Here is a head scratcher for the logical thinking bunch.
My freshly built 455 has a tapping noise coming from the passenger side bank area seemingly from the area of the 2 rear cylinders. This tapping noise is SLOWER than the actual RPM of the motor by about 1/4 to 1/2....ie, the motor idles around 800 and the tapping is around 2-400 taps per min. I located a broken inner valve spring, replaced it and now the motor idles around 5-600, Why?
The rocker is not too tight, there was a new valve stem seal installed.
My questions are these:
What are some possibilities on the noise?
Why did my motor change idle speed?
Any other insight will be greatly appreciated.
Thanks to all who have given so freely of advice, it has been a great resource for me.
Sometimes a bad spark plug wire can make a clicking sound when it misfires. It might not do it on every revolution. You can take something like a wooden dowel and place it against the engine and put the other end near your ear and narrow down where a tapping is coming from. It could even be an exhaust related sound.
this is definately not a spark noise. It sounds like metal to metal tapping. My thoughts were leaning toward a lifter / rocker noise but it sounds deeper than the valve train....like maybe a cam lobe or a collapsed lifter.
Odd thing is that the engine is fresh and has plenty of power????
With the engine running, hold a long screw driver to your ear and the erea in question. It helps pin point the noise, and will sound more distint. I've actually done it putting the driver on each rocker stud to find a bad lifter.
Another way to find a lifter is to loosen and tighten each one at a time.
The broken spring was the 3rd from the front on the passenger side. I took a stethascope and the noise seems to be coming from the back 2 cylinders on the pass. side. The noise seems a little too low to be rockers, but then again, sound can travel. What has me curious is that the noise is directly tied to engine rpm, BUT IS MUCH SLOWER than the actual rpm. In other words, if it were, say a piston, the noise should "tap" around 800 times per min.....idle speed. But this "tap" is 1/2 to 1/4 of that per min, leading me to believe it is something else. It is definatley not the rockers hitting the cover...I checked that by looking for marks on the underside of the cover and found none.
Poncho, the lower idle has me stumped too. As I said, it idled around 800 with a broken inner spring. we replaced that and now it idles around 5-600, and the rocker was too loose. we tightened it and had no effect, still low idle and still has the tapping.
check the distributor drive gear, be sure the distributor is engaged with the oil pump drive shaft, be sure the distributor drive gear pin is not sheared, be sure the distributor is clamped down snugly.
Half of engine speed = cam. Cam drive is in the rear of the block. Cam also drives the distributor, which controls timing.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
im with vikki. has to be something with camshaft as its only there partially and only in the back 2 cylinders where the dist. is located. the reduction in rpm's would hint to this being involved.
Andy
due to budget cutbacks, the light at the end of the tunnel has been disconnected for non payment.
I'm thinking those heads are questionable. Why did it already have a bad valve spring if it's freshly rebuilt? Some people shouldn't build heads. Seriously!
LOL Exactly!! I've got a set of heads(on the bench) that were freshly rebuilt. When they were on the engine a spring broke and then they started ticking..... I didn't wait for what was next, I took em off. I bought a set from a guy that can really build heads. That engine runs perfectly now.
Running the engine with the valve cover off would determine if it was rockers hitting the covers. Why would one end hit and not the other? I guess anything can happen...
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
i went out and started it up just for giggles and now it idles at the proper 800 range. Dont know what happened, we did do alot of "bumping on the starter" last night, so maybe it confused the carb or something. thats the only thing i can think of.
Either way, the knock / tap is still there so the search continues tonight. I guess i am gonna go in thru the intake and see if there is something obvious.
Ok, here is what I know....intake, valley pan, valve covers, are all removed.
Looking at the cam lobes, there appears to be some slight bluing on the lobe side of the cam.....interestingly, there appears to be a little more bluing on the lobe near where the tapping seemed to be coming from ..... oil psi is 60 start up and 30-60 when warm
I turned the engine over without plugs and aside from spraying my buddy with gasoline (forgot about that issue ) i heard nothing out of the ordinary.
The cam lobes are supposed to line up with the lifters. When they move over like that it's called 'cam walk'. When it does it and then stays there it's usually a cam bearing/s gone bad. Here's a picture of a cam bearing going bad;
On further thought; I would check the way your timing gear is mounted on the front of the cam. For the shaft to have walked back like that I bet that the gear is not mounted right or is coming loose. For a reference, there should only be about .008" movement, back and forth, of the cam.
Jim, I am going to check into that and try to take some sequential photos from a 90* position to the cam for a better perspective, and also try to get some of the cam bearings as well. I will post them today.
I'm fairly certain this is a timing gear problem. I would go straight to that and take a look. Sometimes a new gear will be machined badly and not fit right on the end of the cam. Also, sometimes the eccentric and washer can be a problem. If the gear is on right the cam can't walk back like that.
I think it's definitely a timing gear problem. The cam lobes are showing unusual wear due to the 'off center' condition. Get that gear on right and you should be good to go.
It's not very clear, but it looks as if the lobe to lobe spacing is not correct or consistent. Without moving the cam, some lifters line up, others do not. I believe the problem may be more than just cam walk.
The cam's burned lobes would also suggest to me that replacement of cam, lifters and timing set would be a wise idea.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
I have a pontiac 350 on the stand now, assuming it is put together correctly, would that be a good reference for me to use in putting the gear back together?
Also, do you think it would be wise to just get a whole new timing gear & chain?
You need to dig a little deeper before we can answer those questions. The 350 should be a great reference. Like Vikki said, a cam swap would be a good thing after all this unusual wear.
) i heard nothing out of the ordinary.
