Corvair Forum

Well it never ends guys. A knocking started today on there way to an out of town car show. Got there and heard a bad knock from the engine. By the time I parked it went away. Engine was very hot though. When I left, it was fine until I got home and it got really bad then. Just as I pulled in my laneway, it stopped again. Seems to be intermittent,

It sounds lie a much deeper knock than a tappet but it may sound different on a corvair. I'm running 10w 40. Could this be a sticky lifter? Should I go back to 10w 30? It sounds like cylinder #4. Also, plugs are extremely white which indicates a lean burn.

Any ideas will be appreciated.

I've since did a compression test. All are 160 & 170 but #2 is 118. Valve seat?

Hot Day? Could be heat related detonation. Poor gas (I assume you are using 92 Octane or better anything less is prone to detonation particularly on a hot day. Dropped valve seat usually goes boom bang and chunks go all over that side in the head and you have no compression on the effected cylinder, However, a loose seat shifting around that has not disintegrated yet could cause an intermittent bang (which if this is the case will soon be a Boom Bang like I mentioned above). Try adjusting the low cylinder valve a bit. See if you get an improvement. The differential between #2 and the rest is not normal. I assume you read #2 a number of times with the gauge to rule out a leak at the gauge connection and verify the low reading. If adjustment does not help and the compression is truly low, and the banging occurs again I would think that head removal for inspection would be necessary to determine the cause.

It was a very hot day and I use 91 octane but the sound was definitely isolated to cylinder #2. I took a video

k..pulled the valve cover off. Cyl 2..one rocker nut was ran way in too far. It's also a different size nut. Push rod is ok. I backed it off and changed the oil with 20w 50. Noise is gone. It was also pretty advanced so I backed it off and turned up the curb idle. Fingers crossed.

Fingers crossed

This continues to be a problem. As I adjust the tappets, the noise goes away but comes back later. I wonder if the lock nut is bad. Anyway, I had my wife crank the motor while I watched. It seems the very 1st valve is bent or the guide is worn as I can see the valve slide off the rocker as it pushes it in.

It'll run fine all day and then the next day, the rocker is rattling. hmmmm, bad lifter??? Heat is also still an issue. I think i'm just gonna pull the motor this winter and rebuild. Maybe put a lumpy cam in too.

I think your on the right track, I had a succession of valve seat problems and the noise never went away until a total loss of compression on the affected cylinder. After your rocker adjustment and the noise is back is the lock nut backed off I had one that would go loose after a few heat cycles and I just replaced it and it stays in place now. Also I would inspect your rocker arm for cracks as although unlikely it may be flexing a bit under pressure and moving around causing you the problems.

I have a similar noise on the right side of my engine. It goes away once warm. I have yet to yank the cover on that side because when I do its getting new pushrods seals. My car sat since 91 so who knows. It could be a stuck lifter in my case, although no misfire and seems to have decent power.

it is loose but the nut seems relatively where I left it. Is that my issue? While it's off the lobe, I tighten until the rocker is snug and then I give it another 1/4 turn. Should these rockers be torqued?

The rocker nuts do not get torqued

eForce wrote:I tighten until the rocker is snug and then I give it another 1/4 turn. Should these rockers be torqued?

I don't know your expertise level but when you ask about torqueing rocker nuts and mention "snugging" the rocker I'm guessing you're not comfortable with setting the valves. Either that or you use terms we don't.

Anyway, on a cold engine, with the valve off-lobe as you say, you adjust the rocker nut until you have zero lash on the pushrod and then go about a 1/4 turn more. There are tons of tutorials and videos out there on this.

Also, you can have everything adjusted perfectly and still experience some knocking during a morning start up or after a very long period of sitting in storage. It's pretty rare to get that knocking once an engine has been running quiet and is already warmed up but it can happen if you have a dirty or suspect lifter.

I have one lifter that drains once in a while & it takes a couple miles of slow driving before it pumps up & quiets down.
You should hot adjust them, back off the nut until it starts to click/knock then tighten it until the noise stops the give it 1/4 to 1/2 turn more. Sounds like you tightened it too tight and bent a valve or ruined a rocker. You should at least replace the rocker & nut that's making the noise. I did mine at a half turn afer they were quiet.

i only asked about torquing them because some engines (ford) have flat rocker studs that get torqued to 25 ft lbs. I see now that these are adjustable. All are tight but still knocking. Likely a valve seat.

That's it. I'm pulling the motor and rebuilding.

Carb alternator and shroud is off. Mufflers off. Strut rods off at tranny. Working on 1/2 shafts now.

Do I need to remove all the sheet metal and rubber seal in the engine compartment?

eForce wrote: Do I need to remove all the sheet metal and rubber seal in the engine compartment?

Nope, you should be good. Are you removing the complete power pack (engine & trans)? You should as now's the time to clean and check things over. Good luck and keep us posted on what you find.

oh absolutely. Full service.