I have a 496ci big block Chevy that I built about five years ago that has been on the street the whole time. I don’t drag race it, but it does get run pretty hard every once in a while. The other day I started it up and notice a slight ticking sound that was unusual. The engine has a mild solid roller cam, so I pulled the valve covers after it was warmed up to check the lash. I found several exhaust rockers loose about 0.003 to 0.005 inch.
I was going to just re-adjust them all when a friend said that it might be good to do a little more investigation. He said it could be I have a lifter or two going bad. Is that reasonable or is he just trying to scare me? Thanks.
D.E.
Your friend is just looking out for your best interest and that of your engine. You should definitely not even start the engine again and immediately remove the intake manifold and carefully inspect each of the exhaust lifters. Remove each lifter and look for damage or rough-rolling needle bearings in the roller portion of the lifter. I like to roll the lifter across the inside of my forearm where the skin is very sensitive. Once you’ve checked all the exhaust lifters, also check the intakes as well.
What you are looking for is any slight hitch or hesitation that might feel like resistance to rolling. When needle bearings begin to fail, generally one or two of the needles will stick or begin to slide rather than roll. This may cause one of the needle bearings to create a small flat spot which will prevent it from rolling. That will cause its neighbor needles to also resist rolling and it cascades into a series of bearings that no longer roll.
Sometimes if you are lucky, you can hear this as a noisy lifter or a ticking sound that is wearing usually the lobe on the camshaft or elsewhere that is revealed as an increase in lash. So when you discover that increase in lash on more than one lifter that might be a sign of increased wear. That’s why it’s important to immediately check the lifters for a bad roller.
The reason this is so important to catch before the lifter fails is that when the roller bearings in the lifter fail, those tiny little needle bearings will fly around inside the engine and cause enormous damage.
A fellow hot rodder once asked why I was so concerned with these needle bearings. He said they would simply get captured by the oil filter and not be a problem. That could not be further from the truth. The reality is much worse. What happens is when the needle bearings leave even just one lifter, they fly around inside the crankcase and will eventually get pinched between the piston skirt and the cylinder wall.
If the engine runs long enough, (our guess would be probably less than a minute) this will cause enormous damage to the cylinder wall and also gouge one or more pistons. We know this because this happened to a friend of ours who then had to rebuild the entire engine, boring the cylinders out another 0.010 inch in order to clean up the mess. Of course this required new pistons, rings, bearings, and gaskets for the short block and was quite an expensive lesson. In his case, the engine started to squeak but he continued to drive it for about another two miles back to his shop. Those were an expensive couple of miles for convenience.
If you find no bad lifters on initial inspection, it might be worthwhile to have the original manufacturer inspect them and give you their opinion. Many new mechanical roller lifters are now fitted with pressurized pin oilers that help to lubricate the rollers and extend their life expectancy. Some are also rebuildable.
Another option that will prevent needle bearing damage is to opt for roller lifters fitted with bushings rather than needle bearings. Several lifter companies like Comp, Isky, Morel and others offer these lifters. Our research however indicates that for a street-driven engine that the concern for bushing lifters has much to do with clean oil. The lifters will live a long useful life—but they must be cared for with more frequent oil changes.
Clean engine oil is the important point for making sure these bushing lifters live a long life. You can get away with dirty oil with a needle bearing lifter compared to a bushing lifter. I don’t have a maintenance schedule that has any meaning since driving style and oil quality have much to do with how often you should change the oil.
If the engine is driven infrequently and is not allowed to come up to normal oil temperature of above 212 degrees F, impurities will collect in the oil much more quickly than an engine that is operated with the oil up to operating temperature of above this figure. When operated above 212 degrees F, this allows the water in the oil to evaporate and take with it many of the impurities.
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Hopefully we haven’t scared you too badly with this answer. It’s also possible that you will disassemble the top end of the engine and find no problems and that all the lifters look good. If so, reassemble the engine and carefully set the lash at operating temperature. Make sure that when you check lash again that you always check it using the same procedure. If the lash changes again, there is still a problem. If the lash is set accurately, it should not change unless something is either moving or wearing.
This is no small point. Some enthusiasts will try to tell you that the lash will change over time. If it does, something is wearing or moving. That’s the only explanation if you set the lash carefully and recheck it using the same procedure. We have a John Lingenfelter-built 420ci small-block that has seen over 25 years of racing abuse and every time we check the lash, it has never changed. We eventually changed the lifters only because of the time factor involved but they checked out fine.
That should reinforce the point that the lash should not change if all the parts are operating properly.
Hope this helps.
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