wiped cam lobe?

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Aug 6, 2002 | 09:11 PM

Jvette73

Thread Starter

Safety Car

Joined: Jun 2001

Posts: 4,004

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From: Severna Park Md

wiped cam lobe?

Just today I noticed a slight tapping comming from the engine compartment. I removed the valve cover and narowed it down to a loose rocker arm on the drivers side furthest rearward exaust valve. I adjusted the rocker and started the engine with the valve cover off. The noise had subsided with the adjustment so that was cool. However while looking at the rockers and valves going up and down with the engine idiling and the cover off, I noticed that the valve I had just adjusted did not appear to be moving up and down as far as the other exhaust valves were. i held my finger over the pushrod end to feel as it tapped my finger as it went up and down. I then did the same thing over the other rockers. The one in the far rear is definatly not moving up as much as the others are. It is quiet now and still runs like a bat out of hell. Is it unusual to have a partially wiped exhaust lobe and still have the motor run pretty good? I would have thought it would run really crappy. It still runs really great with lots of power. :confused:

Aug 6, 2002 | 10:12 PM

Chuck Harmon

Melting Slicks

Joined: Apr 2000

Posts: 3,286

Likes: 8

From: San Jose California

Re: wiped cam lobe? (Jvette73)

John,

That is a real shame. How many miles on the cam? Any idea as to what would have made it go? Is the lifter still tight in its bore, or does the lifter bore have to be sleaved? I know that cams can still fail even if everything was perfectly installed and run in.

Lastly, what kind of cam are you going to go with once you feel confident about what did or didn't cause the failure? I'm sure you had nothing else you would rather be doing than tearing the engine apart. :rolleyes:

Chuck

Aug 7, 2002 | 03:43 AM

Ben Taylor

Pro

Joined: Dec 2000

Posts: 560

Likes: 0

From: Camino CA

Re: wiped cam lobe? (Jvette73)

I'm pretty sure that you can lose an intake lobe without to many problems, it's when you lose exhaust lobes that you start to have problems.

Aug 7, 2002 | 04:06 AM

Jvette73

Thread Starter

Safety Car

Joined: Jun 2001

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From: Severna Park Md

Re: wiped cam lobe? (Chuck Harmon)

Yeah its a bummer. I guess if the lobe is half wiped now, it wont be long before its totally wiped. Ive had this problem on other SB chevys before. Neither then nor now, do I have any clue what caused it. Im always very carefull with my adjustments. Oh well, cam change is no big deal, although like you say Chuck, Ide rather not have to. On the lighter side, this gives me a chance to to test a downsize to the XE262. I know it has slightly less lift. I should be able to make up for that with better cylinder pressure provided by the slightly lower duration. I always thought the 268 had a bit to rough idle for my taste. I think the 262 will be a nice compromise, offering a tad better bottom end to get out of hole quicker. What do you think?

Only a couple thousand miles on this cam. Havnt been in to check the lifter bore yet. im pretty sure it will be ok.

[Modified by Jvette73, 2:08 AM 8/7/2002]

Aug 7, 2002 | 06:56 AM

Larry B.

Le Mans Master

Joined: Sep 2000

Posts: 5,635

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From: Orlando Floriduh

Re: wiped cam lobe? (Jvette73)

Cams are made from relatively soft steel so the won't break. Then the lobes are flame hardenend so they won't wear. Sort of the best of both world so to speak. When the wear goes beyond the hard surface, then the wear become very rapid and the lobe goes away. Not a good thing. Most of the time the most wear occurs from improper break-in. Idling during the first few minutes will destroy a hi-per cam! The high lift cams, heavy valve springs makes things worse. So if you just put a cam in and then it looses a lobe....... Of cousre on an old engine, if the engine was neglected any time in it's lifetime it is impossible to tell what cause it.... Running low on oil, dirty oil. overheated at one time, over revved, Or just plain old age. Anybody's guess.

Aug 7, 2002 | 10:26 AM

Matt Gruber

Race Director

Joined: Oct 2000

Posts: 14,996

Likes: 79

From: central FL, near the beach.

Re: wiped cam lobe? (Jvette73)

i would get the cam out ASAP! no sense grinding off a pound of iron :lol:
change the oil & filter now, and after running in the new cam for 1/2 hour at 1500-3000 rpm.
others rebuild the engine; a good idea if it is shot; silly if it's not.

Aug 7, 2002 | 01:20 PM

john's '81 mouse

Burning Brakes

Joined: Dec 2000

Posts: 1,183

Likes: 2

From: Des Moines Iowa

Re: wiped cam lobe? (Jvette73)

Yep, it's possible to have an exhaust cam lobe half wiped and engine still seems to be running strong...........That's just what I had........went to do a cam change, from stock L81 to something with more lift/duration, and during the process of the valve guide seal change, discovered a leaking intake valve, which turned out to be due to the bad exhaust lobe, and exhaust being driven back up into the intake, resulting in a buildup of carbon on intake valve seat area. The exhaust lobe on my #7 cylinder was half or more worn down, but I thought the engine was running great.

Aug 7, 2002 | 03:11 PM

Jvette73

Thread Starter

Safety Car

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From: Severna Park Md

Re: wiped cam lobe? (john's '81 mouse)

Yup i need to get it out of service and replace the cam. Its a 70k motor so im not to worried about a bit a metal in there. Ive had wiped cam before and just did the cam, and that motor, years later, is still running strong. She is getting tired of me telling her she cant drive it till its fixed. :boxing Damn........ Women..they just dont understand sometimes :rolleyes:

Thanks for all the input everyone. hmmmm... what about a gear drive this time along with a downswap to XE262?

[Modified by Jvette73, 1:11 PM 8/7/2002]

[Modified by Jvette73, 1:12 PM 8/7/2002]