Rough idle/vibration

[Rising]

If i set my idle at 1000 rpm totally smooths out for me 850 not smooth vibrates like crazy.

Yeah that would totally solve my problem too.

One strange thing I noticed that may point to the pump is... if I rev it manually, slowly moving up to there 1000 rpm should be, it doesnt change at all then spikes to 1000 then drops off even if i`m still holding the lever, anyone know what that is?

Do you know if anyone messed with the governor on this pump? Isnt that kinda what happens when you shim the intermediate spring... part throttle surging?

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[R.O.R-2.0]

If I rev to slightly above 1000 rpm it seems to smooth out.

If i set my idle at 1000 rpm totally smooths out for me 850 not smooth vibrates like crazy.

if i have my idle set to 800 rpms like the book says, stuff will jump out of the door pockets on my mk2 when the doors are open...

with a 1000rpm idle, its quite smooth..

my car is a mk2, totally different engine mounts (hydraulic) and it still vibrates like a paint shaker at low idle...

its the nature of these engines..

having a bent front end will really make it hard, if not impossible to align the engine..

[JamesT]

My car shook so hard at idle it felt like the front wheels were hopping off the ground. I set the idle to 850, pulled the stupid urethane inserts out of the new rubber mounts he put on, replaced the front an rear mounts with rubber ones, and aligned the mounts as best I could. Now it just tries to rattle the dashboard in half.

[R.O.R-2.0]

My car shook so hard at idle it felt like the front wheels were hopping off the ground. I set the idle to 850, pulled the stupid urethane inserts out of the new rubber mounts he put on, replaced the front an rear mounts with rubber ones, and aligned the mounts as best I could. Now it just tries to rattle the dashboard in half.

why not turn up your idle 150 rpm?

[bbob203]

Yea i see no reason not to set the idle to 1000. I turned mine down to do it by the book and i see no benefit of it aside from an annoying massage.

[JamesT]

Because I'm the kind of hipster prick who likes to remind everyone around him that he's driving a diesel. Either that or it just doesn't bother me that much.

[Dakotakid]

Yet, another reason I hated the earlier bodies.

Set your idle up to at least 1,000. Make sure your exhaust has good rubber donuts (with closed centers) and get on with your life.

Better yet, move up to a Mk. II body.

Better yet, buy me out of all of my cars and mountain of parts and let me get on with MY life.........

[CarlosA]

Yet, another reason I hated the earlier bodies.

Set your idle up to at least 1,000. Make sure your exhaust has good rubber donuts (with closed centers) and get on with your life.

Better yet, move up to a Mk. II body.

Better yet, buy me out of all of my cars and mountain of parts and let me get on with MY life.........

Alright so the consensus is that these things are not fixable. WTF. My 1978 is silky smooth with no vibes in the mirrors, steering wheel, or pedals. I did reduce the vibes on this car by about 40% by using an obscure steering column adjustment - but the dash still shakes like crazy.

I guess i`ll just live with it and stop throwing money at it. This has made me hate a vw diesel for the first time though.

BTW... what is in your mountain of parts/cars?

[bbob203]

Yet, another reason I hated the earlier bodies.

Set your idle up to at least 1,000. Make sure your exhaust has good rubber donuts (with closed centers) and get on with your life.

Better yet, move up to a Mk. II body.

Better yet, buy me out of all of my cars and mountain of parts and let me get on with MY life.........

next time I go west ill get a hold of you about parts.

[CarlosA]

This car is excellent in some ways. After not driving for 5 whole days it just started right up in half a crank.

[Gizmoman]

Ok,
I'm going to chime in one more time about balanced parts. You said you changed a few rotating things and I never heard if you checked the weight of the new parts VS the old ones.
While it may be somewhat true that "out of balance" gets worse as RPM's increase (as was mentioned),  there's a lot more to it than that - namely harmonics.

All the rotating parts in every motor affect balance. If the motor vibrates at a given RPM that's because something is "out" of balance at that RPM. There are bits rotating and stuff moving up, down, sideways and what-not. It's all a symphony of various parts and while some may be "in tune" at a given RPM, they go "out of tune" at others.

IMHO - If the motor vibrates at the Bently spec RPM, something is out of balance. "edit" You've done a lot of things to this car but of all the things you did, changing the crank and one rod are the things that could affect balance the most (unless you weighed the new rod against the other three and knew the replacement crank was balanced).

[CarlosA]

Yeah the crank came from another engine that I ran. The rods & pistons are all balanced. I also mentioned that several engines i`ve pulled apart have had fairly wild stock piston & rod weights, these engines were by no means balanced and blueprinted in 1979. Further, just what shade tree mechanics like us are doing now, 30 years later is far more balanced than back then. Anyway, I did take care to grind a bit off the rods so they were all within half a gram, the pistons are a new name brand set. The final weights of pistons, rings, rods was within a gram of each other.

[Gizmoman]

Gotcha.
But it's still a balancing thing and no amount of jigging mounts and twisting frames will make it balanced at 850 - it may even make it worse. As you stated,

several engines i`ve pulled apart have had fairly wild stock piston & rod weights.

That could mean that the engine (with various weighted parts) was balanced as a rotating mass and would explain why that engine didn't vibrate at spec idle (assuming it didn't).

If the engine was smooth before at 850 and the parts you replaced weighed exactly the same as the parts you took out then I would look elsewhere (Ip, injectors, mounts, etc).

Balancing reciprocal mass is tricky stuff. I really appreciate your post because I am doing a rebuild (possibly the slowest on record) and will need to deal with the same issues.

[CarlosA]

Cranks are balanced individually to spin smoothly with no components attached. This is why the average person can balance their rods & pistons to be identical weights and avoid having to have the entire rotating assembly balanced.

This is basically why cranks often have balancing holes from the factory - not only to remove weight but also to be filled with Mallory metal (an alloy of Tungsten) to add weight to the crank.

Anyways, i`m sure I could have the entire engine balanced at a race shop and be light years ahead of what VW was able to do in a production environment 30 years ago. And I agree with you that balancing the engine could solve this problem, but i`m also not convinced - both because of the single RPM problem, and because factory engines are notoriously "out of balance" when compared to what a race shop will attempt to achieve. I have about a dozen rods sitting here and every single one of them is 1-2 grams different than any other rod, in other words no set was ever fully balanced at the factory

I guess i`m just trying to figure out why the car vibrates more now than it did 30 years ago, and hopefully find out for the community that a poorly functioning injection pump, bent frame, or something like that is causing the issue rather than just adding to the issue.

Edit to add that another engine I worked on (the silky smooth 1978) also had a rod, piston, and crank replaced without any other work done to the engine in 30 years. Totally forgot about that. The parts i`ve used to replace components are just good used parts from old engines - not a new Brazil crank or something like that.

[Gizmoman]

I agree with you 100% and to be honest, getting a motor balanced like a race engine (unless that's your use) doesn't make much sense.

Please keep us informed if you get it sorted.