Engine Vibration

Carlini17 · May 31, 2021

Just bought a 1991 GT. Previous owner did a new 347 shortblock with trick flow heads a nice redone supercharger along with a new tremec trans. When first test driving the car it had a nice vibration you can feel in the car around 2k to 3k....pretty heavy. Since getting the car home you can feel it at idle as well and revving it. He said he did a new centerforce clutch with s SVE billet flywheel and you can see a new harmonic balancer on it. Wanna get this fixed as there's only 500 miles on almost everything a dont wanna ruin it. You can feel it heavy in the shifter while driving and just in neutral reving. Where and how do I start?

Potomus Pete · May 31, 2021

A lot of fancy stuff there. Because you don't know the car I would bring it to a Mustang Master if you think you find one. The previous owner would/should have fixed it. Could be anything in my opinion.

7991LXnSHO · May 31, 2021

Sounds like a balance issue from mismatched parts.
+1 to getting it checked out.

90sickfox · May 31, 2021

Sounds like wrong flywheel...should be 28oz and not 50oz. Most folks just order one for a 302 and that won't work in most cases.

( I'm out of hibernation....was gone for a few )

Carlini17 · Jun 1, 2021

The guy I got it from was a long time diesel mechanic. Car is well put together but you can tell he lost interest. I was thinking the flywheel as well. Would the harmonic balancer have any effect as well?

Carlini17 · Jun 1, 2021

Also, if the flywheel and new balancer are what he says they are. If I had to fix the issue/start over what balancer and flywheel would fix this?

Potomus Pete · Jun 1, 2021

You can get the part # off the balancer , and see if it's 28oz or 50. Maybe ask the guy if he has the reciepts. Kind of stinks that you could take it apart, and still have the problem.

Carlini17 · Jun 1, 2021

He has nothing. He got most of the stuff from jobs owed/money/favors and buying the car and kindnof marrying everything. Everything he said was legit except the vibration which he doesn't know how to fix. From top to bottom the motor and trans is new. Even a new Canton oil pan. Couldnt pass on it. Was too reasonable of a price. Driving me nuts. Would hate to pull the trans and go through hell. Really fells like the flywheel.

Mr.Kelley · Jun 1, 2021

If it is the flywheel you want to fix it before running it again. I had a vibration same as you describe on a 351C in my 72. It lasted about 1500 miles before beating the front main out and destroying the block. When I pulled it out I discovered the flywheel was from a 240 six cyl.

7991LXnSHO · Jun 1, 2021

The 347 kit could be internally balanced. Neither stock weight would be correct then. And looking on Summit, that info is not always listed on the site. If he has the receipts, you should be able to contact the kit supplier for the info.
And Yes, the harmonic balancer and flywheel need to match.

Carlini17 · Jun 1, 2021

Here's some picture insight into the balancer. Just from a Google search it says this balancer is for internally balanced ?

7991LXnSHO · Jun 1, 2021

That’s good to know, but it could fit on the snout of any Windsor style crank.
Here is what you are looking for.

347 stroker kit at DuckDuckGo

DuckDuckGo. Privacy, Simplified.

duckduckgo.com

General karthief · Jun 1, 2021

Hey, let's do a little investing before tearing this thing apart,
Since you know little to nothing about the engine (verifiable facts) I would start with firing order, the HO firing order does not play well with a non HO cam. Engine vibration is a symptom.
I would start there.

Carlini17 · Jun 1, 2021

Firing order for a 91 should be 1-5-4-2-6-3-7-8? Correct since it's pre 94?

General karthief · Jun 1, 2021

I don't know what pre 94 means
I mean I know it's 'before 1994' but the sbf (302) firing order changed with the 5.0 HO way before 1994,
The firing order you posted is for a non HO 5.0.
I would find out what the firing order your engine is supposed to use.

Carlini17 · Jun 2, 2021

And I'm guessing the easy way for that one is to pull the lower intake and check for the spider tray?

7991LXnSHO · Jun 2, 2021

No, roller cam does not mean HO. The camshaft determines firing order. If you pull the spark plugs and see what order the cylinders push air out on the compression cycle, you can determine firing order. Or you can switch the spark plugs around and see if it runs better.

2000xp8 · Jun 2, 2021

When you say 3-4000rpm, does it go away at higher rpm?

It does sound like the flywheel.
If you look on lmr's site, it would appear an SVE flywheel comes with weights for 50oz, 28oz and i'll assume zero with no weights. Could you ask the previous owner which weights if any he installed?
Been quite a while since i bought a flywheel, but i think i'd rather just have a factory balanced one than one you add the weights yourself.
While in general i don't like cheap parts, i really have a distaste for putting them in a location hard to undo.

Mstng93SSP · Jun 2, 2021

H.O. firing order 1 3 7 2 6 5 4 8

Carlini17 · Jun 3, 2021

Hard to say if per day goes away because all that rpm the car is ripping and running. But it does it at a dead idle no clutch engaged and engaged. I'm guessing the flywheel as well. Car is as described, block, heads etc. Ripped it apart as I had a brand new trick flow intake to go on.

Engine Vibration

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