- the crate engine is only two weeks old- but there is now a snappy "popping" sound at throttle. It is coming from the carb. All vacuum has been checked. The timing is spot-on.

If it is the cam failing (why?) I want to get a new one in before the weather turns.

Q1 Is it hard to replace a cam- never done one before. Pulled and replaced engines and about everything else; but the bottom end work that goes to the machine shp.

Q2 Can I leave the engine and tranny intact to R&R the cam?

Q3 Here is the cam that is in it: Elgin Pro Stock E-921-P hydraulic cam .450"/.460" lift, 224 @ .050, 292/288. The crate is a 4-bolt with 194 flat top pistons. Initial test results from the builder: oil press: 53/ Oil Flow 44/ Compession 155. 350 CI.
Any reason to go with a different cam?

 

Q1: Not too hard since you have mechanical experience.
Q2: Yes
Q3: It's not a bad cam, but you can get better. What do you want to get out of the engine? Whether or not your car gets emissions tested is a factor too.
And if you replace a flat tappet cam, you want to replace the lifters as well.
What makes you think the cam is bad anyway? Have you tried anything else in an attempt to correct your snap crackle pop problem, such as rechecking the valve lash, checking the timing, checking for a bad spark plug, plug wire, distributor cap, rotor?
Sometimes ignition problems can cause the carb to pop. But if you're popping back big time, or shooting flames out the carb, then definitely look at it as a valve problem.

 

Camaro 69,

Thanks for answering. I am trying to narrow down the problem of course; but the one thing that is haunting me is the valve lash adjustment. I think it may have been a tad too tight- this is because the crate came with instructions to gap to 15,000ths then turn in one more full turn. Boy drag on 15,000ths is even more arbitrary than the method I usually use- take out play, then <s> loosen til push rods can turn </s> tighten until no longer able to turn with fingers.

It was the only thing in this engine swap that I kept kicking around in the back of my head. Given that the popping is started already... does this mean that it is too late to eliminate the noise with a relashing of the valves?

All the valve train is NEW parts. If I swap out a new cam (same model) will I also need to swap out any other parts in the head?

I am not shooting any flames anywhere; but I don't get the feeling that the problem is timing related, unless the Street Fire dist is hosed. It has a tuneable vac advance (through the hole with an allen wrench; but I have been unable to turn **** with any of the 3/32nd wrenches that I have inserted.

The popping is not like a miss that you get with a vacuum leak or a plug not firing... it's predictably loud, and though I would like a simpler fix I want to eliminate the easy fixes before I tear into the front end. Would bad fuel be the culprit. How can I test it? I wonder if I could pull the fuel supply line from the fuel pump and stick it into a jar of KNOWN GOOD fuel?

 

What you're saying about the valve adjustment makes no sense.
If you have hydraulic lifters, you don't "gap" them. You set them by feeling for zero lash in the push rod, then tightening more beyond that.
If you have solid lifters, you set them with a feeler gauge (gapping), but then leave them at that setting.
Which type of lifters do you have? Assuming hydraulic, then you probably have some or all of them too tight. Recheck the lash following this procedure: http://www.chevyhiperformance.com/te...nfo/index.html
No, it's not too late to adjust the valve lash properly. Just don't follow the repair manual two-step procedures, that way doesn't leave all the valves adjusted perfectly.

 

OK fixed the last line of my procedure. Well, I have removed a valve cover (driver side) and it looks like the #1 Intake rod is bent ever-so-slightly. It is a two week old set of Manley pushrods- does this mean I have to buy a whole new set? And is this enough to keep the valve open and create the popping I am hearing. It got to dark to continue so I'll get on it in the morning. I'll fire up the engine and inspect the valve springs, rockers and pushrods. If they all seem to be working on both banks, this probably means that the cam is not flattened or broken... right? I'll say a little prayer and track down a pushrod set. Install and set the lash following the link you supplied. I'll let you all know.

 

So I take it you have hydraulic lifters then? That pushrod may have bent from having the rockers set too tight, assuming that's what happened, which it kinda sounds like. The bent one wouldn't be opening the valve as far, and others might not be closing if the lash is too tight. So it might not be a defect of the pushrods at all. Do you know what weight valve springs your engine has? If you're going to buy new pushrods, you want to make sure they're hefty enough.

 

Also I would like to add make sure that the valve didnt stick or hit the piston and get bent. My Dad and I delt with an engine that kept sucking valves, after the 3rd time we were getting really upset. He is a Machinist (builds aircraft parts) and has all the fancy micrometers to make the proper measurements. What we found out is the guide to valve tollerances were too tight and the guide was grabbing the valve and holding it till the piston made sure it was closed... and way bent. We lost 2 exhaust 1 intake valve and 2 pushrods. Thankfully we didnt lose the cam, pison or heads. The next time the heads went to the machine shop for warranty we told the machinist there what tollerances we wanted and insisted that he set these heads up this way. he was giving us tollerances for cast iron heads and we had Aluminum heads which expand more than iron does. New tollerances, no issues, those heads are still on the truck about 15 years later. When the intake valves were stuck open we had alot of crackling and popping through the carb, I almost didnt get the truck home that night and I was only 2 miles away when It happened.

When I have adjusted hydraulic lifters in the past I have always used the 0 lash to 3/4 of a turn method of setting them and all the CSB engines I have ever built or set the valves on have been happy like that. It is a pretty simple method all you need to do is get the valve on the flat of the cam, tighten the lock nut untill there is 0 lash, and then turn another 3/4 of a turn.

Using the spin method does not guarentee all the lifters are going to be in the same place. Some pushrods can drag more than others, you may get a better grip or hold one tighter and all these factors will make your valves uneven which will rob you of power. The 3/4 turn will ensure that all valves are set exactly the same on all 16 valves.

Massey