Smoke Test Results (Throttle Body: solutions?)

[Cinnabar325is]

Working on refining my 2.8 and next on the list was a smoke test to check for vacuum leaks. The car may never idle smoothly (298* cam) but I know it could be better, plus the car occasionally throws the code for an incorrect air/fuel ratio at idle.

So the smoke test revealed two leaks:

1) Throttle shaft in the TB. This was a pretty bad leak too.

2) Valve cover gasket. Leaking really badly, but shouldn't be a tough fix with a new gasket. I guess they're pretty much one time use; I've had this gasket on and off twice.

Now for my main question: What to do about the TB?

Can they be rebuilt? I haven't seen any kits or anything. I haven't priced out a new one either, but I'm sure it's frightening.

I ran across these: http://www.westcoastriots.com/htmlfiles/Products.html Not sure what the stock plate diameter is, but might this be the best option? The motor is outputting far more than stock, so a bigger TB might be worthwhile in its own right, plus it would solve the vac. leak.

Any thoughts?

[Gregs///M]

Stick with a quality OEM gasket for that valve cover. Be sure to torque it down to using correct sequence.

For the TB, I've actually taken that entire assembly apart including removing the lock ring to find a way to better seal from vacuum leaks. My smoke test also failed there. However, after reassembly, it no longer leaked there. I suspect it will begin to leak eventually.

I assume the "clearance" has increased over the many years of use so perhaps a new TB would be best option. I dont trust another used TB in there because the same problem might occur.

Perhaps others can chime in about solutions to seal the throttle shaft.

[Cinnabar325is]

Stick with a quality OEM gasket for that valve cover. Be sure to torque it down to using correct sequence.

For the TB, I've actually taken that entire assembly apart including removing the lock ring to find a way to better seal from vacuum leaks. My smoke test also failed there. However, after reassembly, it no longer leaked there. I suspect it will begin to leak eventually.

I assume the "clearance" has increased over the many years of use so perhaps a new TB would be best option. I dont trust another used TB in there because the same problem might occur.

Perhaps others can chime in about solutions to seal the throttle shaft.

How difficult was the TB to pull apart and reassemble? Never done an M20 version before. What is the actual "seal" for the throttle shaft?

[UserError]

Here's an exploded view of the throttle body: http://www.realoem.com/bmw/showparts...35&hg=13&fg=15

[Cinnabar325is]

Here's an exploded view of the throttle body: http://www.realoem.com/bmw/showparts...35&hg=13&fg=15

Examining that, there doesn't seem to be a separate part number for the throttle shaft and associated seals. In fact, they're not even shown separated from the throttle "body" itself.

[nando]

you could try adding grease to the bearings that the shaft rotates in. that's where the leak is going to happen.

but with a 298 cam - you need anything other than Motronic to run the thing. yeah, it will run OK. but you can actually get a pretty nice, smooth idle if you had sequential fuel instead of batch fire. it made a night and day difference for me and I only have a 284/272.

[Cinnabar325is]

you could try adding grease to the bearings that the shaft rotates in. that's where the leak is going to happen.

but with a 298 cam - you need anything other than Motronic to run the thing. yeah, it will run OK. but you can actually get a pretty nice, smooth idle if you had sequential fuel instead of batch fire. it made a night and day difference for me and I only have a 284/272.

Interesting nando, is there an actual roller bearing at the top and bottom of the shaft? I would have expected some type of bushing.

Do you have any experience or thoughts on the Riot Racing TB I linked to up top?

What management are you using on your car? I'm assuming there's not a way to change Motronic 1.3 to sequential fire.

[nando]

yeah, there's a little bearing on both ends of the shaft.

I don't have that one, but I bought another "BBTB" that turned out it used the stock 60mm plate. very disappointing. I still get about an 8kpa (8%) drop in manifold pressure above 6500rpm. if you have a way of logging vaccum/manifold pressure, remove your airbox and take a good hard WOT run. if you see a pressure drop at high RPM, then a larger TB could help. if not, it's a waste of money.

I have MS3. there's no PnP for sequential on an M20 yet. I used an M50 vanos harness (fits up with a few mods). It can be great if you don't mind doing all the work. I'm not sure if there's really any "easy" way to do sequential on the M20 - everything will require wiring harness work + a cam sensor.