robyw1

If it is not an exhaust leak I would first pop the valve cover and inspect the rockers. It is possible one could be slipping off and hammering the spring retainer. I have seen it happen and if this is the case you need to catch it before it frees the keepers. Oh and it is VERY most likely you have a bent pushrod as a result of any of the forementioned cases.

Roby

robyw1

This is very true and not many people know this. If the lifter didn't spin in the bore (the flat tappet type) the cam lobe would be wiped out in a day. Lmarth, you must be a gracefully aging engine builder like me.

Roby

Lmarth

Roby--I refuse to respond to that comment on the grounds that it may incriminate me! Lou

Lmarth

Jackhammer-- You can't take anything for granted when you get into a situation like this. There's another thread in this section where there wasn't a lot of oil coming from the pushrods/rocker arms. You need to make sure those lifters are pumping up and not sticking or collapsing. Just trying to help.

Chris288

I had a very bad knock in two cylinders at idle and pulled my hair out looking for the problem, thought it was a lifter, then bearing, was ready to pull engine,, turned out the carb was bad and needed a re-build, was running very lean until the primaires opened and the knock was gone.. just another avenue to explore.

jackhammer

Thanks for all the input!!!

Chris - I am at the time also battling a carb backfire (lean) condition. I had some rochesters on it that would idle fine, but that's about it. I just bought the Holley's (4010's) and was going through the fine tuning on those when the knock showed up. I put some 7.5 power valves and #86 main jets thinking it should be a bit rich... I even put idle adjustment 3 turns out when all I really need is about 1.5-2 for a smooth idle. I thought I had the backfire fixed... drove my neighbors crazy blipping the throttle. There was some hesitation but no backfire. Just before I turned it off I gave it that one last blip after it was sitting idle for minute and POW, another freakin carb backfire!

It's about this time I'm thinking.... hmmm, maybe I should fix the 'lifter' problem and see if that could be the cause of my backfire problem. (I also have the same carb settings on engine #2 and it seems to run okay... I haven't ran it through the ringer like I have engine #1 though).

Okay... Thanks for the input, I'm about to put the top back together... I was really struggling with yanking it back out and going thru it all over again (I once had a $12 part cost me $4000... one of life's lessons learned!).

Jack

jackhammer

I think I found it... It's a demon banging in my oil pan!!! I've heard of this happening before! All my engine needs is an exorcism!!!!!!

I was turning it over watching my new lifters and it started, dong, dong, dong... it hit about 20 times and then stopped. Craziness! Guess it's time to fire up the fork lift! yipee! I can't wait to see what this is!

I had something similar happen with a stroker motor... One rod bolt was just barely hitting the pan. The only difference was it hit every time around.

jackhammer

Found the little bastard!! Course it took out the cam too...

Would you guys think I was nuts if I put a bit more cam in this engine now? leaving the other engine for winter... I'm not going racing (ever) I just want to cruise around a bit before summer is over!!!!!