Phantom Knock

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megacab

megacab

Leglhi
Joined
Jul 11, 2008
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Nipomo California
Went out to start the car the other day and thought i heard a knock.It went away fast though and didnt come back,so i wasnt sure what i had heard.Tonight went out in the garage and fired it,and yup,there it was.Car was cold so it was idleing rough,and it seemed the lower the rpm got the louder it got.So i turned it off,came back to listen to it again,and poof,it was gone.No knock.It sounded like a pretty solid knock,not a tick.I should mention that during this whole thing it has 80 pounds of oil pressure,and nothing in the oil i can see.Any ideas?Motor has maybe 2 hours on it.416 smallblock,solid roller cam.Thanks
 
Sounds like piston rock to me. Whats the side wall clearance on the pistons? You get that on a lot of strokers(not all of them but some)with short piston skirts. Could also be a converter bolt or flex plat bolt but those would be more constant.
 
Thanks jaws.Would that piston rock go away after a minute or so?If the car sits overnight and you fire it,its loud when you start it.If you fire it up a few times it progressively gets quieter.I fired it 4 times the other day to listen to it,and by the 4th time it was pretty much gone.Engine didnt even have time to warm up the oil.but if it sits awhile it makes noise again.Im getting ready to pull it tomorro
 
Pistons should not be loose enough to knock when cold if things were done properly. What was the piston to wall clearance? If it was the pistons it would stop very quickly as it warmed. Do you have a priming shaft? I would try priming the engine when it's cold. Then firing it quickly after. If it knocks then it's more than likely the pistons. If it doesnt, it's more than likely a rod. What oil pump was used?
 
moper said:
Pistons should not be loose enough to knock when cold if things were done properly. What was the piston to wall clearance? If it was the pistons it would stop very quickly as it warmed. Do you have a priming shaft? I would try priming the engine when it's cold. Then firing it quickly after. If it knocks then it's more than likely the pistons. If it doesnt, it's more than likely a rod. What oil pump was used?
Click to expand...

Thats why I was thinking piston rock, because of the short skirts on the stroker pistons, and him saying that it goes away fast. How much clearance is there on the thrust bearing?
 
Sorry you guys.Thanks for the input.I've been pulling the motor.Pulled the pan and it was spotless.Pulled the rod bearings.Perfect.Thrust clearance,.006.Couldnt find anything until...i looked in from the bottom of the timing chain cover,reached in with a screwdriver and found slack.I have a tensioner,and that thing was rock solid when i assembled it.So i pulled the cover.and the gear was way loose on the cam.Since im running an electric pump,we took the fuel pump ecentric off and made a custom spacer to take its place.Worked last time on the last cam,didnt have enough clearance on the washer to push the gear all the way on the cam this time.Tensioner made it feel right on assembly,and the one clearance in the motor i didnt check?Cam end play.Wont make that mistake again.Dont know how it didnt jack up the cam or motor,but it didnt.Put a MP hardened ecentric on with the right washer and tightned it and its fine now.That was close.Thanks for the help guys.
 
Glad to hear you made it through that without anything major. As added assurance, it`s always good to put a little Loc-tite on the cam gear bolt/s .
 
Old trw forgies will rock/knock till they heat up enough and expand they'd run 8 thou skirt clearance.
On a side note my KB hypers are set on the loose for RPM/drag race and you can kind of hear'em when it's cold.

Sometimes you can scuff a piston skirt mildly, have it knock but then go away when warmed up.JMO

Glad you found the knock.
 
A cam knock, whoddathunkit? Glad it was easy.


Yeah, TRW's do rattle, I have an old 318 with them in my mud truck, sounds like a damn diesel til it warms up. Of course, the pistons have a gazillion miles on them, and the bore coulda' used .040 pistons instead of .030's. LOL.

Glad it idles for a living.
 
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