Strange knock - Help

[copper]

First off, the valves were done on my 69T about 2 months ago. Oil's been changed 4 times in the last 2 months. (beginning of season, engine drop, new lower covers, and just because, with Mobil 1 15W50). The carbs were balanced today. Took her out and she drives better than ever.

I have a constant light smoke coming from the exhaust, but that's not why I'm posting. I figure I just need to lean her out a little more.

THE REASON I'm posting is, had her out, ran nicely, idled smoother than ever. Nice and responsive.

Parked her in the garage and then started her again after about 30 minutes and noticed a loud knock on the driver's side at idle. Was fairly loud, and my first thought was valve, but they were all adjusted less than 2 months ago, more like 6 weeks and there's been nothing since.

I touched the side of the top cover during the knock and felt nothing. Was feeling for the knock, or a related vibration.

After about a minute, it stopped and all sounded normal.

Any ideas?

I'm heading on a road trip to NYC (9 hr drive) on Sunday and would hate to have a problem now, after all the work I've put into her.

Please chime in.

Thanks
Jim

(Note, I had tried dino oil to combat some oil leaks, but this caused smoke on rev matched downshifts in 2nd and 1st. Went back to Mobil 1 synth and it seems to have almost eliminated the problem. We're figuring worn guides or rings. After the carb balance, she has a constant light smoke which is a whitish grey, but very faint.)

[copper]

Just delving through tons of threads looking for a similarity.

One mentioned a knock caused by oil getting past the rings causing partial hydraulic lock.

Given that my car was recently showing signs of oil past the rings (smoking on decell) how possible is this. What about too much fuel getting through? She was turning over quite a bit without catching at first. Then I finally put the pedal all the way down to clear her. (was turning the key through the window initially. No throttle, or flooring of the pedal.) Will flooding do this?

It's only happened the once, and only for a short time and disappeared.

??

[copper]

bump

[Bob's Flat-Six]

Define knock ?

Loose valves sound more like a tick.

[island911]

Originally posted by Bob's Flat-Six
Define knock ?

that's what I was wondering too.

Is it one KNOCK . .. or, KNOCK, KNOCK, KNOCK, KNOCK, KNOCK, KNOCK, knock, knock, knock, knock . ....

. ...or?

[copper]

The knock was louder than a valve tick, which I'm familiar with, which also sounds similar to exhaust ticks.

It was a repetitive cyclic type knock from the drivers side which lasted probably 30 seconds and disappeared. Sounded like something tapping from inside, but that was just a guess based on the sound.

I had restarted her after having driven her. It had been about 1/2 hr. I just turned the key, instead of holding the pedal down, as I thought she would have cooled off enough for a regular start. Think I flooded her a bit, and then put the pedal down and she started. That's when the knock kicked in, and then disappeared.

Any correlation?

[Early_S_Man]

Jim,

Can't help with the knock/tick ... but the smoke on decel sounds like an indicator that you have worn valve guides, and will need a top-end rebuild soon. Typical for pre-77 engines with high copper-content bronze valve guides.

[copper]

I had her out for a spin today. No knock at all. Kind of makes me think it was something to do with the fact that I flooded her.

[RoninLB]

Originally posted by copper

It was a repetitive cyclic type knock from the drivers side which lasted probably 30 seconds and disappeared.

maybe piston wrist pin slap on a worn engine.

[randywebb]

A loud knoc has GOT to be bad news.... (Sorry to say). BUT, now its gone... So I dunno.

I'd try several re-starts from cold by someone else with you back there listening....

One thing: if Warren doesn't have any ideas, not many will -- try to get Grady & John Walker to read this post.

And if it happens again, try to record it.

Also, change the oil and inspect the drain plugs carefully and do an oil analysis. Maybe open the filter canister up and pore over the paper...

BTW, I wish you guys were paid what you were worth...

[RoninLB]

oh yeah, I forgot to add in my previous that piston heat will tighten up the clearance.

[copper]

Originally posted by randywebb
BTW, I wish you guys were paid what you were worth...

You and me both buddy, you and me both.

But at least I enjoy it. And the fringe benefits aren't bad...

"Hi, I stopped you because, oh, it's you, see ya later............"

[randywebb]

I work out with 4 cops in my martial arts classes (ok, the deputy sheriff keeps pointing out he isn't a cop, and isn't a sheriff (a loser since I always come back with "you are deputized as one") and have never figured out why they took those jobs... especially since the city police are held in extremely low regard right now (none of them are on this city force but "it's all blue").... not for traffic either -- for rape.

[copper]

ouch... controversy.

I think the US police agencies are extremely underpaid. We do pretty well in Canada. If you aren't paying enough, what kind of applicants do you have to choose from? Maybe that's why some of them are getting into trouble.

Pay here is about 72K base for a street cop.

[randywebb]

wow! sounds alot higher than here. This city (Eugene) should have a good base of applicants -- it's a 'voluntary' location spot for retirees, and lots of other type people. Sorta Berkeley with less aggression - very politically mixed tho a univ. town and left of most of the US - or almost all of the US.

So I dunno - but I do know I'm way off topic...


Like Ron said, the only thing I can think of is piston slap - but I thought the 911 had some way to minimize that...

Check around for anything loose - a loud knock is bad.

[Paulporsche]

Jim,

I can't help you w/ your knock. But after seeing your house, and hearing about the base salary...how about a loan?

Seriously, I hope you have a great trip. Post some updates.

Paul

Randy,
Remember, that's $72 CDN.

[copper]

Paul, move out here. You could sell your place in Downtown T.O. and buy a spot right next to me and still have leftover change. That's that cost of living we were discussing when you were here. The boys in T.O. get about the same, only they're buying one bedroom condos for $250K.

Sure glad I moved.



On the knock issue, it hasn't happened again, and never happened before. I'll listen for it to happen again, but hopefully it won't and I'll never see any fallout from it...

Thanks for the help guys.

[RoninLB]

Originally posted by copper


On the knock issue, it hasn't happened again, and never happened before. I'll listen for it to happen again, but hopefully it won't and I'll never see any fallout from it...

I might not worry if it happend again and I had a chance to rapidly rev engine at idle to pin-point its cause. A crank or rod bearing will sound and respond different from a wrist pin or a piston slap according to reving technique. So far it's a "don't worry".

[vntgspd]

It's a shot in the dark, but check your throttle shafts on the carbs. I have one that is worn beyond the usual slight play and at certain engine vibrations it makes a knocking sound that sounds like it is coming from cylinder 3 or somewhere deep in the engine near there. It had me really worried one day while I was hunting it until I bumped the shaft and linkage and the sound went away. Sure enough, when cold or at low engine speeds, the shaft rattles and goes knock, knock, knock.

It's really obvious from outside but almost impossible to hear from inside the car.

Good Luck!

[avendlerdp]

My 70t does the exact same thing. Knocks far about 30 seconds on an ice cold start up then shuts up. The key here is it has been doing this for 3 years with no ill effects. I just warm it up a bit before letting her rip and stopped worrying about it.