good morning all, i have a 1986 FXRP and a few days ago it started knocking somewhere around the rear cylinder. I did a compression test and there's a 25 PSI difference between the 2 cylinders. the troobleshooting i did so far is a compression test, checked the oil to see if there was gas in it ( i couldn't smell any) The engine is not smoking black or anything and it starts and run really well. the knocking is constant and goes up with the rpm. I have adjustable pushrods in it and it's the last thing i have to check. Any other idea what could cause this if the rods are ok???? thanks.

 

With a 25 psi difference between the cylinders I'd say the top end need to come off. I'd check the front motor mount and make sure the drive train is not hitting the frame around the side stand and bottom rear cross over.

Did you try a squirt of oil in the cylinders and compression again?

 

I'd start in the cam chest........dollars to donuts that you have a failed lifter roller, probably harmed the cam lode as well.
Experienced guestimation.
Scott

 

This is likely a better guess..

 

Truth be known Bruce, the ONLY thing that I am sure of anymore, is that Jeremiah, was, a bullfrog.......
Scott

 

He was a good friend of mine....

 

Do you have adjustable pushrods? if so check for a loose one possibly on the intake side of the cylinder with lower comp.... Also check that same lifter possibly collapsed..