

| Subject: | I4 engine/vibrations - A few quick comments |
| From: | Frank Grunthaner |
| Date: | Sun, 23 Feb 2003 19:48:00 EST |
In a message dated 2/23/03 4:12:07 PM, McNock@EASYSTREET.COM writes: << beat to death yes, but definitively figured out - no! (at least for this van!) I have been to your website may times (fabulous and thanks) and searched the achives many times. Below I have a list of all that has been done. It is mostly everything every discussed. That is why I am so frustated. Better, Absolutely. Fixed - well no. >> You'e definitely correct on your website observations, but fall a bit short on the summary. I have indicated in the past and at some length a number of technical issues that come to the solution including the mounting of the exhaust, the coupling of the exhaust and the details of the engine mount. Of all of these, resonance plays a powerful role. After eliminating the basic engine issues (bent pulleys, H/A mounting brackets and exhaust coupling) you will return to the engine mount and its active or passive isolation technology. All manufacturers of large displacement 4 cylinder in line engines must confront this problem. The problem is minor at 1.6L, more significant at 1.8L, a real discomfort at 2.0L and a major pain in the tush at 2.3 and above. All manufacturers (VW. Porsche, Audi, Mercedes, SAAB, Volvo to name a few Euro's) adopt one of two solutions: Addition of a balance shaft to the engine or the use of hydraulic (actively damped) engine mounts. I have adapted the SAAB hydraulic mount to the VW Vanagon diesel mounting system (refers to the '82 design only since this is what I play with). On my test stand, the Audi 3A 2.0L engine (inline 4) with turbo is vibration free. But I have more work to do for better clearance. I have not yet been able to mount the new engine in the Vanagon, so I haven't conducted any vibration measurements yet. I will! In the meantime feel free to experiment with the hydraulics. BTW your description of differences betwixt the 82 and later varients also misses a few key points. Frank Grunthaner
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