1957 Oldsmobile Camshaft

Hi Guys
I Am Writing This Message In Desperate Need For Help. I Have Owned My `57 Olds` For Over 8 Years And A Couple Of Years Ago I Rebuilt The Engine. After Only 500 Miles There Has Been A Tapping Noise From The Top End. When I Investigated The Noise I Found That The Very Rear Lobe On The Cam Had Worn Down To Almost Round With There Being Only 3/16" Of Metal Left And No Sign Of The High Point Of The Lobe!
So, I Order A New Cam Which Measures Exactly The Same As The Damaged One. The Distributer Drive Is Perfectly In Line, All The Lobes Are The Same And The Timing Gear Measures The Same To The Front Of The Block As The Crank Gear. The Only Thing That Does Not Look Right Is That The Lifters Are Only Just Covering The Lobes! The Original Cam That I Removed From The Engine When I First Rebuilt It Measures The Same As The Later Two Except The Lobes Are A Little Narrower. I Dont Know If This Has Anything To Do With The Wear On The Cam But It Just Doesnt Look Right. Are The Two Problems Related Or Is The Wear On The Cam Due To Lack Of Oil Pressure, Which Seemed Fine When I Rebuilt It.
I Really Need Some Help And It Is A Rare Auto Here In England And No-one Can Help. I Will E-mail Any Pictues If Requested. I Am Running Out Of Money And Cannot Afford For This Cam To Go The Same Way.
Thanks
Tim

First of all, there is no need to capitalize the first letter of every word........it makes your post tough to read and I already have a headache :smile:

You need to understand that the lifters must slowly rotate as the camshaft spins. This evens out the wear on the lifters. So, the lifters are designed NOT to sit squarely over the lobe. They must be off- set to one side a bit to ensure rotation.

If the lifter is not rotating, it will wear out the cam lobe very quickly. I suspect this is what happened in your case.

So, why does it not rotate? When the engine was rebuilt, did you use a new cam and lifters?

The engine builder may have re used the old lifters with a new cam OR, if re using the old cam and lifters, put them back in the wrong order. This is bad because as the lifters and lobes wear, they establish a matched wear pattern. Mixing up used lifters on lobes or old lifters on a new cam produces a wear pattern mis-match and can result in the wear pattern you saw.

If the cam and lifters all were new, it just might be a bad cam, or the camshaft is intended for a different model of Olds engine.

One thing that might work........if the original camshaft looks good, and all the lobes are in good shape with no scoring marks, you can lightly polish the cam with fine emery paper and reinstall it with NEW lifters.
New lifters on a used but good cam is fine, and I have done this on many occasions.
Good luck.

hi magic rat

thans for repling to my question.
i dont know why all the words started with a capital letter. it certainly
wasnt my doing. my typing takes long enough as it is!!!
ok, the cam shaft and lifters where both new when i rebuilt the engine. i dont think there was any
tightness in that particular lifter when i assembled the engine. i have
talked to several car builders and a couple have suggested that a `bad` cam
may be the reason. it just seems very strange that it only happened to one
lobe, could this be the case? as far as i know, and assuming that i was sent
the cam i asked for, that is the only cam that will fit the engine, and it
measures the original cam exactly apart from the lobes are a little wider on
the replacement cam.
please let me have any more views on the subject.

kindest regards

tim

Hi,
In such cases a 'bad' cam usually occurs because the taper on the cam lobe is incorrect.
Usually the lobe is machined with a 3 degree taper so that one side of the lobe is effectively slightly higher than the other. This taper is virtually impossible to see by eye, but can be measured with a micrometer.

Similarly, the bottom of the lifter is machined to be concave. If either the lifter or lobe is not shaped properly a flat cam lobe can result.

Alternatively, if that one lobe was incorrectly hardened during manufacturing, accelerated wear could also occur.

Have you tried to contact the manufacturer of the camshaft? Perhaps they had a run of bad cams or might have some technical advice. They may be willing to send a free replacement.

However, if the old cam is still in good shape, there is nothing wrong with re-using it, with new lifters.

hi magic rat and all
thought you might like to have the latest news on my adventures in cam shaft land.
i have installed the new camshaft, replaced all bits and pieces and refitted the distributer.
i have run the motor with the starter motor without the valley pan cover fitted. as the engine turns all the lifters are spinning merrily............except the suspect one at the back!!!!
it is turning but not has happily as the rest. for example the other lifters are turning approx` 1/4 to 1/2 turn per rotation of the cam and the back one is only turning approx` an 1/8" to 3/16" turn per cam rotation. so, does this point the finger anywhere else?
one thing i have thought of is, i had the heads converted to run on unleaded fuel. could the engineers have cut the new valve seats to deep? which would cause the rocker arm to be further over than the others. i know i have to measure the heads but i am just thinking out loud.
just a theory.............
look forward to any ideas.
thanks
tim

That is an excellent observation!!
My service manual shows all the rocker arms are on a common shaft, correct??
So, if thats the case, the valve gear is of a non-adjustable type. Many other American v8 engines, (but not all) use a system where valve lash can be adjusted individually.

So, what we want to look at is 'lifter pre-load'. For adjustable valve gear, when the valve is closed, usually, the pushrod pushes the plunger (in the top of the lifter) about 2 or 3 mm . This places an initial load on the valve lifter. If this one pushrod is now 'too short' then it does not exert enough pressure on the lifter (just when the valve is closed) and thus does not get enough 'drag' on the cam to turn it sufficiently. I recall that lifters only rotate when the valve is closed. When the lobe opens the valve, it does not spin.

When the valves are closed, try turning a few pushrods, between your thumb and index finger. There should be considerable drag, but you should be able to get them to turn a bit. Compare them to the suspect pushrod. Is that one easier to turn?? If yes, then the lifter pre-load is not sufficient.

What may be needed is an 'adjustable pushrod' These have a threaded collar with a lock nut so their overall length is adjustable.

Try Mondello Performance
http://www.mondellotwister.com/RockersPushrods.htm
They are probably the best place around for Oldsmobile engine parts. They list an adjustable pushrod for $40 US.
Almost all of their parts are for the later model of Olds engines. In the early 60's, GM updated the engine design that you have, to make the Olds 350, 400, 403 and 455 engine family. However, the valve components look the same and might be interchangeable or Mondello has parts for older engines like yours.

I am also sure that Mondello might be able to give you greater insight on this problem.
Good luck!

hi magic rat
thanks for the reply. very interesting advice. i will look into it. you seemed to answer another question as well.
what i was trying to explain was...........if the new valve seat was cut too far into the head, therefore allowing the valve to sit higher out the top of the head. would this in turn cause the pushrod to put more pressure onto the lifter and cause more drag, slowing the lifter spinning on the cam? i really am guessing. i will be able to borrow a dial gauge tommorow and will check the heights of the valves. will keep you informed


thanks again

tim