Strange Knocking Sound

Howdy Folks, First time posting here and a have a question.

Let me begin with a short story. I did the clutch on my 1986 D50 Power Ram and drove it for a while and everything seemed peachy. After about a month I am driving up the dirt road to my home and a loud knocking sound begins. It scared the living crap out of me. I parked the car for a few months as I was quite busy and just recently came back around to investigating.

My first instinct was that I had not tightened down the flywheel sufficiently and it was knockinhg against the block. I pulled the tranny and the flywheel is tight on there. My second theory was rod knock. Listened with a stethoscope and couldn't find any evidence for it. I called my buddys in for some help and my friend pulled off the air cleaner while the truck was running and the knock sound suddenly became a very loud popping sound emanating from the carburator throat. The sound occurs at regular intervals at idle at a rate of nearly one pop per second. It sounds like the noise you would make clicking ones tongue across the roof of ones mouth. If you take stethoscope and listen around the noise can also be heard at the pcv valve but if you disconnect the vacuum line to the valve the noise disappears on the scope which to me indicates the noise is travelling down the vac line from the carb to the pcv. The noise cannot be heard with a scope anywhere on the valve cover or at any of the intake ports.

I am quite befuddled. I am glad the issue does not appear to be mechanical (fingers crossed) but the noise is also acompanied by a shudder and it practically makes the vehicle undrivable.

Can any of you fine folks help me out here.

Best Regards
Walker

Hi and welcome to mightyram. If the noise is there in a regular pattern, my bet is there is something up with the valve train. Have you looked under the rocker cover yet for signs of failure? Popping through the carb also indicates a similar symptom. Look for rocker damage, valve(s) not closing properly, check the plugs for signs of fouling or carbon scouring etc. If your engine is running a jet valve head, the jet valves are prone to failure as well.

*forgot to ask - what other symptoms are present? Rough idle, no throttle response? etc

Other symptoms are hard to quantify but the popping sound is accompanied by the engine wanting to stall and it will occasionally stall at idle speed. I will take a look under the valve cover today and perhaps check out the timing. I also did a compression test on all cylinders and came away with values from the 140 to 160 psi range so feel like all the valves must be closing properly and the head isn't blown. I think this also rules out any sort of piston/ring issues as well. If i can think of ay other pertinenet info I will post.

Another possibility is the EGR is clogged or stuck open. It's only supposed to open on throttle. Not sure how to test it out but maybe try soaking it with carb cleaner.

Welp, figured it out. The camshaft exhaust lobe on the rearmost cylinder is completely flat. Also most of my hydraulic lash adjuster are bunk. So, any tips on camshaft replacement and otherwise?

Been looking at replacement camshafts and they seem to only be offered in .02 and .04 oversize. How do I know which one I need?

ebay has replacement cams, but I never looked to see if they were oversize...

ebay has stock cams but you have to sure you're getting a hydraulic cam and not mechanical. None of them make references to OS cam journals...:shrug:

years will tell you that - 85 and up are hydraulic.