Compression test

All Models and Years
User avatar
terribleted
Posts: 3798
Joined: Sun Apr 18, 2010 2:36 pm
Location: Atlanta, GA
Contact:

Re: Compression test

Post by terribleted »

Walt wrote:
Mon Nov 09, 2020 9:23 am
Good morning and thank you both for your replies. Yes I thought about that after I posted it I set it to 0 lash and ultimately turned them just over another half turn. I have seen so many variances on that I know the manual says one full turn but I've seen various videos and forum posts that only do it for half a turn but I didn't want to go that far off from the manual. Thank you for the details on adjusting the valves with the engine running I have just never done that before but perhaps I will enter into that territory soon... Especially if that is how I should be checking it with a stethoscope as well. Thank you both again and have a great day... I will update when I have more info
Post some video with it running so we can maybe hear the noise.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia

Walt
Posts: 51
Joined: Thu Aug 06, 2020 9:41 pm

Re: Compression test

Post by Walt »

There is a short video at the beginning of this post that has the noise I can post a longer one if you like... The smoke you see in the video is gone after adjusting the valves though

Walt
Posts: 51
Joined: Thu Aug 06, 2020 9:41 pm

Re: Compression test

Post by Walt »

Ok so I'm putting up two short videos... the first is how it sounds when I first start the car - there is no knocking sound - and the white smoke has been fixed so I'm not currently concerned about that:



The second video shows the knocking sound that comes in once the engine has warmed up:



Thanks for any input :)

User avatar
terribleted
Posts: 3798
Joined: Sun Apr 18, 2010 2:36 pm
Location: Atlanta, GA
Contact:

Re: Compression test

Post by terribleted »

That does not sound like a knock to me. It sounds like a misfire. A bad wire? A bad plug? Other ignition issue? A valve a little too tight (or sticking) where it holds open a hair once the engine is warm? Since you have been messing with the valves. I would first approach this by doing a running adjustment on the valves. I would start the engine with valve covers off and valve adjusting partial covers in place. I would start the engine and let it warm up until it starts popping. I would then loosen each valve adjustment nut listening to the pop until that lifter clatters and then return the adjustment to quiet plus 3/8 of a turn (or 1/2 if you prefer as long as the idle does not change in the last 1/8 turn ). If you are lucky, one valve is just a hair tight and as you loosen its adjustment just a little the pop will stop.

Now that I think about it check for flooding as well. There should not be liquid fuel running down in the carb throat at idle. If there is flooding is occurring. Flooding can cause a pop as well.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia

Walt
Posts: 51
Joined: Thu Aug 06, 2020 9:41 pm

Re: Compression test

Post by Walt »

Ok, very good I will check for flooding and do the running valve adj. However, to set a clear timeline, I hadn't touched the valves and this sound just suddenly started... another thought: I had mentioned earlier in this thread that I had just done my first compression check on this car and cyl #1 was at 100 while all the others were around 150... but when I put the spark plugs back in, clearly the threads on cyl #1 were at least partially stripped as I could not tighten the plug past hand-tight... I've just received a kit from Clark's to insert some new threads in there, but could that be the issue here as well? Perhaps the plug is actually moving in there if it's not being held completely? Fyi, wires are brand new, plugs are also new and gapped properly, dist cap, rotor and points all new and gapped properly. Thanks again for your time!

joelsplace
Posts: 1154
Joined: Wed Oct 13, 2010 12:51 pm
Location: Northlake, TX

Re: Compression test

Post by joelsplace »

Sounds like a knock to me. I've heard exactly that before but now my old brain can't remember what it was. I'll post back if it comes to me.
113 Corvairs, 5 Ultravans and counting
Northlake, TX

User avatar
terribleted
Posts: 3798
Joined: Sun Apr 18, 2010 2:36 pm
Location: Atlanta, GA
Contact:

Re: Compression test

Post by terribleted »

joelsplace wrote:
Mon Nov 09, 2020 4:47 pm
Sounds like a knock to me. I've heard exactly that before but now my old brain can't remember what it was. I'll post back if it comes to me.
It could even be detonation. Spark Knock.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia

User avatar
terribleted
Posts: 3798
Joined: Sun Apr 18, 2010 2:36 pm
Location: Atlanta, GA
Contact:

Re: Compression test

Post by terribleted »

Loose plug would not be likely to make a sound like that. It might make a bang one time as it flew out of the head:) Sounds like either a valve not closing or a spark knock to me. timing changes make no difference in the sound. Engine get leaner as it warms fully so advanced timing will be more likely to make detonation when the mixture is leaner.
Corvair guy since 1982. I have personally restored at least 20 Vairs, many of them restored ground up.
Currently working full time repairing Corvairs and restoring old cars.
https://www.facebook.com/tedsautorestoration/

Located in Snellville, Georgia

Post Reply

Return to “Ask your Mechanical Questions here”