Archaea

I've had a summer project that I've not completed yet or even worked on much due to an injury and being out of the country for a few weeks. I've got a 383 motor that was put together by performance engine in Texas. I put the engine in this spring myself but have a vibration issue that I can feel at higher RPMS. I've not driven the car hardly at all since I've put it back together and only once in the last couple months. Here is an e-mail correspondance between the vendor and I. Could you guys read this and comment? Do you think it's the harmonic balancer that could be the problem? That's what the vendor beleives --- Or the Flywheel? Or both? I'm currently using the stock harmonic balancer and a steel mass flywheel that was match balanced to the OEM flywheel. Both would be 350 engine setups. The question being should I be using a 400 flywheel or harmonic balancer for my 383?



If I need only the 400 harmonic balancer is there a certain brand or type you'd recommend? Is the fluid dampener version recommended? What about a Jegs, or Summit racing branded unit?

Is it possible on the C4's to swap the harmonic balancer easily? Or do you really have to pull the engine or the radiator?



**************************************** *e-mail correspondance with vendor********************************** ********




RE: [SPAM] RE: Vibration on 383 engine at higher RPMs From: Ken Slataper (ken@precisionengine.com) Sent: Wed 7/04/07 6:51 PM To: 'Jonathan Von Engeln' (jvonengeln@hotmail.com)



Jonathan, The good news is the vibration is not coming from the flywheel. The problem is probably the balancer. Remove the transmission mount bolts or nuts, same for the motor mounts. This will allow you to jack up the engine to be able to remove the balancer without pulling the engine and not removing the mounts. As you are jacking up the engine have someone watch the top rear of the engine to make sure nothing hits the firewall when lifting up the engine. If there is enough clearance to remove balancer, then it will not be necessary to remove any upper engine parts to allow enough clearance at the top rear of engine. I will be on vacation until Tuesday. Please fell free to call me then @ 800 275 7371 ext. 111 or continue email, I will try to check my email, but sometimes it is difficult.

Ken Slataper <><





--------------------------------------------------------------------------------

From: jvonengeln@hotmail.com
To: herb@precisionengine.com
CC: ken@precisionengine.com
Subject: Vibration on 383 engine at higher RPMs
Date: Fri, 15 Jun 2007 19:00:36 +0000

Herb,

I spoke to you on the phone wednesday evening of this week. I purchased a 383 shortblock from you guys in the winter of 2006. I sent you the stock heads from my L98 which you redid! Your shop was very helpful in working with me to ensure I got the engine I wanted and Ken was very patient with my questions during the ordering/spec process. I got the engine, and working in my garage very slowly put everything back together with lots of assistance from www.corvetteforum.com and from a couple of local knowledgeable engine guys I know when I ran into questions, including the local Kansas City corvette club president. Herb, you helped me with a distributer question along the way too! I myself can turn a wrench and did most of the labor, I've enjoyed the exp thus far, though it's been a lot of work.

I finally got the car all put back together about 3 weeks ago and drove it lightly for only a couple days (prolly 2 hours total?) before going on vacation for a couple weeks. I've not yet run the car hard and don't want to until I can figure out my remaining concern. I feel a noticeable light vibration on the engine that starts about 3,500 to 4,000 RPMs, After I've driven it around the block to warm it up if I put it in neutral and rev the engine I feel it and can see it. I've asked a local hot rod guy that goes to my church what the vibration might be, because the engine sounds good and seems to be firing right. He asked me what flywheel and harmonic balancer I was running. I told him the stock 350 harmonic balancer and a new steel single mass SPEC flywheel that was match balanced to the old dual mass flywheel. He thought that might be the problem. He believed I should be running a 400 flywheel and harmonic balancer rather than the 350 flywheel and harmonic balancer. I've asked on the corvette forums, but there seems to be completely mixed opinions. I spoke with Herb this week on the phone who said I should be running a 400 harmonic balancer but with the stock 350 flywheel. (if I understood correctly) I'm doing all the labor myself and so I'm not out labor costs or anything just time, which I'm mostly enjoying the project so I don't mind.

At this point I would like to have a running corvette for the summer though! So I want to make sure I get this absolutely right if I need to take everything apart again. How can I best test to determine what my vibration is caused by?

If I want to eliminate the possibility of the engine itself vibrating how could I do that? If I take down the transmission and remove the flywheel and start up the car will that tell me? Somewhere I read that a 350 harmonic balancer is neutral balanced, so if that's accurate than I could just remove the flywheel start the engine and see if the vibration continues. But I've read elsewhere that it the harmonic balancer isn't neutral balanced so if that's true then removing the flywheel isn't going to tell me anything.

I'm thinking in order to replace the harmonic balancer on the corvette I'm going to have to have to pull the whole engine again because of a frame cross member that is literally about 1/2" away from the crank pulley. I'm not excited about pulling the engine again---but if I have to - I can do it again. I just want to make sure that If I have to pull the engine again or even simply drop the transmission again that I'm fixing the problem, so I'm not doing it a third time.


Thanks for your help!



In HIS grip, <//><



Jonathan Von Engeln

jvonengeln@hotmail.com

Archaea

my original specsheet follows (somethings were changed- cam, lower intake, superram addition, etc, but generally this should be overall accurate for the engine)


SPECIFICATION SHEET


Jonathan,

Thank you for contacting PrecisionEngine.com.

Please review the following quote and specifications to your custom-built 383/350HP SS performance longblock:

 GM 5.7 block bored, honed, decked and align honed
 Durabond cam bearings
 Performance roller camshaft:
o 224/232 @ .050
o .501 lift
o 114 lobe center
 Matching roller lifters and springs
 New sir steel rods 5.7”
 New cast steel 3.75” stroke
 Crankshaft micro-polished less than a 12 ra finish
 Speedpro pistons with Molly rings
o 9.2 to 1 compression ratio
 Balanced rotating assembly
 New Melling timing set
 New high volume oil pump
 New gasket set
 New push rods
 New head bolts
 Customer’s aluminum cylinder heads will include the 2.02/1.60 valves
 120 lbs. springs
 3 angle seats
 Bronze guides
 Positive seals
 1.6 roller tip stamped rockers
 Ported intake runners


Total price: $ 2795.00 plus shipping



Thank you again,


Ryan P.
ryan@precisionengine.com
1 (800) 275 – 7371 ext. 109

STL94LT1

If the 383 is internally balanced. You will need a neutral balanced flywheel, not one that was matched balanced to your stocker.

CFI-EFI

There are some details missing. First, is it a one piece rear main seal block and crank? Because of the aluminum heads and the roller cam, I am guessing, yes. It says it was balanced, but not to what standards. Here is the history and the deal on 383 balancing.

Before 1986, all 350's were neutrally balanced. The flywheel or flex plate and the damper were balanced to themselves; independently and in balance. The 400 engine, the original donor of the 383, 3.75" stroke crank, was externally balanced. Because of the weight of components and the distance from the crank centerline, that weight was, it was easier to add weight to the 'wheel and damper to balance the engines. The early 383s all used the 400 flywheel or flex plate and damper. Some people wanted the offsetting balance weight inside of the engine rather than cantilevered outside. They added Mallory heavy metal to the counterweights of the crank and balanced the engine in the conventional manner, internally. These were/are the original, internally and externally balanced, 383s.

In 1986 Chevy threw a monkey wrench into the works, when they went to the one piece rear main seal. Because they had to use a smaller flywheel flange on the rear of the crank shaft (to fit over the seal), the rear of the shaft lost weight and all the 350s had to have a small amount of weight added to the flywheel or flex plate. The front of the crank shaft remained neutrally balanced. Note: The 400 was never built with a one piece rear main seal, so the 400 external balance never changed.

With the back ground in place, we have to know (assuming a one piece seal), to what standards was the engine balanced? Most one piece seal 383 engines get balanced to the factory one piece seal 350 balanced, meaning they can use the same factory imbalanced flywheel or flex plate they came with. Some are spec'ed to a true, internal, neutral, (non stock) balance. These engines require a special flywheel or flex plate with the one piece seal bolt pattern but with a specially neutral, internal, (as no stocker is) balance. Note, in no case with a one piece rear main seal, is an imbalanced (externally balanced) damper used. All Gen I and Gen II 350s use a neutrally balanced damper. Therefore, it is unlikely that changing your damper will be the answer. However, if you should elect to replace the damper on your 383, for whatever reason, it will clear the crossmember without unbolting the transmission mount bolts, the motor mounts, or jacking up the engine.

First you will have to know to what standards it was balanced and then you will have to know the details of the parts you added to the engine once it was in your hands. I hope all of that is of use. Good luck, and...

RACE ON!!!

Archaea

I swapped the dampner to a 383/400 chevy dampner.

It's worse.

The whole engine shakes now. Like so bad the body of the car is shaking. It sounds good, and if you weren't watching you'd think it was a mean hot-rod, but it DEFINATELY still isn't right.

I can't figure out how to determine if it's a one piece or two piece rear seal. I'm asking the vendor again.

rodj

READ CFI-EFI's info above.

"New cast steel 3.75” stroke"

You have a aftermarket stroker crank which in either form ,1 or 2 piece seal requires a neutral balance NOT a out of balance 400 one.

The only time a 400 balancer is used on a 383 if you are doing a old style conversion with a cut down OEM 400 crank.

CFI-EFI

1986 and up engines have one piece rear main seals. Based on what has been written, it would appear (as I said before), that you have a one piece seal engine. All 350s have a neutrally balanced damper. The old externally balanced 383s used the unbalanced damper and flywheel of a 400. Because the 400 damper made things worse, it would appear that your engine is a one piece seal type with an internally balanced stroker kit. That would take the 350 damper, as you had. As STL94LT1 commented, for the flywheel, it depends to what standards the balance job was done. Was it internally balanced to match the one piece rear main seal imbalance? Or was it fully internally neutrally balanced? If the former, match balancing the new flywheel to the spec of the old, was proper. If the latter, the flywheel should have been neutrally balanced.

RACE ON!!!

PS. As a further point of information, like the YEAR, would the old flywheel have bolted to the crank of the new engine or did the crank have a different bolt pattern?

Archaea

now I can answer that question.

The new single mass flywheel bolted up directly and had the same bolt pattern as the old dual mass one.

CFI-EFI

The new single mass flywheel bolted up directly to the new engine. Are you positive the old dual mass flywheel also bolted to the new engine? Why would you check it? It still sounds as though you had a one piece rear main seal engine, to start with. For the life of me I can't figure out why you won't tell us the YEAR. Nevertheless, it is all spelled out in my last post.

RACE ON!!!

Archaea

the corvette was a 1990 - but the engine blew and I didn't have the original blown engine rebuilt.

The new engine year is unknown - I bought a short block from a engine builder in texas. I have no idea what year 350 he used to make the 383 I currently am having the trouble with.

Before I EVER had the new 383 engine I hooked up the new fly wheel to my 1990 blown engine - that's how I know the bolt pattern is the same. You see, I first misdiagnosed my power loss problem on the failed engine as a failing clutch/tranny. I bought a new single mass flywheel, new clutch, new pressure plate. I took off the dual mass stock flywheel, and had the new single mass flywheel match balanced to the original dual mass flywheel at a local machine shop. (He drilled two holes in one side of my new singlemass flywheel. (i think he said it was five grams he took off to make them match in rotating weight)

I put the match balanced single mass flywheel, the new clutch disc, and the new pressure plate on my old engine (the blown one).

10 miles later the 1990 engine started knocking so bad I knew I had SERIOUS problems with the engine and my tranny was probably never the problem.

I ordered my new 383 shortblock from the vendor in texas. It came. I put it all together and used my stock 350 harmonic balancer off the blown 1990 engine on the new engine. I put the new match balanced single mass flywheel on the new engine.

I got vibration - hence my original post.

I replaced the harmonic balancer per the engine vendors recommendation.

Then more problems as mentioned a post or two above.

CFI-EFI

OK, you have verified the flywheel interchangeability. Being a '90 to start with, I now know that both engines are one piece seal engines. Did the old engine vibrate at all before it went South? You seem to know that the flywheel was balanced separately from the clutch. Of there isn't a clutch balance problem, I can only guess that the new engine was internally neutrally balanced rather than internally balanced to the one piece seal, external balance specs. I'd see what the builder has to say about that. Good luck, and...

RACE ON!!!

Archaea

The old engine didn't have the shaking problems/out of balance problems before it went south.

I've got an e-mail into the vendor right now asking for direction.

Carpenter

You need a neutrally balanced flywheel and a stock 350 harmonic balancer.

Good luck.

Archaea

That's what I had (more or less) to start with on this 383. The flywheel was match balanced to the stock OEM dual mass flywheel -- I believe they took 5 or 15 (can't remember) grams off one side which is pretty close to neutrally balanced, and I used and OEM/Stock 350 harmonic balancer



...there was vibration, hence my original post.


If the five or 15 gram difference on the flywheel matters then that would be the only difference of what I had to what you suggested.

Carpenter

They 'match balanced' your new flywjeel to your old flywheel. Meaning both flywheels would now work on your externally balanced old engine.

Your new engine is internally balanced, needing a neutrally balanced flywheel.

Carpenter

When I built my 383, I re-installed the old flywheel, having been told (wrongly) by the parts supplier that my LT1 is internally balanced, so my stock flywheel would apparently work. It, of course didn't. Same vibration as you now have. A little bit of research later and I found that he was indeed wrong, that the LT1 is externally balanced. (as are all SBC's, I think)

So, out came the old flywheel and down to the machine shop where they neutral balanced it by removing all the balance weight.

Don't be fooled by how many (or few) ounces of weight they added. Doesn't matter if they added or removed even .05 ounce to balance it....it is MATCHED to your old flywheel, which is still for an externally balanced motor. Your new motor is already fully balanced internally, so when you use your old flywheel, you're causing it to become unbalanced, therefore the vibration.

CFI-EFI

I have been trying to nail down the year and type of balance since August 28th, see post #4. Just getting the year has been like pulling teeth.

As A repeat; Originally, SBCs, including the 350 engines from 1967, were ALL internally balanced engines. The 400, introduced in 1970 (through 1980), on which the first 383s were based were the only SBCs that were externally balanced. In 1986 when GM went to the one piece rear main seal, the crank flange for the flywheel had to be made smaller to fit over the seal. Some external weight on the flange was lost and it was necessary to put that lost weight on the flywheel or flexplate. All Gen I and Gen II (LTx) engines built after 1985 have a one piece rear main seal and are externally balanced in the rear. All 350s remained internally, neutrally, balanced in front.

When told that a one piece rear main seal crank is "internally" balanced, one must ascertain whether it is internally balanced to stock one piece rear main seal (external balance) specs or if it is a truly neutral internal balance. Whew!

RACE ON!!!

Carpenter

So what you're saying CFI......is I essentually 'got lucky' with my guesswork?

I'm totally fine with THAT!

(btw....thank you much for the explaination.)

CFI-EFI

Lucky? After being mislead, it sounds as though you knew what you were doing. I'm glad you were able to follow that explanation. I hope Archaea finally gets it. You are welcome.

RACE ON!!!

89FX3

What he said.

Been there, done that.