Valve adjustment SBC
Thread Starter
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Valve adjustment SBC
OK, this is a serious dumb assed question, since I am grasping straws here, on my '72 with '89 roller engine in it for some time now...
iron heads, forged pistons, around 9.5 comp ratio and DPFI, TPI style with ZZ9 cam.....
so the question is as I recall, I adjusted the valves with cold engine, and so everything has been fine for some time now, EXCEPT when in hot weather the engine warms up totally, NOW on these 80f+ days it's running fine TEMP wise, but runs like crap....I have been all through this damn dawg, and am thinking computer screw ups...but....the thought hit me, when engine is cold and/or in cold weather for Florida that is....40-60f outdoors, car runs fine.....70f++ it has more misses than a HS Prom....so....
I have been adjusting hydraulic valves for decades untill snug...is there a possiblility the engine heating up causes a valve to stay open causing a misfire?? can this happen?? I adjust untill snug on the pushrods, and no further....
any clues ??anyone/??
GENE
iron heads, forged pistons, around 9.5 comp ratio and DPFI, TPI style with ZZ9 cam.....
so the question is as I recall, I adjusted the valves with cold engine, and so everything has been fine for some time now, EXCEPT when in hot weather the engine warms up totally, NOW on these 80f+ days it's running fine TEMP wise, but runs like crap....I have been all through this damn dawg, and am thinking computer screw ups...but....the thought hit me, when engine is cold and/or in cold weather for Florida that is....40-60f outdoors, car runs fine.....70f++ it has more misses than a HS Prom....so....
I have been adjusting hydraulic valves for decades untill snug...is there a possiblility the engine heating up causes a valve to stay open causing a misfire?? can this happen?? I adjust untill snug on the pushrods, and no further....
any clues ??anyone/??
GENE
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
Usually when the engine heats up the clearance gets bigger. I adjsuted my solids cold and checked them when hot and there was a .006 larger difference. I doubt it would be hanging the valve open.
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
I don't thin that the outside temp is going to screw with your valve adjustment to any degree down here, the outside temp swing is only about 30 degrees but the engine temp swing is more like 140. There is some sort of temp sensing for the engine feeding the computer, possibly an outside temp sensor and maybe even ambient air pressure sensor. Thats the place to look, it sounds like the fuel mix is not being compensated correctly for temp. Are there any error codes? What kind of computer? You need to run thru all the sensors on the engine and verify they are working.
Good Luck, let us know
Good Luck, let us know
Thread Starter
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
The computer is a speed denisity 1227730, the sensors have been gone all over completely, there is no code set, but that off idle tip in goes so damn lean on that o2 sensor, i'ts a joke, the idle is ragged as hell.....but it runs fine when cold, but when gets hot enough to go closed loop, it starts running like crap....
GENE
GENE
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
how about the different changes in fuel formulation/additives for the temperature changes???? maybe thats screwing with how its running
Thread Starter
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Originally Posted by bobs77vet
how about the different changes in fuel formulation/additives for the temperature changes???? maybe thats screwing with how its running
GENE
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
you know the engine is in a nice little box created by the fenders hood,etc.......it also creates its own heat......i wonder really how much difference the out side temperature makes on the internal parts? maybe what 20-30* max? and if its only that much of a difference how much is the metal expanding for the temperature change?
