I'm having a knock from the rear of the engine when it is under a load i backed off timing alot still does it i dont know what the problem is i run 87 octane running a 305 with a qjet its the H.O version hooked up to a 5 speed t-5 can sombody help me i was told it might be the pilot bearing but i dont know...

 

probably a rod bearing or wrist pin bore or a combination of the two. when that happens the piston slaps the head. or could be excessive piston to bore clearance. if its not internal engine noise then i don't know what else it could be.

 

if it still runs good but does it it might be a spun bearing witch is usualy the problem

 

In a stock engine there's about .050 or .060" of clearance between the piston and the head, you'd have to be beyond worn in order for them to make contact.

What kind of a knock is it? A rattle, or something more solid and mechanical sounding? How did you locate it to the rear of the engine?

 

i've seen impressions of pistons on the bottoms of cylinder heads from engines with a little knock and the cause was a worn/spun rod bearing. deck clearance varies on most stock engines anyway and most are not square either.

 

Well it sounds like a knock/ping from teh very rear only does it under load strange thing is it doesnt do it all the time ... the way i found out it is from the rear i opened the hood pulled the e brake and had somebody listen when i put a load on the engine and they said its from the very back of the motor.

 

It wont make noise when the engine is at idle or im im cruising but i think when im crusing the engine is louder then the knock/ping sound and my timing is backed off a ways i thought that was the problem but it isnt i really hope its not a main bearing or rod bearing but i was told that it will hammer all the time with a rod bearing going bad idk about a main though.

 

one thing you could check is crankshaft end play. the thrust bearing is vulnerable on manual trans cars.

 

Is that the throwoutbearing?

 

its the rear-most main bearing. it keeps the crank from walking front-to-back. its easy to check if you have a dial indicator (with the engine still in the car) you can probably find a video of it on youtube.

 

if its a rod/piston issue usually you're going to only make it worse by driving... i had a slight, random knock... after a few VERY short trips to and from the parts store... it sounded like i was driving a jack hammer down the road. I also noticed a serious loss in power. I say all this to let you know, fix the problem before driving it. I though mine was top end, tore the heads apart, redid them, and still the knock was there. As far as under load vs. idle, at idle, the knock comes and goes... under load, nice and loud, and consistent.