and the pressure drops. Can you tell where the rattling is coming from? Not really bad pre-ignition is it, had to ask.
You sure your gauge is good? been through that with oil and water temp gauges more than a few times. You could try 20W50 and see what happens, if the rattling stops it could be too much clearance somewhere.
I agree and would say to check your bearing clearances and oil pump. The bearings are where too much clearance normally results in the big pressure drop when it warms up like in high mileage engines. Did you check the bearing clearances when you assembled it? Size the new cam bearings to the old cam? Before replacing things I would do everything I could to track it down. The engine runs so you got that much, anybody can have their engine rebuilt at a shop but the faint-hearted never wins the fair lady.

I'm no experienced engine dude and just wild guessing so this is just my -2 cents woof.

 

Can you tell if the rattle comes from the top or the bottom of the engine? A little more information might help on this issue. Also pull the valve covers and see it oil is pumping to the top

 

Is it a rattle? nock? or tick? does it keep in sync with rpm? Does it go faster as engine is revved? or is it a random rattling noise?
Nocks are usually related to low end
Ticks are associated with valvetrain cam and timing
Where exactly is it coming from?
It's really hard to tell without hearing and seeing.
I had a rattle on my 71 after a rebuild that came from the rear lower part of my engine and it turned out to be loose bolts on the torque converter going to flex plate.

 

Pre ignition the rattle isn't there. But when the motor warms up it is for sure in the valves. I am going to pull the valve covers today and take a look and see if there is oil pumping up through the heads. I am also going to switch oil.. but that is going to have to wait until payday (wife just let me buy a carb)

Thanks guys I really appreicate this.

 

So were the lifters kept in order with the lobe they came off of or were they mixed up???

If they were mixed up the cam could be going flat...

That would put a lot of metal in the oil...

The metal would hurt the bearings and the oil pump...

 

If a lobe goes flat, how does it create lifter noise?

Norm

 

When a cam lobe is "flattened", it's never totally "Flat" per say. It's still tear drop shaped, but doesn't generate enough lift to keep constant pressure on the pushrod, or generate enough to open the valves. Usually, a collapsing lifter is a part of the noise equation.

 

Do a compression test on all of your cylinders. If you have a dead cylinder, the valves are not opening. Or pull the valve covers off and disconnect the coil wire.
crank the motor over, and see if you have an excessive amount of rocker and bridge play.

 

What lifter bank angle is that 425?

 

 

Does it still generate more "lift" than it does when the lifter is on the heel (base circle)?

How would a "collapsing" lifter cause a lobe to flatten? Or how would a "flattened" lobe cause a lifter to collapse?

Norm

 

It should, unless the push rod is bent, or the lifter collapsed.

Of this I am not totally sure. From my experience, they go hand in hand though.
My guess is because of the excessive "Bouncing" of the collapsed lifter in the bore without pressure keeping it in constant surface contact.

 

Either might cause excessive lash, which could cause valve noise, but it doesn't explain how a "flattened" lobe can cause excessive lash.

Does it do it, by changing the heel diameter, or the spring pressure? Both?

I have no experience. All I have is a little common sense and a picture, in my head, of two cams turning and a lifter following each profile. All valvetrain specs are the same, except lift. One is .0025" and the other is 2.500".

How could the lower one cause lifter noise? Would it be louder if there was no lift?

Are all flat cam lobes caused by collapsed lifters? Are all collapsed lifters caused by flat cam lobes?

Norm

 

Good point.
I don't see a flattened lobe instantly causing excessive lash. Sometimes the lobe is worn/flattened on an odd angle from a mismatched lifter and as the lifter is spinning it is stressing the push rod from the varying vibrations, angles and pressures. Eventually, the little "ball" part of the push rod breaks off because that is the weakest point of the rod.
Then the excessive lash could be had. I've seen that happen before, but that motor also had a collapsed lifter on the same cylinder. I can't say for sure that one or the other was the definite cause of the push rod failure. I saved the cam and mashed up lifter, and have them laying around here somewhere.


Thank goodness for that. Common sense makes it much easier to have an intelligent conversation about possible engine failure causes.

I believe they'd both be fine from a simple machine operation functionality standpoint. It would definitely be louder if there was no lift. The lobe profiles help keep the cam from sliding out of the front of the motor when it turns. If they were a perfect flat circle, the cam would walk all over the place and mash up the distributor gears and bind the timing chain.

I'd have to say no. Mismatched, or non crowned lifters, lack of lubrication, and collapsed lifters are all possibilities. I'm sure many other odd things over time have been a factor as well.
The answer to this is probably no as well. I could never say for sure. Every collapsed lifter I've seen has been mated with a damaged cam lobe however.

 

Id think when a lobe goes flat it would put a lot of fine metal powder in the oil...

The metal would get embedded in the bearings and wipe out the polished surface on the crank...

After a short time the clearance would open up causing low oil pressure...

Also all the metal going through the bearings would create heat due to metal on metal possibly leading to a spun bearing...

I don't really know what kind of noise it's making... But he says it has low oil pressure and it's making noise... That sounds like a spun bearing to me...

It's possible there's a bad lobe and a spun or worn bearing...

Id pull the valve covers and check out the rocker arms and pushrods, ect., cut open the oil filter, drain the oil...

A lot of good suggestions here, very hard to diagnose over the internet without hearing it run...

 

I believe what Bluevista meant by pre-ignition is detonation. Since the noise is not heard exclusively at shut down I assume Bluevista is not referring to a run on condition where the ignition is turned off but the engine continues to run roughly.

Detonation is a condition in which the air fuel mixture instantly combusts similiarly to an explosion when ignited. This instant combustion sends a shockwave through the engine which can cause excessive wear or failure of the crankshaft, bearings, pistons, rings, and connecting rods as well as other engine components. Detonation sounds something like a bunch of pennies being shaken inside a coffee can. Detonation is most commonly heard when the engine is under high loads, such as when accelerating up a hill. It is very rare to hear detonation at idle and this would signify major problems with the engine. Detonation will not directly result in reduced oil pressure, but reduced oil pressure can result if certain engine components become excessively worn or damaged by the detonation.

 

Works for me.

Norm

 

Well it appears that there has been quit a bit of talk about this.

Well heres an up date.... IT BLEW UP. I tried to be cheap and go with a straight 50 weight oil saw some metal in the oil (hoping that was due to some break in not break down)... well the oil change took care of the top end sounded pretty good the oil held right at 30psi. Drove up the road after the oil change... and that took care of the bottom end. Knock like a sum bitch on the bottom end so I parked it and found a full race 66 425 that someone else built. They put it on an engine test stand and then I got to see it run, it has about 80psi oil pressure along with a crank scraper and restricters. Not a rattle tick or anything. Hey I tried to build a motor and lost about 1000.00 attempting it. Well for 900.00 I got another one. The guy I am buying the engine from said "Hey you tried but I have found for some guys its cheaper not to "learn" just go with someone that knows. Maybe next time I will be the learning curve and not be part of it.... who knows?! Thanks for all of your help guys. What an awesome group this site has! When I get it all back together I will post some pictures and dyno results.

-Brian

 

Well, at least you tried. Tear it down and learn from it.

 

Well boys I got that new motor paid for and it is set in the car. Should have it runing tomorrow. I will let you know how it does. I have already seen it running on a stand. I know its going to be great. I will have dyno results in a couple of weeks. Once again thanks for all the help. Oh and I will pull that other motor apart and let you know exactly what when gunny bag!

 

Good luck...been down the same road as you...lousy machine shop that went under screwed up my first engine...Just put my new one in last week...A lot of time and money down the drain...

Dont give up on the other one...get her right and you will have a spare..even though there can be some pain in doing it yourself,...thats the best part of the hobby!......doing it yourself as best you can

 

Post some pictures when you get it running. Good luck

 

I got stung real bad from a builder last year, I lost alot of money and the motor ran 20 minutes.
The bottom line is even the best guys screw up now and then. The knowledge you gained is worth the $. I hope your new motor is a good one.
Keep us posted.

 

I got fried by a builder and he kept giving me bogus heads . The labor was killing me since I recommended him I couldn't really charge extra ...

After the fourth head went bad I had to dig up another engine ...

I called up on an alias and had him build a nailhead(something he would have a hard time selling). Kept calling for progress reports . When it was done I stroked him for a couple months stalling about picking it up . He said if I didn't pick it up I would loose my deposit. I told him who I was, why I did what I did and told him where he could "install" the engine and my deposit ...

 

http://www.youtube.com/watch?v=tJAvZwuZ8Es

Check it out. Here is the car at idle.

 

Sounds nice except for the lifter noise ...



...

 

funny guy eh!!

 

funny guy eh!! that was the last one!

 

...

Sounds sweet, I'm just jealous . My motor is making a strange noise...

If it needs a rebuild I might mothball the "number" engine and find a transplant...

 

To each is own sir. I could not be more pleased with what I have done with mine. It has great power and still has the stock gears. Now the next step is 3.55's

 

The car looks and sounds great!
great job

 

I've had it happen more than once on Big block chevys. The lfters flatten out so much you can barely pull them out. On a BBC with only a 1/4 turn preload it takes only .010 wear in the lifter to hear a tic. If your running adjustable pushrods on an Olds close to zero lash, you'll know when you got a lobe heading for the oil filter.