Stock cam 360 idles bad, dies in gear, fixed!

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moparnocar

moparnocar
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I found some others on this site that were having the same problems. Their solution also fixed my problem, a lot of initial timing. It is a fresh rebuild 360, and its been a long time since I built a stock cam motor (340 cam specs). The problem I was having seemed like a valve train problem, or vacuum leak, it idled rough, had a bad flat spot off idle, and died in gear. I had 10 degees of timing and that was not enough, it needed 18 BTC initial degrees to run correctly. I've never advanced a stock motor that much to get it run, maybe it's because of the current gasoline blend?
Thanks to everybody that posted, it saved me a lot of time, and trouble!

Hopefully this will help someone else!
 
moparnocar said:
I found some others on this site that were having the same problems. Their solution also fixed my problem, a lot of initial timing. It is a fresh rebuild 360, and its been a long time since I built a stock cam motor (340 cam specs). The problem I was having seemed like a valve train problem, or vacuum leak, it idled rough, had a bad flat spot off idle, and died in gear. I had 10 degees of timing and that was not enough, it needed 18 BTC initial degrees to run correctly. I've never advanced a stock motor that much to get it run, maybe it's because of the current gasoline blend?
Thanks to everybody that posted, it saved me a lot of time, and trouble!

Hopefully this will help someone else!
Click to expand...
its good that it runs well now but ,18 degrees seems like alot of timing for a stock 340 cam on a 114 lsa.do yo trust the mark on the balancer to be correct?
 
my 73 duster has a pretty stock 360 in it...the cam is a Erson 208/214 @ .050

114 LSA ...it will idel at 5* intial timing...passed smog that way...afterward i kicked it up to 10* for better performance...

18* seems alot
 
340 8BBL said:
its good that it runs well now but ,18 degrees seems like alot of timing for a stock 340 cam on a 114 lsa.do yo trust the mark on the balancer to be correct?
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Yeah, thats exactly what I thought also, 18 is a lot, but I degreed the cam, and checked the balancer for TDC, when I assemble the motor. Also swapped dist. when I was trouble shooting. It seems that this a common problem, because of the other posts that I've seen??? I would have never thought of advancing it that much.
Normally I use a MP dist and set it @ 35 total @ 2400 RPMS's and don't worry about initial timing. But with this being a stock motor and dist, I set it at intial.
 
moparnocar said:
Yeah, thats exactly what I thought also, 18 is a lot, but I degreed the cam, and checked the balancer for TDC, when I assemble the motor. Also swapped dist. when I was trouble shooting. It seems that this a common problem, because of the other posts that I've seen??? I would have never thought of advancing it that much.
Normally I use a MP dist and set it @ 35 total @ 2400 RPMS's and don't worry about initial timing. But with this being a stock motor and dist, I set it at intial.
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Check your total timing. Also check your vacuum advance total. You can never be too careful.
 
If your lifter preload is too great from milled heads, this will cause you to have to run a great amount of initial timing to get a good idle. It's sorta like running valves adjusted too tight. It makes the cam seem bigger than it is. Were the heads milled any?
 
18 is alot for that cam ,really.i ran it in a 9.5 to 1 318 with only 12*initial and it idled fine.my 340 is set at 18*initial with a 284 duration cam.
 
StrokerScamp said:
If your lifter preload is too great from milled heads, this will cause you to have to run a great amount of initial timing to get a good idle. It's sorta like running valves adjusted too tight. It makes the cam seem bigger than it is. Were the heads milled any?
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That's the million question, I don't know the history of the heads. They were a finished set, that I ended up with in a trade. I didn't cc them before I bolted them on?? Could be, that was my 1st thought! I have a set of .020 rocker shafts spacers, I'll give them a try just to see what happens.
 
StrokerScamp said:
If your lifter preload is too great from milled heads, this will cause you to have to run a great amount of initial timing to get a good idle. It's sorta like running valves adjusted too tight. It makes the cam seem bigger than it is. Were the heads milled any?
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As long as you are in the stroke of the lifter piston the amount of preload is not going to impact the idle. A lot of preload can cause issues with lifter pump up at high rpm.
 
I think it's more due to the tune being close, but a little off. New fuels brun very fast, and with the big chambers and lower compression 18° is a little too much advance for my taste. There are better ways to do it to get it smoother and snappier without that much lead, but I think at this point if you're happy and it works for you, good enough.
 
If the cranking compression is on the low side (say 120-140) you need more intial timing.
a bigger cam with the stock compresion will always need more initial timing compared to the stock cam with less duration. I try to set my initial be how easy it is to start the engine. Just keep advancing the timing til it starts to get a bit harder to crank over, then back off the timing about about 5-7 degrees. Yes you most likely will need to recurve the dizzy so you dont go over your 34-36 (eg.) wide LSA's reduce the cranking compression because of the later closing intake valve.
 
18* is too high for a stockish cam, i'd check the manifold vacuum & see where its at, you may have a vacuum leak causeing a crappy idle, my cam is a 218/218 @ 50 on a 112 LSA & it holds 17 inches of vacuum in gear, timing is set at 10* int. & 30* total, now this is a magnum, I would'nt start blameing the gas, are pump gas is mixed & i'm running on 87 octane & it runs great, something is not right with your tune, or you have a vacuum leak or like said, the pre-load is too much.

dgc333, i disagree with what you said, i know 1st. hand how an engine will react (at idle) if theres too much pre-load on the lifters, it will keep the valves open & cause low vacuum, normal preload is between .020" & .060", if you exceed this it will cause problems, standard style lifters can/will bleed out under high RPM, thats why they make "anti pump-up" lifters that have different valveing & a stronger clip so you can run them at 0 pre-load or slight pre-load.
 
If you have so much preload that it is holding the valves open then you are not operating the lifter within its operating range which is what I said. High rpm pump up is another issue which is not what the OP has an issue with.
 
dgc333 said:
As long as you are in the stroke of the lifter piston the amount of preload is not going to impact the idle. A lot of preload can cause issues with lifter pump up at high rpm.
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I'm sorry, but you're just flat out wrong here. You go tryin to tell this to anyone who has ever run a hydraulic cam with adjustable rockers. You can taylor the valve adjustment on a hydraulic lifter very much in the same way that you can with a soild. In some instances, it makes more of a difference than differing the adjustment of a solid. It all depends on the cam grind. With your logic, you're saying that an engine will run the same with .020" preload as it will with .060". Go get a .040" feeler gauge and look at it. Are you really saying that here? Sorry, but you're WRONG.
 
No, he's correct, that is how the lifter is made to operate. Apon lifter pump up, the difference is seen.
 
Sorry, I've seen the evidence on the dirt track for better than twenty years. Them Chevy boys have known about it for YEARS. Varying the hydraulic lifter adjustment DOES make a difference. I don't care what the online tech articles tell ya. REAL world experience says otherwise. It always has.
 
Then we agree that lifter preload cn make a difference. However, the way you describe it, is that the preload makes a difference in this "Idle" problem when it doesn't. DGC333 is correct, you are partialy correct.

Your ignoring the way the lifter is made to operate.

At low RPM, this preload issue is not an issue unless grossly out of wack. The lifter has approx. - .100 total travel. The first and last .010 are not useable. (Give and take on that. Also, I would not run preload down to the last .010)
So, this gives approx. .080 useable adjustment in order to set up the engine correctly.

Moving the pushrod up high or down low in the plungers travel has an effect of the performance of the engine, but not at idle.

DGC333 is correct.
 
Can't say that I have had a lot of experience playing with preload on hydraulic lifters but but back in my younger days working on SBC engines I never noticed an change in the idle quality or manifold vacuum level with a change in preload and most recently on the magnum headed 360 I am running I went from 0.025 to 0.055 preload on the lifters and didn't see any change in the idle quality or manifold vacuum. If there was a change in power it wasn't enough for me to notice.

I have experienced lifter pump up at high rpms from too much preload but that is not the issue being discussed.
 
Ok, fair enough. dgc333, my apologies. Sometimes I get caught up in a discussion and kinda forget the main focus. You're indeed correct about idle. But sure as I'm sittin here, I've witnessed the difference that varying lifter preload can do in different circumstances. Comin outta a turn on the dirt track, for instance. It can make the difference between bein a dead dog outta a turn and overtakin the leader. I've seen it....and I've made it happen. With the same car, same combination, same track, same night, in the next round. Is that fair enough? Lastly, I will also add this.....depending on how quickly the lifters bleed down, and how much oil volume and pressure the pump has, it's not impossible for the valve adjustment to have an effect on idle quality. Personally, I wouldn't look at anything and say "no that can't be it". That makes no sense.
 
whats the cranking psi with this motor?


it should idle with 5*btdc, my .528 cam'd 340 will idle at 800rpm w/5*btdc.....

if the valves were hung open it wouldn't really run, would it, or they would have to be open only a tinge....even then with my 410 and all valves leaking example it ran fine.

something else is up, maybe weak spark, now I'm just guessing. lol
 
StrokerScamp, glad we are on the same page. I would vernture a guess the change in power you are seeing on the dirt track racer is a lifter pump up issue which you can minimize by running with a minimum amount of preload.
 
dgc333 said:
StrokerScamp, glad we are on the same page. I would vernture a guess the change in power you are seeing on the dirt track racer is a lifter pump up issue which you can minimize by running with a minimum amount of preload.
Click to expand...


Could well be......and just for the sake of the discussion, when adjustable, I always adjust 1/4 turn down. I never have liked goin tighter although I know people who swear by one full turn, one and a half.....that's just nuts to me.
 
FWIW, the typical 24 threads per inch lash adjusting fastener equals 0.042" per full turn. A 1/4 turn after removing the lash is going to be 0.010" of preload.
 
dgc333 said:
FWIW, the typical 24 threads per inch lash adjusting fastener equals 0.042" per full turn. A 1/4 turn after removing the lash is going to be 0.010" of preload.
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and that suits the HELL outta me cause I always run lifters with them GOOD snap rings, not them little wirey things. Hell, adjustin um loose probably gives a little more bottom end. Who knows?
 
I think the compression is low and that with the somewhat more duration cam is creating less cranking pressure. This causes less of a pressure drop in the intake and some carbs do not like this type of situation. The idle circuit in some carbs need more of a pressure drop, The advanced timing is lighting the mixture which is not perfect that is why it needs more advance. The pressure spike is slow because of the mixture. More pressure drop creates better atomization, less drop causes large droplets which are harder to light. Look at the specs of some of the stock 360 pistons (sealed power cast is one eg) they are around .100 down in the hole. This cannot be good for moxture quality at idle. I somewhat agree with the lifter preload argument. Max travel shuld be kept under .030 with stock type lifters but excessive preload should not effect the idle too much. Oh well, just my .02 worth.
 
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