A couple of horses found (in the throttle body)
08-28-2004, 06:27 PM
#1
Addict
Rennlist Member
Rennlist Member
Thread Starter
A couple of horses found (in the throttle body)
Sometime ago I was wondering why my throttle body (TB) sensor cap was always cracking open, so it got a good amount of J&B Weld, but to no avail … still cracking open.
A reasonable explanation was excessive leakage through the throttle shaft, especially with my 25 psi boost, which would exert a 50 pound pressure on the cap. Drilling a hole in the cap (eventually increased to the size seen in the picture) did not help, so some serious leakage must have happened.
I purchased another TB on eBay, but with the same result and eventually took my original one apart (picture). Sure enough the needle bearings (good feature) in both ends originally had seals built in, which now have disintegrated. All the rest of the parts looked good, so I am getting some 5/16-1/16 Viton O-rings to fit in the bearings, 2 on the actuator side and 1 on the sensor side. This should improve the low- and high-end boost (I have plenty in the mid-range) and therefore give a few extra horses and even earlier boost.
I strongly suspect that this minor age problem is generic rather than particular to my case.
Laust
PS Sorry for the bad picture; my camera could not decide where to focus.
A reasonable explanation was excessive leakage through the throttle shaft, especially with my 25 psi boost, which would exert a 50 pound pressure on the cap. Drilling a hole in the cap (eventually increased to the size seen in the picture) did not help, so some serious leakage must have happened.
I purchased another TB on eBay, but with the same result and eventually took my original one apart (picture). Sure enough the needle bearings (good feature) in both ends originally had seals built in, which now have disintegrated. All the rest of the parts looked good, so I am getting some 5/16-1/16 Viton O-rings to fit in the bearings, 2 on the actuator side and 1 on the sensor side. This should improve the low- and high-end boost (I have plenty in the mid-range) and therefore give a few extra horses and even earlier boost.
I strongly suspect that this minor age problem is generic rather than particular to my case.
Laust
PS Sorry for the bad picture; my camera could not decide where to focus.
Last edited by Laust Pedersen; 01-14-2013 at 03:32 PM.
08-30-2004, 03:37 PM
#3
Addict
Rennlist Member
Rennlist Member
Thread Starter
Tom, thanks for the feedback. Seeing my thread rapidly sink to the bottom, I was getting a little concerned that the information was found irrelevant.
08-30-2004, 06:58 PM
#6
Addict
Rennlist Member
Rennlist Member
Thread Starter
"What are we supposed to be looking at?"
It is the disassembled throttle body seen from the side and the throttle sensor (black thing).
I'll hone my photographic skills, when the O-rings arrive and it is time for assembly.
It is the disassembled throttle body seen from the side and the throttle sensor (black thing).
I'll hone my photographic skills, when the O-rings arrive and it is time for assembly.
08-30-2004, 08:09 PM
#7
Three Wheelin'
Join Date: Jun 2001
Location: San Jose, CA
Posts: 1,598
Likes: 0
Received 0 Likes
on
0 Posts
Hmm....i wonder if that's where my vacuum leak is. I've 15 in on the vacuum gauge but even the local shop can't get it any better. Oh...and i have a fresh rebuild on the motor. Hmmmmm...good info.
Trending Topics
08-31-2004, 04:47 PM
#8
Intermediate
Join Date: Mar 2002
Location: Union Mi
Posts: 43
Likes: 0
Received 0 Likes
on
0 Posts
I am on my third attempt at sealing the throttle position sensor cap. Thankfully each time it blew off it not get lost on the road. I suspected this may be the problem, but never looked into it very far. I will be awaiting your findings. I see you are counting CFM, are you still on your k26?
Ben
Ben
08-31-2004, 05:15 PM
#9
A bunch of small vacuum leaks in strange places seem to crop up. Some others I found are, Adj. fuel pressure regulator (leak through the locking nut), venturi mess that is now removed, BOV (cap was loose), brake booster to intake manifold fitting, heater valve switch.
08-31-2004, 08:22 PM
#10
Addict
Rennlist Member
Rennlist Member
Thread Starter
Ben, I have 3 specially modified K26-6&8 turbos waiting in line (see picture), but at my recent partial rebuilt (head gasket) I decided to leave my stock K26-6 turbo in place until I get the car on a dyno probably at the end of September. Just to see how far the stock turbo can be pushed.
Wormhole, I would add the ICV (idle motor) to the list. My old one leaked through the housing and connector, which I sealed with J&B Weld, but eventually got a new one, which does not leak.
Laust
Wormhole, I would add the ICV (idle motor) to the list. My old one leaked through the housing and connector, which I sealed with J&B Weld, but eventually got a new one, which does not leak.
Laust
Last edited by Laust Pedersen; 01-14-2013 at 03:32 PM.
09-21-2004, 03:05 PM
#13
Addict
Rennlist Member
Rennlist Member
Thread Starter
I finally completed the shaft sealing of the TB and installed it. As expected, I cannot feel any difference except for a slightly lower idle, but not enough to fiddle with adjustments.
The lid of the sensor now stays on and another advantage is that oil is not pushed into the sensor.
Prior to the installation I had the concern that my high boost pressure would make the O-rings grab the shaft and making it stuck open, but now with a few days testing, I am happy to say that the TB closes easily (with standard return springs).
For those planning to do the sealing please note that the two screws holding the throttle plate are flattened at their ends (Porsche realizes the disadvantage of having the pistons munch on screws
), so I used a Dremmel tool to remove the flaring and red thread-locker for the mounting. Also note the orientation of the throttle plate, which is not symmetric and leave the throttle stop with its torsion spring on the shaft. I manually had to remove the remains of the old seals, cleaned the needle bearings with carb-cleaner and greased it up again with moly-grease.
The sensor pulls easily off the shaft once its two mounting screws are removed and on installation remember to adjust it so the micros-witch engages each time the throttle is closed. It also is a good idea to drill a small hole (maybe 3/32”) in the lid on its lowest point to get rid of future leakage.
Mike, I get the O-rings from “Small-Parts” (P/N ORV-011 found here ). 3 are needed.
Tom, only time will tell how well the turbos will flow. Reducing the huge .060” turbine wheel-housing clearance by half and the other minor geometry changes I have made should at least improve the spool-up time and likely also increase the flow somewhat. After getting on the dyno with my current configuration, I’ll make a switch and test the effects … if I just can leave my current crummy exhaust alone .
The lid of the sensor now stays on and another advantage is that oil is not pushed into the sensor.
Prior to the installation I had the concern that my high boost pressure would make the O-rings grab the shaft and making it stuck open, but now with a few days testing, I am happy to say that the TB closes easily (with standard return springs).
For those planning to do the sealing please note that the two screws holding the throttle plate are flattened at their ends (Porsche realizes the disadvantage of having the pistons munch on screws
), so I used a Dremmel tool to remove the flaring and red thread-locker for the mounting. Also note the orientation of the throttle plate, which is not symmetric and leave the throttle stop with its torsion spring on the shaft. I manually had to remove the remains of the old seals, cleaned the needle bearings with carb-cleaner and greased it up again with moly-grease.The sensor pulls easily off the shaft once its two mounting screws are removed and on installation remember to adjust it so the micros-witch engages each time the throttle is closed. It also is a good idea to drill a small hole (maybe 3/32”) in the lid on its lowest point to get rid of future leakage.
Mike, I get the O-rings from “Small-Parts” (P/N ORV-011 found here ). 3 are needed.
Tom, only time will tell how well the turbos will flow. Reducing the huge .060” turbine wheel-housing clearance by half and the other minor geometry changes I have made should at least improve the spool-up time and likely also increase the flow somewhat. After getting on the dyno with my current configuration, I’ll make a switch and test the effects … if I just can leave my current crummy exhaust alone
.
Last edited by Laust Pedersen; 01-14-2013 at 03:32 PM.
09-21-2004, 03:27 PM
#14
Intermediate
Join Date: Mar 2002
Location: Union Mi
Posts: 43
Likes: 0
Received 0 Likes
on
0 Posts
Laust,
I replaced the two in the bearing cages, where is the other one you replaced? I missed the flattening on the throttle plate screws, now I need to find two new ones. What did you mean about the torsion spring?
Everybody,
While people have it apart they might also replace the throttle body to manifold O-ring and the throttle body to TPS O-ring. Of coarse a missing throttle body to TPS O-ring will help keep the cover from blowing off again. I have the other two O-ring sizes at home( I am at work). O-rings made from Viton (as Laust stated) will last much better than the parts store rubber variety.
Laust,
Good luck on your modified turbo.
Ben
I replaced the two in the bearing cages, where is the other one you replaced? I missed the flattening on the throttle plate screws, now I need to find two new ones. What did you mean about the torsion spring?
Everybody,
While people have it apart they might also replace the throttle body to manifold O-ring and the throttle body to TPS O-ring. Of coarse a missing throttle body to TPS O-ring will help keep the cover from blowing off again. I have the other two O-ring sizes at home( I am at work). O-rings made from Viton (as Laust stated) will last much better than the parts store rubber variety.
Laust,
Good luck on your modified turbo.
Ben
09-21-2004, 03:54 PM
#15
Addict
Rennlist Member
Rennlist Member
Thread Starter
Ben, there were two seals on the actuator side (one on each side on the needle cage) and one seal on the sensor side (closest to the sensor). Probably no harm done by having only one seal (O-ring) on the actuator side except the cage will slide (and wear a little more), each time the pressure changes between positive and negative.
On the torsion spring (coaxial with the shaft), I meant to leave it with its brackets as shown in the picture, because the re-installation can be a little confusing (= time-consuming).
A little O-ring dimension theory (ref. large TB-manifold O-ring): It is important that the cross-sectional area of an O-ring is smaller than the cross-sectional area of the groove so the two flanges can be fully mated without bending them. The idea is that the O-ring is pushed by the air (or liquid) pressure toward the very small flange gap and sealing it. The groove is designed and O-ring dimension chosen so the (new) O-ring protrudes slightly above its groove. Huntley Racing had stuck a too fat O-ring in mine with the potential of bending the flanges.
On the torsion spring (coaxial with the shaft), I meant to leave it with its brackets as shown in the picture, because the re-installation can be a little confusing (= time-consuming).
A little O-ring dimension theory (ref. large TB-manifold O-ring): It is important that the cross-sectional area of an O-ring is smaller than the cross-sectional area of the groove so the two flanges can be fully mated without bending them. The idea is that the O-ring is pushed by the air (or liquid) pressure toward the very small flange gap and sealing it. The groove is designed and O-ring dimension chosen so the (new) O-ring protrudes slightly above its groove. Huntley Racing had stuck a too fat O-ring in mine with the potential of bending the flanges.