307 tapping thoughts?

[techg8]

My 307ci has developed a tapping noise.

It occurs only at light throttle cruise, hot or cold. Not on startup or st idle. Not under moderate to heavy accelleration.

it varies with engine rpm.

It doesnt sound like a rocker arm. Sounds a lot more solid....I am thinking its a lifter with some sort of problem.

when it occurs (at light throttle cruise) I can get it to disappear by getting a -little- into or out of the throttle. It comes right back at light throttle cruise.

Oil pressure is normal. No driveability issues.

Any thoughts on the source? thanks

 

[Peter]

is it pinging? could be a pluged egr or egr passage in the intake

 

[bkb97]

well if it seems to be up top then an adjustment on the cylinder quick is in order before it gets worse.. but engine noises as that can seem to come from one place when its another..did you hit on it and it started ?? regular oil changes?? and engine age..are all possible factors.. a trusted mechanic if your not a do it yourself person cause the first thing is your engine is shot or full rebuild is the diagnosis

 

[pencero]

When I bought my cutlass it was like that and road tests showed it was drive-able but it would stall out at stop signs consistently so it wasn't safe. I found a parts car and gambled on a quick swap-over to a basically identical 307 (didnt know it then but I had the better heads - should've kept them damn it lol) and the swap was like $350 only took a few hours and never looked back. I guess if you're going to tear it down and fix it yourself that sounds stupid probably but the way I looked at it was why would I spend time on a 307 let alone money. For like $350 the car was back on the street after only 1 day and no more being seen stalling out at stop signs w/ knocking engine again!

 

[techg8]

the 307 was torn down and rebuilt prior to this issue. I expect there are no problems with bearings, rings etc. The engine is in healthy shape with whatever exception this is.

I listened to it more today and the sound is centered in the block, below the intake. I think its a lifter problem.

I will lift the valve covers and see what that tells me, then pull the intake and look at the lifters.

for cryin out loud why do these things pop up in the cold weather? I need a warm garage.

 

[Bonnewagon]

I say start simple. Pour in a can of "lifter cleaner" type treatment or a pint of automatic transmission fluid and go for a ride. If it helps, great. Then change the oil and if it comes back do it again. I had a '68 Buick LeSabre 350 that would click like crazy unless I used a can of STP regularly.

 

[woody31]

check your timing,,make sure your wieghts inside the dizzy are not stuck and everything moves freely,,, 8)

 

[techg8]

Thanks for the replies.

I did run a pint of DexMerc in the engine oil, hoping to free something up but it hasnt helped as yet. could be it needs some more drive time, but I really dont like driving with the tapping. I imagine something getting beat to death in there. I'll try just letting it get to heat parked at idle and let it run a bit to circulate the "cleaner"

As for the timing, this is an EST setup - no mechanical or vacuum advance at the dist. All of it computer controlled. But I will recehck my initial to be sure it has not walked.

I will take a look at the egr setup as well.

thanks again

 

[anthonychacon80]

i bet it is one of the lifters. If the little springs that press the lifter into the rods is broken or smushed then as the cam rotates the lose lifter is smacking into the rod and not giving you zero lash. It might now show up if you take the rocker cover off because if you are manually rotating the engine then I bet the rod and lifter will look and appear fine at that slow a speed. Should not be hard to take off the intake manifold, swap out some new lifters, reuse the old rods and relash all the rocker arms to zero lash.

The only other thing I can think of is the lower bearings are going bad and the bolts that hold them on might be rattling? That would mean a total rebuild though.

 

[KmK442]

did you replace the timing chain when you rebuilt it ? that could cause the knocking noise