I agree with skicker above. I had this happen. Put a timing light on your damper and look for scatter at 3500 plus rpm. My issue was a worn out advance plate that wouldn't advance smoothly. I fixed mine with a new distributor, MP/Mallory.
(1) block the rods up & retry it which will give the enrichment from being on the power circuit to see if it is a too lean prob. (2) check rotor phasing. Holler back. EDIT Quicker, You might set the RPM up to where it starts to act up & spray something flammable into the carb (not sure what, I hear starting fluid is harmfull) & see if it gains RPM/straightens out and I would close down the secondary air door (just a WAG there but even a 2bbl will reach 5K by itself).
Last edited by RapidRobert; 09/27/1811:37 AM. Reason: bored
live every 24 hour block of time like it's your last day on earth
In the last year, I know of three people who have had customers cars in their shops to address the exact same problem.
In those three cases, the cam had been installed advanced by 2.5 teeth. They had the bottom gear key way straight up, dot on upper gear straight down........ instead of “dot to dot”, which will have the bottom key way parallel with the #1 cylinder(not straight up). The cam installed key way to dot is advanced 35degrees.
It sounds like some kind of valvetrain issue to me........ cam timing, springs, lifter preload, etc.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
Re: LA 360 - Hits a wall at 4,000rpm
[Re: RapidRobert]
#2555499 09/27/1812:16 PM09/27/1812:16 PM
Verify good spark, an inexpensive tool is an open circuit spark tester, the best ones IMHO look like a spark plug with the center electrode removed, if the spark can jump that gap, with a clean blue spark, it's good. Check fuel pressure and vacuum. A restricted exhaust can cause the symptoms you are describing. Verify your timing, just set it for best idle, then rev it up and make sure it advances smoothly and doesn't break down or start retarding, weak P/U coils or modules can cause this. Please don't go sparking carb cleaner down the throat with the car running, use a propane/MAPP torch to provide some enrichment. You could still have a cam timing problem, dot->dot can fail you, if the idle vacuum is low, or take a lot of initial timing to achieve it's something to think about. HTH, Steve
In the last year, I know of three people who have had customers cars in their shops to address the exact same problem.
In those three cases, the cam had been installed advanced by 2.5 teeth. They had the bottom gear key way straight up, dot on upper gear straight down........ instead of “dot to dot”, which will have the bottom key way parallel with the #1 cylinder(not straight up). The cam installed key way to dot is advanced 35degrees.
It sounds like some kind of valvetrain issue to me........ cam timing, springs, lifter preload, etc.
I am trying to think through your post...
The Cam gear Dot was at 6 o'clock and the Crank gear dot was at 12 o'clock...however I don't recall where the crank key was pointed.
That said, the balancer aligns at 0° on the timing cover with the #1 piston is at TDC. I don't think I can be off by 2.5 teeth if I am dot-to-dot on the gears and #1 is at TDC along with the balancer reading...Right?
In addition, I should mention that the truck never really ran over 4,000rpm before the cam swap. I attributed it to the engine's era and the max power rating for the engine was around 3600-4000rpm when new anyway.
Verify good spark, an inexpensive tool is an open circuit spark tester, the best ones IMHO look like a spark plug with the center electrode removed, if the spark can jump that gap, with a clean blue spark, it's good. Check fuel pressure and vacuum. A restricted exhaust can cause the symptoms you are describing. Verify your timing, just set it for best idle, then rev it up and make sure it advances smoothly and doesn't break down or start retarding, weak P/U coils or modules can cause this. Please don't go sparking carb cleaner down the throat with the car running, use a propane/MAPP torch to provide some enrichment. You could still have a cam timing problem, dot->dot can fail you, if the idle vacuum is low, or take a lot of initial timing to achieve it's something to think about. HTH, Steve
Thanks for the feedback. Blowing out spark is something I was considering as a potential issue as well, I can't say that I am overly confident with the ignition system in it's current state. I do have an MSD 6A box around if I wanted to throw that at it and bypass some of the factory gremlins.
Best idle ignition timing seems to be around 14°, I can idle in gear quite well at 700-750rpm. To me, that doesn't seem "excessive", but I haven't messed with many of these engines.
I'll get a idle vacuum reading on it this afternoon.
Re: LA 360 - Hits a wall at 4,000rpm
[Re: Pacnorthcuda]
#2555506 09/27/1812:30 PM09/27/1812:30 PM
This is from yesterday, it's not as jumpy since i tightened the reluctor gap slightly. This seems to be an obvious ignition/distributor issue to me.
Originally Posted By skicker
I'd be looking at the advance and the distributor... Any chance the timing marks are wrong on the crank?
Originally Posted By Pacnorthcuda
Goody,
I agree with skicker above. I had this happen. Put a timing light on your damper and look for scatter at 3500 plus rpm. My issue was a worn out advance plate that wouldn't advance smoothly. I fixed mine with a new distributor, MP/Mallory.
Thanks. Dropping in another distributor I have on hand is an option, I'll go to storage and grab it. It can't hurt at this point.
many, many years ago, i built a 440 to race in my 68 GTX. it had a HUGE bottom end grunt, and revved like a pro stocker, but at 3500, it fell on it's face ! i had advanced the cam 4*, but had mixed up the marks. upon tear down, i found the valves had lightly kissed the pistons. pistons were ok, but had the heads re-done because of a couple of valves. re-indexed the cam and crank gears, this time DEGREEING in the cam like i should have done in the first place. didn't rev like a pro stocker any more, but ran real good. as was mentioned above, it is very possible the timing chain set is marked wrong, or installed incorrectly. just my experiance, your mileage may vary.
That said, the balancer aligns at 0° on the timing cover with the #1 piston is at TDC. I don't think I can be off by 2.5 teeth if I am dot-to-dot on the gears and #1 is at TDC along with the balancer reading...Right?
There really isn’t any direct link to where you installed the cam vs the balancer being indexed correctly. The balancer is indexed off the key in the crank....... period.
The cam could be installed anywhere and the balancer would still just slide over the key in the same place.
Imagine the piston is at tdc, slide damper off. Remove timing set, rotate cam to any random position, reinstall timing set. Who knows where the cam is. Crank has not moved, damper still where it was.
If you used a typical “3 way” adjustable timing set, there are 3 key ways. Each has a mark to denote zero, advanced, retarded. There is also a corresponding mark roughly 2.5 teeth counterclockwise from the keyway, and it’s that mark that you would use to line up with the mark on the upper gear.
The three instances I referred to all had the dot at the keyway lined up with the mark on the upper gear.
They were using the wrong dot.
If you degree the cam when you’re installing it, you avoid this type of mistake.
I seem to recall a member here experiencing this same thing on a 340 6bbl. I’m pretty sure his ended up being the cam was installed just how I described it.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
That said, the balancer aligns at 0° on the timing cover with the #1 piston is at TDC. I don't think I can be off by 2.5 teeth if I am dot-to-dot on the gears and #1 is at TDC along with the balancer reading...Right?
There really isn’t any direct link to where you installed the cam vs the balancer being indexed correctly. The balancer is indexed off the key in the crank....... period.
The cam could be installed anywhere and the balancer would still just slide over the key in the same place.
Imagine the piston is at tdc, slide damper off. Remove timing set, rotate cam to any random position, reinstall timing set. Who knows where the cam is. Crank has not moved, damper still where it was.
If you used a typical “3 way” adjustable timing set, there are 3 key ways. Each has a mark to denote zero, advanced, retarded. There is also a corresponding mark roughly 2.5 teeth counterclockwise from the keyway, and it’s that mark that you would use to line up with the mark on the upper gear.
The three instances I referred to all had the dot at the keyway lined up with the mark on the upper gear.
They were using the wrong dot.
If you degree the cam when you’re installing it, you avoid this type of mistake.
I seem to recall a member here experiencing this same thing on a 340 6bbl. I’m pretty sure his ended up being the cam was installed just how I described it.
Unfortunately, I think you're on to something. I believe the dot above the keyway is aligned with the dot on my cam gear.
I found this image online. I do not recall using the dot on the outer part of the crank gear. I can now see where the 2-1/2 teeth would come from. I'll need to ponder on it, but it sounds like I need to go ahead and pull the timing cover.
first pull a valve cover (whichever is easier to remove) & with a 1&1/4" socket/breaker bar turn the crank back & forth till either the #1 or #6 (either one is fine) rocker arms are (1) "moveing" & (2) even with each other (go back & forth with the socket when you get "close") & see if the dampener slit is on or very near zero TDC on the timing tab.
live every 24 hour block of time like it's your last day on earth
I lean toward cam timing being the issue. I have done that before, not hard with the multiple keyway setups, esp if you have them on both the crank and cam gear. Another reason to ALWAYS degree your cam. Harder with the head on, but can be done.
That said, I'm going to throw this out there. Is your vac adv set up for timed vac and you're using the untimed port (or vise versa)? That will cause some erratic behavior and in combination with one or more of the carb adjustments being out of spec, it could cause this headache. Of course, assuming your advance mechanism integrity is where it needs to be in the 1st place.
Another though, more of a shot in the dark, but is your PCV valve functioning properly? I once new a guy that had the bright idea to "hollow out" his pcv valve (this guy put a Poncho 301 and metric 200 trans in his 68 Firebird). With his "enhanced" PCV valve, it would lean out and fall flat before 5000. The compression was super low in that thing, like 70lbs cranking pressure and within a couple of numbers cylinder to cylinder. The engine was reportedly from an early 80's turbo Trans Am, so the compression makes sense and I imagine the cam was pretty weak too. Not apples to apples, but an easy check to make.
All I do is pull the valve cover and rotate number 1 cylinder to overlap, which is 180* after firing and look at the rockers for that cylinder.
If both rockers are off the seat the same amount, the cam is in straight up.
If the exhaust rocker is off the seat more the cam is retarded.
If the intake rocker is off the seat more the cam is advanced.
This doesn't tell you how far off you are but your cam should be in advanced a bit and straight up at the very worst.
That's the first thing I'd check.
This is why you never ever NEVER EVER install a cam dot to dot. The cam MUST be degreed in, especially with the advent of all these multi keyed crank gears and the directions that come with them can be confusing.
Degree the cam and none of that matters.
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Just something to think about. Fuel pressure means that there is fuel at the gauge. It does not meam there’s fuel in the carb. I have to run the bigger needle and seats or I will drain the float bowls. Also I run a mechanical and electric pump together. I have forgotten to turn on the electric pump and it acts just like that 4000 just cuts out. Rpm drops comes right back.
Did the engine have exhaust valve rotators ? Did you eliminate them? My 318 would not rev over 4700rpm period {Valve spring limitedIf you have access to point dist try it simply get it to negative side of coil also that tach could have a 8-6-4 setting make sure its on the right one
First small block I ever built would not rev past 4500. Stock rebuild, stock rockers, small comp hydraulic cam, stock rockers. Heads and block decked just to true everything. Found the lifters were pumping up around 4500 holding the valves open. A set of 273 adjustable rockers cured the issue, allowing the lash to be set.
