oilhammer
Certified Volkswagen Nut & Vendor
Swapping around [very] used parts may lead you to be chasing your tail, unfortunately. Your idle compensation numbers are not great, but not so bad that I think that is your problem.
I agree that whatever vibrations remain might be natural. When I compare the hydraulic BMW M42 mounts I'm using to the stock mk3 mounts, I can see that there would be a significant difference in damping. The mk3 engine mounts are pretty hard to incorporate into the 240, but I may look into that- at least on the passenger side. Right now the only bothersome vibration is <1700 RPM in 5th (<60mph).Glad you got it to where it works. Whatever vibes are still left might not be that different from how these are in stock VW applications. Even there, vibration is always noticeable. The pendulum mounts of the Mk4 chassis cars do a great job suppressing it but the tripod setup of the old Mk3/B4 transmits plenty. Perfect control of NVH is a serious challenge with these engines no matter what they are in, so sounds like you got a pretty good outcome.
As was mentioned, still will be interesting to see how the flywheels do now, since the axle bushings probably were not the cause for that. But if you can run an SMF now that doesn't break while still keeping the vibes under control, maybe it doesn't matter. Do you have a SMF in it now?
WOW! Glad you solved it. What a long battle its been. I would not have expected such a difference from those bushings.
To put the vibrations in perspective, they are still much more severe than a mk3 TDI. Mostly now the only range that is annoying is below 1850rpm in 5th under load. That range can be avoided easily, which is why I said it's much more tolerable now. Before replacing the trailing arm bushings, the vibrations were more severe, and occurred up to 2150 rpm.I think you are right that it might not be worth reinventing whatever fabrication work you have in place now. Vibration and buzz are always there even in the stock Mk3/B4 cars. The same is mostly true for the B5. Mounting systems where the same mounts have to both support the weight of the engine and transmit torque for propulsion are challenging in terms of NVH control with a 4-cylinder engine. Pendulum mount systems have the advantage of being able to support the mass of the drivetrain with one set of mounts (which can be fairly soft), and then transmit drivetrain torque with a different and much firmer mount (the dogbone in most such setups). Sometimes, like in the case of the Mk4 VW design, the dogbone is even attached to a rubber isolated subframe as well, which gives a further layer of vibration control. But I think decoupling those mounting and torque forces is what allows the later transverse TDI cars to be so refined compared to the early ones. ALH and AHU engines themselves both vibrate approximately the same amount, but if you put your fingers on the steering wheel of an idling ALH car, you feel almost nothing. With the older chassis cars you feel plenty. Or as another comparison, the AHU TDI in my T4 Eurovan with the factory pendulum mount setup is a much smoother experience than the exact same type engine in a B4 Passat or A3 Jetta with the tripod mount.
Anyway all that to say if you've got the NVH at a tolerable level now with your setup, that's a pretty good victory.
The B5 gas and diesel mounts are externally the same and bolt up the same way, but are different, the gassers are solid and the diesels are hydraulic. They do make a considerable difference in those cars so it's possible some B5 diesel hydraulic mounts would be beneficial in your setup, though again if it's pretty good now you might be chasing diminishing returns since even with new good diesel hydraulic mounts B5's with 4cyl diesels are noted for NVH too. You wouldn't have to import the diesel mounts, they're available from all the usual sources stateside for a US spec 04-05 Passat TDI with BHW engine, though they are pricey, over $100 each.
Be interested to watch your T4 conversion, do you have a thread up for it?