Hey there guys,

I just signed up to the Corvette Forum community in hope of finally getting my C3 on the road and maybe (if my skill permits) help out others with their Corvette issues. You can read my introduction over here.

Okay, on to business. I've had my car laid up for almost two years now and I wouldn't take her out more than two or three times a year (it's not registered with my traffic authority yet). I've been doing minor things here and there, but since I live in Australia - I've spent most of my money making it compliant with our asinine laws.

Recently it's developed this little knock in the engine. I've been told that it could be a sticky valve, it could be a 'carbon knock' or 'carbon slap' (i.e. built up carbon which is loose in the valve), could be a flywheel issue or could simply need some new oil. All of these things may be possible with my C3, but I wanted to get some keen ears on the job to see if they might have a clue.

I'm absolutely talentless when it comes to mechanics (I'm trying to change that) but I'd love it if you could tolerate my complete vehicular ignorance and see if you could lend a hand. Here's a link to me starting the engine:

http://img821.imageshack.us/img821/4...mvsyzrdwnw.mp4

Note that 'pop' just as I start the car? I couldn't get it to do it this time, but normally it makes that pop continuously when the engine is under load. There's also some belt slipping by the sounds of it, then a strange engine rocking noise that is very hard to hear.

Any thoughts?

Thanks guys.

 

Welcome

Sorry I cant't help on this but I know someone will. It is unbelievable the amount of talent on this Forum.

I would like to see more pics of your car. I have a 68 also. It's mostly stock and not a show car.

 

Sure CGC, I'll post some pictures up on this website once I work out this 'garage' section. Mine would be stock if it wasn't for the mods done in the 70's. I have the original purchase slip too would you believe? One helluva buy.

Hopefully someone can give me a hand - it's a crime to have that car locked away 365 days a year. Maybe I'll even find someone in Australia!

 

the pop might be too much timing advance, causing backfire thru carb


The only thing I hear is belt squeal...............

 

me too. What happened to your air cleaner nut?

 

Just crafty editing. I figured I'd trim the video down from 2:00 minutes plus to 30 seconds.

It's really unfortunate that I couldn't get it to pop like it was. I might try it again and post it up later. The belt squeal is really obvious and is easily fixed, but that rocking noise at the end (VERY QUIET) is concerning me a little. It might be nothing.

JDemp reported a similar problem in this post.

I found this great article by Ray T. Bohacz that speaks of internal engine knock.

And lastly I found some information here on piston slap.

By the way, BHRIG - it could quite possibly be a timing advance. The carburettor and idle speed need adjusting something fierce but I haven't gotten around to it yet. The only reason why I haven't fiddled with it yet is because it was just so loud, so rapid and so constant that I thought it might be something more serious.

 

Always start with the least expensive solution.........

We all know you could have an excuse to "Rebuild and improve".

Everyone always looks for a reason to spend excess cash!

Good luck

 

If you are near Bud2 he may be able to help you. He just finished up a 383, so he has the skills you could use. He's on this site often, but you could message him through the forum. I understand it's a big place you live in, so you'll have to be the one to tell how close he may be. Tell him I suggested you contact him. Good luck.

 

You're not doing yourself or that engine any favors by running it with stale gas and engine oil...did you think those things last forever?

From the sound of it, your accessory drive belts are either loose or worn out.

 

My 68 327 started idling too low,almost stalling out and I found that the oil fill cap gasket was leaking and messing up the engine vacuum. Your oil filler cap looks mighty strange. Make sure it does not leak. I would get the correct cap.

 

Oil fill cap has nothing to do with engine vacuum.

 

Actually i have to disagree, I once had a tuned port engine that would develop a crazy whistle just off idle at operating temp. I removed the pvc and plugged. noise dissappeared. I reconnected and found the noise again. It was a loose fitting oil cap. Vac from the pvc was drawing from the leaky oil cap.

 

As I stated above, the idle was horrible and I noticed that my oil fill cap was too loose, and not tightning up. I don't know why, it was only 35 years old! I have had the car 40 years.
Anyway, I took the cap off and put my hand over the oil fill tube and the car's idle smoothed right out and so I replaced the cap with a new one that I had. And thank you forvicjr!

 

Good to see another Brisbane vette on here. Thought I'd add my 2c on possible diagnosis.

The pop almost sounds like a backfire through the carb. Had something similar on mine when I was playing with the carby trying to get it right. Leaned it out too much and there was a nice pop like that just after I started the car. Making sure that carb is right (or in the ballpark of right) woudl be a good start.

Knock in the engine could be a few things. I have found that old/low oil is great for amplifying any knocking coming from these engines. Replacing the sludge that may be in there could be a good start. One other thing to to is to take off the rocker covers and take a look at your valve train. I was getting some odd noises and found the dampers in almost every valve spring were broken. Replaced them all after some advice on how to do it (and some tools) from some Qld Corvette Club members and most of the knocking, tapping noises have gone now.

Azza

 

Great to see so many awesome replies. I'll address you one-by-one!

BHRig - Yeah, I would love an excuse to pull it apart and bore it out but both skill, money and time lacks. Any one of those three and I'll be set! I hate leaving it lying there, so I'll have to do something.

Indiancreek - Thanks for the heads up. I'll check the site member details to see if I can contact him. Hopefully he can provide some insight.

69Chevy - I know, I know. I've been mistreating it. I'm a little concerned about what octane fuel to put in the car as I've heard too higher octane can create that carbon knock. I think the guy who owned it before me used AVGAS so lord knows what its been through.

As for the rest of you - thanks for your contribution. I hadn't thought that something so cheap might be the answer. I always expect the worst. I guess I must look real amateur to all of you - but that's why I'm here. Just trying to learn more.

 

I will correct this.
Oil fill cap has nothing to do with engine vacuum as long as your breather side of the PCV system is not completely clogged or nonexistent in which case fix what is not functioning right or configured incorrectly.

 

Hey guys - I just wanted to say that my Vette's disease has been cured. We worked the problem out to be a stuck valve lifter. I spoke with a friend of mine who told me to run the engine at 1000RPM for a half hour and see what it was like after that. He told me that one of two things could happen:

The lifter would come unstuck, or the engine would blow.

Thankfully the former is what happened. If the engine blew, it shouldn't have done too much damage as it was only running at 1000RPM. It will still need to be looked at in the future however. Now I just have to deal with some cosmetic problems.

Thanks for all your help guys - I've ordered a new oil cap. Ciao.