bad cam

flint9

Veteran Member
Jun 6, 2016
163
st louis mo
just a question for all you guys, have you ever heard of a cam going bad.my sons truck 2010 gmc 5.3 had a knock, took it to dealer and was told he had a bad cam/lifter, was low compression on #8,they did a leak down test and it showed blow by. Truck has 135,000 miles mainly hwy.what is everybodys thoughts.
 

CorkyE

Veteran Member
Lifetime Gold Member
Nov 4, 2004
11,737
Ringgold, GA
A lot of times it just a bad lifter and does the plug show signs of blow by. Has the oil been changed faithfully?
 

Gary S

Administrator
Lifetime Gold Member
Apr 14, 1999
24,520
Bismarck, North Dakota
Older Chevy engines often had cams wear down and go bad. I don't know if the newer 5.3 engines have similar problems. Most of the old cams I've pulled from old Chevy small blocks had easily measureable wear on them.
 

GoldenOne7710

Equal Opportunity Offender
Lifetime Gold Member
Jun 23, 2004
5,707
Athens, GA
I haven't seen very many factory roller cams go bad. However, CorkyE brings up a good point. If trash, sludge, etc gets in the hydraulic plunger...then it could act the same as a collapsed lifer in an old flat-tappet engine. Most of the time it will just tick like crazy.

It is possible I guess for the roller lifter to have come apart. I HAVE seen that a few times over the years with aftermarket lifters.
 

grasmo

Veteran Member
Dec 21, 2005
893
tallahassee, fl
a leakdown test has nothing to do with determining whether a cam is bad or not. if you suspect the cam, pull the valve cover and inspect that cylinders valve train.....if the cyl. showed that leakage was high it will more than likely be a ring problem.....what were the results for the other cylinders?
 

MyBoTy

Veteran Member
Feb 9, 2002
1,567
Lubbock, Texas USA
Screw an adapter into the #5 spark plug hole and hook it to your air compressor. Then listen to find the blowby as you rotate the engine. If you can hear it going into the crankcase, it's a piston/ring issue. If it's coming out the intake or exhaust, you have a valve hanging open. If that's the case, pop the valve cover and loosen the rocker arm on the offending side. If the air leak goes away, you probably have a lifter issue. If it still leaks into the intake or exhaust after loosening the rocker, you probably have a valve hanging open due to debris on the seat or a bent valve.
 

budro6968

Veteran Member
Apr 2, 2016
4,166
Jax Florida
Screw an adapter into the #5 spark plug hole and hook it to your air compressor. Then listen to find the blowby as you rotate the engine. If you can hear it going into the crankcase, it's a piston/ring issue. If it's coming out the intake or exhaust, you have a valve hanging open. If that's the case, pop the valve cover and loosen the rocker arm on the offending side. If the air leak goes away, you probably have a lifter issue. If it still leaks into the intake or exhaust after loosening the rocker, you probably have a valve hanging open due to debris on the seat or a bent valve.
Exhaust valves can burn off on the edge and have the symptom of leakage also.
 

flint9

Veteran Member
Jun 6, 2016
163
st louis mo
oil has been faithfully changed,so we dropped truck off at a different shop, one I trust and let him examine,and I will be able to check too.i will keep you guys posted.
 

flint9

Veteran Member
Jun 6, 2016
163
st louis mo
just a update after talking to several shops my decided to have it repaired,thought he could get by with redoing heads,new lifters etc.shop got it tore apart.the lifter was broke in half destroyed,checked cam lobe was rounded,going for a new engine
 




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