we talked some on my buddys 305 manual trans low power engine vibrating. i changed the harmonic balancer and it helped but he is still crying about it. today he stopped over and i found half the intake bolts finger tight. he could not even fix that. and then i sprayed carb cleaner around the intake to heads and it seemed better. i ran it up to 3000 rpms and around 1700 the engine looked to be moving and not just setting there like it was at 3000 rpm's but this is my question and i just can't get it through this guys head that his issue may be more this than anything else.

he is not using the vacuum advance and i think he has it advanced so far that when the engine gets to around the 1700 rpm range the weights are throwing the time advance so far it is actually kicking back on the crank some. so tell me who is right i say put the damn vacuum back on and he says it will not run good with it on. i say the distributor may be defective he claims that is how he needs it to run. waiting on some advice here.

i told him if the mfg. thought the engine would run good without it they would not have installed it. thanks bp.

 

Duplicate post.

 

It's starting to sound like this guy doesn't even know enough to be dangerous. You mentioned that the engine appeared to move, have you checked the motor mounts? I'd pull the distributor and check for shaft play to see if it's causing spark scatter. If the bushings are okay, then I would start from ground zero and set the dwell and timing and vacuum advance.

If the intake bolts were loose then I would check for water in the oil. I'm assuming that the rest of the ignition system has been checked and/or replaced such as plugs, condenser, coil, wires, etc. Also it might be time to check compression and leak down on this engine.

 

73shark i guess i do not know quite how to describe the movement. the engine is securely fastened to the frame by good mount. what i'm trying to describe is when i rev it up at the start the engine is setting still like it is not running at all, as i rev it up it starts to move back and forth like an engine that has a cam in it. this is the best i can describe this. then as it get to 3000 rpm's it then clams down like it is not running. make sense to you?

believe it or not the center head was tight at the water ports. but loose around the intake runners. they were not actually finger tight but i used that for a reference. i put a wrench on them and it did not take much effort to move them. no water in the oil so were good there.

i told him to just get a new distributor they are not very expensive at all, like 60$ and put it in. but he seems to think he does not need it. so i'm done helping until he gets the distributor either repaired or replaced.

so what i need is the guys here to send me confirmation on the fact he needs to get the distributor set up as the factory sent the engine out with. maybe if he reads it from other corvette guys he will listen.

this is his reason for not using the vacuum. here in muskegon mi there is a company that make the piston rings for most cars sealed power. well a guy that works in the engine test lab told ron that they do not use the vacuum on the distributors and it is not needed. i told ron the reason is the lab runs the engine up to speed to failure to test the rings. they just don't need vacuum advance for static engine testing. but i just can't get that thru this guys head. so if the corvette guys give him hell ha may decide that it is a reasonable thing to repair or replace the distributor so he can get the engine running as intended.

i'm trying to tell him the time is so far out of whack that when he gets to these rpms the engine is fighting itself. does this sound reasonable to you guys? thanks bob p.

 

I wonder if the engine movement might be caused by either crossfire between plug wires or tracking inside the distributor cap.
The technical reason for vacuum advance is that it allows the engine to operate more efficiently under light load conditions thereby improving fuel economy. His engine would run fine without vacuum advance assuming that all the other parts are in good condition and the initial advance is set correctly and the centrifugal advance is proper.
Is his engine basically stock?
I run 12 degrees initial advance, normal vacuum advance, and put lighter springs on the mechanical advance to allow it to come in earlier. Runs very well but probably ruins emissions but that's water under the bridge as EGR is blocked and no AIR pump or pipes.

 

i can't tell you that yet either seems if it was cross fire or tracking it would do it all the time not just at certain rpms.

i can't say if it is stock. i'm kind of thinking that he said it was built up some but i can't say for sure. he is running like 28 to 30 deg full advance. i tell him he needs to go back to the beginning and put it back to stock and then go from there. so like i said earlier i'm not going to work on it anymore until he pust is back to stock and then if it still acts up he knows it is not form some wild advance curves. he can always go back. but i'm thinking the advance is the big issue

what makes me say that is on my 95 lebaron i had a bunch of issues and had to work thru them one at a time. but one of those issues was a stumble when just driving in town. about the same rpm's he is having issues at. anyway i found my timing was set incorrect i set it years ago but i errantly used the wrong timing marks and i think it was kicking back on the crank. when i put the light on the timing marks i can see now and then the timing would just about 5 degrees mroe advanced and i had it at about 20 deg so an occasional 25 deg at 15oo rpms was more than the engine wanted and it would kick back and that show as a stumble.

i'm leaning that way with ron's car. i put the vacuum hose on the distributor but he has no clue what port to use for the vacuum. so we guessed at reving it some and the port the had vacuum on it we plugged the line into. then he said the engine ran terrible. well he still had all the advance on it so it may have retarded the timing to the point the engine would stumble at. i told him to reset the timing to spec and then try it again but he won't do it so all i will do now is get some more opinions on this ans see if he is right or if i'm right. thanks for the help so far. bp.

 

Let us know how's it works out.

 

It sounds to me like he has the expertise. (not) BUT,.....The vac-advace IS there for a reason. Some people are so convinced they are right they just won't listen. Personally I'd tell him to take it to a shop. Don't ask for my help and then contradict facts with lack of intellect.

 

ok talked to ron last night and he claims he has the time at 12 deg btdc at idle and 38 total deg. at ? rpms with no vacuum advance connected. he said the engine has a mild cam in it form a recent rebuild before he got the car. so i'm kind of at a loss as to why he has what he claims is a steering wheel shaking vibration at 1500 to 2300 rpms. we changed the h balancer for a brand new one ant that one looks to be wobbling, i found the intake to be loose that i was able to put about 3/4 turn to tighten the bolts down good and my wrench was a long handle wrench so i got some torque on them. so i still maintain the vacuum needs to be reconnected but he may have the incorrect distributor or a worn out distributor that is causing this problem. and on 2 corvette forums and the car fix group i haven't got many ideas for things to try. not complaining there just may not be anything to try.

your correct c3 he needs to put the damn thing back to stock and start over from scratch and see where it goes.

thanks for the help. bp

 

It would be nice if you could hook up an oscilloscope to the ignition system and that way you can monitor each plugs firing at different RPMs. Probably hard to find one of those these days. A mild cam shouldn't cause any engine shake at higher RPMs. Personally I would put a timing light on it to see where the timing is currently. Then I would verify the vacuum advance by reconnecting it. I will also check the timing and measure the primary and secondary coil resistance. The next thing I would do is, assuming the problem is still there, is to pull the distributor and check for worn bushings. Do we know if the spark plug wires themselves are good?
Does this engine shake persist when the engine is under load?