chef
So here is the story, I have been restoring a 88 grand waggy and I am having trouble with the engine. Specs are stock bore, heads ported and polished three angle valve job, 27 thou off heads (est 9-1 comp ratio). Performer Edelbrock intake, 0-5500 Edelbrock cam, shorty headers, single 3 inch exhaust. DUI ignition, live wires, champion plugs, Howell EFI. Problem is it runs like crap, backfiring through intake, stumble poor idle, dies idling. I have checked timing, there does not appear to be any vacuum leaks. I do however have what I think is low vacuum at idle 8-10HG and the needle is bouncy, bring it up to 1800-2500 its's about 15-19HG. When I ease off it goes up slightly and then drops back to 8-10. If it's idling and i punch it I get the backfire or if I load the engine up, again backfire. Any ideas?
Thanks
tufcj
Welcome to Bulltear! :!: :!: :!:
.027" is a lot to machine off the heads. Did you machine anything off the intake manifold? If you didn't, chances are you have a vacuum leak on the underside (inside the engine). With the Howell system, you might be able to verify that with an OBD I scanner. You can read the O2 sensor values and tell if it's lean. Pop back thru the carb (or throttle body) is usually a lean condition.
A general rule of thumb is that if you machine the heads or block the deck, the same amount should be taken off the sides of the intake, and 1.4 times the amount taken off the ends. So you should mill .027" from each side of the manifold and about .038" from the ends.
Bob
tufcj
Old Rugged Crosser
Have you verified the firing order of your spark plug wires? Also it sounds like your ign. timing is off. :sa: :sa: :sa:
MC
Could also be that our timing set is off as well
juggernaught
You only need to be off one tooth on the dizzy to cause havic similar to your symptoms. Vacuum should be at least 14Hg at 800 rpm min.
Look up links on "how to read a vacuum gauge".
chef
[quote=tufcj]Welcome to Bulltear! :!: :!: :!:
.027" is a lot to machine off the heads. Did you machine anything off the intake manifold? If you didn't, chances are you have a vacuum leak on the underside (inside the engine). With the Howell system, you might be able to verify that with an OBD I scanner. You can read the O2 sensor values and tell if it's lean. Pop back thru the carb (or throttle body) is usually a lean condition.
A general rule of thumb is that if you machine the heads or block the deck, the same amount should be taken off the sides of the intake, and 1.4 times the amount taken off the ends. So you should mill .027" from each side of the manifold and about .038" from the ends.
Bob
tufcj[/quote]
If I do not use the end gaskets, do the ends have to be machined? Just trying to save a buck. :?:
tufcj
I really don't know. I've always used the end gaskets, although I know some people don't. Measure an end gasket, if it's more than .038" thick, you can probably get away with it. If it's thinner, there may be metal/metal interference on the ends when you tighten the intake.
Bob
tufcj
chef
Also someone had mentioned my push-rods maybe too long now with the .027 off the heads? Is there an acceptable tolerance/ speck for this. When the valve is in the down position, I cannot rotate them by hand?
msalaba
I had my heads shaved 0.045"
I had a machine shop mill 0.045" from each side (the intake to head ports) of the intake manifold.
I did not have the ends machined. I am a firm believer of "take those rubber %$^@#*$ and throw them away" Buy not machining, I use less "The Right Stuff" for sealing.
I can't remember what length rods I used. There is a measurement of lifter pre-load (so many thousanths) when the lifter is on the cam base circle. I used an adjustable push-rod and lengthened it to put the lifter pre-load on the light side. I checked every lifter and used the length of the longest measuement for all push rods. IIRC ~0.040" less than stock.
I wish I could remember what the tolerance for the lifter/push rod was. @ 0.027" you should be close. I would look for the port match from the intake to the heads. At 0.045" my ports (or bolt holes) didn't line up at all.
juggernaught
My preload tolerance was .020 to .040 for my 360 / 9.0:1
ironman_gq
put a few more degrees of base timing in it and see if the vacuum picks up or richen up the idle mix a little and see what happens
jeepsr4ever
Could be that you need some spacer shims under your bridges so your valves are slightly open.
chef
So with 25-30 degrees base timing, it runs pretty good, so either I am out a tooth on the engine timing or it's a bad timing chain set. Opinions? Or could the curve on the DUI be that off?
tufcj
Is that going by the mark on the balancer? Is the rubber ring in the balancer in good shape?
I've seen the outer ring slip as the rubber decays with age. I've also seen an engine that has jumped a tooth on the cam run after the spark timing is adjusted.
The only way to check the balancer is to put some sort of piston stop in the #1 plug hole, then rotate the engine by hand each direction and see if the mark on the balancer stops equal distance from TDC each way.
Bob
tufcj
chef
[quote=tufcj]Is that going by the mark on the balancer? Is the rubber ring in the balancer in good shape?
I've seen the outer ring slip as the rubber decays with age. I've also seen an engine that has jumped a tooth on the cam run after the spark timing is adjusted.
The only way to check the balancer is to put some sort of piston stop in the #1 plug hole, then rotate the engine by hand each direction and see if the mark on the balancer stops equal distance from TDC each way.
Bob
tufcj[/quote]
Ya that is on the balancer, when I rotate the engine to TDC. Pop the cap the rotor is about 3/4 inch past number one, when the balancer is TDC
tarior
Just set the timing by ear on a virtually stock motor.
Use your right hand or an assistant to bring the engine up to 2500-3000rpm. Advance the timing until you hear it start to miss, you'll hear it out of the pipes. Back the timing off until it runs smooth again. Lock it down, take it for a spin to make sure it doesn't ping. If it don't, you're done.
PS, make sure you have your vacuum advance hooked up to full manifold vacuum.
Henry Lavrenz
'the needle is bouncing on the vac gauge' - focus on that. That means a intake(s) valves are not closing. Are you a tooth off on the timing chain setup? most likely not. The end gaskets on the intake manifold have nothing to do with this issue. incorrect ignition timing will not cause the manifold vacuum to bounce. I feel Matt is correct, in that you may need to shim your rockers or check your pushrod lengths. You milled your heads .027", that isnot very much if they have not been milled before. Consider that you have aftermarket gaskets and valvetrain parts and several things may be adding up in one direction, this can happen very easily. I preload hyd. lifters at least .050 and have gone as far as .090. I suggest to take off the valve covers and loosen each rocker bolt a half a turn, set the covers back in place, and start it up, you will know right away if it helps. Hankrod
chef
So finally getting back to the engine prob, took the front cover off today the base timing was bang on. Here is one thing I noticed, with both valves closed on number one, if i loosen the rocker arms and retigned the valves go down slightly? so they are not seated fully at TDC. My question is how close do I have to be on the push rod length? I took 27 though of the heads so is 20 though close enough if I can't get one perfect size?
Thanks again guys
tufcj
You may need to go shorter than .020" . If you're holding the valve open, then you're bottoming out the hydraulic lifter. You may need to pull the manifold and see how far the plunger is below the retainer clip when the lifter is on the base circle of the cam. I like to keep the plunger about .030" below the retainer.
Like MC says, you could put shims under the bridges, and see how it runs, then order the shorter pushrods.
Bob
tufcj
chef
K hard to get an accurate reading, I loosened the rocker arms, set the dial indicater at 0, timing strait up on number one. Snug up both rocker arm bolts and the indicater reads .075, then in 5 minutes it bleeds off to 0. So from my understanding, if i get a pushrod 20 though less, i should be good, yes?
Thanks
