Well alot of you know that I had Wheeler Motorsports build a complete short block for me about a year ago....it has had a vibration in the engine since they date it first started up...

James B. and a friend at the Chevy Dealer (Roland) think it is engine balance problem and that is what I am thinking as well...I get a small shake at (in or out of gear) 900-1000 rpms, below and above that it does not shake....also get a faster vibration at 1900-2100 rpms...above 2500+ you can't really feed any vibration because of the engine speed...I do have poly engine and trans mounts but I would expect some aditional vibration which I do get at all rpms...engine runs strong with no misfire under load or wot

I've checked/installed the following:

Compression (dry) is 110 psi on all eight banks (comp is 8.9 to 1)
Installed another new set of plug wires and spark plugs.
Readjusted crane roller rockers (with guide plates)
Replaced BOV to vent at idle/low speed properly
Replaced EGR Valve as it was sticking, but sticking closed.
Checked for external vac leaks, none...retorqued alum intake.
Both my Matco scanner and my friends Tech2 showed misfire at idle and when held at 1000 rpms....more so on cylinder 4, also LTF was reading -3 on right bank compared to 0 on the left bank.
Cam retard set at 1
No coolent loss.
Same vibration with or without MAF+ connected.

Items left to verify:

Disconnect Crane Cams Ignition system
Scope check engine, manual short each cyl, check spark output
Check injectors (these are the new updated ones with out poppets) Runs injector cleaner?
Check PCV valve flow.
Anything else to check.

Vibration checks...

Disconnect Torque Converter and restart engine....disconnect drive belt...that's about all I can do...only thing left would be the flex plate or the engine internal balance?

If anyone has suggestions or who knows someone I can talk to about this please post or PM me asap...thanks!

Engine build up:

383 CID internaly balanced
Late model 5.7 block with 4 bolt mains
5.7 H-beam 4340 rods
Scat 4340 Crank, 4-350-3750-5700-L
SRP Forged pistons with -31cc dish pistons
Street Fluid-damp dampner, double broched, two key ways.
Block zero decked,
Cam 214/220 duration LS 114 ran stright up...cam card:
http://www.crower.com/misc/cam_spec/...rt_num=00401LM
Thorley headers, match ported 80mm bbk, stock MAF descreened, MAFT+
Vortech SC V1-Strim 5psi off boost, single belt system
ATI chromemoly SFI flex plate that was neutral balanced (per Clay at Wheeler)
Vortec iron heads (milled 40ths) cced within 1cc, SS valves, 1.94/1.6 ported biased exhaust flow. 120lbs single springs, harden pushrods, perfect rocker alignment on valve tip. Engine head studs.
http://www.wheelermotorsports.com/383compsb.htm

Ken

 

Could be a bad balancer, you never know there are so many of them built that atleast ones gotta have a problem with it. Thats all I can think of right now.

Alex

 

Bottom end:





Stock L31 use a bob weighted flexplate...was told to use a neutral balanced flexplate since the engine was to be internaly balanced unlike a stock engine?

Ken

 

Has the engine builder you purchased from had any ideas on what might be the problem?

 

I sent Scat an email regarding the problem and I am going to call WMS tomorrow as it is now looking like a balance problem...kind of like it should of had a flexplate "with" a bob weight?

Ken

 

Sounds like a balance prob. A buddy had a similar prob and we checked everything multiple times and it kept coming back to the balance. The engine shop kept insisting that it could NOT be his fault-his balance job was "on the money" We finally tore it down and took the internals to him to get them checked. When he pulled the file to make up the bob weights he immediately saw his mistake and began apologizing. He had left out the weight of the rods when balancing the crank !! He stood behind it-told us that the crank was probably bad after having been drove 5000 miles that far out of balance. He provided new crank, and all new machine work, and we never had any more probs. You need to get in touch with the machinist who actually did your balancing.

 

Well today I installed eight 1.5" long roll pins into each dist. cap outlet and then installed each plug wire on the other end on the metal roll pin...this allow me to short each cylinder to ground with a ground lead.

All eight cylinders dropped the same amount of rpms, vibration never disapeared either

Next took off drive belt and run breifly at same rpms...man you can really feel the vibration with no assessoried running! ...also check damper and crank pulley at the same rpms...they are very smooth.

I'm not going to drive it until I get this figured out...it's got a little over 1K miles on it...hope nothing is getting hurt internaly!

I'm going to disconnect the torque converter next...after than I will pull the trans/transfer case back and put my old flexplate back on which has a counter weight.

What do you guys think so far?