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Motor won't rev over 4,000 rpm. Valve springs?
Posted By: MrBelvedere2
Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 04:04 AM
Hey guys, I got my 383 engine running really nice, just seems to drop off at 4,000 rpm. The tach will not go over 4,000 rpm no matter what I try to do to it. Brand new holley carb custom built for the motor as well. My question is, it has a crane cam hi intensity hydraulic 226 duration. cam card says max lift at 109 ATDC, 119 BTDC. Loads are 95 lbs closed, 244 lbs open. I have been trying to figure out what it could be. In my research it seems to point to valve springs. I am not sure if they are matched for the cam when the motor was built. The receipt I have for the motor is just "HP Springs". I am wondering fit this cam needs more than just HP spec springs? I can't find the part number for it which is 644321. It is an old cam so they probably don't make it anymore. What do you guys think?
Posted By: bonefish
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 04:21 AM
are the lifters old too?mabey their not pumpin up.
Posted By: 440PURSUIT
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 04:26 AM
You'd prob get the engine loaded up and stall if trying to rev it. When the springs float the fuel just floods all cylinders and car wont run until cleared out. Any evidence of a POP when revving?.
You may look for low voltage in ignition system or bad coil. Another likely culprit.
Posted By: Cab_Burge
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 04:27 AM
I like to see at least 110 lbs on the seats and 300 lbs opened
I currently use 150+ on the seats and 350 to 375 opened and shoot for the spings to be within .100 of coil bind at max lift
Posted By: 67Satty
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 04:30 AM
Did you check the timing and reluctor gap?
Posted By: 6PakBee
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 04:35 AM
What does the engine sound like at 4,000 rpm? If you have weak valve springs it'll sound something like a rev limiter, a lot of missing and popping. If this is not happening and the engine is smooth at 4,000 rpm but won't go further, something else is awry.
Posted By: Dunnuck Racing
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 05:19 AM
I'm right there with Cab on what I use for spring pressure,but what you have will pull more rpm than you are getting.
Ignition problems,fuel pump or lines/ plugged filter,or restrictions in the exhaust are all possibilities.
Keith
Posted By: Exit1965
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 05:31 AM
Another possibility is piston/valve interference. I once had a 383 that wouldn't rev past about 3500, and that was the cause. I found out about it once it took out a valve and ate a piston.
I hadn't checked the P/V clearance and it bit me hard.
So, has the piston to valve clearance been checked?
Posted By: Kern Dog
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 05:56 AM
Hey Larry.
I have had similar problems with my stuff. It often came down to an ignition issue. High resistance in the plug wires, worn plugs with excessive gaps, distributor point bounce from a weak spring, Electronic ignition reluctor gap too wide....
Posted By: RapidRobert
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 06:02 AM
As said how does it act at 4K? For a start I'd try to pin it down to inadequate fuel delivery or to ignition. Will it rev past 4K in your driveway? (fuel requirements then are minimal as it ain't under load).
Posted By: Kern Dog
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 06:07 AM
My fat ex wife had an '80 Datsun 280ZX. That was a nice car but at 4000 it hit a wall. It didn't matter if it was in gear or neutral. The problem turned out to be found in the distributor.
Posted By: MrBelvedere2
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 06:57 AM
Hey guys thanks for the responses so far. I am running new Firecore wires, and brand new autolite 85 plugs gap set right. The exhaust is almost straight through with classic chambered mufflers. The distributor however is a stock points type that is a couple years old that did run fine on the old motor. I have a low deck distributor with a pertronix kit in it on the shelf, I might switch that out and see what happens. The motor sounds like it's revving fine and everything, but when your in the car and revving it, you look at the tach and as soon as it hits 4,000 it just doesn't seem to want to go over that at all. No sputtering,maybe some popping noises.
Posted By: That AMC Guy
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 08:06 AM
If you're still running points, check the condensor.
Years ago, on my Gremlin I had the same issue only at 2,000 rpm, it would fuss and fart and break apart.
Asked on here and somebody said change the condensor. .75 cents later and the car ran perfectly again!
Posted By: 68KillerBee
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 11:25 AM
I had bought some rebuilt heads from my uncle that had just sat. The car never did quite run right, but last year it started getting worse. Best described as floating the valves, the motor was getting louder but going nowhere. Some stealth heads fixed that.
After doing that I realized what a baby cam I have and also low compression pistons which were both supposed to be "HP".
I was looking into a whiplash cam, but just bought a 2010 challenger and the car fun is a little low. Snowball effect otherwise.
Posted By: cjs69mope
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 03:19 PM
What kind of timing are you running ? a 383 bone stock in 66 charger with a good tune and 600 Holley DP carb my buddy had in high school was faster than any of the late 80's cars my other friends had at that time a rusty old charger wupin 305 camaro and mustangs on the street HA HA!
Retarded timing , broken vacuum advance , Clogged fuel Filter .
These things i would look at closely first.
Posted By: Firepowerflyer
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 04:12 PM
Do you have the factory stamped rockers or did you run adjustable? Maybe they could be adusted wrong or if your running the factory setup mack sure you have the right push rod length.
Posted By: 70Cuda383
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 04:41 PM
if this is a problem that just started out of nowhere, and it was previously running fine, then I'd look at valve springs.
however, I had a mishap once... mis-read the timing marks on the gears when I installed them. cam ended up about 30 degrees advanced. engine fired right up and ran great. but it would NOT rev over 3,000 rpm.
so don't be afraid to check cam timing either if you find that it's not in your ignition anywhere, and the valve springs are ok. although it's unlikely, I suppose it could be possible somehow if the chain is old and very slack, to have jumped a tooth or 2...but if it was that loose, I would also think that your timing would be eratic as the slop in the chain allowed the cam to lag behind, then get yanked forward, then lag behind...giving you a tick-tock back and forth on your spark timing.
Posted By: Dodgem
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 07:36 PM
Adjustable Rockers or pushrods??
Posted By: autoxcuda
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 08:24 PM
Quote:
if this is a problem that just started out of nowhere, and it was previously running fine, then I'd look at valve springs.
however, I had a mishap once... mis-read the timing marks on the gears when I installed them. cam ended up about 30 degrees advanced. engine fired right up and ran great. but it would NOT rev over 3,000 rpm.
so don't be afraid to check cam timing either if you find that it's not in your ignition anywhere, and the valve springs are ok. although it's unlikely, I suppose it could be possible somehow if the chain is old and very slack, to have jumped a tooth or 2...but if it was that loose, I would also think that your timing would be eratic as the slop in the chain allowed the cam to lag behind, then get yanked forward, then lag behind...giving you a tick-tock back and forth on your spark timing.
I saw that in a Mopar that someone took to shop about 6 monthes ago. Aligned the marks and all was good.
Posted By: sixpack4spd
Re: Motor won't rev over 4,000 rpm. Valve springs? - 11/30/12 09:37 PM
I would check the cam timing.
Posted By: 52savoy
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/01/12 01:59 AM
My turn... I doubt it's the valve spring pressure. I run 105 seat pressure and around 350lbs open on a Lunati .600 solid lifter cam. I've ran those springs for 35 years and will continue to unless something changes drastically.
Did you check/cut the valve guides so the retainer doesn't bottom out at max lift?
Block decked any? Check pushrod scrub pattern?
If all that is good, I would agree with some of the others...ignition and or timing.
This might be pushing it a little.. but did you mash the pedal down all the way and check the carb?
Posted By: IMGTX
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/01/12 03:47 AM
Quote:
This might be pushing it a little.. but did you mash the pedal down all the way and check the carb?
I was thinking the same thing.
I had a car wouldn't get up into the RPM's and it was because the linkage on the carb would bind and not open fully. If the primaries do not open fully it will usually prevent the secondaries from opening at all. If it's vacuum secondary make sure the diaphragm is OK.
2nd thing to do is replace the points & Condenser. As said already, a bad condenser can cause weird problems but a weak points spring can cause the points to float at speed effectively preventing spark and becoming a rev limiter.
While your in the distributor compare the distributor cam to a known good one and make sure the distributor lobes aren't worn down. If you don't have a known good one post pics. Somebody on here will let you know. Don't forget to grease the point's rub block and distributor cam lobe.
I also had a dual point distributor that wouldn't run higher RPM's if one set of pints was disconnected.
If the Carb is opening all the way and the distributor is OK then check the cam timing. IMHO.
Posted By: 52savoy
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/01/12 09:24 AM
In 1981 Me and some friends put my freshly built 426 Sreet Hemi in one of their "The Rod Shop" ex-pro/stock Challengers for the summer. It ran pretty good considering it was just a street Hemi with a .690 Crane roller modded carbs. I think it ran some 10.0s and runnered-up a few times before I reclaimed the motor for my roadrunner.
My roadrunners first pass down the track(Trails), was 7 tenths slower than it was before the engine rebuild.. It should have picked up about a second after the rebuild.
A quick look at carb linkage work I did when the motor was first put in the Dodge brought the problem to light. I had tightened a screw too much and prevented the secondarys from opening on both carbs
I redid the linkage and went back out and ran 11 tenths faster. 10.60.
Big disappointment...Never knowing what that old Rod Shop car would have ran with a hopped up street Hemi.
9.00
ok.. what was problem again...
Posted By: DusterMan
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/01/12 04:48 PM
Does your tach have a rev limiter on it? I had a friend that messed with his car for a few days would not rev over 2500. Someone turn the dial down. A thought.
Posted By: Dodgem
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/01/12 07:30 PM
I wonder if the lifter preload is set so tight it can't rev for holding the valves open when it revs Up?
Posted By: jbc426
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/01/12 07:39 PM
Single point distributor? What is your dwell? When reving the car in neutral past 4000rpm, what does the dwell change to? Is it going to zero?
Can you see any unusual pitting on the contact surfaces of the points? Are you using Accel or Blue Streak points?
Posted By: HYPER8oSoNic
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/01/12 11:38 PM
Just off of what you posted, two areas I would look into first. The ignition system, particularly the mechanical advance. And your valve springs and retainer/valve guide clearances. Save possible carb problems after these checks and/or settings.
Food for thought.
Posted By: p d'ro
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/02/12 02:44 AM
I agree that it may be something simple like the linkage. Mine just had the throttle cable come loose and it wouldn't pull. Check that when gas pedal is down that linkage is wide opened.
Posted By: bogusracer
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/02/12 07:04 PM
As suggested before, check your carb for wide open with someone else mashing the pedal to the floor. If that's ok, check your fuel delivery system. Sounds like its running out of fuel. Could be as easy as a fuel gauge not reading correctly and not enough fuel in the gas tank (that happened to me at the Drag strip once). If you have enough gas in the tank, then check the fuel delivery system. Fuel pump pressure and delivery rate, possible clogged fuel filter, check to see if the pickup in the fuel tank has a sock filter that is collapsed or clogged up. Make sure you don't have too much rubber fuel line on the suction side of the fuel pump which might collapse as the pump suction increases as the rpm increases. Just a few suggestions here as you did not say there were any popping issues etc. in your initial statement concerning the problem. If it just noses over and doesn't pull and it did before, that's where I'd look.
Good Luck.
Bogusracer
Posted By: stumpy
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/02/12 08:15 PM
Just for fun check to make sure your coil is wired correctly. If it's hooked up backwards it will still work but will break down at higher rpms.
Posted By: MrBelvedere2
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/05/12 06:23 AM
Hey guys, thanks for all the advice so far. I was able to work on the car tonight. I got my 750cfm holley double pumper, built by a pro for my engine. I also have firecore spark plug wires that are brand new, also new autolite 85 plugs gapped correctly. I also swapped my points distributor for a known-good pertronix distributor set up with a performance curve. I fired the car up,and it still will no go over 4,000 rpm. I would hate to think its the heads. This motor is pretty much brand new and has about 1500 miles on it.unfortunetly the place that built it is out of business. You rev it up and it sounds like it's running somewhere, just seems to hit a stop at 4,000 rpm. I did put new pushrods in it, they are the stock length. I do know the motor was decked enough to remove the stampings on the distributor pad. Would that be enough to warrant custom length pushrods? I was told when I purchased the motor to use stock length pusrods. I am running a hudraulic cam with stock stamped rockers. I'm running out of ideas.
Posted By: Kern Dog
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/05/12 06:58 AM
Quote:
Hey guys, thanks for all the advice so far. I was able to work on the car tonight.
That explains your absence at tonights car club meeting... 
Posted By: Mr. T
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/05/12 08:07 AM
The way that you describe the probem, is the same thing that I went through two years ago with my 360. I had the 14 year old valve springs replaced. End of problem.
Posted By: autoxcuda
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/05/12 08:48 AM
Quote:
The way that you describe the probem, is the same thing that I went through two years ago with my 360. I had the 14 year old valve springs replaced. End of problem.
That would mean the springs in MrBelvedere2's motor would have not be new. And really shot old springs at that. Maybe pull some valve springs and get them checked. And check if the valve guides are hanging up the valves.
Posted By: autoxcuda
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/05/12 08:53 AM
Quote:
Hey guys, thanks for all the advice so far. I was able to work on the car tonight. I got my 750cfm holley double pumper, built by a pro for my engine. I also have firecore spark plug wires that are brand new, also new autolite 85 plugs gapped correctly. I also swapped my points distributor for a known-good pertronix distributor set up with a performance curve. I fired the car up,and it still will no go over 4,000 rpm. I would hate to think its the heads. This motor is pretty much brand new and has about 1500 miles on it.unfortunetly the place that built it is out of business. You rev it up and it sounds like it's running somewhere, just seems to hit a stop at 4,000 rpm. I did put new pushrods in it, they are the stock length. I do know the motor was decked enough to remove the stampings on the distributor pad. Would that be enough to warrant custom length pushrods? I was told when I purchased the motor to use stock length pusrods. I am running a hudraulic cam with stock stamped rockers. I'm running out of ideas.
Seems like you are going through the elimination process. Before I pulled the heads, I pull off the water pump housing, timing cover and check the timing chain marks.
Could be heads too. Pick your poison. I think checking the timing marks would be less costly in terms of parts.
Posted By: Dodgem
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/05/12 02:49 PM
I'm wondering if there is enough milling to be the problem.
I would check my cam degree first.
Did you check the old pushrods against the new pushrods for length!
really sounds like it is holding the valves open from pushrods too long,
You can buy a shim kit and shim up the rocker shafts .040 then .060 this cannot hurt anything worst it can do is tick.
http://www.hughesengines.com/Index/produ...mp;partid=10406http://www.hughesengines.com/Index/produ...mp;partid=10404
Posted By: MrBelvedere2
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/07/12 02:48 AM
I would love to try those shims for the rockers, but the problem is this motor is an early big block with the 4-bolt max wedge style heads, and has the bolt-on rocker shaft post, not the casted-in style. Maybe I can just make some .040 shims from square stock and try it that way?
Posted By: Kern Dog
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/07/12 02:52 AM
Mopar Action magazine had a blurb on that. They took .040 aluminum sheet and made the shims themselves.
Posted By: Dodgem
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/07/12 03:00 PM
Quote:
I would love to try those shims for the rockers, but the problem is this motor is an early big block with the 4-bolt max wedge style heads, and has the bolt-on rocker shaft post, not the casted-in style. Maybe I can just make some .040 shims from square stock and try it that way?
Yea just shim the post up. .04 then .06
pop cans can be cut square and drilled for low buck shims thin so you have to stack some together!
Posted By: cudaboy
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/07/12 10:28 PM
Quote:
however, I had a mishap once... mis-read the timing marks on the gears when I installed them. cam ended up about 30 degrees advanced. engine fired right up and ran great. but it would NOT rev over 3,000 rpm.
I did the same thing. It ran great, but at 3000, it just stopped.
Dennis
Posted By: fastnos
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/23/12 04:09 PM
Just wondering, did you find/fix the problem?
Posted By: BigBlockMopar
Re: Motor won't rev over 4,000 rpm. Valve springs? - 12/23/12 04:28 PM
Was the cam degreed?
Does the throttle actually open the carb fully?
You really sure you got all the plugwires on in the correct order?
Posted By: MrBelvedere2
Re: Motor won't rev over 4,000 rpm. Valve springs? - 01/20/13 03:01 AM
Hey guys here is an update. I finally got some time to go and work on the car. I put the .040 shims in first. I fired it up, and it still acts the same. Should I still try an additional .020 of shim?
Posted By: RapidRobert
Re: Motor won't rev over 4,000 rpm. Valve springs? - 01/20/13 03:37 AM
I'd go back over the basics starting with a compression test. More detail on how it's acting at 4K. (in the driveway or under load & WHAT is it doing) Did it always act this way since built or happen after a part/tuning change or out of the clear blue
Posted By: buildanother
Re: Motor won't rev over 4,000 rpm. Valve springs? - 01/20/13 04:55 AM
Wonder if it's running out of fuel
mechanical pump?
Posted By: MoparforLife
Re: Motor won't rev over 4,000 rpm. Valve springs? - 01/20/13 11:05 AM
Valve spring shims are not meant to be used to increase valve spring pressures. They are meant to be used to correct installed height. Using them to increase pressures can cause problems like coil bind.
Posted By: 70Cuda383
Re: Motor won't rev over 4,000 rpm. Valve springs? - 01/20/13 06:12 PM
I don't see how it could be fuel delivery problem unless the carb is all junked up, there should be MORE than enough fuel in the bowls to allow the motor to rev up to 3,000 rpm in neutral. I think one time I turned my fuel pump off and the engine kept running at idle for another 5 minutes.
You might not want to hear this, but check the cam timing or valve springs.
or before you check those, tell us what changed right before this problem occured. did you do a cam swap? or did you replace the timing chain/gears? did you change the heads?
instead of just blindly adding shims, pull off your intake and actually look at the lifters to get an idea of how much preload you have in them.
If this is a brand new engine that you're still trying to tune it in, then check the valve springs and check your cam timing. with a degree wheel and a dial indicator, you can check the cam timing and not even remove the timing cover. (but you will have to remove a valve cover to put a dial indicator on #1 intake valve)
Posted By: drew72
Re: Motor won't rev over 4,000 rpm. Valve springs? - 01/20/13 07:22 PM
Quote:
Valve spring shims are not meant to be used to increase valve spring pressures. They are meant to be used to correct installed height. Using them to increase pressures can cause problems like coil bind.
Posted By: MrBelvedere2
Re: Motor won't rev over 4,000 rpm. Valve springs? - 01/22/13 07:24 PM
thanks for the help so far guys. This is a new engine that was built at a machine shop, I bought it second hand from a guy in my car club and the machine shop is not around any longer. I do know the block was decked (how much, not sure) but enough to wipe off the stamping on the distributor pad. That is why I tried the shims, to increase the height for the pushrods. I think I'm going to have to get someone from my club with some free time to come out and help me, as I don't have the expertise or tools to investigate further at this time. Thanks for all the help so far!
Posted By: MoparforLife
Re: Motor won't rev over 4,000 rpm. Valve springs? - 01/22/13 07:37 PM
Sounds like you were using rocker shaft shims which are meant to correct geometry. and you weren't using valve spring shims or if you were valve spring shims will do nothing to push rod length.
I would like to see ow that cam is degreed in. Been down that road with no RPM's and the cam degreeing is off.