88 924s shakes at idle - Rennlist - Porsche Discussion Forums

Notices

88 924s shakes at idle

Reply

Old 09-14-2017, 12:13 PM
  #1
Tampa 928s
Super User
Thread Starter
 
Tampa 928s's Avatar
 
Join Date: Dec 2006
Location: Tampa Florida
Posts: 3,942
Default 88 924s shakes at idle

88 924s
car shakes at idle if it's set at about 1200 Rpm it is smooth and car runs fine other wise.
I have replaced all front timing belt components and YES the belt is adjusted and rollers positioned correctly.
Motor mounts are solid and replaced.
Subbed the Afm, compression is good.
Clutch replaced with none rubber style.
Need some feedback on this running out of options, I am wondering if the clutch and motor mounts maybe the cause.
Tampa 928s is offline  
Reply With Quote
Old 09-14-2017, 01:01 PM
  #2
V2Rocket
Rainman
Rennlist Member
 
V2Rocket's Avatar
 
Join Date: Jan 2007
Location: Alta Loma, CA
Posts: 40,113
Default

shaking at idle is 99% of the time motor mounts, you said they are "solid and replaced" does that mean they are actually SOLID or just new and in good shape?

belt timing most likely wouldn't present at idle - they really start to get noticeable past 3000 rpm or so if it's set wrong.

when you set the engine to its spec'd idle speed of 900 +- 50 rpm how does it feel?
V2Rocket is online now  
Reply With Quote
Old 09-14-2017, 01:06 PM
  #3
Todd951968
Addict
Rennlist Member
 
Todd951968's Avatar
 
Join Date: Nov 2004
Location: Pennsylvania
Posts: 788
Default

I have a similar issue; I just replaced the engine mounts on my '87 924S and noticed the same vibration at idle. My car has zero miles since the mounts were changed along with timing belts and other work because I am waiting on an antique plate from the state so I can drive it.

But, it SEEMS to be vibrating slightly less after running the engine at idle for 20 minutes or so with new gas (car had been sitting for about 4-5 years).

Anyway, is it possible that the mounts need a little time to "bed-in"?
Todd951968 is offline  
Reply With Quote
Old 09-14-2017, 06:02 PM
  #4
Tampa 928s
Super User
Thread Starter
 
Tampa 928s's Avatar
 
Join Date: Dec 2006
Location: Tampa Florida
Posts: 3,942
Default

The motor has been gone through and Mm are new along with a ton of other stuff. You are correct the balance shaft becomes in issue around 3k but that is not my issue. Wondering about the clutch and if I installed it correctly, car has been used by my son he mentioned the idle issue. It's odd at 1200 it's fine seems of clutch assembly is out of balance it would tend to be at all ranges. I just don't want to remove all the crap to check it and find out it's something else. The lower the Rpm it gets worse.
Tampa 928s is offline  
Reply With Quote
Old 09-14-2017, 06:32 PM
  #5
lfisher
User
 
lfisher's Avatar
 
Join Date: May 2009
Posts: 48
Default

Did you use aftermarket motor mounts? I replaced mine a couple years ago with aftermarket and ended up with vibration and body noise at idle. Above 1100-1200 RPMs it went away.

But after changing to genuine Porsche MMs no vibration and all is well.
lfisher is offline  
Reply With Quote
Old 09-14-2017, 10:03 PM
  #6
Tampa 928s
Super User
Thread Starter
 
Tampa 928s's Avatar
 
Join Date: Dec 2006
Location: Tampa Florida
Posts: 3,942
Default

It's been so long but I believe they were after market solid.
Tampa 928s is offline  
Reply With Quote
Old 09-15-2017, 01:35 AM
  #7
alex.rhodes
User
 
alex.rhodes's Avatar
 
Join Date: Sep 2012
Location: Ft. Belvoir, VA
Posts: 76
Default

Sounds like the dreaded early 944 shudder. (it affects all44s, but the early ones moreso). See link for a suggested fix.
alex.rhodes is offline  
Reply With Quote
Old 09-15-2017, 01:45 PM
  #8
Arominus
Super User
 
Arominus's Avatar
 
Join Date: Jan 2009
Location: Colorado
Posts: 3,970
Default

Originally Posted by Tampa 928s View Post
It's been so long but I believe they were after market solid.
Thats your problem, the only mounts that tame the "shake" are the OEM porsche ones. The aftermarket mounts don't have the liquid center and transmit the vibrations to the car. I had the exact same behavior with Lindsey racing semi solids on my S and also when i had a collapsed OEM mount on my S2. Get your hands on a set of OEM mounts if you want it to go away.
Arominus is offline  
Reply With Quote
Old 09-15-2017, 09:49 PM
  #9
Tampa 928s
Super User
Thread Starter
 
Tampa 928s's Avatar
 
Join Date: Dec 2006
Location: Tampa Florida
Posts: 3,942
Default

You may have something on the Mm I did use solids on my 928 with out any issues. Wondering if the 4-Cylinder cars are more prone to this!
Tampa 928s is offline  
Reply With Quote
Old 09-17-2017, 11:56 PM
  #10
951Dreams
Addict
Rennlist Member
 
951Dreams's Avatar
 
Join Date: Feb 2016
Location: Bella Vista, AR
Posts: 868
Default

Originally Posted by Tampa 928s View Post
You may have something on the Mm I did use solids on my 928 with out any issues. Wondering if the 4-Cylinder cars are more prone to this!
Exponentially so. At one time I knew and understood the physics as to why, but that's been lost long ago (power stroke, rotational mass, blah blah blah). The short of it is that a straight 4 is terribly balanced (secondary vibrations, not primary). It's why you rarely see a 4 cylinder bigger than 2.0L. Somewhere back in those physics I've forgot, the problem becomes a big issue once you pass the 2.0L size. Porsche's answer was the balance shafts (not their invention, it was invented in 1911 and Mitsubishi patented it in the 70's and I'm pretty sure I've read Porsche paid them to use it).

The 2.5, 2.7 and 3.0 liter engines Porsche used are some of the biggest (GAS Engine) 4 cylinder ever used in production cars. Not THE biggest, but up there. (3.2L is the most widely excepted king of the non-diesels/passenger car engines) Bigger 4's were used in tractors and other industrial applications where vibrations weren't a huge issue, or where RPM's were lower.

Er.... sorry for the history lesson. Didn't mean to do that. But yeah TL;DR V8 and I4 are totally different beast on the vibration front. I was surprised as well when I first got into these cars.
951Dreams is offline  
Reply With Quote
 

Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
elgy
924/931/944/951/968 Forum
2
12-04-2017 10:07 AM
turbogrill
996 Forum
1
11-27-2017 11:13 PM
Simonripley
996 Forum
16
11-14-2017 05:41 PM
kruinc
996 Forum
5
03-30-2017 03:22 PM
Tabby_924
924/931/944/951/968 Forum
4
12-18-2016 01:07 AM

Thread Tools
Search this Thread
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Forum Jump


All times are GMT -3. The time now is 04:58 PM.


Copyright © 1998 - 2017 Rennlist.com 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.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: