Engine Performance This section is for discussion on all engine building related questions.
Sponsored by:
Sponsored by:

Odd engine vibration

 
Old 11-23-2009, 10:12 AM
  #1  
Elite Member
Thread Starter
iTrader: (2)
 
miata2fast's Avatar
 
Join Date: Aug 2009
Location: Dover, FL
Posts: 3,069
Total Cats: 159
Default Odd engine vibration

I drove the car yesterday, and I am noticing a vibration in the motor. It will do it if my Weber's are out of sync, but I checked, and they are spot on. The vibration occured soon after I installed the 99 head. Seems to be getting worse.

I am suspicious I have a bent rod. Does anyone have experience with a motor vibrating as a result of bent rods? Could it be the flywheel or balancer. I have an aluminum Fidanza, with not many miles on it. Balancer is stock.

My camshaft is bigger but not gigantic. I am turning up to 8000 rpm. Too much for stock rods?
miata2fast is offline  
Old 11-23-2009, 10:27 AM
  #2  
meatbag
iTrader: (50)
 
gospeed81's Avatar
 
Join Date: Nov 2008
Location: Houston, TX
Posts: 7,258
Total Cats: 26
Default

I looks like your turbo fell off.

That's a considerable bit of weight, which sits a good 6-8in off the side of the motor. Find a good one with matching manifold, bolt it on...and you should be in good shape.

jk



Video?

How bad?

Checked all the simple stuff like plugs?



I had a motor vibrate when I BROKE a rod once...
gospeed81 is offline  
Old 11-23-2009, 10:36 AM
  #3  
Elite Member
Thread Starter
iTrader: (2)
 
miata2fast's Avatar
 
Join Date: Aug 2009
Location: Dover, FL
Posts: 3,069
Total Cats: 159
Default

Too much compression!

I have not done anything yet. It could be a weak sparkplug or wire. I plan to replace wires and plugs, and do a compression check.

The vibration is not too bad. It only does it at low rpm. It is like it has one weak cylinder. However, if compression is off, it will show up on the syncrometer. The weak cylinder will have very low vacuum.

I will perform those tasks and get back.
miata2fast is offline  
Old 11-23-2009, 10:40 AM
  #4  
meatbag
iTrader: (50)
 
gospeed81's Avatar
 
Join Date: Nov 2008
Location: Houston, TX
Posts: 7,258
Total Cats: 26
Default

Low rpm or low load?
gospeed81 is offline  
Old 11-23-2009, 11:19 AM
  #5  
Elite Member
Thread Starter
iTrader: (2)
 
miata2fast's Avatar
 
Join Date: Aug 2009
Location: Dover, FL
Posts: 3,069
Total Cats: 159
Default

Originally Posted by gospeed81 View Post
Low rpm or low load?
Low rpm. Seems to go away under load.

I think you may have convinced me it is something simple like a bad wire.
miata2fast is offline  
Old 11-23-2009, 11:21 AM
  #6  
meatbag
iTrader: (50)
 
gospeed81's Avatar
 
Join Date: Nov 2008
Location: Houston, TX
Posts: 7,258
Total Cats: 26
Default

I usually see sparks issues the other way around...more apparent under load...and smooth at idle and low load.

Rule out the simple management issues before you go chasing mechanical nightmares.

You can easily check TDC on each cylinder while the plugs are out...but I seriously doubt you're bending rods...or that that would cause vibration.

I would take another look at the carbs as well. Frustrating...and not undermining your experience...but in a decade of bike ownership nearly every running problem on the carbed bikes was some kind of synchro or jetting issue. Once on a Kawi 500R I synched the carbs five times (seemingly perfect) before I found the setting the bike ran smoothly on.
gospeed81 is offline  
Old 11-23-2009, 11:30 AM
  #7  
Elite Member
Thread Starter
iTrader: (2)
 
miata2fast's Avatar
 
Join Date: Aug 2009
Location: Dover, FL
Posts: 3,069
Total Cats: 159
Default

Thanks for the advice. I will keep digging before I do something drastic.
miata2fast is offline  
Old 11-26-2009, 10:37 PM
  #8  
Elite Member
Thread Starter
iTrader: (2)
 
miata2fast's Avatar
 
Join Date: Aug 2009
Location: Dover, FL
Posts: 3,069
Total Cats: 159
Default

Gospeed81 you were right about it being a carberator problem. I made a few adjustments, and it runs much better, and the vibration is all but disappeared. It is not perfect, but I am getting close to where I can do some track or dyno time.

I have to admit, I was a little paranoid about having a bad rod because of the rods discussion that in going on in another thread.
miata2fast is offline  
Old 11-26-2009, 10:45 PM
  #9  
Elite Member
iTrader: (1)
 
Join Date: May 2009
Location: Jacksonville, FL
Posts: 4,862
Total Cats: 281
Default

Glad you fixed it but you really shouldn't spin a stock BP to 8000 rpm...
Full_Tilt_Boogie is offline  
Old 11-27-2009, 08:46 AM
  #10  
Elite Member
Thread Starter
iTrader: (2)
 
miata2fast's Avatar
 
Join Date: Aug 2009
Location: Dover, FL
Posts: 3,069
Total Cats: 159
Default

Not exactly stock. Rods are polished and motor was balanced. Valves and valve springs have been upgraded. Pistons are JE's.

I usually shift at 7600 to 7800, and I go to 8000 on occassion
miata2fast is offline  
 
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Full_Tilt_Boogie
Build Threads
63
08-09-2018 07:54 PM
nick470
MEGAsquirt
7
06-16-2017 02:53 PM
90 Turbo
MEGAsquirt
19
10-19-2015 04:23 PM
tazswing
Race Prep
20
10-03-2015 12:04 PM


Thread Tools
Search this Thread
Quick Reply: Odd engine vibration


Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.