timing slipping 258

awhile ago I swapped out the 75 ignition system for a 74 points system all seemed well...had some other work to do on the jeep so I never took it out on the road...dropped in new distro timed it, and was happy...so took it out on the road today and was fine for about the first 3 miles...then the rpms dropped off and lost power...not complete power loss but very sluggish and running a tad rough...was very smooth before....got it home put the timing light on it and it was out of time...adjusted the timing...and took it out again but only made it a feww hundreds yards when had total power loss...dropped the timing back a little and it started right up and made it home...and agin the timing slipped..

I have to think its time (no pun) for a new timing set?

UGH

 

Take a look at the balancer to see if it is coming apart. Could be teeth on the cam gear.

 

OK will do Rusty...BTW if I get to that point...will the gears pop off or is puller needed.. I have one for the balancer no problem..the book seems to make it sound like they will just pop off...

 

Think mine just slid or pryed off. Before you pull the timimg cover, take a good look at your distributer for worn bearings and messed up gear.

 

Yeah. Are you sure the advance weights are free, the vacuum can working, etc, when you set the timing?

How much "out" was the timing?

 

Hmm advance weights??? not sure......the timing mark was at about the 1 oclock position...a few inches above tdc marker..so out of three test drives the timing backed up/off several inches each time... it wont stay locked in...I bring the timing back...runs good, but when under load/driving the timing backs off....

 

as far as weights.. I dropped in a 74 distro from rock auto...so it has the points/condenser system...so no weights...

 

The weights are in there, hidden under the rotor - http://www.superchevy.com/how-to/corp-1001-corvette-distributor-rebuild/

Should be fine from the rebuilder though.

 

All timing systems are designed to retard under load. You are allowing for that?

 

unfortunately it retards but doesn't come back up...So tonight will check the distro again, check the vacuum weights..Thanks Timgr for that info...and drop back and punt...I could have missed something with the distro...if the timing jumped would I be able to dial it back in and have idle and throttle up great until under a driving load??/wouldn't it just stay out of time, bucking and back firing etc???
My buddy asked if the distro lock bolt was tight...yes it is...maybe a bad distro from rock auto? They say they are benchchecked before shipment

well thanks for the support guys...good news... I finally put all the pieces of oil bath air filter together form my 2A and it looks great...beats the old hot rod AC that I was using....

 

Also check the roll pin that holds the gear onto the distributor shaft. I've seen these shear causing just what you are describing.

 

I pulled the distro..there is slop verticaly. There is about a 1/16th inch gap/slop between the distro gear and the body...bearing seem rough not smooth at all...and using a pull scale, it take about 20 lbs of pull to get the vacuum advance to move

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Not sure if I see a roll pin in the gear through the shaft? Usually the pin sticks out a little on each side of the gear.

 

Thanks Walt.....Yeah the pin is there...I can't see too much wrong with the distro...not ruling it out but am leaning towards a timing set.....set the timing starts right up first time everytime...idles fine.... revs great.... timing advances and comes back down smooth...only under a load does it jump time...ie 3rd gear and increase the rpms....So will order the gears and chain.....

thanks for the help alll...

cya in a week or so !!! : )

 

The roll pin when it shears frequently the ends will still be in the gear. I'd pop it out real quick and make sure it's intact. If you can't drive it out, then good sign the gear is spun. Not saying this is the problem but while it's out one more thing to eliminate.

 

X2

 

Trying to think that through. I can't see how the timing gears/chain could repeatedly jump without putting the valve timing into total disfunction. Resetting the ignion timing wouldn't correct it to a smooth idle.

 

I thought that too, if the chain had jumped so many times, how could backing the distro correct the timing...and then it purrs like a kitten at idle and high rpms revving...no problem

I agree, adjusting the distro so many times....the chain would still be out of time..the crank and cam would still be out of sync...but I am at a loss the crank pulley is not slipping on the rubber, I used alignment marks, and they have not moved...the gear on the distro is not slipping..roll pin intact

if the chain isn't jumping and the distro isn't moving, what can cause the timing mark to move to about the 1 oclock position....under a load..stuck vacuum advance?

when just revving the rpms up the timing mark will advance up and smoothly back down...take it on the road and the timing slips causing rough running and at times engine stall...if it stalls.. I back the distro back and it starts right up to get me home....these are very short test hops around the block

The chain is the only physical part of the system that I have not inspected...if I pull the cover and all is fine with the chain and gears....then I go back to scratching my head...,,,

 

Well like said, if the timing gears/chain get out of sync then no movement of the dist is going to correct this problem. Did you drive out the roll pin in the gear on the dist shaft? You have to do this to confirm that it is not broken and letting the gear slide back and fourth.

 

I did not...but that is something easy I can do tonight...would be a hoot if it was something that simple...but then what caused the pin to shear...if it is a sheared pin....

Thanks Walt