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11/12/10 11:18am - Original Message: 'Engine Balancing'
jp75vette
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Bloomfield Hills, MI - USA

Vette(s):
1975 Corvette coupe, 4 speed manual, 383 ci 9.5:1,Edelbrock dual plane Air Gap intake, Alum Heads,Comp Cam, roller Rockers, PS,PB,Tilt

Joined: 6/29/2008
Posts: 199

Does anyone have tips on engine balancing?

 

I bought an externally balanced 383 that ran fine in a 67 Chevelle with an automatic transmission. I had the new flywheel and clutch supposedly balanced to the flex plate that was in the Chevelle. I have vibrations at mid teens and 3300. From what I’ve read this is likely clutch/transmission related. I believe the main bearings are wearing as oil pressure seems to be dropping a bit.

 

My plan is to pull engine, take it apart and have all components balanced. The guy I have located will balance the piston/rod, crank, balancer and all the rotating elements.

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11/12/10 2:01pm - Reply: 'Engine Balancing'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

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A real engine balancing job will include the flywheel. If there are any changes in that flywheel, the balance will be off. Of course, it all depends on how well it(the engine) was balanced in the first place. Changing the flywheel for any reason is gonna upset the balance somewhat.
 Are you feeling this vibration at a standstill, or only while moving?
What kind of oil pressure drop are you talking about?
Does it seem to drop more the hotter the engine gets, or is it fairly steady, but lower than it used to be?
Does it rattle when first started?


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11/12/10 2:24pm - Reply: 'Engine Balancing'
jp75vette
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Bloomfield Hills, MI - USA

Vette(s):
1975 Corvette coupe, 4 speed manual, 383 ci 9.5:1,Edelbrock dual plane Air Gap intake, Alum Heads,Comp Cam, roller Rockers, PS,PB,Tilt

Joined: 6/29/2008
Posts: 199
I'm going to run through a check sheet diagnosis this weekend if the weather cooperates.
 
The vibration is at standstill with clutch depressed and also while driving. I suspect the clutch and flywheel.
 
The oil pressure has been drop seems to be about 10 pounds from where it was. I will get measurements when engine is at operating temperature. Driving it used to be around 60 and now its at 50.
 
I do not hear a rattle when I start it.
 
My plan is to use the winter time and do it right; it will be some work, but the whole system will be done.
 
It's my understanding that when I do this, the engine will change from external to internally balanced.


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11/12/10 2:34pm - Reply: 'Engine Balancing'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

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It's hard to get a stroker engine internally balanced...there just ain't enough room on the crank throws to add the mallory metal to....which is why they usually require external balancing. I don't do machine work, so I can't speak from experience...just from what I've learned over the years.

A 10 psi drop in oil pressure, from 60 to 50 doesn't seem like anything to worry about. The "standard" for oil pressure is 10 psi for every 1000 rpms is acceptable.


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11/12/10 6:57pm - Reply: 'Engine Balancing'
yostusota
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York, PA - USA

Vette(s):
1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top

Joined: 5/18/2010
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I think you found an interesting problem that going to a stick from an auto will have..The auto with the torque conveter acts like a damper..with the fluid inside it will cancel some imbalance in the engine..just like a fluid damper that can be put on the front of the engine..It is very difficult to get a torque conveter balanced..usually the reman or company that you buy it from has the machine that will do it..The other issue being the weight of the man trans flywheel..I think they are somewhere around 45 lbs plus the clutch stuff..the auto is barely noticable..it can be balanced but without the crank to balance with it at the same time the machinist is kind of guessing..before you tear the engine apart I would try a fluid damper on the front crank and see if any change is noticed..if that helps ..which it will..put an aluminum flywheel in also..they weigh about 15 lbs..two advantages to this is less rotating mass which equals more horsepower..faster revs and a smoother idle..these need balanced also..you can try and see if the auto trans flywheel and the aluminum flyweel can be matched..I bet they are close in weight so it should be easier to get it balanced..383's are great and make gobs of torque..make sure the rest of the drive train is in top shape or you will find a weak link real quik.
Rich


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11/25/10 10:51am - Reply: 'Engine Balancing'
jp75vette
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Bloomfield Hills, MI - USA

Vette(s):
1975 Corvette coupe, 4 speed manual, 383 ci 9.5:1,Edelbrock dual plane Air Gap intake, Alum Heads,Comp Cam, roller Rockers, PS,PB,Tilt

Joined: 6/29/2008
Posts: 199
I had a guy put an vibration analyzer on the engine to see have bad the out of balance was. We took readings at 1500 and 3200 RPM; this is very the vibration is the most. We also took a reading at 2500 RPM were there is less vibration.

The attached are the graphs. The interrpurtation is that there is .004" out of round at 3200 RPM.

I guess I will pull the engine.



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11/25/10 12:34pm - Reply: 'Engine Balancing'
lukesvette Lifetime Member
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HOWELL, NJ - USA

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1979, Targa Blue (72 Color), Pace Car rear spoiler, L88 hood, Dark blue factory interior, 525HP 406, HD 700R4, 370 gears,Steeroids, composite rear spring, TT IIs wrapped in T/A Radials.

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What kind of damper do you have on the engine? I had a buddy go through 2 flywheels, had the engine apart and put back together only to find out that he had a bad damper on the motor (and it was a brand new after market piece). He upgraded to a Fliudamper and no more vibes...

Ya never know...


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11/25/10 12:43pm - Reply: 'Engine Balancing'
yostusota
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York, PA - USA

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1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top

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I will be putting a fluid damper on mine this winter..I would try that before taking the engine apart..
Rich

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11/26/10 10:46am - Reply: 'Engine Balancing'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19449
I had a situation once on a 427 Cobra SC(replica) that had a vibration like that. The Gomers in the shop kept tellin the guy it was his driveshaft. After about a week of going back/forth on it, they finally called me out to see what I could find. This was a hard vibration that felt like the dang balancer was waaaaaaay off. I told them to take the trans out(again) and pull the flyingwheel. From looking thru the opening in the bellhousing, I could see that the clutch assy was wobbling, but the flywheel itself was running straight. Once the flyingwheel was taken to the machine shop, we found it had been ground "crooked". The surface of the flyingwheel that the clutch dic, and pressure plate bolted to was not parallel to the crank side of the flywheel. This made the entire clutch assy wobble. Once we had the flywheel milled back flat, the problem was gone.
This is something that happens a LOT when a machine shop uses a flywheel grinder that you just drop the flywheel onto, and spin it around by hand...the chances of getting one ground crooked is really high. It's always best, imho, to have a HP flywheel either milled flat, or put on a lathe. ANY small discrepancy in the surface parallelism will create a vibration. On a stock set-up, it's not so noticeable, depending on how bad it is. Do that on something like a stroker, or any other engine that has been balance, and yer just axin for trouble.
Not that this is gonna be YOUR vibration, but it may very well be. It might be a good idea to dial indicate the flywheel surface, if you can't determine the source anywhere else...


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Joel Adams
C3VR Lifetime Member #56    
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11/26/10 11:15am - Reply: 'Engine Balancing'
yostusota
Former Member
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York, PA - USA

Vette(s):
1969 daytona conv. all original 350 350 380 4 sp w/air..and hard top

Joined: 5/18/2010
Posts: 1518
I only use one machinist to do this..flywheel cut wrong is a real bad thing..good idea is to check it thru the bell housing if you can..if you do pull the trans and do the run out with the dial indicator like Joel said..if you get it machined again when you put it back in dial indicate it again to make sure..sounds like you put a new flywheel in this so I would look towards the front big time since most stroker motors need to be externally balanced..
Rich
 


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