Big Block Knock Follow Up

[John R.]

Thanks to everyone who responded to my post last week about the knock in my 67 big block. We tore the engine down this week and found a severely worn cam lobe and lifter. There is just over three thousand miles on the engine rebuild and everything else looks perfect. The engine builder said that the cam wear is a result of not enough oil reaching the cam and that we should have used a roller cam when we rebuilt the engine. He also questions whether this was the source of the knock. I really don't want to have the same problem again but can't understand hoew the original engines avoided this problem.

[Clem Z.]

Re: Big Block Knock Follow Up

the first start up of the engine with a new cam is very important. you must prime the oil system,have the carb float bowls full and make sure the engine fires right away and you vary the engine speed between 2000 to 3000 RPM for 15 20 minutes to break in the cam. make sure the lifters are free to rotate in the lifter bores,i always use a brake cylinder hone in the bores to make sure they are smooth. i would also use GM "EOS" in the oil and use moly disulphide for cam lobe/lifter lube but make sure you change the oil filter after the cam breakin because the moly will plug the oil filter when it cools off. several cam companies now sell solid lifters with a .024 hole EDM in the face to allow oil to reach the lifter cam lobe interface for better oiling. these will work as i used a similar way of getting extra oil to the cam lobes by grinding a .003 deep flat on the side of the lifters to allow the oil to get the lifter cam lobe interface.

[John R.]

Re: Big Block Knock Follow Up

Thanks for the advice, Clem. Do you think that failure to break in the cam initially might be what my current problem was caused by?

[Clem Z.]

Re: Big Block Knock Follow Up

the cam breakin is very very important to cam life. all the things you do prior to that will also increase your chances of not having a failure.

[Dave F.]

Re: Big Block Knock Follow Up

Clem - is the issue the same for hydraulic lifters?

[Clem Z.]

Re: Big Block Knock Follow Up

yes it is but you can not used hyd lifters with the hole EDM in the bottom. hyd lifters must be set one at a time without the rocker arms on the rest of the valves so you do not collaps a lifter while rotating the engine. hyd lifters are best done with the intake off so you can see the .020/.030 preload being set on the hyd lifter plunger.

[Mark #28455]

Re: Big Block Knock Follow Up

ask about your valve spring pressure. Stock is ok. If your seat pressure is over about 135# or open pressure is over about 325# you'll need to be very careful about the break-in.