383 engine on stand vibrates
Thread Starter
Instructor
Joined: Mar 2005
Posts: 129
Likes: 0
From: Layton ut
383 engine on stand vibrates
Ok, so I've fired up my 383 on the test stand. The stand is basically an iron box frame that holds the engine and weighs maybe 50 lbs. It has smooth box tubing on the floor without rollers or legs or anything. The engine is solid mounted into the stand.
The engine at idle to 4000 rpm is fairly smooth. Putting my hand on the block, I can't feel much vibration. But above that, the engine stand starts to vibrate a little and starts to move or walk across the concrete floor (from the engine vibrating).
My question is, is this too much vibration, or is it ok? I know it's not possible to perfectly balance a v-8, but I'm just wondering if anyone has any experience with how much engines vibrate on unsecured stands.
The reason I ask is 'cause I bought the short block used and the harmonic balancer was bad. I got a new one and also converted the flexplate to a flywheel. I had the pressure plate and flywheel balance matched to the old flexplate, which was the standard external balance for the 383. I just want to know if anyone has any experience with this amount of vibration on a test stand like this to see if this is normal or not before I throw the engine in the car. Thanks
The engine at idle to 4000 rpm is fairly smooth. Putting my hand on the block, I can't feel much vibration. But above that, the engine stand starts to vibrate a little and starts to move or walk across the concrete floor (from the engine vibrating).
My question is, is this too much vibration, or is it ok? I know it's not possible to perfectly balance a v-8, but I'm just wondering if anyone has any experience with how much engines vibrate on unsecured stands.
The reason I ask is 'cause I bought the short block used and the harmonic balancer was bad. I got a new one and also converted the flexplate to a flywheel. I had the pressure plate and flywheel balance matched to the old flexplate, which was the standard external balance for the 383. I just want to know if anyone has any experience with this amount of vibration on a test stand like this to see if this is normal or not before I throw the engine in the car. Thanks
Race Director
Joined: Feb 2003
Posts: 11,671
Likes: 20
From: Lake Wylie SC
Motor mounts do absorb some vibration, but not what you are talking about. I'm sure you know that the LTX engine is externally balanced. If you went from flex plate to a flywheel, you need to match balance the flywheel to the flex plate otherwise you lose the rotating balance. I'm not sure of the match balance procedure, so you'll have to check with an automotive machine shop. You could give Mr. Killebrew a call,
http://www.gordonkillebrew.com/pages/800741/index.htm
http://www.gordonkillebrew.com/pages/800741/index.htm
Thread Starter
Instructor
Joined: Mar 2005
Posts: 129
Likes: 0
From: Layton ut
Yeah, the machine shop that match balanced the flywheel and pressure plate knew what they were doing and said it was a regular 400 external balance job.
I saw a 350 once that was out of balance and it vibrated all the time from idle up. This doesn't do that at least. Anyone else have any thoughts? I'll probably call some machine shops tomorrow.
I saw a 350 once that was out of balance and it vibrated all the time from idle up. This doesn't do that at least. Anyone else have any thoughts? I'll probably call some machine shops tomorrow.
Le Mans Master
Joined: Oct 1999
Posts: 6,366
Likes: 34
I had an issue with the engine installed in the car, I had a huge cup on the roof full of water and it walked across the roof from vibration.
mine was a flywheel balance issue. same thing with higher rpms. it just got worse.
This was caused by trying to match a single mass to the dual mass (it failed on startup) after the entire engine was balanced.
I pulled the engine out and had it balanced again to the new dual mass and single mass so I could swap if need be.
mine was a flywheel balance issue. same thing with higher rpms. it just got worse.
This was caused by trying to match a single mass to the dual mass (it failed on startup) after the entire engine was balanced.
I pulled the engine out and had it balanced again to the new dual mass and single mass so I could swap if need be.
Advanced
Joined: Feb 2008
Posts: 98
Likes: 0
From: Southlake Texas
I think you have a flywheel balance issue not matching the engine internals. I would always spend the extra money and have my 383 engines internally balanced. No problem changing flywheels and clutches...everything was zero balanced on the outside of the engine.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
What did you use for a damper when you replaced the one that came on the short block? Based on the comment from the machine shop "said it was a regular 400 external balance job", it sounds to me that you bought a two piece rear main seal block, stroked to a 383 with the standard external balance. In that case, you need to use a stock 400 balance, front vibration damper. Now the stock Chevy damper is 8" in diameter and won't clear the front cross member in a C4. If I am correct you will either need to modify your front cross member to clear the 8" damper or buy a special after market damper with the 400 balance in a smaller diameter. The stock C4 damper (neutral balance) is 6 3/4". I have a 400 damper you can borrow to check if it cures the vibration on your stand before you spend the money for a new damper.
RACE ON!!!
RACE ON!!!
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Le Mans Master
Joined: May 2006
Posts: 9,226
Likes: 9
From: Irvine Ca
What did you use for a damper when you replaced the one that came on the short block? Based on the comment from the machine shop "said it was a regular 400 external balance job", it sounds to me that you bought a two piece rear main seal block, stroked to a 383 with the standard external balance. In that case, you need to use a stock 400 balance, front vibration damper. Now the stock Chevy damper is 8" in diameter and won't clear the front cross member in a C4. If I am correct you will either need to modify your front cross member to clear the 8" damper or buy a special after market damper with the 400 balance in a smaller diameter. The stock C4 damper (neutral balance) is 6 3/4". I have a 400 damper you can borrow to check if it cures the vibration on your stand before you spend the money for a new damper.
RACE ON!!!
RACE ON!!!
Racer
Joined: Jul 2005
Posts: 393
Likes: 1
From: tx
What did you use for a damper when you replaced the one that came on the short block? Based on the comment from the machine shop "said it was a regular 400 external balance job", it sounds to me that you bought a two piece rear main seal block, stroked to a 383 with the standard external balance. In that case, you need to use a stock 400 balance, front vibration damper. Now the stock Chevy damper is 8" in diameter and won't clear the front cross member in a C4. If I am correct you will either need to modify your front cross member to clear the 8" damper or buy a special after market damper with the 400 balance in a smaller diameter. The stock C4 damper (neutral balance) is 6 3/4". I have a 400 damper you can borrow to check if it cures the vibration on your stand before you spend the money for a new damper.
RACE ON!!!
RACE ON!!!
Thread Starter
Instructor
Joined: Mar 2005
Posts: 129
Likes: 0
From: Layton ut
The damper I put on was a 6 3/4" external balanced one new off of eb*y for about 60 bucks. It's not SFI approved, but I'll only be turning 6000 RPM so it should be ok. Yes, the crank is a 2 piece. Thanks for the offer, CFI-EFI, but that's the same thing I have so I won't need yours to check.
I had my buddy bring over his 383 and I compared his engine to mine. Mine was actually smoother than his was, even though his was rubber mounted in his car. I think that with the solid motor mounts on the stand that the little bit of engine vibration at 5000 rpm up caused the stand to move across the floor. I'm going to go with it as is.
Time to get my stealthram welded and ported to match my 1206 gaskets...
I had my buddy bring over his 383 and I compared his engine to mine. Mine was actually smoother than his was, even though his was rubber mounted in his car. I think that with the solid motor mounts on the stand that the little bit of engine vibration at 5000 rpm up caused the stand to move across the floor. I'm going to go with it as is.
Time to get my stealthram welded and ported to match my 1206 gaskets...
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Any chance that you could post video on YouTube of the engine(s)
running at 5,000+ in their stands and skittering around on the floor?
Are the engines currently carb'd? If not, are you using an OEM
harness, aftermarket or one you built yourself?
.
running at 5,000+ in their stands and skittering around on the floor?
Are the engines currently carb'd? If not, are you using an OEM
harness, aftermarket or one you built yourself?
.
Thread Starter
Instructor
Joined: Mar 2005
Posts: 129
Likes: 0
From: Layton ut
Sorry, I can't. I used the carb off my 69 GTO to just fire it up with an old chevy manifold another buddy had. I just plugged a wire from the + battery directly into the HEI "batt" terminal and used jumper cables to fire it jumping the starter with a screwdriver. I already took the carb off and am getting ready to drop the engine in the car. I only built the one engine. It didn't really "skitter around" on the floor, but more of a slow drifting for a couple of inches. Up to about 4000 rpm it doesn't move or vibrate at all feeling with my hand on the block, but that's not a very scientific measurement. There's some risk that it's not balanced perfectly, but I'm ok with that being that it's a daily driver with limited high rpm time expected.
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
While my request for YouTube footage might have seemed frivolous,
it did have a purpose.
I recently suggested that an engine could be run in its crate or on
one of the common tubular metal storage frames.
There was no response to the suggestion - perhaps people were
doubtful. Your thread so soon afterwards serendipitously corroborates
the suggestion. Video footage would have been icing on top.
Best wishes for a speedy and successful completion to your project.
.
it did have a purpose.
I recently suggested that an engine could be run in its crate or on
one of the common tubular metal storage frames.
There was no response to the suggestion - perhaps people were
doubtful. Your thread so soon afterwards serendipitously corroborates
the suggestion. Video footage would have been icing on top.
Best wishes for a speedy and successful completion to your project.
.
Thread Starter
Instructor
Joined: Mar 2005
Posts: 129
Likes: 0
From: Layton ut
Problems I would anticipate from running the engine on its crate stand or in a storage frame would be physically having clearance to install the flywheel/flexplate, starter and the exhaust. The stand I used was not designed very well and I had to put manifolds on upside down as my headers wouldn't fit, and I had to bend some metal out of the way to install the starter. At least it was solid so I had no problems with it torquing itself onto its side as it revved up or anything like that, which could happen if the engine isn't secured very well or if the base isn't very wide.
