Technical 327 Pulsating Surging Vibration

I have a 327 newly rebuilt. I am noticing a pulsatin surging vibration when engine in nuetral (4 Speed car) and RPMs 1500 and over. Seem to be ok at idle.Also when I drive the car and at steady speed and the same RPMs sane vibration. Engine seems to run smooth no shaking or back firing. Not a violent vibration just concerning. I have searched the internet for days to no avail.
Things Ive Checked
1: Removed fan belt no wobble in pullies or Horminic Balancer
2: Checked motor mounts and trans mission mounts
3: Distributor rebuilt.

 

The first thing you should do is hook a timing light up and check your advance curve. Take readings at idle, 1500, 2000, 2500, 3000, etc. and write them down. Post the results here. Also, tell us where you made the connection on your intake for the vacuum advance. In addition, a vacuum gauge reading at idle would be helpful.

 

exhaust rubbing?

 

Check your flex plate or flywheel. A 327 takes a NEUTRAL balance flex plate or flywheel, and if there's an integral weight, either welded on or casted in, you've got the wrong one. Sounds similar to a balance situation I had once, where a vendor included a 454 flexplate in with a 400 SBC based rotating assembly; it had the same sort of situation you're describing, and I assumed the vendor knew what they were doing, when they apparently did't.. This is for the 62-69 style 327's and NOT the "modern" 327, a 5.3L/LM7 designation, that's a completely different engine. I am Butch/56sedandelivery.

 

You don't give a ton of info on the rebuild. Where pistons replaced? Was engine balanced? New flywheel or flexplate? Reason I mention these things is because you could have an imbalance somewhere along the line. We had pressure plates that were out of balance and caused a vibration like you mentioned, also a 427 flywheel on a 454 had a vibration. It could be several things, exactly what was changed and check each component as well as you can.

Pat

 

Butch you type faster than I do!

Pat

 

66- 327 I checked the exhaust ok there. Flywheel was resurfaced. New clutch and preasure plate. Rebuilt M-21. I also ground down the transmission cross member because it was less than a 1/8 of and inch away from the transmission no luck there. Later today I will try to get the reading for the question Rockable posted.

 

condition of harmonic balancer?

 

Wow, you've been a member for a loooooooooooonnnnnnnnnnnnng time and these are your first two posts....is a welcome in order or not? Welcome to your first two posts in 8 years! well OK 8 years on the 15 next month....
Remember this is going to be a process....
I am going to ask, where you sense the vibration, in your steering wheel, shifter, rear view mirror, seat of your pants....you get the drift.

 

I dont see any wooble to it. I beleive that built the engine (a friend) would have said something if there was a problem. (I hope so)

 

People go to prison all the time...

 

Bob you funny!

Pat

 

I am the silent type. HaHa. Didnt know I was a menber. Alway searching the site.
I feel the vibration in the seat pf my pants. and also in the stearing wheel.

 

I had same issue with a rebuilt distributor (bought, not built by me). Surge at steady rpm running down highway. Pulled the line to vacuum advance and capped vacuum port on carb. Problem went away. Defective vacuum advance can.

 

Hear is a dumb question . You are sure of the pilot bushing in the crank? I know this sounds unreasonable as well, but I would pull the trans as a last resort if all the other suggestions fail, even though it is in neutral, it could have an issue with shaft alignment that you can't see. I just don't think it sounds like an internal engine problem with the pulleys running true. The pilot bushing may be wallered out or the input shaft is worn or maybe too tight. Just a guess, but I have had this happen in an old straight six 230 3 speed many moons ago. I just knew it was the motor. It was not.

 

Is this an engine that you owned that ran without vibration ? If sdo , what components were changed ? . If not ,its anybody's guess internally , externally , flywheel , clutch assy and damper ....
Define rebuilt .....

 

Did that the other day same results.

 

Rings bearings, new cam Sorry dont know to much more than that.

Just had the transmission rebuilt by a reputable guy. I am thinking flywheel and clutch assembly. I just pulled the transmission 6 months ago. Before that the car was still sitting in the garage and being started on occasions not driven. Just getting harder to get under the car and pull the transmission by yourself.

 

Ran into a similar problem with my buddy's 34 Ford with a small block and a T-6. We fiddled with it for many months. He had replaced the motor mounts and transmission mount even though they appeared to be in good shape. I knew from the start that it was engine related in the 1500 - 1800 rpm range. That was the one thing that was nice because you could easily replicate the vibration in the shop. I finally borrowed a vibration analyzer from work. By moving the sensor around, I was able to pinpoint the spot of the most intense signal. It turned out to be the rear trans cross member. What we found was a lip on the cross member was grounding out the mount. Trimmed off the lip and no more vibration. If you can find anyone with a Kent Moore vibration analyzer they make it much easier to pinpoint the source. When GM shut down all the dealerships there were a lot of them floating around.

 

Yeah if you have way too much total advance it can cause a surge for sure. I have a 71 Olds 350 that surged so much you could feel at at about 35 mph in 2nd, which I would guess is about 1500 RPM-low load. Couldn't feel it in 3rd but I'll bet was surging. Reduced vacuum advance and been great ever since. I think Rockable may be onto the problem.

 

I know this is a long message I posted a couple of posts ago I did the sane thing and ground down the front of the transmission cross member because it was an 1/8 of an inch away from the back of the transmission Thanks for the reply.

 

May sound "odd", but does it feel like someone's got a-hold of the rear bumper, and holding it back, when you drive the car. That's how my balance issue partially presented. Like I said, it was the wrong flex plate for the engine.
I am Butch/56sedandelivery.

 

Just 2 cents worth. Have you checked the spigot bush in the rear of the crank. Can give you a vibe if it's worn

 

Is that like a pilot bushing

 

I would take the driveshaft out and have it checked for straightness and balance- also the driveline angles and u- joint condition if you have not done so already. When you tighten the bolts on the u joint saddles- don’t over tighten them

 

For sure !!!

Now I’m confused, the thing runs smooth or it don’t?

 

It has this vibration in neutral so the driveshaft will have no bearing on it. My RPU has a very similar issue. I unbolted the torque converter and pushed it back and ran it up, ran very smooth. I would check the clutch area and the ''spigot'' bush/bearing too, its a British thing. JW

 

Ahh the Brits , the ones who coined the words " Shagging" & "Fags" ......????

 

Not to be confused with a "bush pilot"!

 

Vacuum at idle is between 15-17 needle jumping between those.
vacuum line is connected to manifold then to carburetor.
Idle at 900 rpms 8 btdc
2000 rpm 25
3000 rpm 30
I dont have a fancy timing gun just an old Craftman Advance.
when the rpms are at a certian point I dial the gun in until the point on the timing tab registers 0. Stock 327 with 350hp cam set of 194 heads flat top pistons Holley 585 on a stock Winters manifold.