Technical Chasing a vibration-Solved

Just a quick question…I am using ac delco R45TS plugs gapped at about 0.050. Reading online tells me this should be reasonable for this basically stock sbc with hei.
Does this sound correct or should I close up the gap a bit?

 

Hudson48…thanks for the humour. Although I really want to be out putting miles on it instead of working on it, I am finding lots of little things I did back in 1990 that could be improved upon so it is getting me familiar with the car again…jogging those old memory cells.

 

There have only been a few billion Ford style biscuit mounts successfully installed over the years, and the Chassis Engineering ones are some of the best. Check to make sure you installed the lower rubber half under the frame too. If you just have a big washer under there, that's your problem.

 

Picked up a 79 Ranchero 351m years ago that had that type of vibration, Didn't drive it much so it wasn't on my list of things to do. When I finally got around to it I discovered it had the wrong flex plate in it. Didn't surprise me it was a car that someone thru together plus it is a known problem.
Then one day searching the hamb I saw a guy mention he added 2 3/8 flat washers on the convertor studs on each side of the flex plate weight to make up for the wrong weight. Fixed about 98% of the vibration. Drove it that way for a few years until I rebuilt the engine and had the whole thing balanced. Probably won't help you just thought I'd throw it out there.

 

So what is left? I see 2 things, the soft mounts and the flex plate. The mounts come out fairly easily for inspection, I got a set of Energy Suspension mounts for my 355 installation. They probably have something to replace your CE mounts, even if just the rubber portions.

The flex plate... lots of fun working on your back. Try to line up the correct flex plate first, but any decent parts store can get you one in a few days. We used to get them from Car Quest made by Pioneer.

 

Any chance you can soften up the engine mounts by inserting a more pliable rubber? Maybe make rubber 'washers' out of a chunk out of an old tire sidewall and don't 'crank' the bolts too tight. This will throw off your pinion angle (I would assume) but since you felt the vibration with the convertor disconnected, you wouldn't have to drive it to determine if this fixed your issue. Could maybe do the same with the other mount(s).

 

Yeah, I am slowly going back over everything I can think of. Bottom line is that some rotating assembly vibration is either more than it should be or being transmitted somehow and not muted out by mounts etc. I think the list of things I am going to try over the next couple days will help me understand exactly what the issue is. I am obviously hoping for a simple fix but have a nagging suspicion it is internal and will require an engine pull so prepared for whatever it takes. I am not the type to just throw new parts at it unless I have a good reason. I was fairly confident that the old damper was bad because the rubber was cracked and brittle so replaced it to no avail.
The biscuit mounts are installed correctly for sure. The flex plate is correct, not installed backwards and doesn’t seem to have any cracks, bolts all look tight. Transmission internals and torque converter not the issue after unbolting converter from flex plate. Front accessories not the issue after removing fan belt. The possibilities are narrowing down.
Funny thing is I have had other vehicles running on 7 cylinders or with broken mounts, or scrunched exhaust, or bad transmissions…and none had vibrations similar to this.
Appreciate the help! Time to get started on the list. Good thing my hourly rate is so low!

 

Borntoloze…I am going to start with disconnecting exhaust to eliminate that, then unbolt trans mount and just barely lift it off crossmember with jack to eliminate that, then unbolt motor mounts and take weight off them to eliminate that…reconnecting everything after it is eliminated one by one. If it appears that these areas are not the issue then I will start to focus more on the engine and look for possible misfire causes. If that isn’t it then I think I will concede it is internal, drink a beer or ten and make a rational decision then (wrenches will be put away!)

 

I still have a question about spark plugs and gap in post#62. Any advice on plug brand, type and gap that has worked well for similar setups (basic sbc with hei and quadrajet) would be appreciated. Thanks.

 

Why Not Take the Engine out & Put on a Engine Stand & Secure it
and Start it on the Stand.!

Just my 3.5 cents

Live Learn & Die a Fool

 

I have a 350 Chevy that vibrates at around 1100, 2200 and 3300 rpm, not severe, just annoying. Tried all the things mentioned here and more and never could solve it including a Fluidamper, new flex plate and converter. Others told me they had similar experiences with 350’s that seemed to have been solved with a rebuild, but were not sure what exactly was the culprit. I suspect the rebuild on mine has some sort of problem. It runs great and dependable so I live with it although I have been tempted to swap it for a new crate engine. That is an expensive experiment, though.

 

a50merc…it may happen in the fall but trying to check other possibilities first.
Proartguy…That is sort of where I am at now..it runs nice, no nasty noises, and I don’t run it hard so I will just keep trying to isolate it. I have plans for work I am going to do the car over winter so I will just add another item to the list. I broke my back 11 months ago so although I feel pretty damn good I have to be a little cautious not to overdo it each day to avoid ripping all those muscles again. I am learning about patience and healthy posture/lifting.

 

So a quick update if anyone is interested.
1) disconnected exhaust…vibration still there.
2) loosened motor mounts and jacked engine a bit. Found a spot where trans was contacting
Trans cover screw so clearanced that. Very minor contact only when engine was jacked up so doubt that is issue. Still had vibration even with trans cover off.
3) loosened an made sure trans mount had clearance. It may have had minor contact on governor housing so that is clear for sure. Still had vibration.
4) put in a another new set of ACDelco R45ts that I had on the shelf gapped at 0.040. Runs nice but has vibration although it seems to be less (could be my imagination or wishful thinking. I also rechecked firing order for about the 10th time.
At this point I am confident it isn’t the exhaust or mounts although I do think the biscuit type transmit more vibration than standard gm. I am going to button everything back up and drive it a bit and see what happens. I will likely play around with the carb a bit here and there but it runs and starts nice so don’t really think too much is wrong there. Going to check for spark plug wires arcing once it gets dark here.
Just out of curiousity, I remember from way back that some engines had a tendency to misfire is certain spark plug wires were run side by side but it seems to me it was mostly mopar. Can anyone confirm my recollection?

 

Lol,,,,,it’s not Mopar specific if wires arc between themselves.
And I can’t imagine spark plugs would cause your problem,,,unless you are extremely sensitive and can feel anything in the slightest .
It sounds like you have really tried hard and have searched every possibility.
I wish you good luck,,,,,but I’m afraid I know where this is leading to ,,,inside the assembly .
Since it has been 30 years,,,,,and it has always had this vibration,,,and not all rebuilds are equal .
Even national chains have problems sometimes.
Too bad you didn’t investigate sooner,,while you had a warranty.

Tommy

 

Tommy…totally true..every word.
I just seem to recall that some engines, due to the firing order, were extra sensitive to wire routing.
I drove this car a lot when it had the 6 and power glide and it was smooth so I might be expecting too much from this setup. Due to family, job and developing a couple of acreages I more or less parked it after the swap so only 5000 miles or so on it in that time.
I keep reminding myself that I am doing this for fun! It might not sound like it but I am enjoying it…11 months ago I wasn’t sure I would ever be able to do this stuff again so any day playing in the garage is a great day!

 

I believe you're thinking of the 5-7 crossfire due to them being next to eachother on the engine and the firing order. Seperate the plug wires as far as possible if you're concerned. I think it was mostly due to solid core plug wires, I could be wrong, though.

 

Nope! Never bought one...

 

Chevy and Mopar have same firing order ,,,,so we can rule that issue out because of brand .

And I can completely relate to the health issue stopping any progress.
Oh yeah,,,I know exactly where you are coming from brother .

Job,,,family,,,,sometimes life ,,just gets in your path,,,and there is no way around it .
But,,,you are definitely working to the solution,,,,I’m proud of you for that .
Keep trying everything you can,,,,I’m still worried about where it will end up .

The 6 is a fairly smooth runner,,,,,but ,,,so is the small block.
The 350 is a great engine,,,,,,sometimes parts tolerances stack up and something is missed even by big rebuilder chains .
You might have gotten a collection of sorts,,,,and maybe the Bob weight just didn’t come out right,,,you never know .

I hope you find a simple solution,,,,and it doesn’t require a lot of work .

Tommy

 

It is definitely a 350 crank based on this chart.
I am pulling it down off the stands tomorrow and will drive it around a bit. Chances are it is an internal issue but I won’t be able check that out until fall at the earliest.
Thank you all for the help! Cheers!

 

"Based on this chart" I am inclined to agree with you BUT, I am not seeing an example of a 305 crank in your chart. As stated earlier, I couldn't tell a 305 crank from a 350 crank when they were both laying on the floor right in front of me. They were visually identical, right down to the same casting numbers.

Here is a quote taken off the internet, and based on my own personal experience, I can verify that the quote is indeed correct. "They are identical and completely interchangeable. The only internal difference is the bore of the cylinders. The cranks of the 305 and 350 have the same casting numbers and are interchangeable. But the 305 crank is drilled to be lighter."

I would not be in any rush to rule out the possibility that the crank is from a 305 especially since you did state the engine came from a large volume rebuilder. I am not stating it IS the cause of your vibration, I am saying you might not want to rule it out until you can truly verify that your crank is from a 350 and I know that a visual inspection is not enough to determine one from the other.

I wish you the best in your search for the source of your vibration.

Here is a quote taken from https://www.chevytalk.org/fusionbb/showtopic.php?tid/62288/
"The cranks of the 305 and 350 have the same casting numbers and are interchangeable. But the 305 crank is drilled to be lighter. It will work in a 350 but will cause the engine to vibrate. I had a parts store sell me a 305 crank as a 350. After getting the engine build and installed did I discover the difference. (and much waste time trying to figure out what was the problem). A machine shop help me find the problem and I got the right crank and my problems went away!!

 

On the spark plug wire cross firing it was ignition wires against each other or crossing over each other from their path from the distributor to the spark plug on adjacent firing cylinders Only. (ignition wires located on the dist. cap next to each other.)

 

Elcohaulic, what was the fix for that?

 

When I bought my '62 Chevy II it came with a rebuilt 350 which after I installed it I noticed it had quite a vibration. I narrowed it down to the engine so I pulled it, took the oil pan off and found one of the rods was hitting the oil pump. Fixed that problem and that eliminated the vibration.

 

I have found that vibration is caused the most by exhaust and tires. I didn’t read every word of this, but you probably tried new tires.

 

I remember about 10 years ago watching PBS "motorweek", Pat Goss showed an aftermarket product that used the harmonics of the vibration to help tell you what was causing it (engine, tire balance,etc.) but I didn't catch the name or maker of it.
Has anyone heard of this product or anything like it?

 

Thanks all for the comments.
Borntoloze…you could be right on this. Chances are I will pull it apart this winter to see exactly what is going on. I have had many small block Chevs over the years and they were all smooth running. I appreciate your insight about the 305 crank and will put it in the notes for winter.
Elcoholic…I did close up the gap to 0.040 on these new plugs. I will do a video later today or tomorrow at the latest and give what specs I know. Thanks.
Garyf…that is sort of what I recall. I have made sure all wires are separated and crossings have a gap between. Thanks for the comment.
34Ratrod…Thanks for the comment. It will likely come out in the winter…it would also be an opportunity to paint the engine Pontiac blue and fix all the issues…just kidding…sorta.
Rand Man…yeah, it is a vibration when stopped or driving so likely engine. I eliminated exhaust and trans as possibilities. Thanks.

 

Half a glass of water on the air cleaner while it's idling should show how bad the engine is vibrating.....
Also fire up the engine at night time and pop the hood and check for spark leak... You should be able to see that around the plug wires in the dark.... Hope all that helps....

 

That 305/350 crank explanation surely makes sense. Gee, so the builder must not have "balanced" the rotating assembly? Seems that would be an essential part of building/rebuilding any engine.

 

If I understand correctly the longblock is just an off the shelf reman?

It's not standard practice to balance a reman. My experience, most places don't even do a good job of keeping the original rotating assembly together. From what I remember you can put a 305 crank in a 350 without rebalancing and it won't shake most of the time. People did it.

Good news is your engine will run almost forever with the amount of vibration you described. Bad news is it probably needs balanced to make it go away.

 

Maybe I missed it, but are the flywheel flanges the same between the 305 and 350????....