timing issues

[troycalm]

Im at the end of my rope here is the issue.
I finished building a 78 1.8 for my wife and put a lot of money and time into a perforemance engine
port and polished head
4-2-1 exhaust
oversized pistons
4140 cams
dual idf's with matching intake
crane xr3000 electronic ignition
The problem is i cant get it to get out of its own way, its a turd
hesitation during transition is the big problem.
I can advance the timing to a point where it runs great and has a lot of throttle response,but the valve train rattles so bad that it sounds like its gonna suck a valve.
I back down the timing to a point where the valve train quiets down and we are back to crappy transition and no power.
Im completely lost Ive been a mechanic for 25 years and have never had this issue.
yes I have checked and rechecked the timing marks ,they are dead on.
If I advance the distributor 5 degrees the valve rattle is crazy.
Any advice from an expert would be greatly apreciated

[mdrburchette]

Sorry, I'm not an expert but I have a couple questions:
Did you set the timing by the #4 cylinder?
What's your initial timing?
What does it advance to?
Are you sure it's a timing problem? Could it be the carbs?

[So Cal Mark]

what are the cam specs? what valve lash did you set? Are your oversized pistons also higher compression? What vacuum reading do you have at idle? Do you have adjustable cam gears?

[troycalm]

stock comp on pistons .010 over .non adj cams .40/80 80/40 .014/.016 clearance. 10.35 lift 300 duration. They are prt 92400 inter auto new cams .no vacuum port to check vacuum.the other thing I noticed is if you look at the mech advance in the dist and retard it all the way the springs are extremely loose

[So Cal Mark]

I've found that's too much cam for a low compression engine. You didn't mention the valve lash, but opening the clearances will help some to reduce overlap. Or get some adjustable gears. But, don't expect miracles. Thats a lot of cam and carburetion for low compression and stock exhaust

[engineerted]

Pull the exhaust cam and replace with stock. Set ign. timing to 10deg btdc. And there you go! You should also run a min 50 idle jet.

Ted

[So Cal Mark]

is it possible you've swapped the two cam pulleys? Did you degree the cams when you put them in?

[troycalm]

did not degree the cams and i dont believe i crossed the cam pullies is there a way to tell, and what will the stock exhaust cam do to solve the problem.also should there be so much play in the mech advance springs

[troycalm]

almost forget,the pierce manifold i installed has a vacuum port in one runner only #1.when i pulled the plug to check the vacuum at idle i get a pulse from the port instead of a constant vacuum signal

[engineerted]

The reason for the std exhaust cam is to reduce the valve over lap with the intake cam. This reduces the exhaust gas reversion that occurs at idle. When the exhaust gases mix with the incomming intake charge it reduces the flame speed thus more timing advaced is need. What doesn't make sence is your statement that the valve train rattles when you try to advance the timing. What does you plugs look like? White or black. Did you verifiy TDC of pistion #1 to the timing marks on the pully. Depending on the year some of these marks are on the right and some on the left of the timing cover. Exhanust cam pully should have a "s" stamped on it with the flange to the outside and the intake "A" Flange to the inside.

Ted

[Hutch]

I was curious regarding the valve train "rattle" as well. Are you sure it's not detonation that you're hearing?

Ted - thanks for the explanation on the cams, interesting stuff.

[troycalm]

Ok the pullies are correct with the intake, flange to the inside exhaust flange to the outside.some people set there timing by ear they advance it to the point where the valve train will rattle under load then slightly back it off for best perforemance.
if i set the timing to factory specs the car falls all over itself and has no power,if i advance the timing out, the perforefamce jumps up but thats when the valvetrain rattles badly but runs great.the plugs have a coffee color,like i said before the vacuum port on #1 is pulsing during idle.The cam pullies may be off a 72 1.6 as my engine is a 78 1.8 i dont know if that makes a difference but let me know if it does.Yes the engine static timing has been set checking for TDC while the crank mark is verified. I hope this explains the rattle,If you over advance an engine the valve train rattles it may be called somthing else.

[troycalm]

I just looked at some catalogs and the pullies from a 72 1.6 and a 78 1.8 are different pullies could this be my whole problem ,whats the differenc between these pullies.

Thanks

[engineerted]

All the twin cam pullies will work for all years as long as you install them on the right cam. Where did you get your cams? do you know if they have 106deg or 110 deg lobe centers? also what size chokes are you running in the idfs?

I have two hot 1800 motors: one with dual 40 idfs, 40/80 intake, std exh, 10.8 cr this engine pulls very strong from 1500rpm all the way to redline, but if you swap in the 40/80 exhaust cam you loose the low end torque thus 3000 rpm to 7000. ign advance set at 5-10 degrees btdc, idles the best at 10 degrees btdc.

The second is my race motor, 11.5 cr, 42/82 intake & exhaust, single 40 dcnf , won't idle below 1500 screems from 3500 to 7500, not good for the steet. ign advace set static set at 15-17 degree btdc

Ted

[Jim DeShon]

Ted: Re: your 10-1 cr. motor. Can you tell me what your total advance is ? I have a 1800 in pieces. I'm going to put it together when I get the chassis work done. I want about 10-1 cr. 10deg. initial advance sounds about right but, I feel you should also look at the total advance if you are going to get the full potential out of the engine at high RPM's. Any input would be welcome. I'm not ready to do the engine just yet but, hopefully in the next year or so. ...J.D.